Colorless Electrochromic/Electrofluorochromic Dual-Functional Triphenylamine-Based Polyimides: Effect of a Tetraphenylethylene-Based ?-Bridge on optoelectronic properties

Electrochromic/electrofluorescence (EC/EFC) bifunctional polymer materials with electrochemically switchable colors and fluorescence intensities have attracted significant research attention due to their promising applica-tions in optoelectronic devices. Tetraphenylethylene (TPE) can improve nature-state transmittance and exhibit solid fluorescence and cyclic stability when used as a pi-bridge and fluorescence structure in EC/EFC polymer main chains. Herein, 6 novel polyimides with three different TPE-based pi-bridge structures were designed and synthesized to investigate the effect of pi-bridge units (short, extended, and interrupted conjugation) on opto-electronic properties. The structure-property relationships of the six polyimides were investigated by electro-chemistry, electrospectroscopy, and theoretical calculations. Introduction of the TPE structure effectively reduced the polyimide absorption in the ground state, provided different colored states, and induced aggregation-induced emission (AIE) by changing the conjugation type. The structural influences on the electron redox reaction, energy level, absorption/luminescent spectra, and cycle stabilities were systematically investi-gated. The designed polyimides were colorless (L* > 97) and showed good EC/EFC dual-switching properties: colorless-to-colorful EC switching performance (including a black-colored state), AIE-enhanced EFC performance (including deep-blue fluorescence), 1.7/2.1 s colored/bleached switch, and EC/EFC cyclic stability over 500/300 cycles.