Polythiophene nanoparticles that display reversible multichromism in aqueous media

• Published in: Polymer journal 2017-05, Vol.49 (5), p.429-437
• Main Authors: Salikolimi, Krishnachary, Kawamoto, Masuki, He, Pan, Aigaki, Toshiro, Ito, Yoshihiro
• Format: Article
• Language: English
• Subjects: 639/301/923/966; 639/638/298/923/1028; Acids; Agglomeration; Ammonia; Aqueous solutions; Biomaterials; Bioorganic Chemistry; Bubbling; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Dispersion; Doping; Electronics; Ethylene oxide; Eyes; Halochromism; Hydrobromic acid; Media; Melting points; Molecular conformation; Morphology; Nanoparticles; Optical properties; original-article; Polymer Sciences; Polythiophene; Solvents; Surfaces and Interfaces; Tetrahydrofuran; Thin Films; Zeta potential
• ISSN: 0032-3896; 1349-0540
• DOI: 10.1038/pj.2017.5

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. The polythiophene nanoparticles exhibit multichromic responses to solvent, temperature and acid/base, which can be detected by the naked eye in tetrahydrofuran/water mixtures. As the concentration of water increases, the nanoparticles turn from yellow to violet by solvatochromism. The nanoparticles display a reversible thermochromic response between 20 and 90 °C, which originates from the morphological changes between an amorphous solid and isotropic liquid. Halochromic behavior of the nanoparticles is achieved by adding hydrobromic acid and bubbling with ammonia gas owing to p-doping and dedoping of the polythiophene nanoparticles, respectively.