First-principles studies of excitonic effects in organic assemblies
Sahar Sharifzadeh, Boston University
The nature and dynamics of excitons in organic assemblies are controlled by the interplay between inter- and intra-molecular electronic as well as vibrational interactions. Here, we utilize first-principles theory to investigate optical excitations and exciton dynamics in stacks of functionalized perylene diimide DNA base surrogates as a model system to study inter- and intra-molecular interactions. We apply time-dependent density functional theory, along with a Franck-Condon analysis of vibronic effects, to finite stacks of molecules that have been recently synthesized. By stacking the molecules along a backbone and varying the number of stacked molecules, we determine the role of inter-molecular interactions and backbone on the evolution of excited states. We determine that the intra- and inter-molecular interactions result in distinct vibrational, electronic, and optical properties. Additionally, by combining TDDFT with a recently developed time-resolved non-adiabatic dynamics approach, we show that stacking increases the efficiency of non-radiative relaxation dynamics from a high excitonic state to the lowest energy exciton. Overall, this work demonstrates that excitonic properties can be modified via inter-molecular electronic and vibrational interactions.