Interaction of TiO2 Nanocrystals with Imidazolium-Based Ionic Liquids

Semiconductor nanocrystals and room-temperature ionic liquids have been extensively investigated as promising materials for applications in the field of energy conversion and storage. Titanium dioxide nanoparticles are unquestionably the most used material for the fabrication of sensitized solar cells and batteries, in which room-temperature ionic liquids have been used to replace conventional electrolytes. The study of their interactions is, therefore, undoubtedly of large scientific and technological interest for their implementation in innovative energy devices. Here, a spectroscopic study focused on the interactions, in terms of charge and/or energy transfer, between titanium dioxide nanorods and imidazolium-based ionic liquids is reported. Anatase TiO2 rodlike nanocrystals, synthesized by means of a colloidal synthetic procedure, have been dispersed at increasing loading in a series of dialkyl-substituted imidazolium-based ionic liquids, characterized by different anions and alkyl chain lengths. Time-resolved spectroscopic measurements have highlighted a significant increase of the photoluminescence decay times in the presence of TiO2 nanorods. This increase has been shown to directly depend on TiO2 load and has been ascribed to charge-transfer phenomena from photoexcited TiO2 nanorods to imidazolium rings of ionic liquids. The obtained results are of considerable interest for designing batteries and solar cells based on nanostructured materials and ionic liquids.