Photoinduced Electron-Transfer Processes Based on Novel Bipyridine-Ru (II) Complex: Properties of cis-[Ru (2, 2'-bipyridine) 2 (5, 6-bis (3-amidopyridine)-7-oxanorbornene)](PF6) 2 and cis-[Ru (2, 2'-bipyridine) 2 (3-aminopyridine) 2](PF6) 2 Complexes.

11 November 2007

Abstract

This paper presents the synthesis, MO calculations, and photochemical and photophysical properties of cis-[Ru(bpy)2(3Amdpy2oxaNBE)](PF6)2 (2), where bpy is 2,2‘-bipyridine and 3Amdpy2oxaNBE is the novel 5,6-bis(3-amidopyridine)-7-oxanorbornene chelate-ligand (1). Complex 2 is considered in relation to the cis-[Ru(bpy)2(3Amnpy)2](PF6)2 (3) analogous complex, where 3Amnpy is 3-aminopyridine. Complexes 2 and 3 exhibit absorptions near 350 nm and in the 420−500 nm region attributable to a contribution from MLCT transitions (dπ → bpy and dπ → L; L = 3Amdpy2oxaNBE or 3Amnpy).

Whereas complex 3 is photochemically reactive, complex 2 shows luminescence either at 77 K or at room temperature in fluid solution. The emission of 2 assignable as an MLCT (Ru → bpy) emission is characterized by a long lifetime at room temperature (650 ns in CH3CN and 509 ns in H2O). It is independent of λirr, but it is temperature dependent; i.e., it increases as the temperature is lowered. Considering the chelate ring of 1 contributes to the stability of the complex 2 under continuous light irradiation, the difference in the primary photoprocesses of 3 (loss of 3Amnpy) and 2 (luminescence) may be caused by a lowering of the lowest excited state from 3 to 2. The surface crossing to the lowest MC state value of 987 cm-1 (similar to that of [Ru(bpy)3]2+) will be prevented in the case of complex 2, and as a result, efficient 3Amdpy moiety loss cannot occur.

The electronic depopulation of the {Ru(bpy)2} unit and population of a bpy* orbital upon excitation are evident by comparing the photophysical properties with those of a [Ru(bpy)3]2+ related complex. Moreover, a reduction of a bpy ligand in the MLCT excited state is indicated by time-resolved spectra that show features typical of bpy•-. The photocatalytic property of 2 is spectroscopically demonstrated by oxidative quenching using either methylviologen2+ or [RuCl(NH3)5]+2 electron-acceptor ions.

Citation

Inglez, S.D., Lima, F.C., Silva, A.B., Simioni, A.R., Tedesco, A.C., Daniel, J.F., Lima-Neto, B.S. and Carlos, R.M., 2007. Photoinduced Electron-Transfer Processes Based on Novel Bipyridine-Ru (II) Complex: Properties of cis-[Ru (2, 2'-bipyridine) 2 (5, 6-bis (3-amidopyridine)-7-oxanorbornene)](PF6) 2 and cis-[Ru (2, 2'-bipyridine) 2 (3-aminopyridine) 2](PF6) 2 Complexes. Inorganic chemistry, 46(14), pp.5744-5753.

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Categories: Material & Chemical

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