Multichromatic Polarizer Using Redox Responsiveness

For developing multichromatic thin films, perylenediimide-methacrylic anhydride (PMA) was newly designed and synthesized. Conjugation system of PMA core can be reversibly changed by redox responsiveness because the imide groups can stabilize the radical anions. This reversible change of conjugation system causes the shift of the absorption wavelength band of PMA core. Then, the PMA solution’s color changes from red to dark purple because the reduced PMA mostly absorbs all the wavelength of visible light. When the reduced PMA solution is exposed to oxygen or polarized on anode, the solution’s color returns to red because the oxidized PMA specifically absorbs absorption band at λ = 500 nm. Another characteristic of PMA core is suitable for anisotropic optical properties because of its high dichroic ratio. But, in generally, perylendiimide-based molecules have low solubility in both polar and nonpolar solvents due to strong intermolecular π-π interaction. In addition, stability of organic molecules is essential in various circumstance for application feasibility. So, Introduced ionic groups and polymerizable groups at perylenediimide core improve the solubility for process and impart the stability through polymerization. Based on the results of X-ray diffraction and polarized optical microscopy, it was confirmed that the PMA molecule exhibits a lyotropic chromonic liquid crystal (LCLC) phase which is composed of both attractive force (π-π interaction and lateral correlation between perylenediimide core) and repulsive force (between ammonium bromide). To fabricate the multichromatic PMA polarizer, PMA solution was coated on transparent substrate by mechanical shearing and then photopolymerized. The polymerized PMA polarizer exhibits excellent mechanical strength and chemical resistance in both acidic and basic solution than unpolymerized state. Spectroscopic and optical properties of fabricated PMA polarizer was confirmed by ultraviolet-visible spectroscopy and polarized optical microscopy. The results of ultraviolet-visible spectroscopy show that when the polarization direction and shear direction are parallel state, the transmittance is higher than when they are perpendicular state. PMA polarizer shows the characteristic of E-type polarizer which absorbs only the ordinary wave at λ = 500 nm and transmits the extraordinary wave. Thus, the polarized optical microscopy images show the color of the transmitted light presents red image when the polarization direction is perpendicular to shear direction. On the other hand, colorless and transparent state present when the polarization direction is parallel to shear direction. These characteristics show the manufactured PMA polarizer can be applied to sign encryption as well as multichromatic smart window. This work was supported by the BK21 FOUR, Mid-Career Researcher Program (2021R1A2C2009423) and Basic Research Laboratory Program (2020R1A4A1018259).