Three heteroleptic copper(I) complexes with [Cu(P∧P)N2]+ structure and their fluorescence sensing for VOCs

The design and research of luminescent and volatile organic compound (VOC) fluorescent sensing materials are of great significance and challenge. We report herein the ligand substitution reaction and VOC sensing of new heteroleptic [Cu((PP)-P-<^>)N-2](+) type copper(I) complexes. Firstly, three new complexes 1-3 were designed by utilizing a chelate diphosphine ligand 4,5-bis(diphenylphosphino)9,9-dimethylxanthene (Xantphos) and synthesized by the substitution reaction of different N-containing ligands of 4-PBO (1), 3-PBO (2), and 4,4'-Bipy (3) (4-PBO = 2-(4'-pyridyl)-benzoxazole, 3-PBO = 2-(3'-pyridyl)-benzoxazole, 4,4'- Bipy = 4,4'-bipyridine), respectively. Three complexes were characterized by elemental analysis, spectroscopic analysis (IR, UV-Vis), single-crystal X-ray diffraction (SCXRD), and photoluminescence study. The SCXRD study revealed that complexes 1 and 2 both exhibit a molecular structure with tetrahedral copper(I) complex cation and hexafluorophosphate anion, while complex 3 differs in that its cation is a binuclear copper(I) structure bridged by 4,4'-bipyridine. Three complexes 1-3 present supramolecular ribbon, supramolecular dimer, and supramolecular framework structure, respectively. Some differences of their UV-Vis absorption spectra were explained by TD-DFT calculation and wave function analysis. It is found that 1 has an abnormal luminescence blue shift, and a luminescence mechanism through the high-energy T-2 excited state is proposed by TD-DFT calculation. Based on 3, a fluorescent test strip was developed, and its fast and selective fluorescent sensing of pyridine vapor through quenching mechanism was successfully realized. The fluorescent quenching mechanism of the material was also studied, and it was proposed that the quenching should be attributed to the photoinduced electron transfer (PET) mechanism.