The synthesis and characterization of three new uranyl compounds featuring the uranyl-tetrachloride [UO2Cl4]2- dianion paired with various 1,1’-dialkyl-4,4’-bipyridinum dications (i.e. viologens) is reported. A simple uranyl species paired with the redox-active cation may support charge transfer in the solid state providing a unique perspective when probing the photochemistry of uranyl-bearing materials. Irradiation with UV light causes a marked reduction of uranyl emission intensity over time, which can be partially recovered by placing the sample in the dark. Kinetic treatment of the time-dependent data reveals a quenching efficiency and rate constant dependence on viologen identity. We propose a photoinduced electron transfer mechanism for this reaction which is support by experimental and computational data. Density functional theory (DFT) based calculations are utilized to (i) map the band structure of these materials, (ii) determine electronic structure of photochemical products, and (iii) identify the donor and acceptor orbitals involved in charge transfer. Our findings support the formation of a notable oxidized [UO2Cl4]1- species bearing a U(VI) bound to a radicalized chloride ligand. These efforts will inform studies of uranyl as a photocatalyst or in radiation detection, yet perhaps more importantly, may contribute to our fundamental understanding of energy transfer within actinide bearing hybrid materials.

Photoinduced charge transfer of solid-state uranyl-viologen-bearing materials: A structural, optical, and kinetic study

ACS Spring Meeting 2021

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