Synthesis, characterization, crystal structures, and photophysical properties of a series of room-temperature phosphorescent copper(I) complexes with oxadiazole-derived diimine ligand

In this paper, we report four phosphorescent Cu(I) complexes of [Cu(OP)(PPh3)2]BF4, [Cu(Me-OP)(PPh3)2]BF4, [Cu(OP)(POP)]BF4, and [Cu(Me-OP)(POP)]BF4 with oxadiazole-derived diimine ligands, where OP = 2-(5-phenyl-[1,3,4]oxadiazol-2-yl)-pyridine, Me-OP = 2-(5-p-tolyl-[1,3,4]oxadiazol-2-yl)-pyridine, POP = bis(2-(diphenylphosphanyl)phenyl) ether, and PPh3 = triphenylphosphane, including their synthesis, crystal structures, photophysical properties, and electronic nature. The Cu(I) center has a distorted tetrahedral geometry within the Cu(I) complexes. Theoretical calculation reveals that all emissions originate from triplet metal-to-ligand-charge-transfer excited state. It is found that the inter-molecular sandwich structure triggered by inter- and intra-molecular pi-stacking within solid state Cu(I) complexes is highly effective on restricting the geometric relaxation that occurs in excited states, and thus greatly enhances the photoluminescence (PL) performances, including PL quantum yield improvement, PL decay lifetime increase, and emission blue shift.

Graphical abstractThe inter-molecular sandwich structure triggered by inter- and inner-molecular pi-stacking within solid state Cu(I) complex is highly effective on restricting the geometric relaxation that occurs in excited states, and thus greatly enhances the photoluminescence performances, including PL quantum efficiency improvement, PL decay lifetime increase, and emission blue shift.Figure optionsDownload full-size imageDownload as PowerPoint slide