LAUSR

The aggregation and photodegradation of rhodamine derivatives adsorbed to TiO2 are investigated using diffuse reflectance spectroscopy, steady-state fluorescence, and time-correlated single-photon-counting (TCSPC) measurements. Rhodamine dyes containing substituted amines (i.e., 5-ROX, R101, RB) exhibit an ∼50 nm hypsochromic shift in λmax upon adsorption to TiO2 relative to solution. By examining a rhodamine derivative with primary amines (i.e., R560) as well as control experiments on insulating ZrO2 substrates, we demonstrate that photocatalyzed N-dealkylation is largely responsible for the spectral changes observed upon surface adsorption to TiO2. For R560, which does not undergo N-dealkylation, diffuse reflectance spectra show that mainly monomers and J-aggregates are present on TiO2. Comparative lifetime measurements for R560 on TiO2 and ZrO2 show that the injection yield for R560/TiO2 is increased with dye-loading concentration (i.e., from 0.63 for monomers to ∼0.80 for heavily doped films), indicat...