Session: Physical Chemistry Poster:

Excitation energy transfer (EET) in molecular aggregates in the condensed phase has been an area of active research, particularly with respect to the role of intramolecular vibrations in modulating the ultrafast quantum dynamics inherent to these systems. Accurate simulations of exciton-vibration dynamics traditionally pose great challenges due to the exponential scaling of quantum mechanics with aggregate size and the large number of coupled molecular vibrations that are relevant at ambient temperatures.
The modular path integral (MPI) method allows the numerically exact treatment of extended molecular aggregates characterized by local couplings with a linear size-scaling. Alternatively, the small matrix path integral (SMatPI) method offers a complementary approach to study smaller molecular aggregates with non-local couplings. Both methods allow the exact treatment of an arbitrarily large number of vibrational normal modes coupled to each chromophore at finite temperatures with almost no additional cost.
We have used these methods to investigate the EET in chains and rings of bacteriochlorophyll a molecules, with parameters characterizing the B850 ring of the LH2 complex of photosynthetic bacteria. Here, we explicitly treated all 50 relevant normal modes of each pigment using spectroscopic Huang-Rhys factors. We have also explored the role of intramolecular vibrations on the exciton-vibration dynamics in J-aggregates of a perylene bisimide (PBI), including 28 intramolecular modes on each molecule. Our simulations indicate that the damping of coherences as well as the survival of underdamped vibronic oscillations observed in these aggregates are brought about by collective effects of many normal modes, which depend on the intricate interplay of multiple electronic and vibrational timescales.

Simulated exciton-vibration dynamics in an aggregate of bacteriochlorophyll a molecules at room temperature..

Simulated exciton-vibration dynamics in an aggregate of bacteriochlorophyll a molecules at room temperature..

Dr. Nancy Makri

Professor of Chemistry and Physics, University of Illinois Urbana-Champaign

Appearances