Chemical-Electrochemical Sequential Double-Step Polymerization in Liquid Crystal Allows for Imprinting of 3D Molecular Assembly Form Showing Electro-Chiroptical Effect

Chiroptical polypyrrole (PPy) film was prepared by sequential reaction of chemical oligomerization with FeCl3 and subsequent electrochemical polymerization in a cholesteric liquid crystal (CLC) consisting of 4-cyano-4′-pentylbiphenyl (5CB) and cholesteryl oleyl carbonate (COC). Chemical oxidation reaction of pyrrole as a monomer with FeCl3 in the liquid crystal (LC) produces a linear-shaped pyrrole oligomer. The linear-shaped precursor, having a good affinity with the LC molecular, can prealign along the director of the CLC. Subsequent electrochemical polymerization of the precursor in the CLC affords structure transcription from the matrix CLC to the polymer, resulting in the production of PPy with effective imprinting of the LC order. Surface observations of the PPy film with polarizing optical microscopy (POM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) reveal fingerprint textures of the surface, suggesting occurrence of transcription of the helical structure of the CLC to the polymer films. The PPy film shows electrochromism between ？0.7 and 0.3 V. Furthermore, the circular dichroism (CD) optical absorption spectra indicated that the PPy film exhibits optical activity even though there are no chiral centers in the molecular structure. The asymmetry of the resultant polymer is derived from 3-D chiral assembly imprinted from the matrix CLC. Therefore, the CD spectra of the PPy film at the oxidized and the reduced states show a change in chiroptical activity. This phenomenon can be referred to as an electro-chiroptical effect