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Functional Polymers

Polythiophene nanoparticles that display reversible multichromism in aqueous media

Abstract

Conjugated polymer nanoparticles in aqueous media have received much attention because of their specific electronic, optical and medicinal properties. However, flexible hydrophilic chains such as oligo(ethylene oxide) groups on the outer surface of the nanoparticles may induce increases in the particle size resulting from the aggregation of nanoparticles in water. We designed a bolaamphiphilic monomer to produce polythiophene nanoparticles. The resulting nanoparticles exhibit multichromic responses to solvent, temperature and acid/base that can be detected by the naked eye. The nanoparticles, with an average diameter of 170 nm and a large zeta potential of −66.6 mV, remain stable in tetrahydrofuran/water mixtures even after 8 months. As the concentration of water increases, the nanoparticles turn from yellow to violet because the molecular conformation of the thiophene units changes. The nanoparticles dispersed in water display a reversible thermochromic response between 20 and 90 °C, which originates from their different morphologies of an amorphous solid below and an isotropic liquid above their melting point of 60 °C. Adding hydrobromic acid yields an almost colorless dispersion because of the formation of polarons (p-doping), and the nanoparticles revert to their initial violet dispersion upon bubbling with ammonia gas owing to the dedoping of the polythiophene nanoparticles.

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Acknowledgements

We thank Dr Daisuke Hashizume and Ms Tomoka Kikitsu of the Materials Characterization Support Unit, RIKEN Center for Emergent Matter Science (CEMS), for the X-ray diffraction and TEM measurements and for their valuable comments and discussion. We also thank Professor Yu Nagase and Mr Tomoki Mimura of Tokai University for the GPC measurements and their comments. We acknowledge Dr Keisuke Tajima of the Emergent Functional Polymers Research Team, RIKEN CEMS, for the electrical conductivity measurements. We also thank Dr Zhaomin Hou and Dr Masayoshi Nishiura of the Organometallic Chemistry Laboratory, RIKEN, for the thermogravimetric analysis and DSC measurements. We thank Mr Takeo Soejima of the Applicative Solution Laboratory Division, JASCO, for the Raman measurements and technical support. This work was partially supported by a Grant-in-Aid for Scientific Research (C) (No. 15K05639) to MK from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

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Correspondence to Masuki Kawamoto or Yoshihiro Ito.

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Salikolimi, K., Kawamoto, M., He, P. et al. Polythiophene nanoparticles that display reversible multichromism in aqueous media. Polym J 49, 429–437 (2017). https://doi.org/10.1038/pj.2017.5

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