Supramolecular cobaloxime assemblies for H2 photocatalysis: an initial solution state structure-function analysis.

In this report, we have investigated the correlations between structure and light-induced electron transfer of one known and three new axially coordinated cobaloxime-based supramolecular photocatalysts for the reduction of protons to hydrogen. Solution-phase X-ray scattering and ultrafast transient optical spectroscopy analyses were used in tandem to correlate the self-assembled photocatalysts' structural integrity in solution with electron transfer and charge separation between the photosensitizer and catalyst fragments. Biphasic excited state decay kinetics were observed for several of the assemblies, suggesting that configurational dispersion plays a role in limiting photoinduced electron transfer. Notably, an assembly featuring a "push-pull" donor-photosensitizer-acceptor triad motif exhibits considerable ultrafast excited state quenching and, of the assemblies examined, presents the strongest opportunity for efficient solar energy conversion. These results will assist in the design and development of next-generation supramolecular photocatalyst architectures.