Synthesis, structure and photoluminescence of Cu(I) complexes containing new functionalized 1,2,3-triazole ligands

The reaction of a triazole ligand, 2-(1H-1,2,3-triazol-4-yl)pyridine (L1), with 2-bromopyridine afforded three new ligands, 2,2'-(1H-1,2,3-triazole-1,4-diyl)dipyridine (L2), 2,2'-(2H-1,2,3-triazole-2,4-diyl)dipyridine (L3) and 2,2'-(1H-1,2,3-triazole-1,5-diyl)dipyridine (L4). A series of luminescent mononuclear copper(I) complexes of these ligands [Cu(Ln)(P^P)](ClO₄) [n = 1, P^P = (PPh₃)₂ (1); n = 1, P^P = POP (2); n = 2, P^P = (PPh₃)₂ (3); n = 2, P^P = POP (4); n = 3, P^P = (PPh₃)₂ (5); n = 3, P^P = POP (6); n = 4, P^P = (PPh₃)₂ (9); n = 4, P^P = POP (10)] have been obtained from the reaction of Ln with [Cu(MeCN)₄]ClO₄ in the presence of PPh₃ and POP. L3 was also found to form dinuclear compounds [Cu₂(L3)(PPh₃)₄](ClO₄)₂ (7) and [Cu₂(L3)(POP)₂](ClO₄)₂ (8). All of the Cu(I) compounds have been characterized by IR, UV/vis, CV, ¹H NMR, and ³¹P{¹H} NMR. The molecular structures of 1-3, 5, and 7 have been further determined by X-ray crystallography. In CH₂Cl₂ solutions, these Cu(I) complexes exhibit tunable green to orange emissions (563-621 nm) upon excitation at λ_ex = 380 nm. In the solid state, these complexes show intense emissions and it is interesting to note that 1 and 3 are blue-light emitters. Density functional theory (DFT) calculations revealed that the lowest energy electronic transition associated with these complexes predominantly originates from metal-to-ligand charge transfer transitions (MLCT).