Derivative coupling constants of NK1, NK7 dyes and their relation to excited state dynamics in solar cell applications

We analyze derivative coupling constants in dyes NK1 (2E,4E-2-cyano-5-(4-dimethylaminophenyl) penta-2,4-dienoic acid) and NK7 (2E,4E-2-cyano-5-(4-diphenylaminophenyl) penta-2,4-dienoic acid) and relate them to the different dynamics that was observed for these dyes on TiO2. We compute vibronic coupling constants in the excited and cationic states obtained by the ionization of the excited state as well as the electronic part of the internal conversion rate. We conclude that derivative coupling analysis connects molecular structure to excited state dynamics and explains the slower injection from NK7 into TiO2. The analysis suggests this is not due to low-frequency motions of the benzene moieties in NK7.