Photophysical properties of copper(I) complexes containing pyrazine-fused phenanthroline ligands: a joint experimental and theoretical investigation

Two copper(I) complexes [Cu(Pyz-Phen)2]PF6 (1) and [Cu(POP)(Pyz-Phen)]PF6 (2) (Pyz-Phen = pyrazino[2,3-f] [1, 10]phenanthroline, POP = bis[2-diphenylphosphino]-phenyl]ether) have been synthesized and characterized. The photophysical properties of these complexes in solution have been studied. The electronic absorption spectrum of complexes 1 exhibit the lowest-lying MLCT absorption band at 459 nm and high-energy ligand-based transitions at 275 nm, while that of complex 2 exhibits the MLCT/LLCT band at 400 nm and ligand π-π* band at 262 nm. In addition, both 1 and 2 show similar phosphorescence 3MLCT/3LLCT emissions with maximum emission wavelengths of 569 and 572 nm, respectively. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) were employed to rationalize the photophysical properties of the complexes studied. The theoretical data confirm the assignment of the experimental absorption spectra and the nature of the emitting states.