| Photochemical transformations of organic molecules require a photocatalyst whose excited state lifetime is long-lived (≈ ns), with redox properties tuned to match the reactions of interest. The work presented herein explores a new type of molecular chromophore that utilized metal-to-metal charge transfer (MMCT) to generate redox-active metal centers after excitation. These new chromophores are derived from an unsupported, terminal MIII hydroxide (M = Cr, Fe, or Co) that have such properties. The protic nature of the metal hydroxides allows for the design of covalently bonded, oxido-bridged heterobimetallic complexes, which contain a TiIV electron acceptor. These molecules exhibit a chargetransfer band with significant intensity that can be tuned throughout the UV-Vis spectrum through both donor metal substitution and ligand variation. The strongly reducing (> 2.0 eV vs. Fc/Fc +) transient TiIII species, in combination with the long-lived excited state, make this class of molecules an alternative to traditional photoredox MLCT-based catalysts. Understanding observed characteristics of the ground state in addition to relaxation pathways and excited state properties were explored through various electrochemical and spectroscopic techniques. |
