Electropolymerized Polythiophenes Bearing Pendant Nitroxide Radicals

Abstract

We report a facile way to synthesize polythiophenes carrying pendant 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) radicals, here called PTATs, by electropolymerization in boron trifluoride diethyl etherate (BFEE). The spacing between the TEMPO radical and the polythiophene backbone is varied by an alkyl spacer (n = 2, 4, 6), and the electronic and electrochemical properties are examined using UV–vis spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Film morphologies are also studied via scanning electron microscopy (SEM) and atomic force microscopy (AFM), which show that the longer octyl chain placed between thiophene and TEMPO effectively suppresses aggregation. The highest conductivity and electroactivity are observed for n = 4 and n = 6, respectively. Such morphology differences provide an opportunity to better understand the charge transport and energy storage properties in electronic materials.

Unusual Internal Electron Transfer in Conjugated Radical Polymers

“…These results explain the previously observed lower than theoretical capacities and moderate conductivities . Conductivities of CRP‐4, CRP‐6, and CRP‐8 were 8.1×10 −7 , 3.6×10 −7 , and 6.2×10 −9 S cm −1 , respectively, whereas P3BT had a measured conductivity of 1.6×10 −4 S cm −1 . The conductivity differences between the CRPs and P3BT is a consequence from the internal electron transfer process.…”

“…Polythiophenes bearing pendant TEMPO (2,2,6,6‐tetramethylpiperidine 1‐oxyl) radicals with varying alkyl spacer groups (CRP‐4, CRP‐6, and CRP‐8) were synthesized according to our prior report . Poly(3‐butylthiophene) (P3BT), a polythiophene bearing no pendant nitroxide radicals, was synthesized electrochemically and used as a control (Figure a; Supporting Information, Figure S1).…”

A New Conducting Copolymer Bearing Electro‐Active Nitroxide Groups as Organic Electrode Materials for Batteries

“…For the former, due to the presence of radicals, precursors of the polymers involving a protected amine form of TEMPO have to be prepared before a subsequent oxidation (e.g., using chloroperoxybenzoic acid) to generate the targeted TEMPO‐containing polymers . For the latter, nitroxide functions can be elegantly introduced using electro‐polymerizable monomers (e.g., thiophene and pyrrole) to obtain targeted materials. Importantly, although results were interesting in both cases, the capacity measured was lower than the theoretical expected one, clearly demonstrating either that the oxidation process is not quantitative or that the (electro)polymerization leads to partly soluble (oligomeric) materials.…”

“…Indeed, organic and polymer chemistry can provide different nitroxide‐containing materials for their anchoring onto capacitive materials to get polymers. Architectures such as polythiophene‐TEMPO, poly(3,4‐ethylenedioxythiophene) (PEDOT)‐TEMPO, or poly(dithieno[3,2‐ b :2,3‐ d ]pyrrole)‐bearing TEMPO exhibit good conductivity and high theoretical capacity. This strategy emphasizes the importance to match redox‐active polymer potentials with those of electroactive groups.…”

Radical polymerization of radical‐labeled monomers: The triarylmethyl‐based radical monomer as an example

“…It is well known, as quoted from Jia and coworkers: “ free‐radical polymerization techniques cannot be used in the direct polymerization method” involving the presence of stable free radicals. Hence, SORPs are prepared via several alternative routes: (a) the direct route, which involves polymerization of monomers carrying Stable organic radical ‐ SOR by nonradical techniques, (b) conversion of radical precursors into a SOR via different approaches such as oxidation of amines or the C—ON bond homolysis of alkoxyamines; (c) postmodifications of a polymer carrying an activated group. Therefore, route (a) precludes access to cheap and easily prepared polymer via radical polymerization (RP) techniques.…”