Role of Solvent and Secondary Doping in Polyaniline Films Doped with Chiral Camphorsulfonic Acid:  Preparation of a Chiral Metal

Abstract

We present the first study of chirality from the UV to the IR region for a conducting polymer, thereby probing the motion of the metallic "free carriers." Through study of chiral and achiral camphorsulfonic acid (CSA) doped polyaniline (PAN) films cast from different solvents (m-cresol and chloroform) and correlations with secondary doping experiments, we demonstrate that the chirality lies in the order "metallic" regions of the polymer films. Samples were studied by absorption, UV-vis-IR circular dichroism, and charge transport (temperature-dependent dc and microwave frequency conductivity and dielectric constant) measurements. The metallic films (cast from m-cresol) show strong optical activity of the conducting electrons in the visible and IR regions, showing that a chiral metal can be prepared by the methods of organic chemistry. In contrast, the nonmetallic chloroform cast films show weaker optical activity of the polymer backbone and a completely different interaction with CSA compared to m-cresol cast films. However, little difference in temperature-dependent dc conductivity is observed with PAN doped with chiral vs achiral CSA. It is postulated that chiral regions of the polymer backbone segregate in the metallic regions of the polymer film upon evaporation of m-cresol. Secondary doping of chloroform cast films with the vapors of m-cresol yields an increase in electron delocalization but a decrease in optical activity of the polymer backbone, in accord with a picture of inhomogeneous order in these materials.

Electrochemical Synthesis of Optically Active Polyaniline Films

“…This UV-vis spectrum is similar to that of doped PANI prepared chemically in aqueous solution. [23] In contrast to the PANI films prepared without oligomers, UV-vis spectra of PANI films prepared in the presence of oligomers have a peak around 420 nm, and a long tail extending beyond 1000 nm in the near-IR region. This so-called ªfree-carrier tailº has been identified previously as a delocalized polaron, which serves as an indicator of an extended PANI conformation.…”

ITO‐Free and Flexible Organic Photovoltaic Device Based on High Transparent and Conductive Polyaniline/Carbon Nanotube Thin Films

“…[ 9 ] Therefore, achieving high conductivity requires chemical control of the synthesis and properly choice of the so-called the primary (acids, oxidizing agents) and secondary dopants (solvents). [10][11][12] By optimizing the transparency and the conductivity of thin fi lms of PEDOT:PSS, high-effi ciency, completely ITO-free lightemitting devices and solar cells have been constructed. [ 7 , 13 ] Applications of PANI, however, have generally been limited by its poor solubility (which makes diffi cult its processability as thin fi lms).…”

Chiral Polymer–Carbon‐Nanotube Composite Nanofibers

“…It was reported that, such a peak could be observed in the case of (S)-(+)-CSA or (R)-(-)-CSA doped polyaniline films with chirality cast from chloroform solution, but could not from m-cresol solution. [10] Separate controlled experiments were carried out for the understanding of the formation mechanism of the chiral composite nanofibers. A polymerization was performed without using the agent CSA, to which sulfuric acid was added for the purpose of maintaining acidic conditions for polymerization.…”