Tailored Triarylborane Polymers as Supported Catalysts and Luminescent Materials

Two novel luminescent triarylborane polymeric Lewis acids and the corresponding molecular model compounds were prepared, studies on their photophysical properties performed, and applications as supported catalysts in Lewis acid-catalyzed hydrosilylation reactions explored. Variations of the substituents in the ortho-position of a phenylene linker between the Lewis acidic borane and the polystyrene framework lead to steric and electronic fine-tuning while retaining the high Lewis acidity of the boron center. The polymeric Lewis acids serve as effective catalysts in the hydrosilylation of aldehyde, ketone, and imine compounds and because of their distinct solubility characteristics are readily amenable to recycling. In addition, as a result of the twisted biphenyl donor-it-acceptor structure, both the styrene copolymers and model compounds display strong luminescence in solution and the solid state, encompassing prompt fluorescence and in the case of the chlorophenyl-linked derivative also longer-lived room temperature phosphorescence (RTP). Consistent with quantum-chemical calculations, the greater donor strength of the 2,6-dimethylphenyl in comparison to the 2-chlorophenyl linker leads to a red-shifted emission, while the chloro substituent leads to a larger gap between singlet and triplet excited states. In the solid state, distinctly different emission properties are observed for the polymers in comparison to the molecular compounds because of the site isolation of the chromophores embedded in the polymer matrix.