Chiral Fluorescent Photoswitches: Coupling of Chirality and Fluorescence into Photoswitches for Photonic Applications

Multifunctional integrated molecules are increasingly pivotal in various cutting-edge fields including materials science, nanotechnology, and biomedicine. Among these molecules, chiral fluorescent photoswitches (CFPSs) are a class of functional organic molecules that seamlessly integrate chiral, fluorescent, and photoresponsive characteristics. These properties, when combined, allow for a fascinating array of variations in chirality and fluorescence due to the structural changes induced by photoisomerization. The types of photoisomerization further influence these changes, resulting in a wide range of outcomes. In this Account, we present the progressive results of our ongoing research in the field of CFPSs, with a special emphasis on the dynamic regulation and photonics properties of chiral liquid crystal (LC) systems constructed with these molecular switches. To date, we have developed five different types of CFPSs based on α-cyanostilbenes, dicyanodistyrylbenzene, diaryldicyanoethene, sulfonated DAE, and azobenzene, respectively. We have actively explored the molecular engineering of these CFPSs, the performances of the chiral LC assemblies, and the constructed photonic devices that broaden their potential applications.

The main focuses of this Account are structured around the concept of the “molecule engineering-properties-device applications” of the CFPSs. Crucially, CFPSs have the unique ability to amalgamate chiral and fluorescent properties within this photomodulation, serving as an effective medium to achieve sophisticated photomodulation effects. Given this, we focus on the molecular engineering of these CFPSs based on cyano positions, aryl modifications, linking sites, and binaphthyl handedness, which strongly affect the fluorescence intensity, emission wavelength, chiral-induction ability, photoisomerization conversion rate, and reversibility. The comprehensive analysis holds significant implications for guiding the future design and optimization of CFPSs. Furthermore, LC is a versatile enabling material that can integrate CFPSs to create self-assembled 1D helical superstructures known as cholesteric LC (CLC) or 3D blue-phase (BP) cubic structure systems. We reveal that these LC systems not only enable cross-scale regulation of CFPSs but also serve as highly efficient photonic devices in their own right. Such advanced photonic devices we constructed have the ability to adjust both the reflected color, the fluorescence properties, and circularly polarized luminescence (CPL), demonstrating significant potential for visual and smart applications.

These systematic investigations emphasize the importance of the photoswitches’ integrated chirality and fluorescence for optimized molecular design and fabrication, intrinsic regulation mechanism, and advanced photonic applications. Further systematic investigations, including molecular simulation, performance stability, and device friendship, will contribute to the rapid development of CFPSs-LC photonic devices that are suitable for practical applications.