Abstract
We report the ultrafast dynamics of coumarin (7-hydroxycoumarin-3-carboxylic acid, OHCCA) anchored on ZrO2 and TiO2 films. Time-resolved fluorescence measurements reveal that OHCCA undergoes noticeable intramolecular structural relaxations on the film surface, yielding a large vibronic displacement on fluorescence spectra. OHCCA forms an excimer on the ZrO2 and TiO2 films with time constants of 940 and 370 fs for ZrO2, and TiO2 films, respectively, showing further red-shifted charge transfer (CT) emission in the TiO2 film. These suggest an enhanced electronic coupling between OHCCA and metal oxides and that stronger chemisorption in the TiO2 film can significantly hamper an interfacial charge injection via competitive formation of CT exciton state.
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