## 1 Introduction
[26]. Figure 1: Schematic illustration of synthetic strategy with chemical structures, proposed by [PERSON] and [PERSON] for the synthesis of monodomain nematic liquid crystalline elastomers (LCEs) [5]. In an effort to examine the structure-property relationships, a variety of symmetrical and unsymmetrical molecules was designed [27; 28; 29; 30; 31; 32; 33; 34]. The bent-core (banana shape) mesogenic molecules with azobenzene chromophores are of special interest due to their structure relationships with light-triggered phase transition and photo-actuation properties [35; 36; 37; 38]. These azobenzene, bent-core banana molecules were widely studied as intelligent stimuli-responsive materials for technological applications [39; 40; 41; 42; 43]. Merging the elastic property of polymeric elastomers and self-organizing properties of liquid crystals, many scientists have reported prospective works on crosslinked liquid crystalline polymers (CLCPs), which exhibit unique macroscopic shape-changing properties such as bending, contraction, and swirling especially under the influence of light. Most importantly, the photochemical phase transition of azobenzene chromophore (azotolane) containing CLPs has a great influence on the photo-actuation (See Figure 3a-c). [44; 45; 46; 47; 48; 49; 50]. In addition to azotolane moieties in the CLCP film, authors used other components such as platinum(II) tetrapheltetrabenzoporphyrin (sensitizer) and 9,10-bis(diphenylphosphory)anthracene (annihilator) in order to trigger the _trans-cis_ photoisomerization with 635-nm laser at a low power density of 200 mW cm\({}^{-2}\). The actuation performance was driven by low-power excited triplet\(-\)triplet annihilation based upconversion luminescence [50]. Figure 2: The photomechanical effects caused by _trans–cis_ photoisomerization in some selected polymer systems developed by (**a**) [PERSON] et al. [23], (**b**) [PERSON] et al. [24], (**c**) [PERSON] et al. [25], and (**d**) [PERSON] et al. [26]. In brief, photoisomerization is a phenomenon of structural transformation of molecules under photo-excitation. Photoisomerization of azobenzene molecules was demonstrated in Figure 2d. The _trans_ form (up) can be converted to the _cis_ form (down) using ultra-violet (UV) radiation of wavelength of 300-400 nm. The visible light illumination of _cis_ azobenzene at >400 nm can revert the molecule back to _trans_ form. By applying heat to _cis_ form, the molecule can also be relaxed to stable _trans_ form. The photoisomerization process of azobenzene mesogens in CLCPs can result in induced molecular reorientation, and this is the source for photo-actuation [50; 51; 52; 53; 54]. The chemical structures of azobenzene chromophores (monomer and crosslinker) used to prepare photo-actuating liquid-crystalline gels (LCGs) by [PERSON] et al. are shown in Figure 4[51]. [PERSON] et al. [52] studied azobenzene-doped liquid-crystal polymer (azo-LCP) prepared by \"host-guest\" method of fabrication process. 1,4-bis-[4-(3-acryloyloxypropyloxy)]benzoylJ-2-methylbenzene was used as host and 4-4'-bis[6-(acryloxyoxy)hexyloxy]azobenzene as guest material. The authors proposed that the azobenzene monomers elicit the alignment of the mesogens in two ways: (i) photoisomerization of azobenzene and rotation of azobenzene by means of a trans-cis-trans reorientation (TCTR), the latter was activated at around 365 nm. The authors evidently confirmed that the photo-bending speed of azo-LCP in the TCTR case is always faster than that of photo-isomerization (See Figure 5 for Sketch and bending snapshots of azo-LCP). The materials made of azo-LCP can precisely control the actuation that can advantageously be utilized in photo-driven soft robotics. The contraction of LCP along the major alignment direction of mesogens was favored by transformation of nematic to the isotropic phase of mesogens. Conversely, the shape of LCP is recovered when the mesogens transform from isotropic to the nematic phase. This can be achieved by visible-light irradiation [52].