Dendritic Ir(III) complexes functionalized with triphenylsilylphenyl groups: Synthesis, DFT calculation and comprehensive structure-property correlation

We report on the synthesis, DFT calculations and structure-property relationships of phosphorescent Ir(III) complexes with varied number and position of triphenylsilylphenyl substituents. The attachment of the dendritic triphenylsilylphenyl group at the pyridine part of the phenylpyridine ligand induced a stronger metal-to-ligand charge-transfer (MLCT) transition and lower band-gap energy than did the unfunctionalized complex, Ir(ppy)₃. On the other hand, the attachment of the triphenylsilylphenyl group at the phenyl part of the phenylpyridine ligand induced a stronger ligand-centered (LC) transition. It was specifically found that the excited state intermolecular interactions, which give rise to non-radiative decay, were more efficiently suppressed when the triphenylsilylphenyl group was attached at the pyridine part of the phenylpyridine ligand and also when the number of substituents was increased. Such site-isolation effects and improved solubility due to the triphenylsilylphenyl group encapsulation made it possible to fabricate wet-processed polymer light-emitting devices from these functionalized Ir(III) complexes. Both the doped poly(vinylcarbazole) (PVK) films and the neat films of our triphenylsilylphenyl based dendritic Ir(III) complexes afforded moderate to high electrophosphorescence efficiencies with excellent phase homogeneity (4.1%/1.7% for Ir(TPSppy)₃, 5.9%/2.5% for Ir(ppyTPS)₃ and 1.8%/1.8% for Ir(TPSppyTPS)₃ (doped polymer film/neat film, respectively)). Moreover, it is noteworthy that the triphenylsilylphenyl substituents greatly enhanced the thermal stability of the dendritic Ir(III) complexes.