Broadening the scope of uranyl photoreactivity: The oxidation of a uranyl complex anion in solid-state materials

Reported are the syntheses, structural characterizations and luminescence properties of three novel [UO2Cl4]2 bearing compounds containing substituted 1,1’-dialkyl-4,4’-bipyridinum dications (i.e. viologens). These compounds undergo photoinduced luminescence quenching upon exposure to UV radiation. Kinetic analyses indicate the degree of quenching follows a second-order rate law with a rate constant dependent on viologen substituent. This phenomenon is proposed to involve the formal transfer of one electron from the [UO2Cl4]2- to the viologen species. This proposed mechanism is supported through a series of calculations and computational work including Rehm-Weller analysis, time-dependent density functional theory (TD-DFT), and density of states (DOS). This work constitutes the first study of an oxidized uranyl complex anion which expands the conventional understanding of uranyl photoreactivity.