| The aim of the proposal is to investigate first known supramolecular assemblies of functional models of iron-only hydrogenase enzymes, [2Fe2S], capable of photo-induced superstoichiometric generation of dihydrogen as the most promising non-poluting sustainable energy source for the near future. In our case the diiron core binds the bridging propane-1,3-dithiolate (pdt), five or four carbonyl ligands and one or two different pyridylphosphines (or diphosphines) tethering a metalloporphyrin sensitizer in a dynamic equilibrium. Successful preliminary experiments with [Fe(ì-pdt)(CO)5-n(PPh2py)1+n] (n = 0, 1), ZnTPP and diisopropylethylamine as sacrificial electron donor have confirmed the credibility of the proposal. The objectives of the proposal are: 1/ Deep-going studies of the redox, excited-state and electron-transfer properties of the initial hydrogenase models [Fe(ì-pdt)(CO)5-n(PPh2py)1+n] (n = 0, 1) complemented with the ZnTPP and ZnTTP(OMe)4 sensitizers. 2/ Screening the influence of modified electronic properties and stereochemistry of the supramolecular assemblies on the dihydrogen production, achieved by employing different metalloporphyrins and phosphine linkers. 3/ Control of the Fe?Fe distance in the [2Fe2S] hydrogenase model by coordinating a diphosphine ligand with a large bite angle and flexible backbone. 4/ Supramolecular strategy to arrive at assemblies with two different metalloporphyrins P1 and P2 at the disubstituted diiron moiety. 5/ Supramolecular [2Fe2S]-porphyrin-Au nanoparticle-semiconductor system replacing sacrificial electron donor. In the early phase of the project we will concentrate on fundamental understanding of the intimate mechanisms of the electron transfer from the metalloporphyrin sensitizer to the diiron core, the core protonation and the hydride-proton coupling step, employing state-of-the-art experimental techniques and density functional theory. In a later phase of the project significant attention will be paid to the supramolecular architecture of the assemblies and the influence of electronic and steric factors on the light-driven performance. We also intend to focus on the replacement of the sacrificial electron donors by a supramolecular composite consisting of a semiconductor capped by ultrasmall gold nanoparticles capable of electron transfer to an intimately bound porphyrin sensitizer. This very innovative concept has never been proven so far because of lack of the right components to perform the experiments. We trust that the scheduled investigations will open new and interesting routes to investigate photo-induced energy and electron transfer, in particular in the field of artificial hydrogenase models where similar experiments have failed so far. |
