title: 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.
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 (dpi-->bpy and dpi-->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 lambdairr, 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.
authors.affiliation: Instituto de Química de São Carlos, Universidade de São Paulo, CP 780, 13650-970 São Carlos, SP, Brazil.
authors.forename: Simone D
authors.initials: SD
authors.lastname: Inglez
authors.forename: Francisco C A
authors.initials: FC
authors.lastname: Lima
authors.forename: Albérico B F
authors.initials: AB
authors.lastname: Silva
authors.forename: Andreza R
authors.initials: AR
authors.lastname: Simioni
authors.forename: Antônio C
authors.initials: AC
authors.lastname: Tedesco
authors.forename: Juliana F S
authors.initials: JF
authors.lastname: Daniel
authors.forename: Benedito S
authors.initials: BS
authors.lastname: Lima-Neto
authors.forename: Rose M
authors.initials: RM
authors.lastname: Carlos
mesh_terms: D004583:Electrons; D049449:Luminescence; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010777:Photochemistry; D011725:Pyridines / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: D009942:Organometallic Compounds; D011725:Pyridines; C522846:cis-(Ru(2,2'-bipyridine)2(3-aminopyridine)2)(PF6)2; C522847:cis-(Ru(2,2'-bipyridine)2(5,6-bis(3-amidopyridine)-7-oxanorbornene))(PF6)2; D012428:Ruthenium