Multifunctional Flexible Polyimides for Electroactive Devices with Electrochromic, Electrofluorochromic, and Photodetection Properties

In this study, we report three electroactive carbazolyl polyimides (PIs) containing spiropyran, pyrene, and fluorescein fluorescent groups. The PIs exhibit red, blue, and green fluorescence emissions, respectively. The PIs exhibit aggregation-induced emission and electrochromic (EC) and electrofluorochromic properties. Moreover, white light emission can be achieved by adjusting the mixing ratio of the three PIs. The PIs show high photoluminescence intensity in a solution and solid state. Interestingly, as the volume of ethyl acetate in the PI dimethyl sulfoxide solutions increases, the fluorescence intensity increases continuously. This is due to the decrease in solvent polarity and is distorted by the twisted intramolecular charge-transfer effect, enhancing the emission intensity. The PI films have excellent electrochemical stability between the neutral and first oxidation states of 2000 cycles, and their electrical activities are maintained at 99% CzpP-SPP, 99% CzpP-PREP, and 99% CzpP-FRNP. Under the action of an external electric field, the PIs exhibit excellent EC performance, and the highest EC efficiency was 187 cm2 C–1. Furthermore, the fluorescence and color switching between the oxidation state (nonfluorescent state) and reduced state (fluorescent state) of the PI films are reversible. This work provides a simple strategy for the direct functionalization of Cz-based materials and opens the way for exploring more applications of Cz-based materials.