First principle analysis of singlet-triplet transitions in organic molecules

Organic molecules have revealed to be extremely useful building blocks for developing efficient optoelectronic materials. The theoretical design of new molecules has been mostly carried out by focusing attention on energetic aspects, but, as recently remarked, kinetic aspects can also play a predominant role. Herein, we present a full quantum approach for predicting the kinetics of some elementary processes frequently occurring in optoelectronic devices: i) photo-induced charge transfer; ii) charge diffusion within donor and acceptor domains; iii) charge recombination process at donor/acceptor interface, both via singlet and triplet states. Triplet state are indeed expected to play an important role both in organic light emitting diodes (OLED) and in solar energy conversion devices We have also simulated from first principles the spectral band shapes of singlet-triplet transitions of some aromatic compounds used in solid-state optoelectronic devices. Computed spectral shapes are indeed in excellent agreement with experimental results, opening the way for reliable calculations of the rates of nonradiative singlet-triplet transitions, an important step for the optimization of the molecular structure of dyes for solar energy conversion cells and for light-emitting diodes.