Interfacial Charge-Transfer Transitions between TiO₂ Nanoparticles and Benzoic Acid Derivatives

Interfacial charge-transfer transitions (ICTTs) between organic compounds and inorganic semiconductors have recently attracted increasing interest for their potential applications in photoenergy conversions and chemical sensing because of the unique features of visible-light absorption with colorless organic molecules and direct photoinduced charge separation. The exploration of new organic-inorganic hybrid materials for ICTT is an important subject for expanding the scope and utility of ICTT widely. TiO2 nanoparticles chemically linked to aromatic carboxylic acids are one of the most important photoinduced electron-transfer systems in the above applications. Here, we systematically examine the electronic and optical properties of surface coordination complexes of TiO2 nanoparticles with benzoic acid (BA) and its derivatives experimentally and computationally. Our research unambiguously reveals that ICTT generally takes place between TiO2 nanoparticles and BA derivatives possessing electron donating groups, and the absorption wavelength range can be controlled by adjusting the electron-donating ability and the number of substituent groups. Our research widely expands the scope and utility of ICTT and provides a new guiding principle for material development of interfacial light absorbers featuring direct photoinduced charge separation for photoenergy conversions.