Syntheses, structural characterization and photophysical properties of 4-(2-pyridyl)-1,2,3-triazole rhenium(I) complexes

Novel chelators, i. e., 4-(2-pyridyl)- 1,2,3- triazole derivatives, were synthesized by means of Cu( I)- catalyzed 1,3- dipolar cycloaddition and used to prepare luminescent Re( I) complexes [ReCl(CO)(3)( Bn- pyta)], [ ReCl(CO)(3)(AcGlc- pyta)] and [ ReCl(CO)(3)(Glc- pyta)] (Bn- pyta = 1- benzyl- 4-( 2- pyridyl)- 1,2,3- triazole, AcGlc- pyta = 2-( 4-( 2- pyridyl)- 1,2,3- triazol- 1- yl) ethyl 2,3,4,6- tetra- O- acetyl- beta-D- glucopyranoside, Glc- pyta = 2-( 4-( 2- pyridyl)- 1,2,3- triazol- 1- yl) ethyl beta-D- glucopyranoside). X- Ray crystallography of Bn- pyta and Glc- pyta indicated an azocompound-like structure while the 1,2,4- triazole isomer has an azine character. [ ReCl( CO) 3( Bn- pyta)] crystallized in the monoclinic system with space group P2(1)/n. Bn- pyta ligand coordinates with the nitrogen atoms of the 2- pyridyl group and the 3- position of 1,2,3- triazole ring, which is a very similar coordinating fashion to that of the 2,2' - bipyridine derivative. The glucoconjugated Re( I) complexes [ ReCl( CO)(3)( AcGlc- pyta)] and [ ReCl( CO)(3)( Glc- pyta)] hardly crystallized, and were analyzed by applying extended X- ray absorption fine structure ( EXAFS) analysis. The EXAFS analyses suggested that the glucoconjugation at the 1- position of the 1,2,3- triazole makes no influence to the coordinating fashion of 4-( 2- pyridyl)- 1,2,3- triazole. [ ReCl( CO) 3( Bn- pyta)] showed a blue-shifted maximum absorption (333 nm, 3.97 x 10(3) M-1 cm(-1)) compared with [ReCl(CO)(3)(bpy)] ( 371 nm, 3.35 x 10(3) M-1 cm(-1)). These absorptions were clearly assigned to be the mixed metal- ligand-to-ligand charge transfer (MLLCT) on the basis of time-dependent density functional theory calculation. The luminescence spectrum of [ReCl(CO)(3)( Bn- pyta)] also showed this blue- shifted feature when compared with that of [ ReCl( CO) 3( bpy)]. The luminescence lifetime of [ ReCl( CO)(3)( Bn- pyta)] was determined to be 8.90 mu s in 2-methyltetrahydrofuran at 77 K, which is longer than that of [ReCl(CO)(3)( bpy)] ( 3.17 mu s). The blue- shifted electronic absorption and elongated luminescence lifetime of [ ReCl( CO)(3)( Bn- pyta)] suggested that 4-( 2- pyridyl)- 1,2,3- triazole functions as an electron-rich bidentate chelator.