Synthesis and Characterization of Polythiophene With Liquid Crystalline Azobenzene as Side Chains

Abstract

In this study a series of azobenzene-functionalized liquid crystalline (LC) polythiophene derivatives: poly{2-[N-ethyl-N- [4-[4′-(nitrophenyl)azo]phenyl]amino]ethyl-3-thiophene acetate}, Poly(Th3AA-RedI), poly{2-[N-ethyl-N-[4-[4′-(nitrophenyl)azo]-phenyl]amino]ethyl-3-thiophene acetate-co-thiophene}, Poly(Th3 AA-RedI-co-Th), poly{2-[N-ethyl-N-[4-[4′-(nitrophenyl)azo]-phenyl]amino]ethyl-3-thiophene acetate-co-pyrrole}, Poly(Th3 AA-RedI-co-py) were synthesized. Novel 3-substituted thiophene with liquid crystalline side chain (Th3AA-RedI) was synthesized by the direct reaction of thiophene -3-acetic acid with 2-[N-ethyl-N-[4-[4′-(nitrophenyl)azo]-phenyl]amino]ethanol (RedI). Chemical polymerization of (Th3AA-RedI), and its copolymerization with thiophene and pyrrole were carried out, by using ferric perchlorate as oxidation agent. The composition, structure and thermal property of these LC polythiophene derivatives were fully characterized by FTIR, 1H,13C-NMR, and UV-Visible spectroscopic methods, and its LC behavior and photoresponsive property were also investigated by polarized optical microscope and differential scanning calorimeter (DSC). The results show that Poly(Th3AA-RedI) exhibited the smecticC (SC) and nematic (N) liquid crystalline behavior. Conclusion shifted phase transition temperatures of the poly(Th3AA-RedI) in the heating process are as follows: C → Sc (108°C), Sc → N (200°C), and N → I (261°C). Electrical conductivity of polymer [poly(Th3AA-RedI)] and of two its copolymers [poly(Th3AA-RedI-co-Th) and poly(Th3AA-RedI-co-Py)], has been studied by four probe methods and produced 3.6 × 10−6, 4.9 × 10−3, and 7.5 × 10−3 Scm−1 conductivities, respectively.