A Series of Luminescent [(Xantphos)CuILN] Complexes and Their Luminescence Sensing Properties for VOCs Detection and TD-DFT Calculation

Abstract

The design and research of luminescent and volatile organic compounds (VOCs) fluorescent sensing/stimuli–response materials are of great significance and challenge. We report herein a series of new [(Xantphos)CuIL_N] type complexes with tetrahedral CuIP₂N coordination, showing luminescence from blue to red and luminescence sensing for VOCs detection (Xantphos is 4,5-bis (diphenylphosphino)-9,9-dimethylxanthene, L_N is N-containing ligand). Firstly, six new complexes 1–6 were designed and ball-milling synthesized by the ligand-addition reaction of a raw material [(Xantphos)CuI] with different N-containing ligands 2-aminopyridine (1), 3-cyanopyridine (2), 4-cyanopyridine (3), 2-(3′-pyridyl)-benzoxazole (4), 3-I-4-aminopyridine (5), and imidazole (6). Time-dependent density functional theory (TD-DFT) calculations assign the low-energy band (absorption edge) of 1–6 in UV–Vis absorption as a mixed (XL + ML)CT transition, the corresponding (XL + ML)CT excited state is also thought to be the source of photoluminescence (PL). Material 4 has the highest PL efficiency (~44%), which may benefit from its greatest structural rigidity. Material 5 exhibiting the worst PL efficiency should be related to the iodine atom in the L_N ligand (I dominate the highest unoccupied orbitals of the S₁ and T₁ states). Based on its very weak PL, the corresponding thin-film sensor (5) achieve significantly enhanced luminescence sensing (lighting-up mode) for pyridine and 4-methylpyridine vapor. The sensor also achieves the lowest detection limit (LOD = 2.51 ppm) and the fastest response speed (T₅₀ = 30 s) for pyridine. In addition, the series of materials also show interesting quenching and vapochromic luminescence sensing/stimuli–response for a variety of VOCs vapors.