Organic semiconductors are tunable light absorbers for solar energy conversion, with their efficiency highly dependent on the nature, energy, and motion of electron-hole pairs or excitons formed upon light absorption. Excitons in these materials are controlled by the interplay between inter- and intra-molecular electronic as well as vibrational interactions. Here, we utilize first-principles theory to investigate the excitonic properties of experimentally-realized stacks of functionalized perylene diimide (PTCDI) DNA base surrogates as a model system to study the role of inter-molecular interactions on photo-induced excited-state dynamics. First, we apply time-dependent density functional theory (TDDFT), along with a Franck-Condon analysis of vibronic effects, to supramolecular assemblies containing one, two, and three PTCDI molecules. We determine that the intra- and inter-molecular interactions result in distinct vibrational, electronic, and optical properties. Furthermore, to understand the time evolution of the excited state, we couple TDDFT to a recently developed time-resolved non-adiabatic dynamics approach. We investigate the role of stacking and the environment on the time-scales associated with excited-state evolution. Lastly, by performing an analysis of the vibrational excitations that couple to the electronically excited-state at each time-scale, we demonstrate that the evolution of the excited-state in organic assemblies can be modified via inter-molecular electronic and vibrational interactions.

Investigating excited-state dynamics in stacked perylene diimide assemblies

ACS Fall 2020 Virtual Meeting

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