Uniaxially Oriented and Polymerized Chromonic Nanocolumns for Redox-Responsive Smart Glass

Abstract

Bandwidth-tunable anisotropic spatial light modulators are fabricated with redox-responsive dichroic mesogens. By introducing an ionic group and a polymerizable group into the chromophore, the programmed reactive mesogen (PDI-MA) exhibits a lyotropic chromonic liquid crystal (LCLC) phase. The PDI-MA molecule forms a stable aromatic dianion state so that the absorption wavelengths of the dichroic mesogen can be reversibly tuned by redox reactions. Through a continuous process of coating, molecular self-assembly, and polymerization, redoxresponsive and uniaxially oriented LCLC polymer films are fabricated. Because of the high dichroic ratio of PDI-MA, the uniaxially oriented LCLC network is capable of anisotropic light modulation in the visible-light spectrum. Uniaxially oriented LCLC films are applied to flexible multichromic smart windows and optical security filters for anticounterfeiting.

Security use of bilayer dichroic films made of liquid crystal polymer networks

“…The anthraquinone derivative cyan dichroic dye was purchased from Nematel GmbH in Germany. The bis-azobenzene derivative red dichroic dye was synthesized according to a previous research [23].…”

“…The absorbance in the 'red' layer decreased because the polarization direction of the incident light, and the absorption axis of the 'red' layer were no longer parallel as θ ' became 90°. At the same time, the absorbance of the 'cyan' layer increased because the polarization direction of the incident light and the absorption axis of the 'cyan' layer became closer to parallel [23]. (Figure 3).…”

“…The fabrication process is as follows (Figure 1(a)). (i) Two kinds of dichroic dyes that absorb different wavelengths were prepared: bis-azo benzene dye, synthesized following previous research [23] and denoted as 'red,' and anthraquinone derivative dye, denoted as 'cyan.' In this study, a reactive mesogen that showed both nematic and smectic phases was used to fabricate the LC films (Figure 1(b,c)).…”

“…(iv) The LC mixture was polymerized using UV light with a power of ∼ 1.23 mW/cm 2 for 30 min at 25°C (Cr phase). The molecular arrangement of reactive mesogens does not change even when they are polymerized in the Cr phase [23], so photo-polymerization was carried out in the Cr phase with the highest molecular alignment. (v) The sandwich cell was opened and the unpolymerized parts were developed with ethanol and washed with water.…”

“…These two LC films are laminated. Thus, each film perpendicularly crosses the absorption axis of the other film [23]. BDLC films show different transmission colors, not a different brightness from that of the conventional single-layer films, when the direction of the incident LPL changes.…”