Studies of zeolite-based artificial photosynthetic systems .

摘要

Two ruthenium polypyridyl compounds of structural formula [(bpy) 2RuL]2+ (RuL) and [(bpy)2RuLDQ]4+ (RuLDQ) (where bpy = bipyridine, L = trans-1,2-bis-4-(4'-methyl)-2,2'-bipyridyl) ethane, LDQ = 1-[4-(4'-methyl)-2,2'-bipyridyl)]-2-[4-(4'-N,N'-tetramethylene-2,2'-bipyridinium)] ethene) were synthesized and purified.; From pH titrations, it was found that the Ru complex was a stronger base (pKa* = 6) in the excited state than in the ground state (pKa = 4). Photolysis of the RuL complex in solutions at pH 7 and 12 led to formation of species with increased emission quantum yields, ∼55 nm blue-shift of the emission maximum to 625 nm and disappearance of the absorption band at 330 nm, the latter arising from the olefinic bond of the L ligand. Photoproducts formed at neutral pH have been analyzed. It was found that the major product was a dimer of RuL, dimerizing around the double bond. Photoreactions did not occur in the dark or in the aprotic solvent acetonitrile. We proposed that a Ru(III) radical intermediate was formed by photoinduced excited-state electron and proton transfer, which initiated the dimerization. The radical intermediate also underwent photochemical degradative reductions. Below pH 4, the emission quenching was proposed to arise via protonation of the monoprotonated RuLH + followed by electron transfer to the viologen-type moiety created by protonation. The products of photodegradation at pH > 12 were different from those of pH 7, but the mechanism of the degradation at pH > 12 was not elucidated. RuLDQ was stable under visible irradiation.; We examined nanocrystalline zeolite as a host for light absorbing sensitizers (electron donors) and electron acceptors. Nanocrystalline zeolite Y (NanoY) with uniform particle size, pure phase was prepared. NanoY was obtained by periodically removing nanocrystals from the mother liquor and recycling the unused reagents. The nanoparicles were characterized by XRD and TEM. Optically clear colloidal solutions of NanoY were obtained. The Ru complexes were anchored on the surface of zeolites via ion-exchange or "ship-in-bottle" synthesis. The spectroscopic properties of the NanoY-entrapped species including methyl viologen (MV2+), RuL were measured via transmission techniques. The zeolite-encapsulated species were found to have red-shift absorption and emission bands and longer MLCT life times. By incorporating both donors Ru complexes and acceptors MV2+ in NanoY, electron transfer kinetics was examined. LFP study showed a slower back-electron-transfer rate as compared to forward electron transfer.; Photochemically generated long-lived charge separation is the key step in processes that aim for conversion of solar energy into chemical energy. We incorporated RuL complex on the surface of a pinhole-free zeolite membrane by quaternization of L and surrounded with intrazeolitic bipyridinium ions (N,N'-trimethyl-2,2'-bipyridinium ion, 3DQ2+). Visible-light irradiation of the Ru complex side of the membrane in the presence of a sacrificial electron donor led to formation of PVS-· on the other side. Pore-blocking disilazane-based chemistry allows for Na+ to migrate through the membrane to maintain charge balance, while keeping the 3DQ2+ entrapped in the zeolite. These results provided encouragement that the zeolite membrane based architecture has the necessary features for not only incorporating molecular assemblies with long-lived charge separation but also for ready exploitation of the spatially separated charges to store visible light energy in chemical species.; The pore-narrowing strategy applied under mild conditions can be used in control-release of active substances such as drug, pesticides, and herbicides. Methyl viologen (MV2+) was chosen as the guest molecule, since it is widely used as an herbicide and its release is of interest in agricultural applications. To explore the controlled-release capability of the surface-modified zeolite, MV2+-encapsulated zeolite Y pa