Enhancing the photoluminescence of imidazolium-based ionic liquid crystal by doping with carbon quantum dots

Over the past decade, photoluminescent liquid crystal materials have attracted increasing attention, particularly for the dispersion of carbon quantum dots (CQDs) in liquid crystal systems. In this study, CQDs were combined with an ionic liquid crystal (CBphCM) via ionic self-assembly to successfully prepare a new photoluminescent composite material (CBphCM–CQDs). The process of CBphCM and CQDs recombination was monitored via multiple experimental techniques such as Fourier transform-infrared spectroscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). The experimental results revealed that the rich carboxyl groups on the surface of the CQDs provided accessible sites for further functionalization, thereby facilitating uniform dispersion of CQDs in the ionic liquid crystal matrix. The presence of N–O bonds in the XPS spectra indicates the formation of a new mixture between CBphCM and CQDs. The liquid-crystalline behavior of CBphCM–CQDs was investigated. The results indicate that CBphCM–CQDs exhibit the SmA phase within the temperature range of 173.9–146.8 °C, in conjunction with a focal conic texture. Within the temperature range of 146.8–105 °C, the material exhibits a SmC phase, characterized by a broken focal conic texture. Fluorescence measurements revealed that although the fluorescence lifetime of CBphCM–CQDs was shorter than that of the CQDs, their quantum yield was 2.47 times that of the CQDs. This pronounced enhancement in photoluminescence intensity of the nanocomposites can be attributed to the constructive combination of emissions from CQDs and CBphCM. Furthermore, CBphCM–CQDs exhibit good photoluminescence stability and retain fluorescence properties even when the temperature increased to 170 °C.