Nonconjugated Dimesitylboryl-Functionalized Phenylpyridines and Their Cyclometalated Platinum(II) Complexes

To investigate possible through-space charge transfer transitions between a Pt(II) ion and a triarylborane unit, the two new nonconjugated molecules 1 and 2 have been synthesized and fully characterized. Compound 1 has a V-shaped geometry, while 2 has a U-shaped geometry. In 1 a BMes2Ar group and a ppy group (Mes = mesityl, ppy = phenylpyridine) are linked together by a SiPh2 unit, while in 2 these groups are joined together by a 1,8-naphthyl linker. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analyses. Their cyclometalated compounds Pt-1 and Pt-2 with a Pt(acac) unit chelated to the ppy site have been synthesized. Computational and experimental examinations on the photophysical properties of the free ligands and the Pt(II) compounds revealed that the molecular shape and geometry of the molecule have a distinct impact on the fluorescence and phosphorescence of these molecules. Pt-1 is a bright phosphorescent emitter with λem 490 nm and Φ = 66% while Pt-2 is very weakly emissive with λem 567 nm and Φ = ∼0.05%. Anions such as fluoride were found to have no impact on the phosphorescence of these two Pt(II) compounds, thus establishing that phosphorescence of these molecules does not involve a through-space charge transfer transition between the Pt(ppy)(acac) unit and the BMes2Ar unit.