Dynamics of accelerated excimer formation of coumarin dyes anchored on semiconductor films

•Coumarin (7-hydroxycoumarin-3-carboxylic acid, OHCCA) shows intramolecular structural relaxations on the surface of ZrO2 and TiO2 films.•OHCCA forms an excimer on the ZrO2 and TiO2 films with time constants of 940 and 350 fs, respectively.•Electronic coupling between OHCCA and metal oxides is stronger in the TiO2 film.•A competitive formation of the charge transfer exciton state can hamper an interfacial charge injection of OHCCA on the TiO2 film.