Stability of reduced polypyrrole

Abstract

A processible and stable polyaniline derivatives was synthesir:ed,:Erom the electrochemical oxidations of modified aniline monomers. Assynthesized poly(n-anilino-1-alkanesulfonic acid) sodium salt (PZWAS) showed reversible electrochromic properties by changing their co:Lors from pale yellow to green when applied potentials were varied between 0.2 and 0.6 V (vs Ag/AgCl). Electrochromic reversibility of these polymers-were determined by an in s i t u spectroelectrochemical and a cyclic voltammetric study. Combined with the electrochromic properties, these polymers were found to form liquid crystalline solutions in water.The interesting anisotropic behavior was inferred from observations of depolarization of plane-polarized light and the existence of a critical concentration range for the formazion of the liquid crystalline phase. Electrochemical doping level. of these polymer and ambient temperature were also found to be critical to the phase behavior. The relevant redox structure of these polymer to the phase behavior will be discussed based on electrochemical and spectral analysis.Electrochemically 'polymerized polypyrrole(PPy) shows changes in visible light spectrum on reduction revealing changes in electron states of the conjugated double bond. The reduced PPy is unstable t o show changes in the visible light spectrum in less than one minute after cutting off applied potential. The absorption peak at 420 nm assigned as xx * transition in the conjugated double bond shrinks fast to show a strong absorption around 800 nm assigned as bipolaron. When the reaction system is purged with nitrogen, the spectral changes slow down significantly to prove that oxygen accererates the structural changes in PPy. It is observed that the spectral changes slow down when hydroquinone is added to the system.The addition of hydroquinone in the system produces little polaron on oxidation of PPy and makes the polymer segments trun directly into bipolaron states. Hydroquinone is ionized in an aqueous system t o produce pioton which seems t O stabilize free radicals in the polaron state. A decrease of pH in the system makes PPy become stable in repeated redox reaction while the polymer shows poor repeatability of cyclovoltammometry in the system with high pH. It is suggested that deprotonation of -NH in the pyrrole ring develops into production of an imine structui'e t o loose the electrochemical reactivity. 698

Interlayer excitons in transition metal dichalcogenide heterostructures

“…This effect was also found in Ref. [48] in which a bottom and top gate were placed on the hBN substrate above and below the material, respectively. In Fig.…”

“…The green curve is the experimental result for the 1s interlayer exciton from Ref. [48]. The dashed blue curve is our theoretical result when we reduce the interlayer distance from 1 nm to 0.53 nm.…”

“…We model the TMDs by monolayers. The green curve is the experimental result for the 1s interlayer exciton from Ref [48]…”

1-5 Napthalenedisulphonic Acid Doped Polypyrrole thin films as Coatings to Optical Fibers for Organophosphate Sensing

“…Raman spectroscopy is one of the important techniques to obtain structural information on polypyrrole. There have been many researchers who have studied raman spectra of polypyrrole [19][21] [22]. The sharp peak occurring at 1593cm Ellipsometry involves the measurement of the change in the state of polarization of the incident light beam after reflection from the surface of interest.…”