Structural Dynamics of Bismuth Triiodide in Solution Triggered by Photoinduced Ligand-to-Metal Charge Transfer

Bismuth triiodide, BiI₃, is one of the simplest bismuth halides, which have recently attracted considerable attention because of their promising properties. Here, we investigate the structural dynamics of a photoinduced reaction of BiI₃ in solution phase using time-resolved X-ray liquidography (TRXL) and density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The photoreaction was initiated by excitation at 400 nm, which corresponds to the ligand-to-metal charge-transfer transition. The detailed structures and kinetic profiles of all relevant intermediate species from the TRXL data show that the trigonal planar structure of BiI₃, which is predicted to be the most stable structure of the lowest excited state by TDDFT calculation, was not observed, and the photoreaction proceeds via two parallel pathways within the time resolution of 100 ps: (i) isomer formation to produce iso-BiI₂-I, which relaxes back to the ground-state structure, and (ii) dissociation into BiI₂· and I· radicals, which nongeminately recombine to generate ground-state BiI₃ and I₂.