Aqueous coordination chemistry of excited state uranyl(VI)

Photoexcitation of uranyl(VI) ion occurs via singlet-to-singlet transition. After rapid internal conversion and intersystem crossing, it converges to the lowest-lying triplet state which has relatively long lifetime of ~ μs. The relaxation process of excited state uranyl(VI) has been a subject of investigation by Ghosh et al. [1] using picosecond transient absorption spectroscopy. Time-resolved X-ray absorption spectroscopy is well-suited for such investigation, however, to the best of my knowledge there has been no such application to uranyl(VI) systems.
Here, excited state chemistry of uranyl(VI) has been explored by density functional theory calculations mainly focusing on the lowest-lying triplet states. The structures of the lowest-lying triplet states were found to predict photochemical reactivities of uranyl(VI) complexes, e.g. photochemical reduction [2], luminescence quenching [3], and photochemical decomposition [4]. The lowest-lying triplet state of uranyl(VI) ion in the presence of ethanol was found to have an asymmetric bond distances in its transdioxo O-U-O unit with the U-O distances of 1.791 and 1.962 Å, and the formal oxidation state of uranium was found to be U(V). These theoretical findings were experimentally confirmed by Ghosh et al. using transient absorption spectroscopy [1].
[1] R.Ghosh et al., J. Phys. Chem. A 114, 5263-5270 (2010).
[2] S.Tsushima, Inorg. Chem. 48, 4856-4862 (2009).
[3] S.Tsushima et al., Chem. Eur. J. 16, 8029-8033 (2010).
[4] S.Tsushima et al., Dalton Trans. 39, 10953-10958 (2010).