Reversible color control

Tamaoki et al. reported a series of planar chiral dopant which was employed in commercially available nematic LC to achieve phototunable reflection colors [69, 70]. These compounds were designed based on an azobenzenophane compound having conformational restriction on the free rotation of naphthalene moiety to impose an element of planar chirality. Due to the good solubility, moderately high HTPs, and large changes in HTPs during photoisomerization of the dopant, a fast photon mode reversible color control in induced CLCs was achieved. 

Thermochromic Gel Networks for Reversible Color Control with Temperature... 

M. Mathews, N. Tamaoki, Planar chiral azobenzenophanes as chiroptic switches for photon mode reversible reflection color control in induced chiral nematic liquid crystals. J. Am. Chem. Soc. 130, 11409-11416 (2008)... 

R. Eelkema, B.L. Feringa, Reversible full-range color control of a cholesteric liquid-crystalline film by using a molecular motor. Chem. Asian J. 1, 367-369 (2006)... 

Guan, J. Zhang, M. Gao, W Yang, H. Wang, G. Reversible reflection color-control in smectic liquid crystal switched by photo-isomerization of azobenzene. ChemPhysChem 2012,13,1425-1428. 

Gel Networks for Reversible Transparency and Color Control with Temperature. A novel class of polymer gel networks which change both their color and transparency with changing temperature has been developed (61). Starting from a... 

Chromogenic Polymer Gels for Reversible Transparency and Color Control... 

The oxidized (doped) form of PBT can be reduced (dedoped) reversibly by controlling the potential of the polymer coated electrode. The redox process is accompanied by a drastic change in the properties of the polymer (e.g. PBT), such as electrical conductivity (cf. Sect. 3.2.3, BU4NCIO4), stability (cf. Sect. 4.3, the doping/dedopping degree), color (cf. Sect. 3.4.3), optical properties (cf. Sect. 3.5) and wettability (see Sect. 3.11) [217,261-263]. The reversible redox behavior of PT depends on the monomer concentration [264,265]. PT films electrochemically formed in solutions of 0.4 M thiophene have reversible redox behavior, in contrast to PT films formed in 0.01 M solutions of thiophene. This is explained by overoxidation due to the limited transport of the monomer by... 

Figure 5.9 Recovery of enzyme activity after rapid dilution as described in Figure 5.8. Curve a represents the expected behavior for a control sample that was pre-incubated and diluted in the absence of inhibitor. Curve b represents the expected behavior for a rapidly reversible inhibitor. Curve c represents the expected behavior for a slowly reversible inhibitor, and curve d represents the expected behavior for an irreversible or very slowly reversible inhibitor. See color insert.

The anthocyanins exist in solution as various structural forms in equilibrium, depending on the pH and temperature. In order to obtain reproducible results in HPLC, it is essential to control the pH of the mobile phase and to work with thermostatically controlled columns. For the best resolution, anthocyanin equilibria have to be displaced toward their flavylium forms — peak tailing is thus minimized and peak sharpness improved. Flavylium cations are colored and can be selectively detected in the visible region at about 520 nm, avoiding the interference of other phenolics and flavonoids that may be present in the same extracts. Typically, the pH of elution should be lower than 2. A comparison of reversed-phase columns (Ci8, Ci2, and phenyl-bonded) for the separation of 20 wine anthocyanins, including mono-glucosides, diglucosides, and acylated derivatives was made by Berente et al. It was found that the best results were obtained with a C12 4 p,m column, with acetonitrile-phosphate buffer as mobile phase, at pH 1.6 and 50°C. 

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