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• Stephanie N. Choing, Aaron J. Francis, Graham Clendenning, Michael S. Schuurman, Roger D. Sommer, Isaac Tamblyn, Walter W. Weare, and Tanja Cuk^*
• J. Phys. Chem. C, 2015, 119 (30), pp 17029–17038. DOI: 10.1021/acs.jpcc.5b00513. Download

The excited state dynamics of a d⁰ vanadium(V) oxido ligand-to-metal charge transfer (LMCT) complex, VOL^F, were investigated via a combination of static optical and X-ray absorption (XAS) spectroscopy, transient optical absorption spectroscopy, and time-dependent density functional theory (TD-DFT). Upon excitation of the LMCT in the visible region, transient absorption data reveal that internal conversion traps the excited carrier population into a long-lived charge transfer state of 3d_xy electron character, S₁(d_xy). The internal conversion is substantiated by an isosbestic point in the transient absorption data, two nearby charge transfer states that couple well by TD-DFT, multiple rates in the ground state recovery, and the decay kinetics of an excited state absorption with the energy of a d-d transition in O K-edge XAS spectra. The long lifetime (∼420 ps) of S₁(d_xy) can be ascribed to its poor optical and vibrational coupling to a distorted ground state (S₀^*) via a negligible electronic dipole transition in TD-DFT. The lack of luminescence or an identifiable triplet state also suggests attributing the lifetime to electronic contributions. In conjunction with its strong visible absorption and reduction potential, the long-lived LMCT suggests that molecules such as VOL^F could have potential utility for energy conversion applications. Moreover, the results show that internal conversion between two nearby charge transfer states, differentiated by their 3d character, can form a long-lived charge transfer excitation, broadly informing the discovery of 3d metal-centered optical absorbers with long-lived charge transfer lifetimes.