Luminescent color tuning with polymer films composed of boron diiminate conjugated copolymers by changing the connection points to comonomers

A series of alternating copolymers composed of boron diiminate were synthesized with variable connection points to the comonomer units. All polymers had aggregation-induced emission (AIE) properties, and their films presented diverse colors from green to orange depending on the type of comonomer such as fluorene and bithiophene and the connection points. From mechanistic studies, it was found that the charge transfer character was varied in the emission properties of the polymers. Theoretical investigation proposed that boron diiminate worked as a strong electron-acceptor in the excited state when the comonomers were connected to one or both the phenyl groups on the nitrogen atoms. In contrast, when the comonomers were linked at the phenyl groups on the carbon atoms in the boron-containing six-membered ring, a weak electron-donating property was induced. This is the first example, to the best of our knowledge, to tune the luminescence properties with AIE-active conjugated polymers without changing the chemical components.