Luminescent properties of Ag(i)/Cu(i) coordination polymers: crystal structures and high intensity luminescence of a PMMA-doped hybrid material based on a quinoline-2,3-dicarboxylic acid ligand

Abstract

Three one-dimensional (1D) Ag(I)/Cu(I) coordination polymers, formulated as [Ag(2,3-Hqldc)]_n (Ag1), [Ag(3-qlc)]_2n (Ag2) and [CuI(3-Hqlc)]_n (Cu1) based on the ligand quinoline-2,3-dicarboxylic acid (H₂qldc), were synthesized through hydrothermal (solvothermal) method and structurally characterized by single-crystal X-ray diffraction, IR spectroscopy and elemental analysis. Molecular structural analysis reveals that Ag1 was a 1D + 1D → 1D infinite chain synthesized at a relatively low temperature 80 °C, which further forms a three-dimensional (3D) structure by π–π stacking interactions. Ag2 forms a 1D dimer chain structure and via π⋯π packing interactions shows a two-dimensional (2D) supramolecular network. Both Ag1 and Ag2 display stable blue luminescent in the solid state and in organic solvents (DMSO, CH₃CN and CH₃OH) at 298 K and 77 K. However, Cu1 possess a 1D ladder chain structure, which further forms a 2D structure by hydrogen bonding interactions. Cu1 shows tunable luminescence at 298 K and 77 K in the solid state with a large red-shift of 70 nm and the CIE color shifts from bright yellow (0.51, 0.48) to red (0.67, 0.30), indicating thermochromic luminescence for Cu1. After doping with poly(methylmethacrylate) (PMMA), not only are the luminescence intensity and lifetimes enhanced, but the thermal stability is also increased in comparison with Cu1. After Cu1 was doped with PMMA (Cu1@PMMA), the lifetime of the polymer film material Cu1@PMMA increases and reaches a maximum at 1.0% (τ = 95.57 μs), which is more than eight times longer than that of Cu1 (τ = 13.78 μs). Cu1@PMMA is confirmed as a bright yellow luminescent polymer film material.