51
|
Nie Z, Long R, Li J, Zheng YY, Prezhdo OV, Loh ZH. Selective Excitation of Atomic-Scale Dynamics by Coherent Exciton Motion in the Non-Born-Oppenheimer Regime. J Phys Chem Lett 2013; 4:4260-4266. [PMID: 26296176 DOI: 10.1021/jz401945m] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Time-domain investigations of the nonadiabatic coupling between electronic and vibrational degrees of freedom have focused primarily on the formation of electronic superpositions induced by atomic motion. The effect of electronic nonstationary-state dynamics on atomic motion remains unexplored. Here, phase-coherent excitation of the two lowest electronic transitions in semiconducting single-walled carbon nanotubes by broadband <5-fs pulses directly triggers coherent exciton motion along the axis of the nanotubes. Optical pump-probe spectroscopy with sub-10-fs time resolution reveals that exciton motion selectively excites the high-frequency G mode coherent phonon, in good agreement with results obtained from time-domain ab initio simulations. This observed phenomenon arises from the direct modulation of the C-C interatomic potential by coherent exciton motion on a time scale that is commensurate with atomic motion. Our results suggest the possibility of employing light-field manipulation of electron densities in the non-Born-Oppenheimer regime to initiate selective atomic motion.
Collapse
Affiliation(s)
- Zhaogang Nie
- †Division of Chemistry and Biological Chemistry, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 631371, Singapore
| | - Run Long
- ‡Department of Chemistry, University of Rochester, RC Box 270216, Rochester, New York 14627, United States
- §School of Physics, Complex Adaptive Systems Laboratory, University College Dublin, Belfield, Dublin 4, Ireland
| | - Jialin Li
- †Division of Chemistry and Biological Chemistry, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 631371, Singapore
| | - Yi Ying Zheng
- †Division of Chemistry and Biological Chemistry, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 631371, Singapore
| | - Oleg V Prezhdo
- ‡Department of Chemistry, University of Rochester, RC Box 270216, Rochester, New York 14627, United States
| | - Zhi-Heng Loh
- †Division of Chemistry and Biological Chemistry, and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 631371, Singapore
| |
Collapse
|
52
|
Casanova D. Electronic Structure Study of Singlet Fission in Tetracene Derivatives. J Chem Theory Comput 2013; 10:324-34. [PMID: 26579913 DOI: 10.1021/ct4007635] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A detailed theoretical study of the singlet fission process in tetracene and two of its derivatives, that is 5,12-diphenyltetracene (DPT) and rubrene, is presented. This work aims to unravel the intricacies and the differences of their singlet fission mechanism by means of electronic structure calculations using molecular and cluster models and a variety of computational tools. Although the electronic structure at the molecular level is very similar for the three compounds, their different crystal packing has important consequences in their ability to produce two triplet states from a single exciton. The results obtained indicate that the lowest singlet is found to delocalize at least over seven molecules. Computed relative energies rule out the presence of charge transfer (CT) states as intermediates in a two-step mechanism in all cases. On the other hand, CT states do play a role as mediators, specially in tetracene. They decisively participate in the coupling between single and multiexcitonic states through second-order contributions. Finally, the present study pinpoints that the transition from the optically allowed exciton to the dark multiexciton state might be facilitated by intramolecular motion toward the lowest excited singlet geometry.
Collapse
Affiliation(s)
- David Casanova
- IKERBASQUE, Basque Foundation for Science , 48011 Bilbao, Spain.,Kimika Fakultatea, Euskal Herriko Unibertsitatea (UPV/EHU) , P.K. 1072, 20080 Donostia, Spain.,Donostia International Physics Center (DIPC) , 20018 Donostia, Spain
| |
Collapse
|
53
|
Abstract
The photophysical behavior of organic semiconductors is governed by their excitonic states. In this review, I classify the three different exciton types (Frenkel singlet, Frenkel triplet, and charge transfer) typically encountered in organic semiconductors. Experimental challenges that arise in the study of solid-state organic systems are discussed. The steady-state spectroscopy of intermolecular delocalized Frenkel excitons is described, using crystalline tetracene as an example. I consider the problem of a localized exciton diffusing in a disordered matrix in detail, and experimental results on conjugated polymers and model systems suggest that energetic disorder leads to subdiffusive motion. Multiexciton processes such as singlet fission and triplet fusion are described, emphasizing the role of spin state coherence and magnetic fields in studying singlet ↔ triplet pair interconversion. Singlet fission provides an example of how all three types of excitons (triplet, singlet, and charge transfer) may interact to produce useful phenomena for applications such as solar energy conversion.
Collapse
|
54
|
Vallett PJ, Snyder JL, Damrauer NH. Tunable electronic coupling and driving force in structurally well-defined tetracene dimers for molecular singlet fission: a computational exploration using density functional theory. J Phys Chem A 2013; 117:10824-38. [PMID: 24053123 DOI: 10.1021/jp407426q] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Singlet fission (SF), a process by which two excited states are formed in a chromophoric system following the absorption of a single photon, has the potential to increase the theoretical efficiency of solar energy conversion devices beyond the single-junction Shockley-Quiesser limit. Although SF is observed with high yield in the solid state of certain molecules, linearly linked dimers based on these same constituents exhibit small yields in part due to small interchromophore electronic coupling. Previous work from our group demonstrated enhancement of SF yield in polycrystalline tetracene (Tc) via excitation of intermolecular motions, which increased direct overlap of monomer π-systems. In this current work, a series of norbornyl-bridged bistetracene (BT) dimers are investigated using DFT and the ability to control SF thermodynamics along with important interchromophore electronic coupling parameters via bridging geometry is shown. Although the electronic coupling of a series of C2v-symmetric dimers (BT1-BT3) that differ in norbornyl bridge length is larger than in previously studied Tc dimers, a key nonhorizontal electron-transfer (ET) matrix element used in determining the SF rate is zero due to symmetry. In these systems, SF may be expected but electronic excitation will require coupling to vibrational modes that break symmetry. Singly bridged dimer isomers BT1-trans and BT1-cis, which break the C2v symmetry of BT1 by exploiting attachment of the norbornyl bridge at the 1,2 instead of the 2,3 Tc positions, are expected to be significantly more favorable for SF due to an exoergic driving force, increased electronic coupling, a lower charge-transfer-state energy (particularly in the case of BT1-cis), and nonhorizontal ET matrix elements that are nonzero.
Collapse
Affiliation(s)
- Paul J Vallett
- Department of Chemistry and Biochemistry, University of Colorado Boulder , Boulder, Colorado 80309, United States
| | | | | |
Collapse
|
55
|
Vallett PJ, Damrauer NH. Experimental and Computational Exploration of Ground and Excited State Properties of Highly Strained Ruthenium Terpyridine Complexes. J Phys Chem A 2013; 117:6489-507. [DOI: 10.1021/jp404248z] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Paul J. Vallett
- Department
of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, Colorado 80309,
United States
| | - Niels H. Damrauer
- Department
of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, Colorado 80309,
United States
| |
Collapse
|
56
|
Mastron JN, Roberts ST, McAnally RE, Thompson ME, Bradforth SE. Aqueous Colloidal Acene Nanoparticles: A New Platform for Studying Singlet Fission. J Phys Chem B 2013; 117:15519-26. [DOI: 10.1021/jp4057972] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Joseph N. Mastron
- Department of Chemistry
and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089, United States
| | - Sean T. Roberts
- Department of Chemistry
and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089, United States
| | - R. Eric McAnally
- Department of Chemistry
and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089, United States
| | - Mark E. Thompson
- Department of Chemistry
and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089, United States
| | - Stephen E. Bradforth
- Department of Chemistry
and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089, United States
| |
Collapse
|
57
|
Burdett JJ, Bardeen CJ. The dynamics of singlet fission in crystalline tetracene and covalent analogs. Acc Chem Res 2013; 46:1312-20. [PMID: 23360099 DOI: 10.1021/ar300191w] [Citation(s) in RCA: 141] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Singlet fission (SF) is a spin-allowed process in which an excited singlet state spontaneously splits into a pair of triplet excitons. This relaxation pathway is of interest as a mechanism for increasing the efficiency of photovoltaic solar cells, since ionization of the triplets could produce two charge carriers per absorbed photon. In this Account, we summarize our recent work on trying to understand how SF occurs using both covalent and noncovalent assemblies of tetracene. We first give a brief overview of the SF process and discuss why tetracene, where the singlet and triplet pair energies are nearly degenerate, is a particularly useful molecule for studying this process. Then we describe our experiments, beginning with the study of phenylene-linked tetracene dimers as covalent analogs for the crystal form, where SF is known to be very efficient. We found that only 2-3% of the initially excited singlets underwent SF in these dimers. These results motivated us to study crystalline tetracene in more detail. Transient absorption and photoluminescence experiments on polycrystalline thin films provided evidence for a delocalized singlet exciton that decays with a complicated temperature-dependence, but we were unable to unambiguously identify the signature of the triplet pair formed by SF. Then, using ultrathin single crystals, we observed quantum beats in the delayed fluorescence arising from recombination of spin-coherent triplet pairs. Analyzing these quantum beats revealed that SF proceeds through a direct one-step process occurring within 200 ps at room temperature. The product of this reaction is a pair of unperturbed triplets that have negligible interaction with each other. Looking at the overall SF process in tetracene, remaining issues that need to be clarified include the role of exciton diffusion, the temperature dependence of the SF rate, and how to use insights gained from the solid-state studies to generate design principles for high-efficiency covalent systems. Our experiments provide a good illustration of why the polyacenes, and tetracene in particular, play an important role as systems for the study of SF.
Collapse
Affiliation(s)
- Jonathan J. Burdett
- Department of Chemistry, University of California, Riverside, 501 Big Springs Road, Riverside, California 92521, United States
| | - Christopher J. Bardeen
- Department of Chemistry, University of California, Riverside, 501 Big Springs Road, Riverside, California 92521, United States
| |
Collapse
|
58
|
Zimmerman PM, Musgrave CB, Head-Gordon M. A correlated electron view of singlet fission. Acc Chem Res 2013; 46:1339-47. [PMID: 23427823 DOI: 10.1021/ar3001734] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Singlet fission occurs when a single exciton splits into multiple electron-hole pairs, and could dramatically increase the efficiency of organic solar cells by converting high energy photons into multiple charge carriers. Scientists might exploit singlet fission to its full potential by first understanding the underlying mechanism of this quantum mechanical process. The pursuit of this fundamental mechanism has recently benefited from the development and application of new correlated wave function methods. These methods-called restricted active space spin flip-can capture the most important electron interactions in molecular materials, such as acene crystals, at low computational cost. It is unrealistic to use previous wave function methods due to the excessive computational cost involved in simulating realistic molecular structures at a meaningful level of electron correlation. In this Account, we describe how we use these techniques to compute single exciton and multiple exciton excited states in tetracene and pentacene crystals in order to understand how a single exciton generated from photon absorption undergoes fission to generate two triplets. Our studies indicate that an adiabatic charge transfer intermediate is unlikely to contribute significantly to the fission process because it lies too high in energy. Instead, we propose a new mechanism that involves the direct coupling of an optically allowed single exciton to an optically dark multiexciton. This coupling is facilitated by intermolecular motion of two acene monomers that drives nonadiabatic population transfer between the two states. This transfer occurs in the limit of near degeneracies between adiabatic states where the Born-Oppenheimer approximation of fixed nuclei is no longer valid. Existing theories for singlet fission have not considered this type of coupling between states and, therefore, cannot describe this mechanism. The direct mechanism through intermolecular motion describes many experimentally observed characteristics of these materials, such as the ultrafast time scale of photobleaching and triplet generation during singlet fission in pentacene. We believe this newly discovered mechanism provides fundamental insight to guide the creation of new solar materials that exhibit high efficiencies through multiple charge generation.
Collapse
Affiliation(s)
- Paul M. Zimmerman
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan, United States
| | - Charles B. Musgrave
- Department of Chemical and Biological Engineering, University of Colorado at Boulder, Boulder, Colorado, United States
| | - Martin Head-Gordon
- Lawrence Berkeley National Laboratory, Berkeley, California, United States
- Department of Chemistry, University of California at Berkeley, Berkeley, California, United States
| |
Collapse
|
59
|
Lee J, Bruzek MJ, Thompson NJ, Sfeir MY, Anthony JE, Baldo MA. Singlet exciton fission in a hexacene derivative. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2013; 25:1445-1448. [PMID: 23293054 DOI: 10.1002/adma.201203982] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2012] [Revised: 11/14/2012] [Indexed: 06/01/2023]
Abstract
Hexacene, an acene with six benzene rings, is notable for its exceptionally small triplet energy, around one third of the singlet energy. Herein, singlet fission, i.e., conversion of a singlet exciton into two triplets, is demonstrated in a thin film of hexacene derivative, employing both transient absorption spectroscopy and magnetic field effects on photocurrent.
Collapse
Affiliation(s)
- Jiye Lee
- Energy Frontier Research Center for Excitonics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | | | | | | | | | | |
Collapse
|
60
|
Abstract
A survey is provided of recent progress in the understanding of singlet fission, a spin-allowed process in which a singlet excited molecule shares its energy with a ground-state neighbor to produce two triplet excited molecules. It has been observed to occur in single-crystal, polycrystalline, and amorphous solids, on timescales from 80 fs to 25 ps, producing triplet yields as high as 200%. Photovoltaic devices using the effect have shown external quantum efficiencies in excess of 100%. Almost all the efficient materials are alternant hydrocarbons of the acene series or their simple derivatives, and it is argued that a wider structural variety would be desirable. The current state of the development of molecular structure design rules, based on first-principles theoretical considerations, is described along with initial examples of implementation.
Collapse
Affiliation(s)
- Millicent B Smith
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA
| | | |
Collapse
|
61
|
Tayebjee MJY, Clady RGCR, Schmidt TW. The exciton dynamics in tetracene thin films. Phys Chem Chem Phys 2013; 15:14797-805. [DOI: 10.1039/c3cp52609g] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
62
|
Hewitt JT, Vallett PJ, Damrauer NH. Dynamics of the 3MLCT in Ru(II) Terpyridyl Complexes Probed by Ultrafast Spectroscopy: Evidence of Excited-State Equilibration and Interligand Electron Transfer. J Phys Chem A 2012; 116:11536-47. [DOI: 10.1021/jp308091t] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Joshua T. Hewitt
- Department of Chemistry
and Biochemistry, University of Colorado, Boulder, Colorado
80309, United States
| | - Paul J. Vallett
- Department of Chemistry
and Biochemistry, University of Colorado, Boulder, Colorado
80309, United States
| | - Niels H. Damrauer
- Department of Chemistry
and Biochemistry, University of Colorado, Boulder, Colorado
80309, United States
| |
Collapse
|
63
|
Lynch MS, Slenkamp KM, Khalil M. Communication: Probing non-equilibrium vibrational relaxation pathways of highly excited C≡N stretching modes following ultrafast back-electron transfer. J Chem Phys 2012; 136:241101. [DOI: 10.1063/1.4731882] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Michael S. Lynch
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
| | - Karla M. Slenkamp
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
| | - Munira Khalil
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
| |
Collapse
|
64
|
Burdett JJ, Bardeen CJ. Quantum Beats in Crystalline Tetracene Delayed Fluorescence Due to Triplet Pair Coherences Produced by Direct Singlet Fission. J Am Chem Soc 2012; 134:8597-607. [DOI: 10.1021/ja301683w] [Citation(s) in RCA: 218] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Jonathan J. Burdett
- Department of Chemistry, University of California, Riverside, 501 Big Springs Road, Riverside,
California 92521, United States
| | - Christopher J. Bardeen
- Department of Chemistry, University of California, Riverside, 501 Big Springs Road, Riverside,
California 92521, United States
| |
Collapse
|
65
|
Roberts ST, McAnally RE, Mastron JN, Webber DH, Whited MT, Brutchey RL, Thompson ME, Bradforth SE. Efficient Singlet Fission Discovered in a Disordered Acene Film. J Am Chem Soc 2012; 134:6388-400. [DOI: 10.1021/ja300504t] [Citation(s) in RCA: 246] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Sean T. Roberts
- Department
of Chemistry and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089-0482, United States
| | - R. Eric McAnally
- Department
of Chemistry and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089-0482, United States
| | - Joseph N. Mastron
- Department
of Chemistry and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089-0482, United States
| | - David H. Webber
- Department
of Chemistry and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089-0482, United States
| | - Matthew T. Whited
- Department
of Chemistry and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089-0482, United States
| | - Richard L. Brutchey
- Department
of Chemistry and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089-0482, United States
| | - Mark E. Thompson
- Department
of Chemistry and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089-0482, United States
| | - Stephen E. Bradforth
- Department
of Chemistry and the Center for Energy Nanoscience, University of Southern California, Los Angeles, California
90089-0482, United States
| |
Collapse
|
66
|
Ramanan C, Smeigh AL, Anthony JE, Marks TJ, Wasielewski MR. Competition between singlet fission and charge separation in solution-processed blend films of 6,13-bis(triisopropylsilylethynyl)pentacene with sterically-encumbered perylene-3,4:9,10-bis(dicarboximide)s. J Am Chem Soc 2011; 134:386-97. [PMID: 22111926 DOI: 10.1021/ja2080482] [Citation(s) in RCA: 208] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The photophysics and morphology of thin films of N,N-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-bis(dicarboximide) (1) and the 1,7-diphenyl (2) and 1,7-bis(3,5-di-tert-butylphenyl) (3) derivatives blended with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pn) were studied for their potential use as photoactive layers in organic photovoltaic (OPV) devices. Increasing the steric bulk of the 1,7-substituents of the perylene-3,4:9,10-bis(dicarboximide) (PDI) impedes aggregation in the solid state. Film characterization data using both atomic force microscopy and X-ray diffraction showed that decreasing the PDI aggregation by increasing the steric bulk in the order 1 < 2 < 3 correlates with a decrease in the density/size of crystalline TIPS-Pn domains. Transient absorption spectroscopy was performed on ~100 nm solution-processed TIPS-Pn:PDI blend films to characterize the charge separation dynamics. These results showed that selective excitation of the TIPS-Pn results in competition between ultrafast singlet fission ((1*)TIPS-Pn + TIPS-Pn → 2 (3*)TIPS-Pn) and charge transfer from (1*)TIPS-Pn to PDIs 1-3. As the blend films become more homogeneous across the series TIPS-Pn:PDI 1 → 2 → 3, charge separation becomes competitive with singlet fission. Ultrafast charge separation forms the geminate radical ion pair state (1)(TIPS-Pn(+•)-PDI(-•)) that undergoes radical pair intersystem crossing to form (3)(TIPS-Pn(+•)-PDI(-•)), which then undergoes charge recombination to yield either (3*)PDI or (3*)TIPS-Pn. Energy transfer from (3*)PDI to TIPS-Pn also yields (3*)TIPS-Pn. These results show that multiple pathways produce the (3*)TIPS-Pn state, so that OPV design strategies based on this system must utilize this triplet state for charge separation.
Collapse
Affiliation(s)
- Charusheela Ramanan
- Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, Illinois 60208-3113, USA
| | | | | | | | | |
Collapse
|
67
|
Burdett JJ, Gosztola D, Bardeen CJ. The dependence of singlet exciton relaxation on excitation density and temperature in polycrystalline tetracene thin films: Kinetic evidence for a dark intermediate state and implications for singlet fission. J Chem Phys 2011; 135:214508. [DOI: 10.1063/1.3664630] [Citation(s) in RCA: 142] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
|
68
|
Zimmerman PM, Bell F, Casanova D, Head-Gordon M. Mechanism for singlet fission in pentacene and tetracene: from single exciton to two triplets. J Am Chem Soc 2011; 133:19944-52. [PMID: 22084927 DOI: 10.1021/ja208431r] [Citation(s) in RCA: 277] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Singlet fission (SF) could dramatically increase the efficiency of organic solar cells by producing two triplet excitons from each absorbed photon. While this process has been known for decades, most descriptions have assumed the necessity of a charge-transfer intermediate. This ab initio study characterizes the low-lying excited states in acene molecular crystals in order to describe how SF occurs in a realistic crystal environment. Intermolecular interactions are shown to localize the initially delocalized bright state onto a pair of monomers. From this localized state, nonadiabatic coupling mediated by intermolecular motion between the optically allowed exciton and a dark multi-exciton state facilitates SF without the need for a nearby low-lying charge-transfer intermediate. An estimate of the crossing rate shows that this direct quantum mechanical process occurs in well under 1 ps in pentacene. In tetracene, the dark multi-exciton state is uphill from the lowest singlet excited state, resulting in a dynamic interplay between SF and triplet-triplet annihilation.
Collapse
Affiliation(s)
- Paul M Zimmerman
- Department of Chemistry, University of California, Berkeley, California 94720, USA.
| | | | | | | |
Collapse
|
69
|
Holcman J, Al Choueiry A, Enderlin A, Hameau S, Barisien T, Legrand L. Coherent control of the optical emission in a single organic quantum wire. NANO LETTERS 2011; 11:4496-4502. [PMID: 21928810 DOI: 10.1021/nl2031822] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We report on the first coherent control experiments on a purely electronic exciton state in an extended quasi-perfect organic quantum wire, a polydiacetylene chain isolated in the crystalline matrix of its own monomer. The time-integrated luminescence of a single wire is measured as the relative phase between two exciting sub-picosecond laser pulses is varied. From visibility functions the exciton dephasing time is extracted and its temperature dependence studied. Our work points the predominant role of thermalization upon the phase relaxation dynamics. By means of microscopic imaging spectroscopy we also show that despite local excitation coherent control is achieved on states delocalized over the chain at the micrometric scale.
Collapse
Affiliation(s)
- Jeremy Holcman
- Institut des NanoSciences de Paris (INSP), UMR 7588 CNRS/UPMC ( Université Pierre et Marie Curie ), 4 place Jussieu, 75252 Paris Cedex 05, France
| | | | | | | | | | | |
Collapse
|