Novel indoloquinoxaline-tetraphenylethylene star-like conjugated isomers: aggregation-induced emission and acidichromism for versatile fluorescent applications

Abstract

A pair of star-like conjugated isomers (Tetra-8-IQ and Tetra-9-IQ) with indolo[2,3-b]quinoxaline as the star arm and tetraphenylethylene as the star core have been designed and synthesized. A comparative study has been conducted on the structural characteristics, electronic energy levels, spectral absorption, aggregation-induced emission, acid-stimulus response, and fluorescent applications of the two isomers. The results show that Tetra-8-IQ has lower lowest unoccupied molecular orbital/highest occupied molecular orbital energy levels, more redshifted optical absorption, and stronger fluorescence emission than Tetra-9-IQ. The two isomers are novel organic fluorescent materials as they both possess aggregation-induced emission characteristics and reversible acidichromism features. Tetra-8-IQ and Tetra-9-IQ were successfully applied in filter paper test strips and PMMA-based blending film to achieve fluorescent switch signals. Based on these findings, the INHIBIT and IMPLICATION molecular logic gates were successfully established, where acid and base were adopted as the input stimuli.