Photolysis of Novel Ir (II)Ru(II)Ir) Complexes as an effective photocatalyestfor H2production using hplc
Younis, Hamid M.
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Photoinduced electron transfer processes within a precatalyst for intramolecular hydrogen evolution [Ir(LL)2Cl2]PF6 , [Ru(LL)2Cl2]PF6 and [Ir(LL)3 CL3] PF3 type [Ir(LL) 2 (L-L)]Xn such as Ir(dmbpy)2(phpytr)](CF3SO3)2, where LL is an N^N bound polypyridyl ligand [X2bpy, X2phen, where X = H-, CH3-, (CH3)3C-, or phenyl-, and bpy = 2,2′-bipyridyl, phen = 1,10- phenanthroline], dmbpy is 4,4'-dimethyl- 2,2'-bipyridyl and Hphpytr is (3-phenyl)-5-(pyridine-2-yl)-1,2,4-triazole) have been studied by High performance Liquid Chromatography HPLC, absorption spectroscopy, and comparing the photophysics of the complexes subunit RuII, IrII with that of the supramolecular catalyst IrIII, the individual electron-transfer steps are assigned to kinetic components, and their dependence on solvent is discussed. HPLC data reveal that the initial excitation of the molecular ensemble is spread over the terminal (Hphpytr) and the (dmbpy) ligands. The subsequent excited-state relaxation of both IrIII and RuIrII on the picosecond timescale involves formation of the phenyl-centered intraligand charge-transfer state, which in RuII,IrII precedes formation of the IrIII-reduced state. The photoreaction in the heterodinuclear supramolecular complex is completed on a subnanosecond timescale. Taken together, the data indicate that mechanistic investigations must focus on potential rate- determining steps other than electron transfer between the photoactive center and the IrII unit. Furthermore, structural variations should be directed towards increasing the directionality of electron transfer and the stability of the chargeseparated states. Two distinct strategies can be adopted to realise homogeneous photocatalytic proton reduction into H2. The inter-molecular approach is based on the use of a mixture containing both photosensitiser and catalyst components and a sacrificial agent to regenerate the photosensitiser after light- induced electron transfer to the catalyst has taken place.