Benzyl Alcohol Photo-oxidation Based on Molecular Electronic Transitions in Metal Halide Perovskites

Vacancy ordered double perovskites Cs2Te(IV)X6 have been found to exhibit molecule-like electronic behavior when X is Cl- or Br- due to the zero-dimensional (0D) nature of their octahedral units. Electronically isolated building blocks, the [TeBr6]2- ionic octahedron, serve as the fundamental electronic unit of the Cs2TeBr6 solid. Herein, a detailed understanding of the Cs2TeBr6 electronic structure and its photoexcitation is presented with consideration of individual molecular orbitals from these isolated octahedral building blocks. Two optical absorption features correspond to two unique electronic transitions, (1) a highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition under 455 nm excitation and (2) mixed transitions including lower HOMO states to LUMO transition and HOMO to higher LUMO states transition under 365 nm excitation. With this in mind, we examined the excitation wavelength-dependent photo-oxidation of benzyl alcohol using Cs2TeBr6 as the photocatalyst. Significant differences in photocatalytic performance were observed, and different forms of activated alcohol radicals were detected under the two excitation wavelengths. As a case study, this work highlights the application of molecule-like halide perovskites in photocatalysis. The highly tunable energy band structures and catalytic centers in perovskites can offer a valuable platform for photocatalytic mechanistic studies and catalyst development in the foreseeable future.

Automated summary

Cs2Te(IV)X6 double perovskites exhibit molecule-like electronic behavior when X is Cl- or Br-, thanks to the zero-dimensional (0D) nature of their octahedral units. The Cs2TeBr6 solid is composed of electronically isolated [TeBr6]2- ionic octahedra. The electronic structure and photoexcitation of Cs2TeBr6 are discussed, and two optical absorption features corresponding to HOMO-LUMO transitions under 455 nm and 365 nm excitations are identified. The photocatalytic performance of Cs2TeBr6 in the photo-oxidation of benzyl alcohol is studied, revealing differences in the activated alcohol radicals depending on the excitation wavelength. This work highlights the application potential of molecule-like halide perovskites in photocatalysis.