UNDERSTANDING EXCITONS IN STACKED PERYLENE DIIMIDE DERIVATIVES*

π-stacked organic chromophores are promising class of materials for optoelectronics with their electronic properties strongly dependent on the chemical structure of the molecule and inter-molecular interactions. Here, we investigate the optical properties of recently synthesized stacked perylene diimide derivatives via time-dependent density functional theory with a Franck-Condon Herzberg-Teller approximation of vibronic effects, validating our approach by comparison to measurement. By stacking the molecules along a DNA-like backbone and varying the number of stacked molecules from one to three, we determine the role of inter- and intra- molecular interactions on the nature of optical excitations. We determine that for stacked molecules, ground-state vibrational excitations play an important role in the optical absorption spectrum, which we account for via molecular dynamics. Additionally, we apply a nonadiabtic dynamics method to study the role of the backbone on evolution of excited-states. We demonstrate that inter-molecular interactions and backbone strongly influence optical properties, providing new design strategies for efficient optoelectronic materials.