Two luminescent pseudo-polymorphic cuprous complexes with different optical properties: Synthesis, characterization and TD-DFT calculations

Abstract

Two luminescent pseudo-polymorphs based on a new cuprous complex, [Cu(2-iQBO)(POP)]PF6 (2-iQBO = 2-(1′-isoquinolyl)benzoxazole, POP = bis[2-(diphenylphosphino)phenyl]ether), have been synthesized and characterized by UV–Vis, elemental analysis and single-crystal X-ray diffraction analyses. The pseudo-polymorphs 1 and 2 are characterized as a dichloromethane solvate and an acetonitrile solvate, respectively. Single-crystal X-ray diffraction data reveal that 1 and 2 are both mononuclear cuprous complexes with a tetrahedral CuN2P2 coordination configuration, consisting of two P atoms from the POP ligand and two N atoms from the 2-iQBO ligand. The pseudo-polymorphic complexes 1 and 2 can be distinguished by their crystal color, UV–Vis spectra and PL spectra. Time-dependent density functional theory (TD-DFT) calculations reveal that the P–Cu–P angle is a key structural factor influencing the absorption and emission properties. Based on the TD-DFT calculations, the lowest singlet excited state corresponding to the UV–Vis absorption edge can be definitely assigned as a metal-to-ligand charge transfer (MLCT) mixed with a ligand-to-ligand charge transfer (L'LCT), and the lowest triplet excited states should be both assigned as a mixed 3(ML + L'L)CT character.