Electrochemical polymer reaction of Poly(3-hexylthiophene) via Anodic C–H Phosphonylation Kohei Taniguchi, Ikuyoshi Tomita, Shinsuke Inagi Tokyo Institute of Technology, Japan Polythiophene derivatives are remarkable materials for electronic devices due to the high stability of their doped state and solution processability. For tuning their electrochemical properties, functionalization of their main chains is a promising approach. Among the functionalization methods, electrochemical polymer reaction is an attractive strategy for introducing functional groups or units into precursor polymers under mild reaction conditions. 1 Using the reactions, functional groups or units can be introduced at aromatic C–H bonds; therefore, ubiquitous π-conjugated polymers can be used for the reactions because aromatic C–H bonds are the most common structures in π-conjugated polymers. Moreover, the degree of substitution can be controlled by tuning the amount of charge passed through the electrode. To date, anodic C–H chlorination of poly(3-hexylthiophene) (P3HT) has been reported (Figure 1 (a)). 2 However, the available functional groups or units for this electrochemical polymer reaction remain limited to those derived from ionic nucleophiles, such as a chloride ion. In this study, to expand the functional groups applicable to electrochemical polymer reactions, the anodic C–H phosphonylation of P3HT was performed with non-nucleophilic dopants and triethyl phosphite as an electrically neutral nucleophile (Figure 1 (b)). 3 As a result, although some of the polymer films were dissolved during the constant-current electrolysis, the 1 H and 31 P NMR spectra of the obtained polymer (P3HT-Phos(Et)) indicated that the diethyl phosphonate was successfully installed at the 4-position of the thiophene rings. The degree of substitution (m) was calculated by comparing the integral signal of the aromatic protons before and after anodic phosphonylation (m: 0.25). Furthermore, the degree of substitution could be controlled by tuning the amount of charge until 2.0 F/mol. It was found that the optoelectronic properties of P3HT-Phos(Et) were gradually changed by controlling the degree of substitution. In addition, various trialkyl phosphite reagents such as P(O n Bu) 3 and P(O n Hex) 3 were found to be suitable for the anodic C–H phosphonylation of P3HT. Finally, the relationship between the molecular weights of P3HT and the degree of substitution in the anodic C–H phosphonylation was investigated. When the molecular weight of P3HT was decreased, the degree of substitution and the yield decreased because the low molecular weight P3HT films were easily dissolved during anodic C–H phosphonylation.
References 1. T. Kurioka, S. Inagi, Chem. Rec. , 2021 , 21 , 2107–2119.
2. T. Kurioka, N. Shida, I. Tomita, S. Inagi, Macromolecules , 2021 , 54 , 1539–1547. 3. K. Taniguchi, T. Kurioka, N. Shida, I. Tomita, S. Inagi, Polym. J. , 2022 , 54 , 1171–1178.
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