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Issue 12, 2020

Protonic acid doping of low band-gap conjugated polyions

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Abstract

This paper describes the design and synthesis of a series of conjugated polyions (CPIZ-T, CPIZ-TT and CPIZ-TT-DEG) that incorporate a formal positive charge into their conjugated backbones, balanced by anionic pendant groups with increasing electron-donating ability. The energy levels and the bandgap of these conjugated polyions were determined by using optical absorption spectroscopy and cyclic voltammetry (CV) and were easily modulated by varying the electron donating group. The energies of the occupied states increase with increasing electron-donating ability, while the energies of the unoccupied states are almost unchanged due to the presence of tritylium ions in the conjugated backbone. All conjugated polyions exhibit pristine semiconducting properties in weak protonic acids, but with sufficiently strong acids, the polymers exhibit spontaneous spin unpairing and convert to a metallic state. The required strength of the acids varies with the electron-donating ability, with higher HOMO levels leading to more facile proton acid doping and higher electrical conductivities. The mechanism of protonic acid doping of conjugated polyions involves a spinless doping process (dehydration) followed by a spontaneous spin unpairing leading to the formation of polarons. While protonic acid doping occurs in polyaniline, conjugated polyions offer synthetic tunability and selective processing into insulating, semiconducting and metallic states simply by controlling acidity.

Graphical abstract: Protonic acid doping of low band-gap conjugated polyions

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Article information


Submitted
29 Apr 2020
Accepted
10 Jun 2020
First published
11 Jun 2020

This article is Open Access

Mater. Chem. Front., 2020,4, 3585-3593
Article type
Research Article

Protonic acid doping of low band-gap conjugated polyions

G. Ye, Y. Liu, J. Liu, X. Qiu, L. J. A. Koster and R. C. Chiechi, Mater. Chem. Front., 2020, 4, 3585 DOI: 10.1039/D0QM00278J

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