Nonadiabatic Excited-State Dynamics in Perylene Diimides*

Perylene diimides (PDI) are promising materials for optoelectronics. We study the photo-induced excited-state dynamics of a PDI derivative using the NEXMD software that goes beyond the Born-Oppenheimer description of electron-nuclear interactions. By comparing the internal conversion processes of the monomer and dimer, we determine the role of inter-molecular interactions on the time-scales associated with energy transfer and exciton localization dynamics. We predict that energy conversion in the dimer happens significantly faster than in the monomer. For the dimer, analysis of the electronic transition density during photo-dynamics reveals the transient trapping of the exciton, suggesting that the strength of thermal fluctuations exceeds electronic coupling between the two molecules. Lastly, vibrational normal mode analysis during the dynamics allows us to identify the intra- and iner-molecular modes that assist the electronic relaxation.