[FeFe]-hydrogenase mimic with organic photosensitizers for long-lived excited states and efficient photocatalytic H2 production

We report a [FeFe]-hydrogenase mimic complex bearing two organic photosensitizers (PS-CAT, C70H44Fe2N2O6S6) aimed at achieving superior light-absorbing properties. PS-CAT is a dyad with two light-harvesting moieties (PS) and one catalytic center (CAT). The present study investigates the electro- and photo-reduction properties of PS-CAT, combining experimental and theoretical approaches to achieve a comprehensive understanding of the (photo)reduction mechanism of the dyad. To this aim, PS-CAT was studied by means of cyclic voltammetry, IR-spectroelectrochemistry, nanosecond-transient absorption, and scalar relativistic-time-dependent-density functional theory. The results reveal that the dyad can access the photo-excited state with a large absorption coefficient due to multiple PSs. Moreover, the PS-CAT produced long-lived excited species with a ligand-centered or charge-separated character by photon absorption. The subsequent quenching can produce the catalytically active reduced species. Furthermore, the photocatalytic activities of PS-CAT under visible light irradiation were examined, and the PS-CAT exhibited high efficiency (turnover frequency 33 h−1) of H2 generation as a PS-bearing [FeFe]-H2ase mimic.