Singlet fission in carotenoid aggregates: insights from transient absorption spectroscopy

Wang, Chen; Angelella, Maria; Kuo, Chun-Hung; Tauber, Michael J.

doi:10.1117/12.958612

Cited by 32 publications

(56 citation statements)

References 48 publications

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“…The spectra were acquired with a home-built system. 37 The pump wavelength was 431 nm, where the strong Soret transition of ZnTPP accounted for more than ∼80% of the absorbed photons. For steady-state Raman spectroscopy of the triplet excited state, a toluene solution of 1 (∼30 μM) with ZnTPP (∼14 μM) was prepared in an oxygen-free environment and contained in a sealed cuvette.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Resonance Raman Spectra of a Perylene Bis(dicarboximide) Chromophore in Ground and Lowest Triplet States

2013

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Resonance Raman spectroscopy is employed to probe the ground (S0) and lowest triplet (T1) excited states of a perylene bis(dicarboximide) (PDI) dimer. Four bands at ~1324, 1507, ~1535, and 1597 cm(-1) are signatures of the T1 excited state; a fifth band at ~1160 cm(-1) is tentatively assigned. Density functional calculations of an asymmetrically substituted PDI monomer match the experimental bands of the PDI dimer in both S0 and T1 states. The match supports a T1 excited state that is localized on a single PDI moiety of the dimer. The normal modes of the asymmetrically substituted PDI are correlated with ones calculated for the unsubstituted PDI in the D2h point group. Patterns in the Raman intensities are consistent with an A-term mechanism of enhancement. The positions of six bands are predicted for the resonance Raman spectrum of unsubstituted PDI in its T1 excited state. The spectra and normal-mode analysis reported here are expected to facilitate future studies of singlet fission in PDI crystals or other assemblies.

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Section: ■ Experimental Sectionmentioning

confidence: 99%

Resonance Raman Spectra of a Perylene Bis(dicarboximide) Chromophore in Ground and Lowest Triplet States

2013

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“…In either case we expect slower generation rate of triplets through SF in the polyenes than in pentacene, in agreement with observations. [24][25][26][27]52] Finally, errors incurred if the calculations of 1 (TT) states in polyenes are done in the reduced space of six basis functions are huge, close to 50%. This is because bonding (antibonding) MOs much lower (higher) than the HOMO (LUMO) make very significant contributions to the 1 (TT) here.…”

Section: %mentioning

confidence: 99%

Theory of Singlet Fission in Polyenes, Acene Crystals, and Covalently Linked Acene Dimers

2015

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We report quadruple configuration interaction calculations within the extended Pariser−Parr−Pople Hamiltonian on the excited states of aggregates of polyenes, crystalline acenes and covalently linked dimers of acene molecules. We determine the precise energy orderings and analyze the cluster wavefunctions in order to arrive at a comprehensive physical understanding of singlet fission in these diverse families of materials. Our computational approach allows us to retain a very large number of basis states, and thereby obtain the correct relative energy orderings of one electron-one hole Frenkel and charge-transfer excitons versus intra-and intermolecular two electron-two hole triplet−triplet excited states. We show that from the energy orderings it is possible to understand the occurrence of singlet fission in polyene and acene crystals, as well as its near total absence in the covalently linked acene dimers. As in the acene crystals, singlet fission in the polyenes is a multichromophoric phenomenon, with the well known 2 1 A − g playing no direct role. Intermolecular charge-transfer is essential for singlet fission in both acenes and polyenes, but because of subtle differences in the natures and orderings of the aggregate excited states, the mechanisms of singlet fission are slightly different in the two classes. We are thus able to give qualitative physical reasoning for the slower singlet fission in the polyenes, relative to that in crystalline pentacene. Our work also gives new insight to the complex exciton dynamics in tetracene crystals, which has been difficult to understand theoretically. Our large-scale many-body calculations provide us with the ability to understand the qualitative differences in the singlet fission yields and rates between different classes of π-conjugated materials.

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“…1 In light of this potential utility in the design of photovoltaic systems, there has been a recent explosion of experimental studies on a variety of molecular materials [2][3][4][5][6][7][8][9][10][11][12][13][14] and fabricated devices. [15][16][17] Currently, a detailed microscopic understanding of this process is lacking.…”

Section: Introductionmentioning

confidence: 99%

Microscopic theory of singlet exciton fission. II. Application to pentacene dimers and the role of superexchange

Berkelbach

Hybertsen²,

Reichman³

2013

The Journal of Chemical Physics

364

690

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We apply our theoretical formalism for singlet exciton fission, introduced in the previous paper [T. C. Berkelbach, M. S. Hybertsen, and D. R. Reichman, J. Chem. Phys. 138, 114102 (2013)] to molecular dimers of pentacene, a widely studied material that exhibits singlet fission in the crystal phase. We address a longstanding theoretical issue, namely whether singlet fission proceeds via two sequential electron transfer steps mediated by charge-transfer states or via a direct two-electron transfer process. We find evidence for a superexchange mediated mechanism, whereby the fission process proceeds through virtual charge-transfer states which may be very high in energy. In particular, this mechanism predicts efficient singlet fission on the sub-picosecond timescale, in reasonable agreement with experiment. We investigate the role played by molecular vibrations in mediating relaxation and decoherence, finding that different physically reasonable forms for the bath relaxation function give similar results. We also examine the competing direct coupling mechanism and find it to yield fission rates slower in comparison with the superexchange mechanism for the dimer. We discuss implications for crystalline pentacene, including the limitations of the dimer model.

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Singlet fission in carotenoid aggregates: insights from transient absorption spectroscopy

Cited by 32 publications

References 48 publications

Resonance Raman Spectra of a Perylene Bis(dicarboximide) Chromophore in Ground and Lowest Triplet States

Resonance Raman Spectra of a Perylene Bis(dicarboximide) Chromophore in Ground and Lowest Triplet States

Theory of Singlet Fission in Polyenes, Acene Crystals, and Covalently Linked Acene Dimers

Microscopic theory of singlet exciton fission. II. Application to pentacene dimers and the role of superexchange

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