Effects of N-heteroaromatic ligands on highly luminescent mononuclear copper(I)–halide complexes

A series of mononuclear Cu(I)–halide complexes, [CuX(PPh3)2(L)] (X = Cl−, Br−, I−; PPh3 = triphenylphosphine; L = pyridine (py), isoquinoline (iq), 1,6-naphthyridine (nap)), were synthesized. The emission color of [CuX(PPh3)2(L)] varies from blue to red by changing the L ligands and the halide ions, and all the complexes exhibit high emission quantum yields (0.16–0.99) in the crystals. The emission studies revealed that the emissive states of [CuX(PPh3)2(L)] differ depending on the L ligand. Complexes [CuX(PPh3)2(py)] and [CuX(PPh3)2(nap)] mainly emit from the singlet metal-to-ligand charge transfer mixed with the halide-to-ligand charge transfer (1(M + X)LCT) state at room temperature. In contrast, emissions from [CuX(PPh3)2(iq)] at room temperature originate from both 3(M + X)LCT and 3ππ* states. These results indicate that N-heteroaromatic ligands play an important role in the emission properties of mononuclear Cu(I)–halide complexes.