# Investigating the Electro-Optic Response of Steroid Doped Liquid Crystal Devices
## 3 Results and Discussion
To ensure red tuning of the selective reflection, a low concentration of initiator was added to the formulation; additionally, the sample was cured for 3 min at a lower UV light intensity to reduce the ion concentration [41]. The red tuning PSCLC is shown in Figure 4a; the initial reflection peak is located in the near-infrared region at 1250 nm. Upon application of a DC voltage, the selective reflection shifts; at 80 V, the selective reflection is shifted to 2300 nm. This represents an increase in the selective reflection position of 13 nm/V. Red tuning is representative of an elongation of the helical pitch as the polymer network is deformed. Figure 3: Switchable LC devices in (**a**) normal mode which is focal conic at 0 V and switches to a transparent homeotropic state when 95 V AC is applied. (**b**) Reverse mode switchable LLC that is (i) in the transparent planar state at 0 V, (ii) switches to the scattering focal conic state with 35 V DC, (iii) is stable in the focal conic state when the DC voltage is removed, (iv) switches back to the transparent planar state upon application of 40 V AC, and (v) remains stable in the planar state when the voltage is stable. To generate a PSCLC with blue tuning behavior, a photoinitiator with a higher ion concentration and an increase in curing time was employed. The photoinitiator chosen, I-369, has a higher ion concentration when exposed to UV light than I-651, which was used for the red-tuning sample [41]. The sample was then cured at a higher UV light intensity over a time period of 30 min. The blue tuning of the PSCLCs selective reflection is shown in Figure 4b. The initial reflection is placed at 950 nm; as the voltage is applied to the sample, the selective reflection shifts to shorter wavelengths. At the highest applied voltage of 100 V DC, the selective reflection is centered near 450 nm, a shift of 5 nm/V. In addition to the chirality present in steroids (and other biomolecules in general), many also possess functional groups that can be synthetically modified to change the properties of the compound. In this way, a host of new chiral dopants can be developed from widely available biomolecules. Lithocholic acid (LA), for instance, is sparingly soluble in many LCs due to the two polar functional groups, an alcohol and a carboxylic acid. However, these functional groups can be chemically modified to improve the miscibility of LA, potentially creating chiral dopants for CLCs. To test this hypothesis, two LA derivatives, LA-Bn and LA-Me, were synthesized via nucleophilic substitution of LA onto alkyl halides (benzyl bromide and iodomethane, respectively). These new derivatives serve as excellent model compounds due to their facile, one step synthesis. The synthetic scheme for the synthetic modification of LA is shown in Figure 5a. In each case, the phase compatibility of the derivatives is superior to that of the parent compound. LA is immiscible in E7 at 5 wt. %, and POM images show irregular LLC reflections and numerous oily streak defects originating in phase separated crystallites (Figure 5b). LA-Bn and LA-Me are both miscible at 5 wt. % with uniform reflection colors and few defects (Figure 5c,d). Similar to progesterone, both LA derivatives show miscibility with LC E7 at 10 wt. % (Figure S1). For the modified lithocholic acid derivatives we be used as chiral dopants, their incorporation into responsive CLC devices was explored. The electro-optic responses of both bulk CLCs and PSCLCs were examined in mixtures formulated with LA-Bn and LA-Me, respectively. The selective reflection of LA-Bz and LA-Me in E7 are shown in Figure S5b and c, respectively. First, the electro-optic response of LA-Bn and LA-Me in normal mode switching CLCs was investigated as these samples require the least complex formulation. To achieve the focal conic texture, CLC mixtures were loaded into ITO-coated glass cells with no alignment layer. At 0 V, the CLC containing LA-Bn as the chiral dopant had transmittance values under 10%, as shown in Figure 6a.