Blue to yellow-emitting neutral Cu(i) complexes with μ-bridging 1,2,4-triazole: synthesis, photophysical characterization and DFT calculations

Abstract

A series of Cu(I) complexes having 1,2,4-triazole as bridging ligand and aminophosphanes as chelating [NP]-donors were successfully isolated and spectroscopically characterized. The structure of the Cu(I) derivatives was ascertained through single-crystal X-ray diffraction confirming the formation of dimers. The Cu(I) species were characterized by absorptions below 400 nm, with no metal-to-ligand charge transfer (MLCT) band observable in the visible region of the spectrum. Upon excitation with UV light, the Cu(I) complexes exhibited appreciable blue to yellow emissions with lifetimes in the 2–9 μs range and photoluminescent quantum yields up to 0.42. The photophysical properties were investigated in the solid state and polymeric matrix both at room temperature and 77 K. The increased lifetimes τ at low temperatures and the two orders of magnitude different radiative decay constants k_r at 297 and 77 K suggest the presence of two different decay channels (fluorescence and phosphorescence), thus indicating thermally activated delayed fluorescence (TADF). The experimental data were supported by computational studies, further confirming the presence of TADF properties.