2,4,6-Triphenyl-1,3,5-triazine functionalized <i>fac</i>-tris(2-phenylpyridine)Ir(<scp>iii</scp>) complexes with polarity sensitive T₁ state properties

Here, we report the synthesis and study of three Ir(III) complexes, which are derivatives of <i>fac</i>-Ir(ppy)₃ (Hppy - 2-phenylpyridine). In these derivatives, the third position of the pyridine ring of one of the ppy ligands is functionalized with a tolyl (Ir-tol) or triphenyl triazine group (Ir-meta and Ir-para). Ir-meta has a 3-(3,5-diphenyl-2,4,6-triazinyl)phenyl group on the ppy pyridyl ligand, giving a <i>meta</i> disposition of the triazine to the ppy ligand, and Ir-para has a 4-(3,5-diphenyl-2,4,6-triazinyl)phenyl group bound to the ppy ligand, placing the triazine moiety <i>para</i> to the ppy ligand. The complex Ir-tol shows electrochemical properties and phosphorescence characteristics nearly identical to the unfunctionalized <i>fac</i>-Ir(ppy)₃. Complexes Ir-meta and Ir-para show reduction potentials that are anodically shifted from those of Ir-tol by <i>ca.</i> 0.6 V, consistent with the reduction centered on the triazine moiety. In non-polar media, the lowest triplet state (T₁) of Ir-meta and Ir-para has mixed metal-to-ligand charge transfer (MLCT) and ligand centered (LC) character localized on the Ir-ppy moiety of the functionalized ligand. With an increase in solvent polarity, <i>i.e.</i> CH₂Cl₂ and dimethyl sulfoxide (DMSO), the T₁ state of these complexes gains character of intraligand charge transfer (ILCT) from Ir-ppy to the triazine moiety of the functionalized ligand. This change in excited state character is accompanied by a distortion in the molecular geometry towards planarization of the acceptor and donor units. Such polarity-controlled modulation of T₁ state character is observed using transient absorption (TA) spectroscopy and is found to markedly affect the photoluminescence properties of the complexes.