A series of [Cu(N–N)(P–P)]BF4 complexes: Luminescence quenching caused by electron-configuration transformation in excited state

In this paper, we report a series of [Cu(N–N)(P–P)]BF4 complexes based on two phosphorous ligands and three 1,10-phenanthrolin derived diimine ligands, including their syntheses, characterizations, crystal structures. Their photophysical properties were experimentally measured and theoretically analyzed by time-dependent density functional theory (TD-DFT). It is found that the introduction of too many fused phenyl rings into diimine ligand leads to luminescence absence of corresponding [Cu(N–N)(P–P)]+ complexes at room temperature. A detailed analysis suggests that the thermal activated electron-configuration transformation between the [Cu(N–N)(P–P)]+ triplet metal-to-ligand-charge-transfer (3MLCT) state and the lowest lying excited state of its diimine ligand (3LC) is responsible for the luminescence quenching.