Fluorescein-Nano TiO2 Interface Complexion and Photo-Induced Electron Transfer

This paper reports the complexion of TiO2 with fluorescein dianion (F2-) in ethanol-water under neutral pH condition. We found that F2--TiO2 complex showed very different spectral behavior from that of H3F+-TiO2 formed under strong acidic system. F2--TiO2 is 30 nm red shifted in absorption, it also emits fluorescence. The binding constant of the complex was measured to be 470 L.mol(-1) by UV-Vis absorption spectrum. The fluorescence quantum yield (Phi(f)) and fluorescence lifetime (tau(f)) of F2- moiety in the complex were measured to be 0.14 and 1.08 ns by steady state and time-resolved fluorescence spectrometer, respectively, remarkably reduced from that of free F2- (Phi(f)=0.92, tau(f)=4.68 ns) due to photo-induced electron transfer (PET) within the complex. PET is highly favored by the thermodynamic driving force (Delta G=-1.1 eV). The rate constant of PET is 7.1x10(8) s(-1), which is three times larger than other competitive processes. PET efficiency is calculated to be 77%.