Synthesis, photophysical properties and DFT studies of the pyridine-imidazole (PyIm) Cu(I) complexes: Impact of the pyridine ring functionalized by different substituents

A series of the pyridine-imidazole (PyIm) Cu(I) complexes with different substituents (bromide (P1), methyl (P2), and phenyl (P3)) attached on the pyridine ring are synthesized and characterized. All the complexes show the typical metal-to-ligand charge transfer (MLCT) absorption in the visible region. Complex P1 with an electron-withdrawing substituent on the pyridine ring, e.g., a bromine group, shows a red shift of the emission wavelength. Conversely, an electron-donating substituent on the pyridine ring in complex P2, e.g., a methyl group, shifts the emission to longer wavelength. Similarly, complex P3 containing the extended pi-conjugation system of the ligand also exhibits a red shift of the emission wavelength. All of the complexes exhibit efficient green-yellow emission in PMMA films at room temperature with emission wavelength of 547-569 nm and quantum yields of 24.8-53.0%. Meanwhile, DFT and TDDFT methods were employed to explain the photophysical properties.