A transient molecular probe for characterizing the surface properties of TiO2 nanoparticle in colloidal solution

A transient molecular probe for characterization of the surface properties of TiO2 nanoparticles in colloidal solution developed recently in our laboratory is briefly reviewed. The probe molecule is all-trans-retinoic acid (ATRA) adsorbed at the TiO2 nanoparticle surface. After photoexcitation, the photoinduced interfacial charge recombination would generate ATRA triplet state (ATRAT) with a substantial quantum yield. It is found that the triplet-triplet absorption spectrum of ATRA adsorbed molecule is sensitive to its binding form with the surface Ti atom through the carboxylic group, as well as to the polarity of the medium. Especially the apparent lifetime of ATRAT at the TiO2 surface changes substantially when the local polarity around the TiO2 nanoparticle changes. Therefore the ATRAT monolayer adsorbed at the surface can be used as a transient molecular probe for the surface binding forms, coordination state of the surface Ti atoms and the light-induced wettability change of the TiO2 nanoparticle.