A series of pure-blue-light emitting Cu(i) complexes with thermally activated delayed fluorescence: structural, photophysical, and computational studies.

Four mononuclear Cu(i)-halide complexes containing phosphines and pyridine ligands with strong electron donor substituents, [CuCl(PPh)(4-NMepy)] (1), [CuI(PPh)(4-NHpy)] (2), [CuI(POP)(4-NHpy)] (3), and [CuI(POP)(4-NMepy)]·0.5(EtO) (4), (PPh = triphenylphosphine, 4-NMepy = 4-(dimethylamino)pyridine, POP = bis[(2-diphenyl-phosphino)phenyl]ether, 4-NHpy = 4-aminopyridine, EtO = diethyl ether) were synthesized and studied with regard to their structural, photophysical properties and theoretical calculations. The complexes exhibit pure blue thermally activated delayed fluorescence (λ = 442 (1), 436 (2), 464 (3), and 448 nm (4)) in crystalline at room temperature. Emission lifetime analyses and density functional theory (DFT) calculations show that the blue-light emission at room temperature is the singlet (metal + halide)-to-ligand charge transfer state, ((M + X)LCT), while that at 77 K is the state of (M + X)LCT transition character, owing to the small singlet-triplet energy gaps (ΔE = 660-1680 cm). X-ray diffraction structure analysis, photophysical studies and theoretical calculations suggest that the much larger torsion angle between the N-heterocyclic rings and N-Cu-X planes of complex 3 than that of 1, 2 and 4 might causes the bathochromic shift of luminescence, although these complexes containing similar heterocycle ligands.