A new series of three-coordinate cuprous complexes formed by steric hindrance of a phosphine ligand: Synthesis, structure characterization, properties and TD-DFT calculations

Abstract

Four new three-coordinate cuprous complexes with a CuN2P core, 1-QBO, 2-Phen, 3-MePBO, 4-QBI, were designed and synthesized by utilizing a steric hindrance of phosphine ligand o-Anisyl3P [QBO = 2-(2′-quinolyl)benzoxazole, Phen = 1,10-Phenanthroline, MePBO = 5-methyl-2-(2′-pyridyl)-benzoxazole, QBI = 2-(2′-quinolyl)benzimidazole, o-Anisyl3P = tri(2-methoxyphenyl)-phosphine]. As a counterpart to 1-QBO, a four-coordinate complex 5-QBOP2 has also been synthesized with a CuN2P2 core. All complexes were characterized by single-crystal X-ray diffraction, spectroscopic analysis (IR, UV–Vis), elemental analysis, and photoluminescence study. Single-crystal X-ray diffraction revealed that complexes 1–4 all adopt trigonal CuN2P coordination geometry with one phosphine and one diimine ligand. Their UV–Vis absorption spectra exhibit concentration dependences of absorption edge shift. Time-dependent density functional theory (TD-DFT) calculations reveal that their S1 states and the peak transition states can be mainly assigned as ligand–ligand & metal–ligand charge transfer (L′LCT + MLCT) and intra-ligand charge transfer (ILCT) states, respectively. It is noteworthy that all three-coordinate complexes 1–4 do not display obvious photoluminescence (PL), whereas the PL of four-coordinate complex 5 is turned on by an extra coordination of a phosphine ligand to 1. This PL complex has also been synthesized and characterized as 5-QBOP2 from 1-QBO. This model of three-coordinate to four-coordinate change with PL turn-on behavior could be used for sensing volatile organic compounds (VOCs).