TY - JOUR
T1 - Vibronic Coupling and Exciton Chirality
T2 - Electronic and Structural Rearrangement between Helical to Zero Momentum Molecular Exciton States
AU - Rich, Christopher C
AU - Frontiera, Renee R.
N1 - Funding Information:
This research was supported through funding by the U.S. Department of Energy, DE-SC0018203.
Publisher Copyright:
© 2021 American Chemical Society
PY - 2021/10/7
Y1 - 2021/10/7
N2 - Helical porphyrin aggregates are attractive macromolecular nanostructures for biomimetic light-harvesting and energy transfer in solar energy technology due to their large light absorbing cross sections and promising energy conservation benefits from chiral-induced spin selectivity. However, with these soft materials, it is imperative that we understand how the nuclear degrees of freedom impact the excitonic energy landscape and dynamics, particularly pertaining to how it influences the chiral angular momentum of the excitons. To this end, we have measured time-resolved depolarization ratios using femtosecond stimulated Raman spectroscopy to uncover the vibronic coupling guided by molecular vibrations between excitons of different angular momentum in helical tetra(sulfonatophenyl)porphyrin aggregates. We find that while transient absorption anisotropy reveals rapid (1 ps lifetime) exciton rotation from helical to achiral states in the Q-band, time-resolved vibrational depolarization ratios evolve on remarkably faster time scales (<500 fs lifetime) for the totally symmetric 1530 cm-1vibration and the nontotally symmetric 1540 cm-1vibration. The time-resolved depolarization ratios of the 1540 cm-1vibration, in particular, show strong evidence of vibronic coupling and nonadiabatic exciton behavior that mediates the nonradiative transition between chiral and achiral excitons. Our study shows that for rational design of helical molecular aggregates for exciton transport, the vibronic coupling between excitons of different angular momenta driven by molecular vibrations must be considered especially in the case where chiral-induced spin selectivity is desired.
AB - Helical porphyrin aggregates are attractive macromolecular nanostructures for biomimetic light-harvesting and energy transfer in solar energy technology due to their large light absorbing cross sections and promising energy conservation benefits from chiral-induced spin selectivity. However, with these soft materials, it is imperative that we understand how the nuclear degrees of freedom impact the excitonic energy landscape and dynamics, particularly pertaining to how it influences the chiral angular momentum of the excitons. To this end, we have measured time-resolved depolarization ratios using femtosecond stimulated Raman spectroscopy to uncover the vibronic coupling guided by molecular vibrations between excitons of different angular momentum in helical tetra(sulfonatophenyl)porphyrin aggregates. We find that while transient absorption anisotropy reveals rapid (1 ps lifetime) exciton rotation from helical to achiral states in the Q-band, time-resolved vibrational depolarization ratios evolve on remarkably faster time scales (<500 fs lifetime) for the totally symmetric 1530 cm-1vibration and the nontotally symmetric 1540 cm-1vibration. The time-resolved depolarization ratios of the 1540 cm-1vibration, in particular, show strong evidence of vibronic coupling and nonadiabatic exciton behavior that mediates the nonradiative transition between chiral and achiral excitons. Our study shows that for rational design of helical molecular aggregates for exciton transport, the vibronic coupling between excitons of different angular momenta driven by molecular vibrations must be considered especially in the case where chiral-induced spin selectivity is desired.
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U2 - 10.1021/acs.jpcc.1c05827
DO - 10.1021/acs.jpcc.1c05827
M3 - Article
AN - SCOPUS:85116597334
SN - 1932-7447
VL - 125
SP - 21511
EP - 21520
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 39
ER -