Photoinduced reactive species in interfacial charge transfer complex between TiO2 and taxifolin: DFT and EPR study

The TiO2-based interfacial charge transfer (ICT) complex with taxifolin (dihydroquercetin), a polyphenol with pronounced antioxidant ability, displays light absorption in the visible spectral range. The extent of the red absorption shift, obtained using the density functional theory (DFT) calculations on a cluster model that mimics the ICT complex, is in excellent agreement with spectroscopic measurements. The reactive paramagnetic species generated in the dispersed pristine and surface-modified TiO2 powders with taxifolin upon excitation with ultraviolet and visible light were identified by indirect electron paramagnetic resonance (EPR) spectroscopy techniques. The spin trapping and spin scavenging revealed the differences between the behavior of the pristine and surface-modified TiO2 powders with taxifolin before and upon excitation. On one side, the TiO2-based ICT complex with taxifolin efficiently scavenges reactive oxygen species by the taxifolin's hydroxyl groups and, on the other side, the promotion of electrons from the ground state of taxifolin to the conduction band of TiO2 takes place under visible light excitation.