AIE-active electrochromic materials based on tetraphenylethylene cored benzoates with high optical contrast and coloration efficiency

Abstract

In this work, a series of dual functional materials, 4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl)tetrabenzoates (ETBAs), were developed with an aggregation-induced emission (AIE) luminogenic center (tetraphenylethylene) and electrochromically active moieties (benzoates). The highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of the ETBAs were determined via density functional theory calculations. The fluorescent, electrochemical, and electrochromic performances of the ETBAs were characterized via fluorescence spectroscopy, cyclic voltammetry, UV–Vis spectroscopy, and chronoamperometry. All the ETBAs demonstrated an AIE effect in water/N-methyl pyrrolidone. The ETBAs underwent a quasi-reversible reduction-oxidation. Electrochromic devices based on the ETBAs exhibited a significant color change from a transparent bleached state to a colored blue state, high optical contrast (ca. 80%), and large coloration efficiency. The used substituents markedly influenced the cyclability and response time, and compounds with a larger conjugation degree had lower energy gap values and faster response time. Compound c with a longer alkyl chain length had the best performance with regards to coloration efficiency and cyclability. In summary, this work demonstrated a strategy for the design of novel high-performance ECMs and could extend the applications of such multi-functional materials.