Regioregular and random conjugated polymers based on a boron-fused azomethine unit were synthesized. Optical measurements and microscopic observation indicated the existence of aggregation domains in the spin-coated film of the regioregular polymer and no aggregation in that of the regiorandom polymer. Furthermore, fluorescence enhancement was brought about via aggregation disassembly of the regioregular polymer chains by thermal annealing treatment.

Abstract

Regioregular and random conjugated polymers based on a boron-fused azomethine unit were synthesized by Sonogashira–Hagihara cross coupling reaction. Although these polymers exhibited similar optical properties in the solution states, a distinct difference was observed in the aggregation forming ability in the film states; scanning electron microscope (SEM) observation indicated the existence of fiber-like aggregates in the spin-coated film of the regioregular polymer, while regiorandom polymer showed no aggregate in the film state. Accordingly, the UV–vis absorption spectrum of the regioregular polymer showed an increased shoulder peak due to the aggregate formation, whereas the random one showed no change. Furthermore, an absolute fluorescence quantum efficiency of the regioregular polymer was enhanced in response to the aggregate disassembly via thermal annealing treatment. In this study, we demonstrate that controlling regioregularity of the conjugated polymers can induce the different morphological structures and thermal-responsive behaviors. These findings could be beneficial for the design strategy and potential applications of thin-film optoelectronic devices with stimuli-responsive properties.