Enhancing Single-Crystal Dichroism of an Asymmetric Azo Chromophore by Perfluorophenyl Embraces and Boron Coordination

We describe the use of perfluorophenyl embraces and boron coordination (B ← N) to enhance dichroism in single crystals of an asymmetric azo chromophore. Specifically, a tripod-shaped boron adduct comprised of tris(pentafluorophenyl)borane (BCF) and 4-phenylazopyridine (4PAzP) self-assembles as supramolecular helices through perfluorophenyl embraces, wherein the azo chromophores are aligned in parallel through B ← N bonds. The alignment of molecular transition dipole moments in (BCF)·(4PAzP) results in enhanced dichroism compared to pure 4PAzP as confirmed by polarized optical microscopy. The study offers a novel supramolecular strategy to enhance dichroism in single-crystalline materials.