Charge-Transfer Dynamics of Light-Harvesting Systems in Complex Environments

BRYAN M. WONG; MARÍA BELÉN OVIEDO

San Francisco, California

Congreso; 2015 MRS Spring Meeting & Exhibit; 2015

Materials Research Society

Photo-initiated charge-transfer processes play a central role in natural systems such as human vision and photosynthesis. While researchers have successfully modified these processes to control simple isolated systems, our understanding of photon-to-electronic mechanisms in realistic and complex environments is still in its infancy. In particular, recent experiments have shown that simple descriptions of solvent interactions (either via classical force fields or effective solvent models) are unable to accurately capture the electron dynamics in even relatively simple systems. These ongoing observations open an entirely new field of research in the properties of light-activated processes in complex environments, with the opportunity to deeply understand the real-time electron dynamics between complex interfaces. To this end, we have developed a new real-time time-dependent density functional tight binding (RT-TDDFTB) approach to calculate the electron dynamics of donor-acceptor complexes in the presence of explicit solvent molecules - all treated at the quantum mechanical level. Our approach significantly differs from previous linear-response TD-DFT methods in that we directly propagate the one-electron density matrix in the presence of a non-perturbative external field. Furthermore, and most importantly, our implementation in the TD-DFT code allows us to calculate the electron dynamics of large solvated systems (~10,000 atoms), whereas conventional approaches are computationally limited to only hundreds of atoms. Using this new capability, we are able to understand and rationalize electron-hole recombination effects as a function of solvent polarity, configuration, and energy transfer. Furthermore, this new capability gives us mechanistic insight into the electron dynamics of new systems in complex environments with the goal of guiding experiments in the exploration of charge-transfer dynamics driven by time-dependent external fields.