Multifunctional Janus Particles Composed of Azo Polymer and Pyrene-Containing Polymer

This study investigated Janus particles (JPs) composed of an azo polymer and a pyrene-containing polymer, focusing on preparation, formation mechanism, photoinduced deformation behavior, and fluorescent properties as well as tunable colors of the dispersions. A methacrylate-based copolymer containing pyrenyl groups (P(MMA-co-PyMA)) and two azo polymers, i.e., a methacrylate-based polymer (PCNAZO) and an epoxy-based polymer (CH-TZ-NT) both bearing push-pull-type azo chromophores, were synthesized for this purpose. Two types of Janus particles, P(MMA-co-PyMA)/PCNAZO JPs and P(MMA-co-PyMA)/CH-TZ-NT JPs, were fabricated through microphase separation of the components in the droplets dispersed in aqueous media, induced by the evaporation of the organic solvent. The process of JP formation was thoroughly investigated by exploiting the function of pyrene moieties as a molecular probe through measuring the fluorescence emission spectra at different times during the structure evolution. The photoluminescent (PL) intensity, excimer emission, and vibrational fine structure of the fluorescence spectra were observed to give information about phase separation and solidification occurred in the dispersed droplets. The observations were rationalized by analysis with ternary phase diagrams calculated on the basis of the Flory-Huggins theory. Upon irradiation with a linearly polarized laser beam at 488 nm, the azo polymer parts in the P(MMA-co-PyMA)/PCNAZO JPs were observed to be elongated along the electric vibration direction of the polarized light and transformed into particles with unique morphologies. The dispersions of JPs with different compositions of the two types of the polymers showed highly tunable color changes originating from both fluorescence of the pyrenyl fluorophores and light absorption of the azo chromophores.