Aggregation-enhanced emission and multicolored electrochromic behavior of polyphenyl benzoates†

By functionalizing various polyphenyl nuclei with ester groups, five kinds of polyphenyl benzoate based electrochromic materials (M1–M5) are synthesized and characterized. These materials show typical aggregation-induced emission and aggregation-enhanced emission in water/N-methylpyrrolidone, good electrochemical properties, and an obvious electrochromic phenomenon. In the process of electrochemical reduction, each material shows distinct and well-separated redox couples, the introduction of ester moieties makes electron transfer much easier compared to the polyphenyl nuclei, and the synergistic effect of the ester group and polyphenyl structure reduces the LUMO level of the corresponding polyphenyl benzoates. In contrast, the polyphenyl nuclei markedly affect their electrochromic properties, and the electrochromic devices based on M1–M5 exhibit five different colored states. By combining with density functional theory calculations, it is found that an appropriate amount of benzene rings in the central benzene cores (M2 and M4) can effectively improve the coloration efficiency, response time, and switching stability; fewer benzene rings in the central benzene core (M1) cannot achieve stable conjugation of the material in the reduced state, while an excess of benzene rings in the central benzene core (M5) leads to excessive molecular volume, and this will lead to space congestion and is not beneficial for electron transfer. The application of M1–M5 in multi-colored functional display devices is explored, indicating its potential application prospect in display fields.