Photoactive Boron–Nitrogen–Carbon Hybrids: From Azo-borazines to Polymeric Materials

In this paper, we describe synthetic
routes for preparing a novel
switchable BNC-based chromophore, composed of a borazine core peripherally
functionalized with azobenzene moieties. Capitalizing on the Pd-catalyzed
Suzuki cross-coupling reaction between a tris-triflate borazine and
an organoboron azobenzene derivative, a photoswtichable azo-borazine
derivative was successfully prepared. The molecule showed reversible E/Z photoisomerization upon irradiation
at the maximum of the intense π–π* absorption feature
(360 nm). X-ray crystallographic investigations revealed a nonplanar
orientation of the three azobenzene moieties and the trans configuration
of the −NN– bonds. Building on the synthetic
versatility of the borazine-azobenzene derivative, we used this photoactive
scaffold to engineer soluble BN-doped polythiophene polymers. Photophysical
characterization performed in solvents of different polarity suggested
that the polymer undergoes intramolecular charge transfer (ICT).