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

Abstract

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(MMAco-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.

Shedding Light on Luminescent Janus Nanoparticles: From Synthesis to Photoluminescence and Applications

“…[86] For instance, Liao et al once prepared two types of fluorescent multifunctional Janus particles, composed of pyrenyl groups (P(MMA-co-PyMA)), azo polymers (methacrylate-based polymer (PCNAZO)) and an epoxy-based polymer (CH-TZ-NT), through the micro-phase separation induced by the evaporation of the organic solvent (Figure 9A). [135] Specifically, due to the presence of multiunits, the as-prepared Janus nanoparticles exhibited varied functionalities, including photoluminescence, photoinduced deformation, and tunable colors.…”

“…More important, the multielement mixture was also used as the dispersed phase to achieve high-order Janus droplets in one step, including core-shell, ternary, and multiple-typed Janus Small 2022, 18, 2200020 Reproduced with permission. [135] Copyright 2020 American Chemical Society. B-a) Phase separation strategy of Fe 3 O 4 @PS/PGMA magnetic Janus nanoparticles.…”

“…Reproduced with permission. [ 135 ] Copyright 2020 American Chemical Society. B‐a) Phase separation strategy of Fe 3 O 4 @PS/PGMA magnetic Janus nanoparticles.…”

“…Photoluminescence refers to a process, in which susceptible atoms (molecules) absorb incident light (photons) at a certain wavelength and radiates light with a different wavelength [ 146 ] Generally, the photoluminescence obeys the Stoke's law that the released emission light should have lower energy, i.e., longer wavelength than that of incoming light, termed “downconversion luminescence.” [ 147 ] However, in some circumstances, the wavelength of released luminescence may even be shorter than that of excitation light, which is an “anti‐Stokes luminescence” or “upconversion luminescence.” [ 148 ] As mentioned earlier, photoluminescence either downconversion or upconversion offers Janus nanoparticles a straightforward and nondestructive tool for sensing as well as photobased diagnostic and therapeutic applications. Table 2 [ 17,30,45,48,95,104,117,135,149–166 ] compares some of the reported luminescent Janus nanoparticles in the aspects of composition, synthesis strategy, photoluminescence mechanism, and applications. Besides, the photoluminescence mechanism is discussed in more detail in this section.…”

“…b) Optical microscopic images of P(MMA-co-PyMA)/ PCNAZO Janus particles (scale bar, 10 µm). c) Optical microscopic images of P(MMA-co-PyMA)/CH-TZ-NT Janus particles (scale bar, 10 µm).Reproduced with permission [135]. Copyright 2020 American Chemical Society.…”