High-quality freestanding flexible poly(5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-1H-indole) film: Electrosyntheses, characterization, and optical properties

The electron-donating substituted indole is generally difficult to be polymerized into high-quality film. The electrochemical polymerization of the electron-donating 3,4-ethylenedioxythiophene (EDOT)-monosubstituted indole may be a challenge. Herein, we designed and synthesized a novel fluorescent comonomer based on the combination of indole and EDOT groups, namely, 5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-1H-indole (EDTI), and subsequently electrodeposited into flawless freestanding flexible poly(5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-1H-indole) (PEDTI) film with a resistance of 60 M omega/cm in CH2Cl2 containing 0.1 M Bu4NBF4. Electrochemical results showed that the oxidation onset potential of EDTI was at 0.8 V vs Ag/AgCl, which was lower than those of indole (0.96 V vs Ag/AgCl) and EDOT (1.35 V vs Ag/AgCl). FTIR spectra indicated that the polymerization of EDTI occurred at the 5-position on thiophene ring and 2,3-positions on indole ring, forming the crosslinking polymer film. The colors of as-prepared PEDTI could switch reversibly from purple to brown under applied potentials of 1.3 and -1.3 V, which were distinctly different from those of polyindole, poly(3,4-ethylenedioxythiophene) (PEDOT), and poly(EDOT-bis-substituted indole) (PETI). Fluorescence spectral studies revealed that the comonomer and corresponding polymer were good blue-green light emitters. These results implied that PEDTI had potential applications for photoelectric devices such as electrochromic devices, light-emitting diodes, and fluorescence sensors. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47016.