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(PPh3)2(4-NMe(2)py)] (1), [CuI(PPh3)(2)(4-NH(2)py)] (2), [CuI(POP)(4-NH2py)] (3), and [CuI(POP)(4-NMe(2)py)]center dot 0.5(Et2O) (4), (PPh3 = triphenylphosphine, 4-NMe(2)py = 4-(dimethylamino) pyridine, POP = bis[(2-diphenyl-phosphino) phenyl] ether, 4-NH(2)py = 4- aminopyridine, Et2O = 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 (lambda(max) = 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, ((1)(M + X) LCT), while that at 77 K is the state of 3(M + X) LCT transition character, owing to the small singlet-triplet energy gaps (Delta E = 660-1680 cm(-1) ). 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.