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Huxter VM. Advancing Organic Photoredox Catalysis: Mechanistic Insight through Time-Resolved Spectroscopy. J Phys Chem Lett 2024:7945-7953. [PMID: 39074366 DOI: 10.1021/acs.jpclett.4c00895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/31/2024]
Abstract
The rapid development of light-activated organic photoredox catalysts has led to the proliferation of powerful synthetic chemical strategies with industrial and pharmaceutical applications. Despite the advancement in synthetic approaches, a detailed understanding of the mechanisms governing these reactions has lagged. Time-resolved optical spectroscopy provides a method to track organic photoredox catalysis processes and reveal the energy pathways that drive reaction mechanisms. These measurements are sensitive to key processes in organic photoredox catalysis such as charge or energy transfer, lifetimes of singlet or triplet states, and solvation dynamics. The sensitivity and specificity of ultrafast spectroscopic measurements can provide a new perspective on the mechanisms of these reactions, including electron-transfer events, the role of solvent, and the short lifetimes of radical intermediates.
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Affiliation(s)
- Vanessa M Huxter
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
- Department of Physics, University of Arizona, Tucson, Arizona 85721, United States
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2
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Verma P, Budkina DS, Vauthey E. Photoinduced Electron Transfer between Dipolar Reactants: Solvent and Excitation Wavelength Effects. J Phys Chem B 2024; 128:1231-1240. [PMID: 38265415 DOI: 10.1021/acs.jpcb.3c07922] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2024]
Abstract
Electron transfer (ET) quenching in nonpolar media is not as well understood as in polar environments. Here, we investigate the effect of dipole-dipole interactions between the reactants using ultrafast broadband electronic spectroscopy combined with molecular dynamics simulations. We find that the quenching of the S1 state of two polar dyes, coumarin 152a and Nile red, by the polar N,N-dimethylaniline (DMA) in cyclohexane is faster by a factor up to 3 when exciting on the red edge rather than at the maximum of their S1 ← S0 absorption band. This originates from the inhomogeneous broadening of the band due to a distribution of the number of quencher molecules around the dyes. As a consequence, red-edge excitation photoselects dyes in a DMA-rich environment. Such broadening is not present in acetonitrile, and no excitation wavelength dependence of the ET dynamics is observed. The quenching of both dyes is markedly faster in nonpolar than polar solvents, independently of the excitation wavelength. According to molecular dynamics simulations, this is due to the preferential solvation of the dyes by DMA in cyclohexane. The opposite preferential solvation is predicted in acetonitrile. Consequently, close contact between the reactants in acetonitrile requires partial desolvation. By contrast, the recombination of the quenching product is slower in nonpolar than in polar solvents and exhibits much smaller dependence, if any, on the excitation wavelength.
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Affiliation(s)
- Pragya Verma
- Department of Physical Chemistry, University of Geneva, 30 Quai Ernest-Ansermet, 1211 Geneva, Switzerland
| | - Darya S Budkina
- Department of Physical Chemistry, University of Geneva, 30 Quai Ernest-Ansermet, 1211 Geneva, Switzerland
| | - Eric Vauthey
- Department of Physical Chemistry, University of Geneva, 30 Quai Ernest-Ansermet, 1211 Geneva, Switzerland
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Wega J, Vauthey E. Bimolecular photoinduced symmetry-breaking charge separation of perylene in solution. Photochem Photobiol Sci 2024; 23:93-105. [PMID: 38133700 PMCID: PMC10834668 DOI: 10.1007/s43630-023-00504-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Accepted: 11/05/2023] [Indexed: 12/23/2023]
Abstract
Photoinduced symmetry-breaking charge separation (SB-CS) results in the generation of charge carriers through electron transfer between two identical molecules, after photoexcitation of one of them. It is usually studied in systems where the two reacting moieties are covalently linked. Examples of photoinduced bimolecular SB-CS with organic molecules yielding free ions remain scarce due to solubility or aggregation issues at the high concentrations needed to study this diffusion-assisted process. Here we investigate the excited-state dynamics of perylene (Pe) at high concentrations in solvents of varying polarity. Transient absorption spectroscopy on the subnanosecond to microsecond timescales reveal that self-quenching of Pe in the lowest singlet excited state leads to excimer formation in all solvents used. Additionally, bimolecular SB-CS, resulting in the generation of free ions, occurs concurrently to excimer formation in polar media, with a relative efficiency that increases with the polarity of the solvent. Moreover, we show that SB-CS is most efficient in room-temperature ionic liquids due to a charge-shielding effect leading to a larger escape of ions and due to the high viscosity that disfavours excimer formation.
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Affiliation(s)
- Johannes Wega
- Department of Physical Chemistry, University of Geneva, Quai Ernest Ansermet 30, 1205, Geneva, Switzerland
| | - Eric Vauthey
- Department of Physical Chemistry, University of Geneva, Quai Ernest Ansermet 30, 1205, Geneva, Switzerland.
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Liu Z, Hu H, Sun X. Multistate Reaction Coordinate Model for Charge and Energy Transfer Dynamics in the Condensed Phase. J Chem Theory Comput 2023; 19:7151-7170. [PMID: 37815937 PMCID: PMC10601487 DOI: 10.1021/acs.jctc.3c00770] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Indexed: 10/12/2023]
Abstract
Constructing multistate model Hamiltonians from all-atom electronic structure calculations and molecular dynamics simulations is crucial for understanding charge and energy transfer dynamics in complex condensed phases. The most popular two-level system model is the spin-boson Hamiltonian, where the nuclear degrees of freedom are represented as shifted normal modes. Recently, we proposed the general multistate nontrivial extension of the spin-boson model, i.e., the multistate harmonic (MSH) model, which is constructed by extending the spatial dimensions of each nuclear mode so as to satisfy the all-atom reorganization energy restrictions for all pairs of electronic states. In this work, we propose the multistate reaction coordinate (MRC) model with a primary reaction coordinate and secondary bath modes as in the Caldeira-Leggett form but in extended spatial dimensions. The MRC model is proven to be equivalent to the MSH model and offers an intuitive physical picture of the nuclear-electronic feedback in nonadiabatic processes such as the inherent trajectory of the reaction coordinate. The reaction coordinate is represented in extended dimensions, carrying the entire reorganization energies and bilinearly coupled to the secondary bath modes. We demonstrate the MRC model construction for photoinduced charge transfer in an organic photovoltaic caroteniod-porphyrin-C60 molecular triad dissolved in tetrahydrofuran as well as excitation energy transfer in a photosynthetic light-harvesting Fenna-Matthews-Olson complex. The MRC model provides an effective and robust platform for investigating quantum dissipative dynamics in complex condensed-phase systems since it allows a consistent description of realistic spectral density, state-dependent system-bath couplings, and heterogeneous environments due to static disorder in reorganization energies.
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Affiliation(s)
- Zengkui Liu
- Division
of Arts and Sciences, NYU Shanghai, 567 West Yangsi Road, Shanghai, 200124, China
- NYU-ECNU
Center for Computational Chemistry at NYU Shanghai, 3663 Zhongshan Road North, Shanghai, 200062, China
- Department
of Chemistry, New York University, New York, New York, 10003, United States
| | - Haorui Hu
- Division
of Arts and Sciences, NYU Shanghai, 567 West Yangsi Road, Shanghai, 200124, China
| | - Xiang Sun
- Division
of Arts and Sciences, NYU Shanghai, 567 West Yangsi Road, Shanghai, 200124, China
- NYU-ECNU
Center for Computational Chemistry at NYU Shanghai, 3663 Zhongshan Road North, Shanghai, 200062, China
- Department
of Chemistry, New York University, New York, New York, 10003, United States
- Shanghai
Frontiers Science Center of Artificial Intelligence and Deep Learning, NYU Shanghai, 567 West Yangsi Road, Shanghai, 200124, China
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Pratihar S, Prasad E. Effect of positional isomerism on the excited state charge transfer dynamics of anthracene-based D-π-A systems. Phys Chem Chem Phys 2023; 25:5226-5236. [PMID: 36723193 DOI: 10.1039/d2cp03958c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Understanding the dynamics of the back electron transfer (BET) rate of ion pairs from the electronically excited state of donor-acceptor systems is crucial for developing materials for organic electronics. The structure-property relationships in the organic molecular architectures play a key role in controlling the BET rate and have been utilized as a criterion to design systems with a reduced BET rate. Here, we examine the influence of isomerism on the BET rate in anthracene based systems, viz., (E)-2-(2-(anthracen-9-yl)vinyl)benzonitrile (ortho-CN) and (E)-3-(2-(anthracen-9-yl)vinyl)benzonitrile (meta-CN) with N,N-diethylaniline (DEA) in methylcyclohexane using time-resolved spectroscopy. The radical cation (DEA˙+) and the radical anion (ortho-CN˙- or meta-CN˙-) generated after photoexcitation show synchronous decay kinetics, and the rate constant of back electron transfer (kBET) for the DEA/ortho-CN pair was 6.6 × 104 s-1, which is ca. 2 orders of magnitude lower compared with the DEA/meta-CN pair. The role of isomerism in providing resonance stabilization for the organic radicals is expected to have implications for strategies that retard charge recombination in photovoltaics. The role of the molecular structural features that dictate the kinetics for charge recombination has been further identified using quantum calculations.
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Affiliation(s)
- Swatilekha Pratihar
- Department of Chemistry, Indian Institute of Technology Madras, Chennai-600036, Tamil Nadu, India.
| | - Edamana Prasad
- Department of Chemistry, Indian Institute of Technology Madras, Chennai-600036, Tamil Nadu, India.
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Jiao Z, Yang C, Zhou Q, Hu Z, Jie J, Zhang X, Su H. Sequence-specific binding behavior of coralyne toward triplex DNA: An ultrafast time-resolved fluorescence spectroscopy study. J Chem Phys 2023; 158:045101. [PMID: 36725513 DOI: 10.1063/5.0133913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Triplex DNA structure has potential therapeutic application in inhibiting the expression of genes involved in cancer and other diseases. As a DNA-targeting antitumor and antibiotic drug, coralyne shows a remarkable binding propensity to triplex over canonical duplex and thus can modulate the stability of triplex structure, providing a prospective gene targeting strategy. Much less is known, however, about coralyne-binding interactions with triplex. By combining multiple steady-state spectroscopy with ultrafast fluorescence spectroscopy, we have investigated the binding behaviors of coralyne with typical triplexes. Upon binding with a G-containing triplex, the fluorescence of coralyne is markedly quenched owing to the photoinduced electron transfer (PET) of coralyne with the G base. Systematic studies show that the PET rates are sensitive to the binding configuration and local microenvironment, from which the coexisting binding modes of monomeric (full and partial) intercalation and aggregate stacking along the sugar-phosphate backbone are distinguished and their respective contributions are determined. It shows that coralyne has preferences for monomeric intercalation within CGG triplex and pure TAT triplex, whereas CGC+ triplex adopts mainly backbone binding of coralyne aggregates due to charge repulsion, revealing the sequence-specific binding selectivity. The triplex-DNA-induced aggregation of coralyne could be used as a probe for recognizing the water content in local DNA structures. The strong π-π stacking of intercalated coralyne monomer with base-triplets plays an important role in stabilizing the triplex structure. These results provide mechanistic insights for understanding the remarkable propensity of coralyne in selective binding to triplex DNA and shed light on the prospective applications of coralyne-triplex targeted anti-gene therapeutics.
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Affiliation(s)
- Zeqing Jiao
- College of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Chunfan Yang
- College of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Qian Zhou
- College of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Zheng Hu
- College of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Jialong Jie
- College of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Xianwang Zhang
- College of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Hongmei Su
- College of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China
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Sarkar S, Chatterjee A, Biswas K. A Recent Update on Rhodamine Dye Based Sensor Molecules: A Review. Crit Rev Anal Chem 2023:1-27. [PMID: 36705594 DOI: 10.1080/10408347.2023.2169598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Herein we have discussed such important modified rhodamine compounds which have been used as chemosensors for the last 7-8 years. This review covered some chemosensors for the detection of metal ions like Al(III), Cu(II), Hg(II), Co(II), Fe(III), Au(III), Cr(III), and some anion like CN-. The selectivity, sensitivity, photophysical properties (i.e., UV-Vis spectral studies, fluorescence studies giving special emphasis to absorption wavelength in UV-Vis spectra and excitation and emission wavelength in fluorescence spectra), binding affinity, the limit of detection, and the application of those chemosensors are described clearly. Here we have also discussed some functionalized rhodamine-based chemosensors that emit in the near-infrared region (NIR) and can target lysosomes and detect lysosomal pH. Their versatile applicability in the medicinal ground is also delineated. We have focused on the photophysical properties of spirolactam rhodamine photoswitches and applications in single-molecule localization microscopy and volumetric 3D light photoactivable dye displays. The real-time detection of radical intermediates has also been exemplified.
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Affiliation(s)
- Soma Sarkar
- Department of Chemistry, Raiganj University, Raiganj, Uttar Dinajpur, West Bengal, India
| | - Abhik Chatterjee
- Department of Chemistry, Raiganj University, Raiganj, Uttar Dinajpur, West Bengal, India
| | - Kinkar Biswas
- Department of Chemistry, University of North Bengal, Darjeeling, West Bengal, India
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Ramamurthy V, Sen P, Elles CG. Ultrafast Excited State Dynamics of Spatially Confined Organic Molecules. J Phys Chem A 2022; 126:4681-4699. [PMID: 35786917 DOI: 10.1021/acs.jpca.2c03276] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This Feature Article highlights the role of spatial confinement in controlling the fundamental behavior of molecules. Select examples illustrate the value of using space as a tool to control and understand excited-state dynamics through a combination of ultrafast spectroscopy and conventional steady-state methods. Molecules of interest were confined within a closed molecular capsule, derived from a cavitand known as octa acid (OA), whose internal void space is sufficient to accommodate molecules as long as tetracene and as wide as pyrene. The free space, i.e., the space that is left following the occupation of the guest within the host, is shown to play a significant role in altering the behavior of guest molecules in the excited state. The results reported here suggest that in addition to weak interactions that are commonly emphasized in supramolecular chemistry, the extent of empty space (i.e., the remaining void space within the capsule) is important in controlling the excited-state behavior of confined molecules on ultrafast time scales. For example, the role of free space in controlling the excited-state dynamics of guest molecules is highlighted by probing the cis-trans isomerization of stilbenes and azobenzenes within the OA capsule. Isomerization of both types of molecule are slowed when they are confined within a small space, with encapsulated azobenzenes taking a different reaction pathway compared to that in solution upon excitation to S2. In addition to steric constraints, confinement of reactive molecules in a small space helps to override the need for diffusion to bring the reactants together, thus enabling the measurement of processes that occur faster than the time scale for diffusion. The advantages of reducing free space and confining reactive molecules are illustrated by recording unprecedented excimer emission from anthracene and by measuring ultrafast electron transfer rates across the organic molecular wall. By monitoring the translational motion of anthracene pairs in a restricted space, it has been possible to document the pathway undertaken by excited anthracene from inception to the formation of the excimer on the excited-state surface. Similarly, ultrafast electron transfer experiments pursued here have established that the process is not hindered by a molecular wall. Apparently, the electron can cross the OA capsule wall provided the donor and acceptor are in close proximity. Measurements on the ultrafast time scale provide crucial insights for each of the examples presented here, emphasizing the value of both "space" and "time" in controlling and understanding the dynamics of excited molecules.
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Affiliation(s)
| | - Pratik Sen
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, UP 208 016, India
| | - Christopher G Elles
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States
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