The role of the electron density of the acceptor in efficient diphenylphosphino-gold(i) TADF emitters

Abstract

We report the synthesis of a series of diphosphino-gold(I) complexes (1–4) using the cis-1,2-bis(diphenylphosphino)ethylene (dppe), 1,2-bis(diphenylphosphino)benzene (dppBz), 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) and 1,8-bis(diphenylphosphino)naphthalene (dppn) chelating ligands in combination with the [Au(C₆F₅)(tht)] precursor. The bis(diphosphine)-gold(I) complexes are designed for investigating how thermally activated delayed fluorescence (TADF) depends on the ligand. The emission wavelength of the intense luminescent emissions of 2, 3 and 4 at room temperature (RT) and at 77 K is modulated by the electronic nature of the ligands. Temperature-dependent lifetime measurements and computational studies suggest that 2, 3 and 4 exhibit TADF at RT. Rate constants of intersystem crossing (ISC) and reverse ISC (RISC) were calculated at the ADC(2) level using an ONIOM approach to consider solid-state environmental effects on the molecular structures and spin–orbit coupling matrix elements calculated at the density functional theory (DFT) level. The photophysical studies show that the observed RT emissions arise from TADF with contributions in the range of 67–84% depending on the diphosphine ligand.