Photonic Crystals (PCs) are periodic dielectric structures that can be utilized to restrict, confine, or manipulate the propagation of light within a specific wavelength range, called the photonic bandgap (PBG). Materials with PBG are quite attractive owing to their potential applications in all optical integrated circuits, low threshold lasers, optical switches, tunable filters and so on. [1]. It is all the more advantageous if the required periodic structure of PCs is obtained through the selfassembly of the associated entities and this is possible in liquid crystal (LC) systems. Self-assembled structures of chiral nematic (Ch) and twist grain boundary smectic C* (TGBC*) LC phases are excellent examples, exhibiting PBG in one and three dimensions, respectively [2,3]. The latter phase has a frustrated phase character and is analogous to the Abrikosov phase seen in type-II superconductors. Owing to their periodic structures, both the LC phases exhibit fascinating properties, for example, selective reflection in the Ch/TGB helical axis direction, two-dimensional periodicity of SmC* helix resulting in square grid pattern and so on. My research focuses on exploring the impact of various external factors on the thermal and PBG features of Ch and TGBC* phases. Specifically, the effects of nanoinclusions, actinic light, and polymer template structure have been investigated. The addition of anisotropic nanoparticles, such as Gold nanorods (GNRs), significantly influences the PBG characteristics of these phases and also stabilizes the TGBC* phase, which will be discussed in detail. Additionally, the actinic light-driven switching on the structure and transition of materials exhibiting both Ch and TGBC* phases will be discussed. The interaction between light and photoactive molecules shows fascinating properties such as photo-driven isothermal phase change across the TGBC*-Ch transition, control of PBG characteristics in all three dimensions. Such novel interactions between light and LC materials offer the potential to construct tunable and effective optical devices that can be dynamically controlled by actinic light. Lastly, the advantages of using the polymer template technique to create wide-band multiple PBG structures in a single cholesteric LC device will be discussed. This technique has the potential to be applied in various applications such as filters, broad-band polarizers, and IR reflectors.

References: 1. R. Balamurugan, J. H. Liu, Reactive and Functional Polymers, 105, 9-34 (2016). 2. P. A. Pramod et. al. Liq. Cryst. 28, 525-533 (2001). 3. Rajalaxmi Sahoo et. al. Journal of Molecular Liquids, 299, 112117-1-10 (2020).