Molecular Devices Based On Porphyrin Chromophores For Photoinduced Hydrogen Production

Three molecular devices, with formulas of [Zn(TPP-NHCO-BpyCH3)]-[Pt11Cl2] (1, H2TPP-NHCO-BpyCH3=5-[4-(4-methyl-2,2'-bipyridine-4'-carboxyamidyl)phenyl]-10,15,20-triphenylporphyrin), [Zn(TPP-NHCO-BpyCOOH)]-[Pt11Cl2] (2, H2TPP-NHCO-BpyCOOH= 5-[4-(4-carboxyl-2,2'-bipyridine-4'-carboxyamidyl)phenyl]-10,15,20-triphenylporphyrin) and [H2TPP-NHCO-BpyCH3]-[Pt11Cl2] (3) were prepared, in which a porphyrin or zinc porphyrin (ZnPor) chromophore and a Pt11-based catalyst were connected by an amide linkage. Fluorescence emission intensities and lifetimes provided supports for the convincible possibility of intramolecular electron transfer from the singlet excited state of the ZnPor unit to the Pt11 catalytic centre. Photocatalytic hydrogen production experiments showed that supramolecular complexes 1 and 2 were indeed active, with turnover numbers (TON) up to 29 for 1 and 78 for 2 using ascorbic acid (H2A) as both proton source and electron donor in DMF/H2O over 8 h irradiation of visible light(λ>ca.400nm).The other type of the molecular device [{Co(dmgH)2Cl}{Zn(apPyTPP)}] (9, dmgH2= dimethylglyoxime, apPyTPP=5-[4-(isonicotinamidyl)phenyl]-10,15,20-triphenylporphyrin) was prepared, which is completely free of precious metals. The TON for hydrogen evolution was 35 in the presence of 500 equiv Et3N in THF/H2O over 12 h irradiation of visible light(λ>ca.400 nm). The plausible mechanism for the photochemical H2 generation was proposed on the basis of fluorescence emission intensities, fluorescence lifetimes, and time-dependent UV-vis spectroscopy.