Synthesis of conductive polymer poly([thiophene]-[benzo[1,2,3]thiadiazole] [thiophene]) (abbreviated as P(T-Btdaz-T)) was achieved by electrochemical polymerization in hydroxypropyl cellulose (HPC)/N,N-dimethylformamide (DMF) in liquid crystal state. The polymer thus obtained shows fingerprint texture, which is derived from helical structure of the HPC in cholesteric liquid crystal state. Fourier transform infrared spectroscopy measurements revealed that the polymer film is P(T-Btdaz-T)/HPC composite. Circular dichroism optical absorption spectroscopy measurements show that the polymer has the optical activity. Next, electrochemical polymerization of 3,4-ethylene - dioxythiophene (EDOT) was carried out in columnar phase liquid crystal. The polymer transcribes the columnar structure and shows optical structure resembling columnar liquid crystal electrolyte solution.
Polybenzothiadiazole is one of the most studied conductive polymers as a low-bandgap polymer for applications such as photo voltaic cells, transistors [
Electrochemical synthesis of poly(3,4-ethylelnedioxythiophene) (PEDOT) is also carried out in columnar liquid crystal electrolyte solution. Hexadecyltrimethylammonium chloride (HTAC) is used as a columnar liquid crystal. HTAC shows lyotropic liquid crystallinity. Columnar liquid crystal also acts as a template for electrochemical polymerization.
Monomer [thiophene]-[Btdaz]-[thiophene] (T-Btdaz-T) was prepared by previously reported method [
Electrochemical polymerization of monomer [thiophene]-[Btdaz]-[thiophene] (T-Btdaz-T) was carried out in hydroxypropyl cellulose (HPC),
Monomer | Matrix | Solvent | Supporting salt |
---|---|---|---|
HPCb | N,N-dimethylformamide (DMF) | ||
701.0 mg | 397.3 mg | 4.1 mg |
a. [thiophene]-[benzo[1,2,3]thiadiazole]-[thiophene]; b. Hydroxypropyl cellulose; c. Tetrabutylammonium perchlorate.
glass rod for 1 min. Then, the electrolyte solution containing the monomer was injected to the sandwiched cell (two ITO glass electrode, ITO = indium tin oxide). The sandwich cell polymerization method thus performed was developed by our group previously. Direct current (dc) voltage of 3.0 V was applied across to the cell for 60 min. A thin polymer film was deposited on an anode side (+) of the electrode. After electrochemical polymerization, the sandwich cell was soaked into the distilled water to dissolve residual electrolyte solution and disassemble the cell. The polymer film thus deposited onto the ITO glass was washed with large volume of water, and acetone to remove residual HPC, monomer, and TBAP.
Next, electrochemical polymerization of 3,4-ehylenedoxythiophene (EDOT) was carried out in hexadecyltrimethylammonium chloride (HTAC) (
Polarizing optical microscopy measurements were carried out by using an ECLIPX LV 100 high-resolution polarizing microscope (Nikon). Fourier Transform Infrared absorption spectroscopy measurements were carried out with a
Monomer | Matrix | Solvent |
---|---|---|
HTACb | Water | |
200.0 mg |
a. 3,4-ethylenedioxy thiophene; b. Hexadecyltrimethylammonium chloride.
FT-IR 4600 (Jasco) by using the KBr method. UV-vis absorption spectroscopy measurements were carried out by using a V-630 (Jasco). Cyclic voltammetry were carried out with a μAUTOLAB TYPE III (ECO Chemie). Electrolyte solution contained 0.1 M tetrabutylammonium perchlorate in acetonitrile. Circular dichroism spectroscopy measurements were carried out with a J-720 (Jasco).
Optical texture of the polymer prepared in HPC liquid crystal was observed by polarizing optical microscopy (POM),
Fourier transform infrared red (FT-IR) results of the HPC (LC matrix), T-Btdaz- T (monomer), and the resultant polymer are shown in
This results revealed that the polymer film prepared in HPC contains HPC, and forms P(T-Btdaz-T)/HPC composite. FT-IR spectra of PEDOT prepared in columnar liquid crystal are shown in
In situ UV-vis absorption measurements were performed during cyclic voltammetry. The UV-vis absorption spectra of P(T-Btdaz-T)/HPC composite at various applied potential are shown in
Cyclic voltammetry (CV) analysis of P(T-Btdaz-T)/HPC composite was performed at various scan rates. The CV of the polymer is shown in
The CV measurements of PEDOT prepared in HPC liquid crystal were also carried out at scan rates of 100, 200 and 500 mV/s,
Circular dichroism (CD) optical absorption spectroscopy measurements was carried out for the as prepared polymer film and reduces P(T-Btdaz-T)/HPC composite film. The CD spectra are shown in
Polaron band decreases at <700 nm region in reduction. On the other hands, CD absorption of π-π* transition of the main chain increases. This result de-
monstrates that optically activity of the composite can be tuned through redox process.
We achieved preparation of P(T-Btdaz-T)/HPC composite film by electrochemical polymerization in HPC liquid crystal. The POM observation of P(T-Btdaz-T)/HPC composite reveals that the film showed fingerprint texture. The FT-IR result indicated that the polymer film is composite of P(T-Btdaz-T)/ HPC. The CV measurements show that this polymer has the repeatable redox character. The polymer has optical activity derived from helical aggregation through transcription of chirality from the HPC liquid crystal matrix.
Electrochemical polymerization of EDOT in columnar liquid crystal is successfully carried out. The POM observation for the columnar shaped PEDOT confirms occurrence of transcription of columnar structure to the polymer during the electrochemical polymerization process.
We would like to thank Tsukuba Research Center for Interdisciplinary Materials Science (TIMS).
Eguchi, N. and Goto, H. (2017) Lyotropic Liquid Crystal Electrochemical Polymerization of Thiophene-Based Monomers: Polymerization in Cholesteric Liquid Crystal and Columnar Phase. Soft, 5, 9-19. https://doi.org/10.4236/soft.2017.52002