1
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O'Connor JP, Schultz JD, Tcyrulnikov NA, Kim T, Young RM, Wasielewski MR. Distinct vibrational motions promote disparate excited-state decay pathways in cofacial perylenediimide dimers. J Chem Phys 2024; 161:074306. [PMID: 39145558 DOI: 10.1063/5.0218752] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2024] [Accepted: 07/29/2024] [Indexed: 08/16/2024] Open
Abstract
A complex interplay of structural, electronic, and vibrational degrees of freedom underpins the fate of molecular excited states. Organic assemblies exhibit a myriad of excited-state decay processes, such as symmetry-breaking charge separation (SB-CS), excimer (EX) formation, singlet fission, and energy transfer. Recent studies of cofacial and slip-stacked perylene-3,4:9,10-bis(dicarboximide) (PDI) multimers demonstrate that slight variations in core substituents and H- or J-type aggregation can determine whether the system follows an SB-CS pathway or an EX one. However, questions regarding the relative importance of structural properties and molecular vibrations in driving the excited-state dynamics remain. Here, we use a combination of two-dimensional electronic spectroscopy, femtosecond stimulated Raman spectroscopy, and quantum chemistry computations to compare the photophysics of two PDI dimers. The dimer with 1,7-bis(pyrrolidin-1'-yl) substituents (5PDI2) undergoes ultrafast SB-CS from a photoexcited mixed state, while the dimer with bis-1,7-(3',5'-di-t-butylphenoxy) substituents (PPDI2) rapidly forms an EX state. Examination of their quantum beating features reveals that SB-CS in 5PDI2 is driven by the collective vibronic coupling of two or more excited-state vibrations. In contrast, we observe signatures of low-frequency vibrational coherence transfer during EX formation by PPDI2, which aligns with several previous studies. We conclude that key electronic and structural differences between 5PDI2 and PPDI2 determine their markedly different photophysics.
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Affiliation(s)
- James P O'Connor
- Department of Chemistry and Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, Illinois 60208-3113, USA
| | - Jonathan D Schultz
- Department of Chemistry and Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, Illinois 60208-3113, USA
| | - Nikolai A Tcyrulnikov
- Department of Chemistry and Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, Illinois 60208-3113, USA
| | - Taeyeon Kim
- Department of Chemistry and Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, Illinois 60208-3113, USA
| | - Ryan M Young
- Department of Chemistry and Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, Illinois 60208-3113, USA
| | - Michael R Wasielewski
- Department of Chemistry and Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, Illinois 60208-3113, USA
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2
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Roy R, Chawla S, Sharma V, Pal AK, Silori Y, Datta A, De AK, Koner AL. Ultrafast symmetry-breaking charge separation in Perylenemonoimide-embedded multichromophores: impact of regioisomerism. Chem Sci 2024; 15:6363-6377. [PMID: 38699268 PMCID: PMC11062123 DOI: 10.1039/d3sc05325c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Accepted: 03/20/2024] [Indexed: 05/05/2024] Open
Abstract
Symmetry-breaking charge separation (SB-CS) has recently evolved as an emerging concept offering its potential to the latest generation of organic photovoltaics. However there are several concerns that need to be addressed to reach the state-of-the-art in SB-CS chemistry, for instance, the desirable molecular geometry, interchromophoric distance and extent of electronic coupling. To shed light on those features, it is reported herein, that ortho-functionalized perylene monoimide (PMI) constituted regioisomeric dimer and trimer derivatives with varied molecular twisting and electronic conjugation have been synthesized. In steady-state photophysical studies, all the dimers and trimer derivatives exhibit a larger bathochromic shift in the emission spectra and a significant reduction of fluorescence quantum yield in polar DMF. Among the series of multichromophores, ortho- and self-coupled dimers display the strikingly different optical feature of SB-CS with a very fast charge separation rate (τCS = 80.2 ps) upon photoexcitation in DMF, which is unveiled by femtosecond transient absorption (fs-TA) studies. The SB-CS for two dimers is well-supported by the formation of PMI˙+ and PMI˙- bands in the fs-TA spectra. Further analysis of fs-TA data revealed that, among the other multichromophores the trimer also exhibits a clear charge separation, whereas SB-CS signatures are less prominent, but can not be completely disregarded, for the meta- and para-dimers. Additionally, the charge separation dynamics of those above-mentioned PMI derivatives are devoid of a kinetically favorable excimer or triplet formation. The evidence of a profound charge transfer phenomenon in the ortho-dimer is characterized by density functional theory (DFT) calculations on excited state electronic structures. The excitonic communications in the excited state electronic arrangements unravel the key role of dihedral twisting in SB-CS. The thermodynamic feasibility of CS (ΔGCS) and activation barrier (ΔG≠) of the derivatives in DMF are established from the Rehm-Weller equation and Marcus's theory, respectively. This work is an in-depth study of the effect of mutual orientation of PMIs and regioisomerism in determining sustainable guidelines for using SB-CS.
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Affiliation(s)
- Rupam Roy
- Bionanotechnology Lab, Department of Chemistry, Indian Institute of Science Education and Research Bhopal Bhopal Bypass Road, Bhauri Bhopal Madhya Pradesh 462066 India
| | - Sakshi Chawla
- Condensed Phase Dynamics Group, Department of Chemical Sciences, Indian Institute of Science Education and Research Mohali Knowledge City, Sector 81, SAS Nagar Punjab 140 306 India
| | - Vikas Sharma
- Bionanotechnology Lab, Department of Chemistry, Indian Institute of Science Education and Research Bhopal Bhopal Bypass Road, Bhauri Bhopal Madhya Pradesh 462066 India
| | - Arun K Pal
- School of Chemical Sciences, Indian Association for the Cultivation of Science 2A and 2B Raja S. C. Mullick Road, Jadavpur Kolkata West Bengal 700032 India
| | - Yogita Silori
- Condensed Phase Dynamics Group, Department of Chemical Sciences, Indian Institute of Science Education and Research Mohali Knowledge City, Sector 81, SAS Nagar Punjab 140 306 India
- Department of Physics, University of Michigan Ann Arbor Michigan 48109 USA
| | - Ayan Datta
- School of Chemical Sciences, Indian Association for the Cultivation of Science 2A and 2B Raja S. C. Mullick Road, Jadavpur Kolkata West Bengal 700032 India
| | - Arijit K De
- Condensed Phase Dynamics Group, Department of Chemical Sciences, Indian Institute of Science Education and Research Mohali Knowledge City, Sector 81, SAS Nagar Punjab 140 306 India
| | - Apurba Lal Koner
- Bionanotechnology Lab, Department of Chemistry, Indian Institute of Science Education and Research Bhopal Bhopal Bypass Road, Bhauri Bhopal Madhya Pradesh 462066 India
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3
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Thakur K, Datta S, Blom PWM, Chaudhuri D, Ramanan C. Competitive Charge Separation Pathways in a Flexible Molecular Folda-Dimer. J Phys Chem B 2024; 128:1760-1770. [PMID: 38340068 PMCID: PMC10895663 DOI: 10.1021/acs.jpcb.3c07134] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2024]
Abstract
We report the photophysical properties of a molecular folda-dimer system PDI-AnEt2-PDI, where the electron-donating N,N-diethylaniline (AnEt2) moiety bridges two electron-accepting perylene diimide (PDI) chromophores. The conformationally flexible PDI-AnEt2-PDI adopts either an open (two PDIs far apart) or folded (two PDIs within π-stacking distance) conformation, depending on the solvent environment. We characterized the photoinduced charge separation dynamics of both open and folded forms in solvents of varying polarity. The open form undergoes charge separation to give PDI•--AnEt2•+-PDI (Bridge electron transfer) independent of solvent polarity. The folded form exhibits two charge separation photoproducts, yielding both PDI•--AnEt2•+-PDI and PDI•--AnEt2-PDI•+, the latter of which is formed via symmetry-breaking charge separation (SBCS) between the two π-stacked PDI chromophores. Our results further indicate that the conformational flexibility of the folda-dimer leads to unexpected excimer formation in some open form conditions. In contrast, no excimer formation is observed in the folded form, indicating that this geometry preferentially yields the SBCS instead. Our results provide insight into how conformationally flexible folda-dimer systems can be designed and built to tune competitive photophysical pathways.
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Affiliation(s)
- Kalyani Thakur
- Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany
| | - Saptarshi Datta
- Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur 741246, India
| | - Paul W M Blom
- Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany
| | - Debangshu Chaudhuri
- Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur 741246, India
| | - Charusheela Ramanan
- Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany
- Department of Physics and Astronomy, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081HV Amsterdam, Netherlands
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4
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Bradley JM, Coleman AF, Brown PJ, Huang Y, Young RM, Wasielewski MR. Harvesting electrons and holes from photodriven symmetry-breaking charge separation within a perylenediimide photosynthetic model dimer. Proc Natl Acad Sci U S A 2023; 120:e2313575120. [PMID: 37983509 PMCID: PMC10691211 DOI: 10.1073/pnas.2313575120] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Accepted: 10/11/2023] [Indexed: 11/22/2023] Open
Abstract
Understanding how to utilize symmetry-breaking charge separation (SB-CS) offers a path toward increasingly efficient light-harvesting technologies. This process plays a central role in the first step of photosynthesis, in which the dimeric "special pair" of the photosynthetic reaction center enters a coherent SB-CS state after photoexcitation. Previous research on SB-CS in both biological and synthetic chromophore dimers has focused on increasing the efficiency of light-driven processes. In a chromophore dimer undergoing SB-CS, the energy of the radical ion pair product is nearly isoenergetic with that of the lowest excited singlet (S1) state of the dimer. This means that very little energy is lost from the absorbed photon. In principle, the relatively high energy electron and hole generated by SB-CS within the chromophore dimer can each be transferred to adjacent charge acceptors to extend the lifetime of the electron-hole pair, which can increase the efficiency of solar energy conversion. To investigate this possibility, we have designed a bis-perylenediimide cyclophane (mPDI2) covalently linked to a secondary electron donor, peri-xanthenoxanthene (PXX) and a secondary electron acceptor, partially fluorinated naphthalenediimide (FNDI). Upon selective photoexcitation of mPDI2, transient absorption spectroscopy shows that mPDI2 undergoes SB-CS, followed by two secondary charge transfer reactions to generate a PXX•+-mPDI2-FNDI•- radical ion pair having a nearly 3 µs lifetime. This strategy has the potential to increase the efficiency of molecular systems for artificial photosynthesis and photovoltaics.
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Affiliation(s)
- Jillian M. Bradley
- Department of Chemistry, Northwestern University, Evanston, IL60208-3113
- Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, IL60208-3113
| | - Adam F. Coleman
- Department of Chemistry, Northwestern University, Evanston, IL60208-3113
- Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, IL60208-3113
| | - Paige J. Brown
- Department of Chemistry, Northwestern University, Evanston, IL60208-3113
- Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, IL60208-3113
| | - Yuheng Huang
- Department of Chemistry, Northwestern University, Evanston, IL60208-3113
- Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, IL60208-3113
| | - Ryan M. Young
- Department of Chemistry, Northwestern University, Evanston, IL60208-3113
- Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, IL60208-3113
| | - Michael R. Wasielewski
- Department of Chemistry, Northwestern University, Evanston, IL60208-3113
- Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, IL60208-3113
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5
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Yang W, Jo SH, Tang Y, Park J, Ji SG, Cho SH, Hong Y, Kim DH, Park J, Yoon E, Zhou H, Woo SJ, Kim H, Yun HJ, Lee YS, Kim JY, Hu B, Lee TW. Overcoming Charge Confinement in Perovskite Nanocrystal Solar Cells. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2304533. [PMID: 37390092 DOI: 10.1002/adma.202304533] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2023] [Revised: 06/27/2023] [Accepted: 06/28/2023] [Indexed: 07/02/2023]
Abstract
The small nanoparticle size and long-chain ligands in colloidal metal halide perovskite quantum dots (PeQDs) cause charge confinement, which impedes exciton dissociation and carrier extraction in PeQD solar cells, so they have low short-circuit current density Jsc , which impedes further increases in their power conversion efficiency (PCE). Here, a re-assembling process (RP) is developed for perovskite nanocrystalline (PeNC) films made of colloidal perovskite nanocrystals to increase Jsc in PeNC solar cells. The RP of PeNC films increases their crystallite size and eliminates long-chain ligands, and thereby overcomes the charge confinement in PeNC films. These changes facilitate exciton dissociation and increase carrier extraction in PeNC solar cells. By use of this method, the gradient-bandgap PeNC solar cells achieve a Jsc = 19.30 mA cm-2 without compromising the photovoltage, and yield a high PCE of 16.46% with negligible hysteresis and good stability. This work provides a new strategy to process PeNC films and pave the way for high performance PeNC optoelectronic devices.
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Affiliation(s)
- Wenqiang Yang
- Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
- Research Institute of Advanced Materials, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Seung-Hyeon Jo
- Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Yipeng Tang
- Department of Materials Science and Engineering, University of Tennessee, 1001-1099 Estabrook Rd, Knoxville, TN, 37996, USA
| | - Jumi Park
- Department of Chemistry, Yonsei University, 50 Yonsei-ro, Seodaemoon-gu, Seoul, 03722, Republic of Korea
| | - Su Geun Ji
- Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Seong Ho Cho
- Department of Mechanical Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Yongseok Hong
- Department of Chemistry, Yonsei University, 50 Yonsei-ro, Seodaemoon-gu, Seoul, 03722, Republic of Korea
| | - Dong-Hyeok Kim
- Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Jinwoo Park
- Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Eojin Yoon
- Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Huanyu Zhou
- Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Seung-Je Woo
- Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Hyeran Kim
- Advanced Nano Research Group, Korea Basic Science Institute (KBSI), 169-148 Gwahak-ro, Yuseong-gu, Daejeon, 34126, Republic of Korea
| | - Hyung Joong Yun
- Advanced Nano Research Group, Korea Basic Science Institute (KBSI), 169-148 Gwahak-ro, Yuseong-gu, Daejeon, 34126, Republic of Korea
| | - Yun Seog Lee
- Department of Mechanical Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Jin Young Kim
- Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
| | - Bin Hu
- Department of Materials Science and Engineering, University of Tennessee, 1001-1099 Estabrook Rd, Knoxville, TN, 37996, USA
| | - Tae-Woo Lee
- Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
- Research Institute of Advanced Materials, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
- SN Display Co. Ltd., 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
- School of Chemical and Biological Engineering, Institute of Engineering Research, Soft Foundry, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea
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6
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Yoneda Y, Kuramochi H. Rapid-Scan Resonant Two-Dimensional Impulsive Stimulated Raman Spectroscopy of Excited States. J Phys Chem A 2023. [PMID: 37289973 DOI: 10.1021/acs.jpca.3c02489] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Photochemical reactions occur in the electronically excited state, which is effectively represented by a multidimensional potential energy surface (PES) with a vast degree of freedom of nuclear coordinates. The elucidation of the intricate shape of the PES constitutes an important topic in the field of photochemistry and has long been studied both experimentally and theoretically. Recently, fully time-domain resonant two-dimensional Raman spectroscopy has emerged as a potentially powerful tool to provide unique information about the coupling between vibrational manifolds in the excited state. However, the wide application of this technique has been significantly hampered by the technical difficulties associated with experimental implementation and remains challenging. Herein, we demonstrate time-domain resonant two-dimensional impulsive stimulated Raman spectroscopy (2D-ISRS) of excited states using sub-10 fs pulses based on the rapid scan of the time delay, which facilitates the efficient collection of time-domain vibrational signals with high sensitivity. As a proof-of-principle experiment, we performed 2D-ISRS of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) in solution. Through 2D Fourier transformation of the high-quality time-time oscillatory signal, we obtained a 2D frequency-frequency correlation map of excited-state TIPS-pentacene in the broad frequency window of 0-2000 cm-1. The data clearly resolve a number of cross peaks that signify the correlations among excited-state vibrational manifolds. The high capability of the rapid-scan-based 2D-ISRS spectrometer presented in this study enables the systematic investigation of various photochemical reaction systems, thereby further promoting the understanding and applications of this new multidimensional spectroscopy.
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Affiliation(s)
- Yusuke Yoneda
- Research Center of Integrative Molecular Systems (CIMoS), Institute for Molecular Science, National Institutes of Natural Sciences, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
- Graduate Institute for Advanced Studies, SOKENDAI, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
| | - Hikaru Kuramochi
- Research Center of Integrative Molecular Systems (CIMoS), Institute for Molecular Science, National Institutes of Natural Sciences, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
- Graduate Institute for Advanced Studies, SOKENDAI, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
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7
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Kim T, Feng Y, O'Connor JP, Stoddart JF, Young RM, Wasielewski MR. Coherent Vibronic Wavepackets Show Structure-Directed Charge Flow in Host-Guest Donor-Acceptor Complexes. J Am Chem Soc 2023. [PMID: 37018535 DOI: 10.1021/jacs.2c13576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/07/2023]
Abstract
Designing and controlling charge transfer (CT) pathways in organic semiconductors are important for solar energy applications. To be useful, a photogenerated, Coulombically bound CT exciton must further separate into free charge carriers; direct observations of the detailed CT relaxation pathways, however, are lacking. Here, photoinduced CT and relaxation dynamics in three host-guest complexes, where a perylene (Per) electron donor guest is incorporated into two symmetric and one asymmetric extended viologen cyclophane acceptor hosts, are presented. The central ring in the extended viologen is either p-phenylene (ExV2+) or electron-rich 2,5-dimethoxy-p-phenylene (ExMeOV2+), resulting in two symmetric cyclophanes with unsubstituted or methoxy-substituted central rings, ExBox4+ and ExMeOBox4+, respectively, and an asymmetric cyclophane with one of the central viologen rings being methoxylated ExMeOVBox4+. Upon photoexcitation, the asymmetric host-guest ExMeOVBox4+ ⊃ Per complex exhibits directional CT toward the energetically unfavorable methoxylated side due to structural restrictions that facilitate strong interactions between the Per donor and the ExMeOV2+ side. The CT state relaxation pathways are probed using ultrafast optical spectroscopy by focusing on coherent vibronic wavepackets, which are used to identify CT relaxations along charge localization and vibronic decoherence coordinates. Specific low- and high-frequency nuclear motions are direct indicators of a delocalized CT state and the degree of CT character. Our results show that the CT pathway can be controlled by subtle chemical modifications of the acceptor host in addition to illustrating how coherent vibronic wavepackets can be used to probe the nature and time evolution of the CT states.
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Affiliation(s)
- Taeyeon Kim
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Yuanning Feng
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - James P O'Connor
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - J Fraser Stoddart
- Stoddart Institute of Molecular Science, Department of Chemistry, Zhejiang University, Hangzhou 310027, China
- ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou 311215, China
- School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Ryan M Young
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Michael R Wasielewski
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
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8
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Kumar P, Kuramochi H, Takeuchi S, Tahara T. Photoexcited Plasmon-Driven Ultrafast Dynamics of the Adsorbate Probed by Femtosecond Time-Resolved Surface-Enhanced Time-Domain Raman Spectroscopy. J Phys Chem Lett 2023; 14:2845-2853. [PMID: 36916655 PMCID: PMC10042161 DOI: 10.1021/acs.jpclett.2c03813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 02/21/2023] [Indexed: 06/18/2023]
Abstract
Metal nanoparticles have high potential in light-harvesting applications by transferring absorbed photon energy to the adsorbates. However, photoexcited plasmon-driven ultrafast dynamics of the adsorbate on metal nanoparticles have not been clearly understood. We studied ultrafast plasmon-driven processes of trans-1,2-bis(4-pyridyl)ethylene (BPE) adsorbed on gold nanoparticle assemblies (GNAs) using time-resolved surface-enhanced impulsive stimulated Raman spectroscopy (TR-SE-ISRS). After photoexciting the localized surface plasmon resonance (LSPR) band of the GNAs, we measured femtosecond time-resolved surface-enhanced Raman spectra of the adsorbate, which exhibited transient bleach in the Raman signal and following biphasic recovery that proceeds on the time scale of a few tens of picoseconds. The TR-SE-ISRS data were analyzed with singular value decomposition, and the obtained species-associated Raman spectra indicated that photoexcitation of the LSPR band alters chemical interaction between BPE and the GNAs on an ultrafast time scale; initial steady-state BPE is recovered through a precursor state that has weaker interaction with the GNAs.
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Affiliation(s)
- Pardeep Kumar
- Molecular
Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan
- Ultrafast
Spectroscopy Research Team, RIKEN Center
for Advanced Photonics (RAP), 2-1 Hirosawa, Wako 351-0198, Japan
| | - Hikaru Kuramochi
- Molecular
Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan
- Ultrafast
Spectroscopy Research Team, RIKEN Center
for Advanced Photonics (RAP), 2-1 Hirosawa, Wako 351-0198, Japan
| | - Satoshi Takeuchi
- Molecular
Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan
- Ultrafast
Spectroscopy Research Team, RIKEN Center
for Advanced Photonics (RAP), 2-1 Hirosawa, Wako 351-0198, Japan
| | - Tahei Tahara
- Molecular
Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan
- Ultrafast
Spectroscopy Research Team, RIKEN Center
for Advanced Photonics (RAP), 2-1 Hirosawa, Wako 351-0198, Japan
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9
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Sebastian E, Hariharan M. A Symmetry-Broken Charge-Separated State in the Marcus Inverted Region. Angew Chem Int Ed Engl 2023; 62:e202216482. [PMID: 36697363 DOI: 10.1002/anie.202216482] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Revised: 12/23/2022] [Accepted: 01/24/2023] [Indexed: 01/27/2023]
Abstract
We report a long-lived charge-separated state in a chromophoric pair (DC-PDI2 ) that uniquely integrates the advantages of fundamental processes of photosynthetic reaction centers: i) Symmetry-breaking charge-separation (SB-CS) and ii) Marcus-inverted-region dependence. The near-orthogonal bichromophoric DC-PDI2 manifests an ultrafast evolution of the SB-CS state with a time constant of τ S B - C S ${{\tau }_{{\rm S}{\rm B}-{\rm C}{\rm S}}}$ =0.35±0.02 ps and a slow charge recombination (CR) kinetics with τ C R ${{\tau }_{{\rm C}{\rm R}}}$ =4.09±0.01 ns in ACN. The rate constant of CR of DC-PDI2 is 11 686 times slower than SB-CS in ACN, as the CR of the PDI radical ion-pair occurs in the deep inverted region of the Marcus parabola ( - Δ G C R ${{-{\rm \Delta }G}_{{\rm C}{\rm R}}}$ >λ). In contrast, an analogous benzyloxy (BnO)-substituted DC-BPDI2 showcases a ≈10-fold accelerated CR kinetics with τ C R / τ S B - C S ${{\tau }_{{\rm C}{\rm R}}/{\tau }_{{\rm S}{\rm B}-{\rm C}{\rm S}}}$ lowering to ≈1536 in ACN, by virtue of a decreased CR driving force. The present investigation demonstrates a control of molecular engineering to tune the energetics and kinetics of the SB-CS material, which is essential for next-generation optoelectronic devices.
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Affiliation(s)
- Ebin Sebastian
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram (IISER TVM), Maruthamala P.O., Vithura, Thiruvananthapuram, 695551, Kerala, India
| | - Mahesh Hariharan
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram (IISER TVM), Maruthamala P.O., Vithura, Thiruvananthapuram, 695551, Kerala, India
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10
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Li G, Stefanczyk O, Kumar K, Mineo Y, Nakabayashi K, Ohkoshi SI. Low-Frequency Sub-Terahertz Absorption in Hg II -XCN-Fe II (X=S, Se) Coordination Polymers. Angew Chem Int Ed Engl 2023; 62:e202214673. [PMID: 36522797 DOI: 10.1002/anie.202214673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Revised: 12/14/2022] [Accepted: 12/14/2022] [Indexed: 12/23/2022]
Abstract
Self-assembly FeII complexes of phenazine (Phen), quinoxaline (Qxn), and 4,4'-trimethylenedipyridine (Tmp) with tetrahedral building blocks of [HgII (XCN)4 ]2- (X=S or Se) formed six new high-dimensional frameworks with the general formula of [Fe(L)m ][Hg(XCN)4 ]⋅solvents (L=Phen, m/X=2/S, 1; L=Qxn, m/X=2/S, 2; L=Qxn, m/X=1/S, 3; L=Qxn, m/X=1/Se, 3-Se; L=Tmp, m/X=1/S, 4; and L=Tmp, m/X=1/Se, 4-Se). 1, 3, and 3-Se show an intense sub-terahertz (sub-THz) absorbance of around 0.60 THz due to vibrations of the solvent molecules coordinated to the FeII ions and crystallization organic molecules. In addition, crystals of 1, 4, and 4-Se display low-frequency Raman scattering with exceptionally low values of 0.44, 0.51, and 0.53 THz, respectively. These results indicate that heavy metal FeII -HgII systems are promising platforms to construct sub-THz absorbers.
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Affiliation(s)
- Guanping Li
- Department of Chemistry, School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Olaf Stefanczyk
- Department of Chemistry, School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Kunal Kumar
- Department of Chemistry, School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Yuuki Mineo
- Department of Chemistry, School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Koji Nakabayashi
- Department of Chemistry, School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
| | - Shin-Ichi Ohkoshi
- Department of Chemistry, School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
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11
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Ma L, Kuang Z, Wang Z, Zhao H, Wan Y, Zhang XF, Li Y, Xia A. Ultrafast Charge Separation Driven by Torsional Motion in Orthogonal Boron Dipyrromethene Dimer. J Phys Chem Lett 2023; 14:702-708. [PMID: 36646067 DOI: 10.1021/acs.jpclett.2c03581] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
In this work, the photoinduced charge separation (CS) via symmetry breaking in an orthogonal meso-β-linked boron dipyrromethene (BODIPY) dimer was investigated by polarized transient absorption spectroscopy. The time constant about 0.76 ps of the CS reaction determined in dimethyl sulfoxide is much faster than the solvation dynamics. The observed transient anisotropy of the BODIPY anion band implies that both hole and electron transfers occur with similar probabilities. The bidirectional charge transfer processes suggest that the locally excited state is weakly coupled to the polar solvent, and the solvation coupled excited-state structural relaxation within the BODIPY monomeric unit is rather limited. In combination with the electronic excitation analysis based on time-dependent density-functional theory calculations, we deduced that the CS in the orthogonal BODIPY dimer is enabled via the torsional motion associated with covalently connected BODIPY units, promoting the electronic coupling, and irrelevant to the dynamic solvent relaxation.
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Affiliation(s)
- Lin Ma
- State Key Laboratory of Information Photonic and Optical Communications and School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, People's Republic of China
| | - Zhuoran Kuang
- State Key Laboratory of Information Photonic and Optical Communications and School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, People's Republic of China
| | - Zeming Wang
- State Key Laboratory of Information Photonic and Optical Communications and School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, People's Republic of China
| | - Hongmei Zhao
- State Key Laboratory of Information Photonic and Optical Communications and School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, People's Republic of China
| | - Yan Wan
- College of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Xian-Fu Zhang
- Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong 518055, People's Republic of China
| | - Yang Li
- State Key Laboratory of Information Photonic and Optical Communications and School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, People's Republic of China
| | - Andong Xia
- State Key Laboratory of Information Photonic and Optical Communications and School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, People's Republic of China
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12
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Mattos RS, Burghardt I, Aquino AJA, Cardozo TM, Lischka H. On the Cooperative Origin of Solvent-Enhanced Symmetry-Breaking Charge Transfer in a Covalently Bound Tetracene Dimer Leading to Singlet Fission. J Am Chem Soc 2022; 144:23492-23504. [PMID: 36534052 DOI: 10.1021/jacs.2c10129] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Singlet fission in covalently bound acene dimers in solution is driven by the interplay of excitonic and singlet correlated triplet 1(TT) states with intermediate charge-transfer states, a process which depends sensitively on the solvent environment. We use high-level electronic structure methods to explore this singlet fission process in a linked tetracene dimer, with emphasis on the symmetry-breaking mechanism for the charge-transfer (CT) states induced by low-frequency antisymmetric vibrations and polar/polarizable solvents. A combination of the second-order algebraic diagrammatic construction (ADC(2)) and density functional theory/multireference configuration interaction (DFT/MRCI) methods are employed, along with a state-specific conductor-like screening model (COSMO) solvation model in the former case. This work quantifies, for the first time, an earlier mechanistic proposal [Alvertis et al., J. Am. Chem. Soc. 2019, 141, 17558] according to which solvent-induced symmetry breaking leads to a high-energy CT state which interacts with the correlated triplet state, resulting in singlet fission. An approximate assessment of the nonadiabatic interactions between the different electronic states underscores that the CT states are essential in facilitating the transition from the bright excitonic state to the 1(TT) state leading to singlet fission. We show that several types of symmetry-breaking inter- and intra-fragment vibrations play a crucial role in a concerted mechanism with the solvent environment and with the symmetric inter-fragment torsion, which tunes the admixture of excitonic and CT states. This offers a new perspective on how solvent-induced symmetry-breaking CT can be understood and how it cooperates with intramolecular mechanisms in singlet fission.
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Affiliation(s)
- Rafael S Mattos
- Aix Marseille University, CNRS, ICR, Marseille 13013, France.,Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro 21941-909, Brazil
| | - Irene Burghardt
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, 60438 Frankfurt, Germany
| | - Adelia J A Aquino
- Department of Mechanical Engineering, Texas Tech University, Lubbock, Texas 79409, United States
| | - Thiago M Cardozo
- Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro 21941-909, Brazil
| | - Hans Lischka
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, United States
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13
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Absolute excited state molecular geometries revealed by resonance Raman signals. Nat Commun 2022; 13:7770. [PMID: 36522323 PMCID: PMC9755279 DOI: 10.1038/s41467-022-35099-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 11/18/2022] [Indexed: 12/23/2022] Open
Abstract
Ultrafast reactions activated by light absorption are governed by multidimensional excited-state (ES) potential energy surfaces (PESs), which describe how the molecular potential varies with the nuclear coordinates. ES PESs ad-hoc displaced with respect to the ground state can drive subtle structural rearrangements, accompanying molecular biological activity and regulating physical/chemical properties. Such displacements are encoded in the Franck-Condon overlap integrals, which in turn determine the resonant Raman response. Conventional spectroscopic approaches only access their absolute value, and hence cannot determine the sense of ES displacements. Here, we introduce a two-color broadband impulsive Raman experimental scheme, to directly measure complex Raman excitation profiles along desired normal modes. The key to achieve this task is in the signal linear dependence on the Frank-Condon overlaps, brought about by non-degenerate resonant probe and off-resonant pump pulses, which ultimately enables time-domain sensitivity to the phase of the stimulated vibrational coherences. Our results provide the tool to determine the magnitude and the sensed direction of ES displacements, unambiguously relating them to the ground state eigenvectors reference frame.
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14
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Sebastian E, Sunny J, Hariharan M. Excimer evolution hampers symmetry-broken charge-separated states. Chem Sci 2022; 13:10824-10835. [PMID: 36320683 PMCID: PMC9491171 DOI: 10.1039/d2sc04387d] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2022] [Accepted: 08/18/2022] [Indexed: 08/26/2023] Open
Abstract
Achieving long-lived symmetry-broken charge-separated states in chromophoric assemblies is quintessential for enhanced performance of artificial photosynthetic mimics. However, the occurrence of energy trap states hinders exciton and charge transport across photovoltaic devices, diminishing power conversion efficiency. Herein, we demonstrate unprecedented excimer formation in the relaxed excited-state geometry of bichromophoric systems impeding the lifetime of symmetry-broken charge-separated states. Core-annulated perylenediimide dimers (SC-SPDI2 and SC-NPDI2) prefer a near-orthogonal arrangement in the ground state and a π-stacked foldamer structure in the excited state. The prospect of an excimer-like state in the foldameric arrangement of SC-SPDI2 and SC-NPDI2 has been rationalized by fragment-based excited state analysis and temperature-dependent photoluminescence measurements. Effective electronic coupling matrix elements in the Franck-Condon geometry of SC-SPDI2 and SC-NPDI2 facilitate solvation-assisted ultrafast symmetry-breaking charge-separation (SB-CS) in a high dielectric environment, in contrast to unrelaxed excimer formation (Ex*) in a low dielectric environment. Subsequently, the SB-CS state dissociates into an undesired relaxed excimer state (Ex) due to configuration mixing of a Frenkel exciton (FE) and charge-separated state in the foldamer structure, downgrading the efficacy of the charge-separated state. The decay rate constant of the FE to SB-CS (k FE→SB-CS) in polar solvents is 8-17 fold faster than that of direct Ex* formation (k FE→Ex*) in non-polar solvent (k FE→SB-CS≫k FE→Ex*), characterized by femtosecond transient absorption (fsTA) spectroscopy. The present investigation establishes the impact of detrimental excimer formation on the persistence of the SB-CS state in chromophoric dimers and offers the requisite of conformational rigidity as one of the potential design principles for developing advanced molecular photovoltaics.
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Affiliation(s)
- Ebin Sebastian
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram Maruthamala P.O., Vithura Thiruvananthapuram Kerala 695551 India
| | - Jeswin Sunny
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram Maruthamala P.O., Vithura Thiruvananthapuram Kerala 695551 India
| | - Mahesh Hariharan
- School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram Maruthamala P.O., Vithura Thiruvananthapuram Kerala 695551 India
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15
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Xu X, Gunasekaran S, Renken S, Ripani L, Schollmeyer D, Kim W, Marcaccio M, Musser A, Narita A. Synthesis and Characterizations of 5,5'-Bibenzo[rst]pentaphene with Axial Chirality and Symmetry-Breaking Charge Transfer. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2022; 9:e2200004. [PMID: 35156332 PMCID: PMC9259715 DOI: 10.1002/advs.202200004] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/01/2022] [Revised: 01/23/2022] [Indexed: 05/31/2023]
Abstract
Exploration of novel biaryls consisting of two polycyclic aromatic hydrocarbon (PAH) units can be an important strategy toward further developments of organic materials with unique properties. In this study, 5,5'-bibenzo[rst]pentaphene (BBPP) with two benzo[rst]pentaphene (BPP) units is synthesized in an efficient and versatile approach, and its structure is unambiguously elucidated by X-ray crystallography. BBPP exhibits axial chirality, and the (M)- and (P)-enantiomers are resolved by chiral high-performance liquid chromatography and studied by circular dichroism spectroscopy. These enantiomers have a relatively high isomerization barrier of 43.6 kcal mol-1 calculated by density functional theory. The monomer BPP and dimer BBPP are characterized by UV-vis absorption and fluorescence spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy. The results indicate that both BPP and BBPP fluoresce from a formally dark S1 electronic state that is enabled by Herzberg-Teller intensity borrowing from a neighboring bright S2 state. While BPP exhibits a relatively low photoluminescence quantum yield (PLQY), BBPP exhibits a significantly enhanced PLQY due to a greater S2 intensity borrowing. Moreover, symmetry-breaking charge transfer in BBPP is demonstrated by spectroscopic investigations in solvents of different polarity. This suggests high potential for singlet fission in such π-extended biaryls through appropriate molecular design.
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Affiliation(s)
- Xiushang Xu
- Max Planck Institute for Polymer ResearchAckermannweg 10Mainz55128Germany
- Organic and Carbon Nanomaterials UnitOkinawa Institute of Science and Technology Graduate University1919‐1 Tancha, Onna‐sonKunigami‐gunOkinawa904‐0495Japan
| | - Suman Gunasekaran
- Department of Chemistry & Chemical BiologyCornell UniversityIthacaNY14853USA
| | - Scott Renken
- Department of Chemistry & Chemical BiologyCornell UniversityIthacaNY14853USA
| | - Lorenzo Ripani
- Dipartimento di Chimica “Giacomo Ciamician”Università di Bolognavia Selmi 2Bologna40126Italy
| | - Dieter Schollmeyer
- Department of ChemistryJohannes Gutenberg University MainzDuesbergweg 10–14Mainz55128Germany
| | - Woojae Kim
- Department of Chemistry & Chemical BiologyCornell UniversityIthacaNY14853USA
| | - Massimo Marcaccio
- Dipartimento di Chimica “Giacomo Ciamician”Università di Bolognavia Selmi 2Bologna40126Italy
| | - Andrew Musser
- Department of Chemistry & Chemical BiologyCornell UniversityIthacaNY14853USA
| | - Akimitsu Narita
- Max Planck Institute for Polymer ResearchAckermannweg 10Mainz55128Germany
- Organic and Carbon Nanomaterials UnitOkinawa Institute of Science and Technology Graduate University1919‐1 Tancha, Onna‐sonKunigami‐gunOkinawa904‐0495Japan
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16
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Kim T, Lin C, Schultz JD, Young RM, Wasielewski MR. π-Stacking-Dependent Vibronic Couplings Drive Excited-State Dynamics in Perylenediimide Assemblies. J Am Chem Soc 2022; 144:11386-11396. [PMID: 35699940 DOI: 10.1021/jacs.2c03993] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Vibronic coupling, the interplay of electronic and nuclear vibrational motion, is considered a critical mechanism in photoinduced reactions such as energy transfer, charge transfer, and singlet fission. However, our understanding of how particular vibronic couplings impact excited-state dynamics is lacking due to the limited number of experimental studies of model molecular systems. Herein, we use two-dimensional electronic spectroscopy (2DES) to launch and interrogate a range of vibronic coherences in two distinct types of perylenediimide slip stacks─along the short and long molecular axes, which form either an excimer or a mixed state between the Frenkel exciton (FE) and charge transfer states. We explore the functionality of these vibronic coherences using quantum beatmaps, which display the Fourier amplitude signal oscillations as a function of pump and probe frequencies, along with knowledge of the characteristic signatures of the FE, ionic, and excimer species. We find that a low-frequency vibrational mode of the short-axis slip stack appears concomitantly with the formation of the excimer state, survives 2-fold longer than in the FE state in the reference monomer, and shows a phase shift compared to other modes. For the long-axis slip stacks, a pair of low-frequency modes coupled to a high-frequency coordinate of the FE state were found to play a critical role in mixed-state generation. Our findings thus experimentally reveal the complex and varying roles of vibronic couplings in tightly packed multimers undergoing a range of photoinduced processes.
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Affiliation(s)
- Taeyeon Kim
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Chenjian Lin
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Jonathan D Schultz
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Ryan M Young
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Michael R Wasielewski
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
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17
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Accelerating symmetry-breaking charge separation in a perylenediimide trimer through a vibronically coherent dimer intermediate. Nat Chem 2022; 14:786-793. [PMID: 35469005 DOI: 10.1038/s41557-022-00927-y] [Citation(s) in RCA: 48] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Accepted: 03/10/2022] [Indexed: 11/08/2022]
Abstract
Understanding the photophysics and photochemistry of molecular π-stacked chromophores is important for utilizing them as functional photonic materials. However, these investigations have been mostly limited to covalent molecular dimers, which can only approximate the electronic and vibronic interactions present in the higher oligomers typical of functional organic materials. Here we show that a comparison of the excited-state dynamics of a covalent slip-stacked perylenediimide dimer (2) and trimer (3) provides fundamental insights into electronic state mixing and symmetry-breaking charge separation (SB-CS) beyond the dimer limit. We find that coherent vibronic coupling to high-frequency modes facilitates ultrafast state mixing between the Frenkel exciton (FE) and charge-transfer (CT) states. Subsequently, solvent fluctuations and interchromophore low-frequency vibrations promote CT character in the coherent FE/CT mixed state. The coherent FE/CT mixed state persists in 2, but, in 3, low-frequency vibronic coupling collapses the coherence, resulting in ultrafast SB-CS between the distal perylenediimide units.
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18
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Hong Y, Kim W, Kim T, Kaufmann C, Kim H, Würthner F, Kim D. Real-time Observation of Structural Dynamics Triggering Excimer Formation in a Perylene Bisimide Folda-dimer by Ultrafast Time-Domain Raman Spectroscopy. Angew Chem Int Ed Engl 2022; 61:e202114474. [PMID: 35075813 PMCID: PMC9306572 DOI: 10.1002/anie.202114474] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Indexed: 01/31/2023]
Abstract
In π-conjugated organic photovoltaic materials, an excimer state has been generally regarded as a trap state which hinders efficient excitation energy transport. But despite wide investigations of the excimer for overcoming the undesirable energy loss, the understanding of the relationship between the structure of the excimer in stacked organic compounds and its properties remains elusive. Here, we present the landscape of structural dynamics from the excimer formation to its relaxation in a co-facially stacked archetypical perylene bisimide folda-dimer using ultrafast time-domain Raman spectroscopy. We directly captured vibrational snapshots illustrating the ultrafast structural evolution triggering the excimer formation along the interchromophore coordinate on the complex excited-state potential surfaces and following evolution into a relaxed excimer state. Not only does this work showcase the ultrafast structural dynamics necessary for the excimer formation and control of excimer characteristics but also provides important criteria for designing the π-conjugated organic molecules.
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Affiliation(s)
- Yongseok Hong
- Department of ChemistrySpectroscopy Laboratory for Functional π-Electronic SystemsYonsei University03722SeoulRepublic of Korea
| | - Woojae Kim
- Department of ChemistrySpectroscopy Laboratory for Functional π-Electronic SystemsYonsei University03722SeoulRepublic of Korea
- Department of Chemistry and Chemical BiologyCornell UniversityIthaca14853New YorkUSA
| | - Taeyeon Kim
- Department of ChemistrySpectroscopy Laboratory for Functional π-Electronic SystemsYonsei University03722SeoulRepublic of Korea
- The Institute for Sustainability and Energy at NorthwesternNorthwestern UniversityEvanston60208IllinoisUSA
| | - Christina Kaufmann
- Institut für Organische Chemie & Center for Nanosystems ChemistryUniversitat WürzburgAm Hubland97074WürzburgGermany
| | - Hyungjun Kim
- Department of ChemistryIncheon National University119 Academy-ro, Yeonsu-gu22012IncheonRepublic of Korea
| | - Frank Würthner
- Institut für Organische Chemie & Center for Nanosystems ChemistryUniversitat WürzburgAm Hubland97074WürzburgGermany
| | - Dongho Kim
- Department of ChemistrySpectroscopy Laboratory for Functional π-Electronic SystemsYonsei University03722SeoulRepublic of Korea
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19
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Hong Y, Kim W, Kim T, Kaufmann C, Kim H, Würthner F, Kim D. Real‐time Observation of Structural Dynamics Triggering Excimer Formation in a Perylene Bisimide Folda‐dimer by Ultrafast Time‐Domain Raman Spectroscopy. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202114474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Yongseok Hong
- Department of Chemistry Spectroscopy Laboratory for Functional π-Electronic Systems Yonsei University 03722 Seoul Republic of Korea
| | - Woojae Kim
- Department of Chemistry Spectroscopy Laboratory for Functional π-Electronic Systems Yonsei University 03722 Seoul Republic of Korea
- Department of Chemistry and Chemical Biology Cornell University Ithaca 14853 New York USA
| | - Taeyeon Kim
- Department of Chemistry Spectroscopy Laboratory for Functional π-Electronic Systems Yonsei University 03722 Seoul Republic of Korea
- The Institute for Sustainability and Energy at Northwestern Northwestern University Evanston 60208 Illinois USA
| | - Christina Kaufmann
- Institut für Organische Chemie & Center for Nanosystems Chemistry Universitat Würzburg Am Hubland 97074 Würzburg Germany
| | - Hyungjun Kim
- Department of Chemistry Incheon National University 119 Academy-ro, Yeonsu-gu 22012 Incheon Republic of Korea
| | - Frank Würthner
- Institut für Organische Chemie & Center for Nanosystems Chemistry Universitat Würzburg Am Hubland 97074 Würzburg Germany
| | - Dongho Kim
- Department of Chemistry Spectroscopy Laboratory for Functional π-Electronic Systems Yonsei University 03722 Seoul Republic of Korea
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20
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Zhang W, Kong J, Xu W, Niu X, Song D, Liu W, Xia A. Probing effect of solvation on photoexcited quadrupolar donor-acceptor-donor molecule via ultrafast Raman spectroscopy. CHINESE J CHEM PHYS 2022. [DOI: 10.1063/1674-0068/cjcp2111223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
The symmetric and quadrupolar donor-acceptor-donor (D-A-D) molecules usually exhibit excited-state charge redistribution process from delocalized intramolecular charge transfer (ICT) state to localized ICT state. Direct observation of such charge redistribution process in real-time has been intensively studied via various ultrafast time-resolved spectroscopies. Femtosecond stimulated Raman spectroscopy (FSRS) is one of the powerful methods which can be used to determine the excited state dynamics by tracking vibrational mode evolution of the specific chemical bonds within molecules. Herein, a molecule, 4,4′-(buta-1,3-diyne-1,4-diyl)bis( N, N-bis(4-methoxyphenyl)aniline), that consists of two central adjacent alkyne (-C≡C-) groups as electron-acceptors and two separated, symmetric N, N-bis(4-methoxyphenyl)aniline at both branches as electron-donors, is chosen to investigate the excited-state photophysical properties. It is shown that the solvation induced excited-state charge redistribution in polar solvents can be probed by using femtosecond stimulated Raman spectroscopy. The results provide a fundamental understanding of photoexcitation induced charge delocalization/localization properties of the symmetric quadrupolar molecules with adjacent vibrational markers located at central position.
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Affiliation(s)
- Wei Zhang
- State Key Laboratory of Information Photonic and Optical Communications, School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, China
- Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Jie Kong
- Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China
| | - Wenqi Xu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- STU SIOM Joint Laboratory for Superintense Lasers and the Applications, Shanghai 201210, China
| | - Xinmiao Niu
- Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Di Song
- State Key Laboratory of Information Photonic and Optical Communications, School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, China
| | - Weimin Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- STU SIOM Joint Laboratory for Superintense Lasers and the Applications, Shanghai 201210, China
| | - Andong Xia
- State Key Laboratory of Information Photonic and Optical Communications, School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, China
- Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
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21
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Renner R, Stolte M, Heitmüller J, Brixner T, Lambert C, Würthner F. Substituent-dependent absorption and fluorescence properties of perylene bisimide radical anions and dianions. MATERIALS HORIZONS 2022; 9:350-359. [PMID: 34816838 DOI: 10.1039/d1mh01019k] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Perylene-3,4:9,10-bis(dicarboximides) (PBIs) rank among the most important functional dyes and organic semiconductors, but only recently have their radical anions and dianions attracted interest for a variety of applications. Here, we systematically elucidate the functional properties (redox, absorption, and emission) of five PBI anions and dianions bearing different bay-substituents attached to the chromophore core. Cyclic voltammetry measurements reveal the influence of the substituents ranging from electron-withdrawing cyano to electron-donating phenoxy groups on the oxidation and reduction potentials that relate to the HOMO and LUMO levels ranging from -7.07 eV to -6.05 eV and -5.01 eV to -4.05 eV, respectively. Spectroelectrochemical studies reveal a significant number of intense absorption bands in the NIR-spectral range (750-1400 nm) for the radical anions, whereas the dianionic species are characterized by similar spectra to those for the neutral dyes, however being bathochromically shifted and with increased molar extinction coefficients of approximately 100 000 M-1 cm-1. The increase of the transition dipole moment is up to 56% and accompanied by an almost cyanine-like red-shifted (by 300 nm) absorption spectrum for the most electron-poor tetracyanotetrachloro PBI. Whilst the outstanding fluorescence properties of the neutral PBIs are lost for the radical anions, an appreciable near-infrared (NIR) fluorescence with a quantum yield of up to 18% is revealed for the dianions by utilizing a custom-built flow-cell spectroelectrochemistry setup. Time-dependent density functional theory calculations help to assign the absorption bands to the respective electronic transitions.
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Affiliation(s)
- Rebecca Renner
- Universität Würzburg, Institut für Organische Chemie, Am Hubland, 97074 Würzburg, Germany.
| | - Matthias Stolte
- Universität Würzburg, Institut für Organische Chemie, Am Hubland, 97074 Würzburg, Germany.
- Universität Würzburg, Center for Nanosystems Chemistry (CNC), Theodor-Boveri-Weg, 97074 Würzburg, Germany
| | - Julia Heitmüller
- Universität Würzburg, Institut für Physikalische und Theoretische Chemie, Am Hubland, 97074 Würzburg, Germany
| | - Tobias Brixner
- Universität Würzburg, Center for Nanosystems Chemistry (CNC), Theodor-Boveri-Weg, 97074 Würzburg, Germany
- Universität Würzburg, Institut für Physikalische und Theoretische Chemie, Am Hubland, 97074 Würzburg, Germany
| | - Christoph Lambert
- Universität Würzburg, Institut für Organische Chemie, Am Hubland, 97074 Würzburg, Germany.
- Universität Würzburg, Center for Nanosystems Chemistry (CNC), Theodor-Boveri-Weg, 97074 Würzburg, Germany
| | - Frank Würthner
- Universität Würzburg, Institut für Organische Chemie, Am Hubland, 97074 Würzburg, Germany.
- Universität Würzburg, Center for Nanosystems Chemistry (CNC), Theodor-Boveri-Weg, 97074 Würzburg, Germany
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22
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Batignani G, Sansone C, Ferrante C, Fumero G, Mukamel S, Scopigno T. Excited-State Energy Surfaces in Molecules Revealed by Impulsive Stimulated Raman Excitation Profiles. J Phys Chem Lett 2021; 12:9239-9247. [PMID: 34533307 PMCID: PMC8488957 DOI: 10.1021/acs.jpclett.1c02209] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Accepted: 08/16/2021] [Indexed: 05/14/2023]
Abstract
Photophysical and photochemical processes are ruled by the interplay between transient vibrational and electronic degrees of freedom, which are ultimately determined by the multidimensional potential energy surfaces (PESs). Differences between ground and excited PESs are encoded in the relative intensities of resonant Raman bands, but they are experimentally challenging to access, requiring measurements at multiple wavelengths under identical conditions. Herein, we perform a two-color impulsive vibrational scattering experiment to launch nuclear wavepacket motions by an impulsive pump and record their coupling with a targeted excited-state potential by resonant Raman processes with a delayed probe, generating in a single measurement background-free vibrational spectra across the entire sample absorption. Building on the interference between the multiple pathways resonant with the excited-state manifold that generate the Raman signal, we show how to experimentally tune their relative phase by varying the probe chirp, decoding nuclear displacements along different normal modes and revealing the multidimensional PESs. Our results are validated against time-dependent density functional theory.
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Affiliation(s)
- Giovanni Batignani
- Dipartimento
di Fisica, Universitá di Roma “La
Sapienza”, Roma I-00185, Italy
- Istituto
Italiano di Tecnologia, Center for Life Nano Science @Sapienza, Roma I-00161, Italy
| | - Carlotta Sansone
- Dipartimento
di Fisica, Universitá di Roma “La
Sapienza”, Roma I-00185, Italy
| | - Carino Ferrante
- Dipartimento
di Fisica, Universitá di Roma “La
Sapienza”, Roma I-00185, Italy
- Istituto
Italiano di Tecnologia, Center for Life Nano Science @Sapienza, Roma I-00161, Italy
| | - Giuseppe Fumero
- Dipartimento
di Fisica, Universitá di Roma “La
Sapienza”, Roma I-00185, Italy
| | - Shaul Mukamel
- Department
of Chemistry, University of California, Irvine, California 92623, United States
| | - Tullio Scopigno
- Dipartimento
di Fisica, Universitá di Roma “La
Sapienza”, Roma I-00185, Italy
- Istituto
Italiano di Tecnologia, Center for Life Nano Science @Sapienza, Roma I-00161, Italy
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23
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Kang S, Kim T, Hong Y, Würthner F, Kim D. Charge-Delocalized State and Coherent Vibrational Dynamics in Rigid PBI H-Aggregates. J Am Chem Soc 2021; 143:9825-9833. [PMID: 34165972 DOI: 10.1021/jacs.1c03276] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Herein, the ultrafast photoinduced dynamics and vibrational coherences for two perylenebisimide (PBI) H-aggregates showcase the formation of the excimer state and the delocalized radical anion state in the excited state, respectively. Using femtosecond transient absorption (fs-TA) and time-resolved impulsive stimulated Raman scattering (TR-ISRS) measurements, we unveiled excited-state dynamics of PBI H-aggregates in two aspects: (1) the intermolecular interactions between PBI units in H-aggregates induce the formation of new excited states, excimer and delocalized radical anion states, and (2) the intermolecular out-of-plane along the aggregate axis and the PBI core C═C stretch Raman modes can be a crucial indicator to understand the coherent exciton dynamics in H-aggregates. Notably, those excited-state Raman modes showed stationary peak positions during the excited-state dynamics. TR-ISRS analysis provides insights into the excited-state vibrational coherences concerning the formation of the excimer and charge-delocalized state in each aggregate system.
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Affiliation(s)
- Seongsoo Kang
- Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University, Seoul 03722, South Korea
| | - Taeyeon Kim
- Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University, Seoul 03722, South Korea
| | - Yongseok Hong
- Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University, Seoul 03722, South Korea
| | - Frank Würthner
- Institut for Organische Chemie and Center for Nanosystems Chemistry, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Dongho Kim
- Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University, Seoul 03722, South Korea
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24
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Kuramochi H, Tahara T. Tracking Ultrafast Structural Dynamics by Time-Domain Raman Spectroscopy. J Am Chem Soc 2021; 143:9699-9717. [PMID: 34096295 PMCID: PMC9344463 DOI: 10.1021/jacs.1c02545] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
![]()
In traditional Raman spectroscopy,
narrow-band light is irradiated
on a sample, and its inelastic scattering, i.e., Raman scattering,
is detected. The energy difference between the Raman scattering and
the incident light corresponds to the vibrational energy of the molecule,
providing the Raman spectrum that contains rich information about
the molecular-level properties of the materials. On the other hand,
by using ultrashort optical pulses, it is possible to induce Raman-active
coherent nuclear motion of the molecule and to observe the molecular
vibration in real time. Moreover, this time-domain Raman measurement
can be combined with femtosecond photoexcitation, triggering chemical
changes, which enables tracking ultrafast structural dynamics in a
form of “time-resolved” time-domain Raman spectroscopy,
also known as time-resolved impulsive stimulated Raman spectroscopy.
With the advent of stable, ultrashort laser pulse sources, time-resolved
impulsive stimulated Raman spectroscopy now realizes high sensitivity
and a wide detection frequency window from THz to 3000 cm–1, and has seen success in unveiling the molecular mechanisms underlying
the efficient functions of complex molecular systems. In this Perspective,
we overview the present status of time-domain Raman spectroscopy,
particularly focusing on its application to the study of femtosecond
structural dynamics. We first explain the principle and a brief history
of time-domain Raman spectroscopy and then describe the apparatus
and recent applications to the femtosecond dynamics of complex molecular
systems, including proteins, molecular assemblies, and functional
materials. We also discuss future directions for time-domain Raman
spectroscopy, which has reached a status allowing a wide range of
applications.
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Affiliation(s)
- Hikaru Kuramochi
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan
- Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), 2-1 Hirosawa, Wako 351-0198, Japan
- Research Center of Integrative Molecular Systems (CIMoS), Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan
- JST, PRESTO, 4-1-8 Honcho, Kawaguchi 332-0012, Japan
| | - Tahei Tahara
- Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan
- Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), 2-1 Hirosawa, Wako 351-0198, Japan
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25
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Zhang W, Xu W, Zhang G, Kong J, Niu X, Chan JMW, Liu W, Xia A. Direct Tracking Excited-State Intramolecular Charge Redistribution of Acceptor-Donor-Acceptor Molecule by Means of Femtosecond Stimulated Raman Spectroscopy. J Phys Chem B 2021; 125:4456-4464. [PMID: 33902280 DOI: 10.1021/acs.jpcb.1c01742] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Symmetric quadrupolar molecules generally exhibit apolar ground states and dipolar excited states in a polar environment, which is explained by the excited state evolution from initial charge delocalization over all molecules to localization on one branch of the molecules after a femtosecond pulse excitation. However, direct observation of excited-state charge redistribution (delocalization/localization) is hardly accessible. Here, the intramolecular charge delocalization/localization character of a newly synthesized acceptor-donor-acceptor molecule (ADA) has been intensively investigated by femtosecond stimulated Raman scattering (FSRS) together with femtosecond transient absorption (fs-TA) spectroscopy. By tracking the excited state Raman spectra of the specific alkynyl (-C≡C-) bonds at each branch of ADA, we found that the nature of the relaxed S1 state is strongly governed by solvent polarity: symmetric delocalized intramolecular charge transfer (ICT) characters occurred in apolar solvent, whereas the asymmetric localized ICT characters appeared in polar solvent because of solvation. The solvation dynamics of ADA extracted from fs-TA is consistent with the time constants obtained by FSRS, but the FSRS clearly tracks the excited state intramolecular charge transfer delocalization/localization.
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Affiliation(s)
- Wei Zhang
- School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, P. R. China.,Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R China.,University of Chinese Academy of Sciences, Beijing 100049, P. R China
| | - Wenqi Xu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, P. R. China.,STU & SIOM Joint Laboratory for Superintense Lasers and the Applications, Shanghai 201210, P. R. China
| | - Guoxian Zhang
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie Pvt., Ottawa, Ontario K1N 6N5, Canada
| | - Jie Kong
- Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R China.,University of Chinese Academy of Sciences, Beijing 100049, P. R China
| | - Xinmiao Niu
- Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R China.,University of Chinese Academy of Sciences, Beijing 100049, P. R China
| | - Julian M W Chan
- Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie Pvt., Ottawa, Ontario K1N 6N5, Canada
| | - Weimin Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, P. R. China.,STU & SIOM Joint Laboratory for Superintense Lasers and the Applications, Shanghai 201210, P. R. China
| | - Andong Xia
- School of Science, Beijing University of Posts and Telecommunications (BUPT), Beijing 100876, P. R. China.,Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R China
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26
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Young RM, Wasielewski MR. Mixed Electronic States in Molecular Dimers: Connecting Singlet Fission, Excimer Formation, and Symmetry-Breaking Charge Transfer. Acc Chem Res 2020; 53:1957-1968. [PMID: 32786248 DOI: 10.1021/acs.accounts.0c00397] [Citation(s) in RCA: 118] [Impact Index Per Article: 29.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
ConspectusChromophore aggregates are capable of a wide variety of excited-state dynamics that are potentially of great use in optoelectronic devices based on organic molecules. For example, singlet fission, the process by which a singlet exciton is down converted into two triplet excitons, holds promise for extending the efficiency of solar cells, while other processes, such as excimer formation, are commonly regarded as parasitic pathways or traps. Other processes, such as symmetry-breaking charge transfer, where the excited dimer charge separates into a radical ion pair, can be both a trap and potentially useful in devices, depending on the context. Thus, an understanding of the precise mechanisms of each of these processes is vital to designing tailor-made organic chromophores for molecular optoelectronics.These excited-state phenomena have each been well-studied in recent years and show tantalizing connections as the molecular systems and environments are subtly changed. These seemingly disparate phenomena can be described within the same unifying framework, where each case can be represented as one point in continuum of mixed states. The coherent mixed state is observed experimentally, and it collapses to each of the limiting cases under well-defined conditions. This framework is especially useful in demonstrating the connections between these different states so that we can determine the factors that control their evolution and may ultimately guide the state mixtures to the product state of choice. The emerging picture shows that tuning the electronic coupling through proper arrangement of the chromophores must accompany environmental tuning of the chromophore energies to produce a fully mixed state. Changes in either of these quantities leads to evolution of the admixture and ultimately collapsing the superposition onto a given state, producing one of the photophysical pathways discussed above.In our laboratory, we are utilizing covalent dimers to precisely arrange the chromophores in rigid, well-defined geometries to systematically study the factors that determine the degree of state mixing and its fate. We interrogate these dynamics with transient absorption spectroscopy from the UV continuously into the mid-infrared, along with time-resolved Raman and emission and magnetic resonance spectroscopies to build a complete and detailed molecular level picture of the dynamics of these dimers. The knowledge gained from dimer studies can also be applied to the understanding the dynamics in extended molecular solids. The insight afforded by these studies will help guide the creation of new designer chromophores with control over the fate of the excited state.
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Affiliation(s)
- Ryan M. Young
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Michael R. Wasielewski
- Department of Chemistry and Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States
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