Spotlight on the ligand: Luminescent cyclometalated Pt(IV) complexes containing a fluorenyl moiety

Abstract

The synthesis, electrochemistry and photophysical properties of a family of Pt(iv) complexes with cyclometalated 2-(9,9-dimethylfluoren-2-yl)pyridine (flpy) are reported. Homoleptic and heteroleptic tris-cyclometalated complexes with a meridional configuration, mer-[Pt(C^N)2(flpy)]OTf, with C^N = flpy or cyclometalated 2-phenylpyridine (ppy), were prepared by reacting the bis-cyclometalated precursors [Pt(C^N)2Cl2] with flpyH in the presence of two equivalents of AgOTf. The corresponding facial isomers were obtained by photoisomerization. The Pt(iv) complexes with flpy display intense absorptions in the near-visible region and yellow phosphorescence in fluid solutions at 298 K, with quantum yields in the range 0.06-0.28 and lifetimes of hundreds of microseconds. The emissions arise from essentially 3LC(flpy) states in all cases, with little metal-orbital contribution. However, computational calculations and experimental data demonstrate that subtle variations in the contribution of metal orbitals to the emitting state have a profound impact on quantum yields, while nonradiative deactivation through the thermal population of deactivating LMCT states does not have a significant influence.