Synthesis, Characterization, and Photophysical Properties of Heteroleptic Copper(I) Complexes with Functionalized 3‑(2′-Pyridyl)-1,2,4-triazole Chelating Ligands

A new series of mononuclear copper­(I) complexes (1–9) with functionalized 3-(2′-pyridyl)-1,2,4-triazole chelating ligands, as well as the halide and/or phosphine ancillary ligands, have been synthesized. Complexes 1–9 were fully characterized by elemental analysis, NMR spectroscopy, mass spectroscopy, electronic absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and X-ray crystallography (1–8). They adopt a distorted tetrahedral configuration, and are considerably air-stable in solid state and in solution. All these Cu­(I) complexes display a comparatively weak low-energy absorption in CH2Cl2 solution, assigned to charge-transfer transitions with appreciable MLCT character, as supported by TD-DFT studies. Cu­(I) halide complexes 1–4 each shows bright solid-state emission at room temperature, although they are nonemissive in fluid solutions, in which the emission markedly depends on the halide and the substituent on the 2-pyridyl ring. Complexes 5–9 bearing 2-pyridyl functionalized 1,2,4-triazole and phosphine exhibit good photoluminescence properties in solution and solid states at ambient temperature, which are well-modulated via the alteration of the auxiliary phosphine ligand and the structural modification of 3-(2′-pyridyl)-1,2,4-triazole. Interestingly, cationic complex 6 and neutral derivative 7 can readily be interconverted through the ring inversion of the 1,2,4-triazolyl regulated by the NH ↔ N– transformation.