Homoleptic Alkynylphosphonium Au(I) Complexes as Push–Pull Phosphorescent Emitters

A series of compounds P1–P4 bearing terminal alkynyl sites connected with a phosphonium group via different π-conjugated linkers have been synthesized. The compounds themselves are efficient push–pull emitters and exhibit bright fluorescence in blue and near-UV regions. P1–P4 were used as alkynyl ligands to obtain a series of homoleptic bis-alkynyl Au(I) complexes 1–4. The complexes demonstrate bright phosphorescence and dual emission with dominating phosphorescence (2–4). Terphenyl derivative complex 3 exhibits warm white emission in DMSO solution and pure white emission in PMMA films. Time-dependent density functional theory calculations have shown that the T1 excited state has a hybrid MLCT/ILCT nature with a dominant contribution of charge transfer across a ligand-centered “D-π-A” system. The variation of linker allows tuning the effect of intermolecular charge transfer and thus changing the electronic and photophysical properties of the organogold “D-π-A” system. The results presented unambiguously display the advances of the conception of organometallic “D-π-A” construction.