Morphology Regulation and Quenching Mechanism of AIE Nanobowls by Side Chain Engineering of Azobenzene Homopolymers

The precise regulation of the luminescent properties of fluorophores by molecular engineering strategies has evolved into a crucial method for constructing intelligent photoresponsive nanomaterials. However, the factors influencing the fluorescence quenching efficiency and the mechanism of aggregation-induced emission (AIE) nanoparticles are still unclear. In this study, a series of amphiphilic azobenzene homopolymers with different side chains containing ether, amino, and amide bonds were synthesized, and the linkage has a significant impact on the UV–vis absorption of azobenzene. When coassembled with a tetraphenylethylene (TPE)-containing homopolymer, nanobowls with controlled size and openings were formed, and the fluorescence of TPE was quenched due to the inhibitory effect of azobenzene. It was found that the opening size of the nanobowls decreased with the increase of azobenzene content, and the quenching efficiency derived from the intensity of the amide-bonded azobenzene homopolymer was 10 times higher than that of the others due to the formation of hydrogen bonds. While the quenching efficiencies of the ether- and amino-bonded azobenzene homopolymers were quite low, owing to the red-shift of the emission wavelength induced by the formation of exciplexes. Overall, a hydrogen bond-enhanced fluorescence quenching mechanism is proposed, and the formation of exciplexes in polymeric nanoparticles is also observed and verified, providing a fresh perspective for an in-depth understanding of the quenching mechanism of fluorophores by chromophores.