Probing the adsorption behavior of triphenylphosphine oxide on the surface of Ga-SiO₂ with different binding sites

This study theoretically investigates the adsorption dynamics and fluorescence characteristics of triphenylphosphine oxide (TPPO) as a fluorescent probe on Lewis acid (Ga-La) and Brønsted acid (Ga-Ba) sites of gallium silicate (Ga-SiO₂) surfaces. It was determined that TPPO binds to the Ga-La site via a coordination bond and to the Ga-Ba site through a hydrogen bond. When excited to the first singlet (S₁) state, the coordination interactions at the Ga-La sites experienced slight weakening, which caused a blue shift in the fluorescence emission of TPPO from 478 nm to 453 nm. The excited state intermolecular proton transfer occurring at the Ga-Ba site leads to a red shift of the TPPO fluorescence peak to 528 nm. The contrasting fluorescence behaviors provide a sensitive probe for distinguishing Ga-La and Ga-Ba sites, advancing the detection and mechanistic understanding of Ga-SiO₂'s catalytic acid centers. This work highlights the potential of fluorescence spectroscopy in elucidating surface-active sites for catalysis.