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

Abstract

Chiroptical polypyrrole (PPy) film was prepared by sequential reaction of chemical oligomerization with FeCl 3 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 FeCl 3 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 electrochiroptical effect.

Chiroptical Properties in Thin Films of π-Conjugated Systems

“…A large number of oligomers and polymers with π-conjugated backbone have been reported to give significant ECD in thin films, including polyaramides, 570 polyazoureas, 571 polyisocyanides, 280,572,573 poly(Nsulfonylamidine)s, 574 polyazulenes and polybiazulenes, 575 perylene diimide (PDI) polymers, 576 thieno[3,2-b]thiophene 577,578 and thieno [3,4-b]thiophene-based systems, 579,580 poly(9,9′-bifluorenylidene)s, 581 polycarbazoles, 582 polypyrroles, 583,584 and polyanilines. 585−597 Below, we shall emphasize the most important classes of these π-conjugated systems: (i) polyacetylenes and polydiacetylenes; (ii) oligo/poly(p-phenylene)s and their derivatives, i.e., oligo/poly(p-phenylenevinylene)s and oligo/poly(p- Polyacetylenes are the oldest class of chiral π-conjugated polymers synthesized in the literature, with the polymerization of optically active 4-methyl-1-hexyne described in 1967 by Ciardelli and co-workers.…”

“…A large number of oligomers and polymers with π-conjugated backbone have been reported to give significant ECD in thin films, including polyaramides, polyazoureas, polyisocyanides, ,, poly­( N -sulfonylamidine)­s, polyazulenes and polybiazulenes, perylene diimide (PDI) polymers, thieno­[3,2- b ]­thiophene , and thieno­[3,4- b ]­thiophene-based systems, , poly­(9,9′-bifluorenylidene)­s, polycarbazoles, polypyrroles, , and polyanilines. − …”

HCl guided morphology and conductivity of chiral PPy nanostructures toward efficient electromagnetic wave absorption

“…Additionally, the PPy planar helixes formed at various [HCl]=0.5-2.0 M exhibit a weak negative peak over 645-731 nm. In addition to the helical arrangement of PPy chains caused by [HCl], these optical absorption bands should be associated with the π-π* transition and polaron (radical cations) generated in the PPy main chain by doping [45]. These findings demonstrate that changing [HCl] can adjust the helical structure and the optical properties of PPy samples.…”

A possibility of polaron vortex magnet of polypyrrole prepared in virus liquid crystal

“…Chemical oxidative polymerization with FeCl 3 and subsequent electrochemical polymerization were carried out sequentially. This method is based on a chemical–electrochemical double‐step polymerization method, which was developed previously 15 . First, linear oligomers were formed by adding an oxidation catalyst to the monomer.…”

“…The optical rotation and circular dichroism absorption could be controlled by applying an external electrochemical electric field due to the redox properties of the conductive polymer and the atropic optically active structure, which was transferred from the chiral liquid crystal. Recently, cholesteric liquid crystals in bio field for applications have been studied 15–18 . In this study, polypyrrole (PPy) was synthesized in a nontoxic fd phage liquid crystal as a natural chiral reaction field.…”