Theoretical studies of spectra properties of cyclometalated platinumII complexes with 8-hydroxyquinolines and quinolino-8-thiol ligand

A series of luminescent complexes (C∧N)PtQ (where C∧N is bidentate cyclometalating ligand and Q is 8-hydroxyquinoline or quinoline-8-thiol ligand) are investigated using density functional theory (DFT). The optimized ground state geometries show that all these complexes show a nearly square-planar structure. The positions of the lowest absorption bands are blue-shifted for complexes with electron-deficient pyridine-type C∧N ligand while is red-shifted with quinoline-8-thiol ligand. In addition, with the increasing of electron-releasing ability of substituents, the HOMO–LUMO gap decreases while the ΔE values (the energy difference between d–d transition and HOMO–LUMO gap) increase which will benefit the (ligand-to-ligand charge transition) LLCT or (metal-to-ligand charge transition) MLCT. Also, solvent effects are discussed in toluene, chloroform, dichloromethane and acetone solution. In general, all the complexes show a blue-shifted with the increasing of solvent polarity. Furthermore, three methods are used to investigate the electron-rich or -deficient effect of pyridine-type C∧N ligand. These results reveal that this pyridine-type C∧N ligand is an electron-deficient type ligand.