Structural and photophysical study of copper iodide complex with P^N or P^N^P ligand

Two P^N-type ligands, 8-(diphenylphosphino)quinoline (L1) and 2-[2-(diphenylphosphino)ethyl]pyridine (L2), and two P^N^P-type ligands, 2,6-bis((diphenylphosphino)methyl)pyridine (L3) and 2,6-bis((di-tert-butylphosphino)methyl)pyridine (L4), were synthesized to coordinate with copper iodide (CuI). As a result, CuI complexes with rich structures, such as discrete complexes with formulae of [Cu2I2(L1)2] (5), [Cu3I3(L2)2] (6), and [CuI(L3)] (7), and polymeric complexes with repeating units of [Cu2I2(L4)] (8), and [Cu3I3(L4)] (9) were synthesized and characterized by single crystal X-ray diffraction. Besides the intriguing structures, these complexes showed rich photoluminescent properties, with emission colour that varied from blue to red and a photoluminescence quantum yield (PLQY) from 1.6 to 29.9% in the solid state. Molecular orbital calculation and experimental study showed that the emissions involve halide to ligand charge transfer (XLCT), metal to ligand charge transfer (MLCT), and/or cluster-centered (CC) excited states.