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 (L-1), with 2-bromopyridine afforded three new ligands, 2,2 '-(1H-1,2,3-triazole-1,4-diyl)dipyridine (L-2), 2,2 '-(2H-1,2,3-triazole-2,4-diyl)dipyridine (L-3) and 2,2 '-(1H-1,2,3-triazole-1,5-diyl)dipyridine (L-4). A series of luminescent mononuclear copper(I) complexes of these ligands [Cu(L-n)(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 L-n with [Cu(MeCN)(4)]ClO4 in the presence of PPh3 and POP. L-3 was also found to form dinuclear compounds [Cu-2(L-3)(PPh3)(4)](ClO4)(2) (7) and [Cu-2(L-3)(POP)(2)](ClO4)(2) (8). All of the Cu(I) compounds have been characterized by IR, UV/vis, CV, H-1 NMR, and P-31{H-1} 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 lambda(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).