Interfacial charge transfer complex between TiO2 and non-aromatic ligand squaric acid

The attachment of squaric acid, a non-aromatic molecule, to the surface of TiO2 powder induced the optical absorption of the obtained hybrid material in the visible spectral range due to the interfacial charge transfer complex formation. The optical characterization of the hybrid is supported by the density functional theory calculations of the model cluster. The paramagnetic species generated upon excitation with ultraviolet or visible light, in both TiO2 powders, pristine and surface-modified, were identified conducting low-temperature solid-state and indirect electron paramagnetic resonance (EPR) spectroscopy experiments (spin trapping and spin scavenging). The solid-state EPR experiments indicated the promotion of electrons from the organic moiety to the titania conduction band under visible-light excitation of hybrid. Also, the spin scavenging experiments showed that the electrons generated in the hybrid upon the visible-light activation facilitate the reduction of the radical cations present in the dispersion, while these effects are not observed for pristine TiO2

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