# Investigating the Electro-Optic Response of Steroid Doped Liquid Crystal Devices
## 3 Results and Discussion  
A large portion of biomolecule chiral dopants reported previously are steroids or have the same core structure common in steroids. Although many steroids have been studied in previous reports, numerous remain untested. In order to identify new steroidal chiral dopants, nine steroids were investigated for their ability to act as chiral dopants for LC systems. In addition to the nine steroids, the bile acid lithocholic acid was chosen due to its structural similarity to the other biomolecules tested. These molecules were chosen for their structural similarity to cholesterol benzoate, the original LC. For comparison, cholesterol and \(\beta\)-estradiol were included in the study as both have been used as chiral dopants in previous studies [18; 19; 20; 21; 22]. The structures of the steroids chosen for this study are shown in Figure 1.  
To determine the miscibility of the steroids with common nematic LCs, mixtures containing 5 wt. % steroid in LC E7 were prepared, loaded into glass cells, and viewed with a polarized optical microscope (POM). The POM images shown in Figure 2 indicate that two-thirds of the steroids chosen were immiscible with nematic LC E7. Notably only progesterone, cholesterol, and \(\beta\)-estradiol were miscible. To further explore the miscibility of progesterone, cholesterol, and \(\beta\)-estradiol, the loading of these steroids in E7 was increased to 10 wt. %. POM images revealed that only progesterone remained miscible while cholesterol and \(\beta\)-estradiol began to crystallize out of the solution, shown in Figure S4. Lithocholic acid will be discussed below. Once phase compatibility had been established and progesterone was identified as a suitable chiral dopant, the utility of biomolecules in responsive LC devices was investigated. Progesterone was chosen as the bio-chiral dopant due to its superior miscibility relative to the other steroids, allowing for a greater loading. The selective reflection of progesterone in E7 is shown in Figure S5a. Progesterone was incorporated into a switchable CLC devices that exhibited either \"normal mode\" or \"reverse mode\" behavior. In \"normal mode\" switchable CLCs, the sample is opaque due to the sample adopting the focal conic texture as unaligned cells are used, and, when a voltage is applied, the LCs reorient to form a transparent state as the molecules adopt a homeotropic texture [32; 33; 34]. \"Reverse mode\" CLCs are aligned in a planar texture in the absence of an electric field but are transparent as the selective reflection is placed in the infrared region. Upon the application of an electric voltage, the planar texture is lost and the sample adopts a focal conic texture leading to high scattering. The planar texture can be recovered when a sufficiently high electric field is applied [35]. The difference between the two modes is dictated by the sample preparation. Figure 1: Chemical structures of the steroids used as chiral dopants. It is important to note that ternary mixtures of the biodopants with small concentrations of commercially available dopants are used for all responsive CLC systems. The ternary mixtures reduce the risk of crystallization when using commercially available dopants while placing the selective reflection in the near-IR for greater electro-optic properties. A \"normal mode\" switchable LC was fabricated using 10 wt. % progesterone; the full sample formulation for the NM1 sample is shown in Table S2. An LC with a positive dielectric anisotropy was chosen as the mesogens will reorient with the applied electric field, enabling the LCs to switch from the focal conic state to the homeotropic state. The \"normal mode\" LC device, shown in Figure 3a, exhibits low light transmittance (<20%) across the visible spectrum due to the focal conic orientation of the LCs scattering light. When a voltage of 95 V AC is applied, the LCs reorient with the electric field, adopting a homeotropic orientation that leads to an optically transparent clear state with ~60-80% transmittance across the visible spectrum.