Efficiently red emitting cycloplatinated(II) complexes supported by N^O and N^P benzimidazole ancillary ligands

Abstract

Eight neutral luminescent cyclometalated platinum(II) complexes with general formula (piq)Pt(N^O) and (piq)Pt(N^P), where piq = 1-phenylisoquinoline, N^O = deprotonated (2-(1H-benzimidazole)-phenyl)diphenylphosphine oxide derivatives and N^P = deprotonated (2-(1H-benzimidazole)-phenyl)diphenylphosphine derivatives, have been synthesized and characterized. These complexes display distorted square-planar molecular geometries around platinum(II) centers without obvious π-π interactions and Pt-Pt metallophilic interactions in the crystal lattice, due to the presence of sterically bulky N^O and N^P benzimidazole ancillary ligands. Hence, these complexes exhibit good monomeric emissions with the luminescent quantum yields of 15%-23%, which are far more than that of (piq)Pt(acac) (0.9%) in dichloromethane (DCM) at 298 K. The emission colors of platinum(II) complexes can be finely tuned in the range 600–645 nm by changing the chelating types of ancillary ligands. The structured emission combined with microsecond emission lifetimes and the support of TD-DFT calculations for these complexes indicate that their emissions mainly come from an admixture of intraligand (3ILCT) and metal-to-ligand charge transfer (3MLCT).