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

Abstract

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-β-D-glucopyranoside, Glc-pyta = 2-(4-(2-pyridyl)-1,2,3-triazol-1-yl)ethyl β-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 groupP2₁/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 × 10³ M⁻¹ cm⁻¹) compared with [ReCl(CO)₃(bpy)] (371 nm, 3.35 × 10³ 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 μs in 2-methyltetrahydrofuran at 77 K, which is longer than that of [ReCl(CO)₃(bpy)] (3.17 μs). 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.