ABSTRACT
The need for a light-weight, inexpensive, and easy-to-use light sensor or detector has been highly motivated by the growing concerns such as adverse health and environmental issues induced by light radiations from natural sunlight and artificial light sources including lasers. Photochromic chiral liquid crystals (LCs) that combine the photochromic phenomenon of molecular switches or motors with dynamic light reflection of chiral LCs hold a promise in design and fabrication of smart light sensors. The light-directed reflection color tuning of photochromic chiral superstructures for light sensing would not only help the human eye to directly “see” the light radiations (especially invisible lights) and even “feel” their intensities under ambient light without the aid of additional complex components but also can be easily incorporated in the tags or packages of perishable products and any other portable daily items, which would greatly increase the public awareness of these hazardous irradiations. In this chapter, we cover the recent advances in light-driven photochromic cholesteric (CLC) and blue phase (BP) LCs for light sensing. Flat thin films and spherical microdroplets and microshells of photochromic CLC containing various chiral molecular switches and capable of dynamic circularly polarized visible light reflections are discussed in addition to the systems with upconversion nanoparticles (UCNPs). Moreover, photochromic BP LCs containing light-driven molecular switches and functionalized gold nanorods that exhibit tunable lattice constants are described in the context of light sensing. The chapter is concluded with a perspective on the future opportunities and challenges for these emerging photochromic chiral LCs in light sensing applications.
