Ligand and counter-ion effects on the photoluminescence of dinuclear bis(diphenylphosphino)amine gold(i) complexes

Abstract

We report the synthesis and characterization of two series of dinuclear gold(I) complexes with different N-substituted (R) bridging bis(diphenylphosphino)amine (PNP) ligands (R = n-butyl, cyclobutyl, cyclopentyl, cyclohexyl, 2-butyl, 1,2-dimethylpropyl): paired with either nitrate or hexafluoroantimonate counterions. Single-crystal X-ray diffraction studies on four hexafluoroantimonate salts revealed Au⋯Au distances ranging from 2.754 Å to 2.830 Å. These crystal structures provide the first crystallographic evidence of an aliphatic N-substituent in complexes of this nature. Despite these structural variations, solid-state photoluminescence studies showed no significant variation in the emission and excitation wavelengths of these complexes across the N-substituted series. In contrast, significant differences in the photophysical properties (especially the emission energies and lifetimes) were observed as a function of the counterion, highlighting the important role of anion identity in modulating photophysical properties. Time-dependent density functional theory (TD-DFT) computations at the TPSSh level reproduced the experimental trends and attributed the counterion-induced emission redshift to weak bonding interactions between the gold centers and coordinating anions, such as nitrate and chloride.