Indolo-[2,3-b]quinoxaline: A Core for the Stabilization of Room Temperature Liquid Crystalline Self-Assembly, Aggregation-Induced Emission, and Bioimaging Applications.

Abstract

Aggregation-induced emission (AIE) is a significant property that enables the translation of the fluorescence emission of chromophores in solution to the solid state. In recent years, the development of AIE-active liquid crystals has garnered considerable interest. In this context, we introduce a class of indolo[2,3-b]quinoxaline (IQ) based luminescent liquid crystals, demonstrating excellent solubility and thermal stability. The efficient space-filling interactions in compounds with seven and ten peripheral N-alkoxy chains (IQ3 and IQ4) stabilize a columnar liquid crystalline phase at room temperature. Interestingly, these compounds exhibit tunable luminescence and liquid crystalline self-assembly in addition to technologically important AIE properties, in contrast to the commonly observed aggregation-caused quenching (ACQ) in the case of discotic liquid crystals (DLC). Compound IQ4 was selected for bioimaging studies due to its robust fluorescence behavior and AIE-active properties, facilitating uniform staining throughout the nematode cell body. Under aggregated conditions, visualization of the nematode body was significantly enhanced. Additionally, IQ4 was explored as a fluorescent probe for staining MCF7 cancer cells, where cellular uptake and localization studies revealed its exceptional fluorescence intensity and remarkable ability to target and visualize cancer cells. Its ability to stain individual cancer cells enabled high-contrast imaging with striking fluorescence signals, while its precise localization illuminated distinct cellular structures, thereby enhancing the resolution of bioimaging.