Phosphonylation of Conjugated Polymers By Redox Mediator-Induced Electrochemical Post-Functionalization
Authors: Taniguchi Kohei , Sato Kosuke , Inagi Shinsuke 
Published: December 2024

π-Conjugated polymers (CPs) are attractive optoelectronic materials due to the extended π-conjugation systems along with their main chains.1 Considering the π-conjugation systems, the introduction of functional groups or units into the aromatic main chain is an effective method to modify the properties of CPs. To introduce functional groups or units into molecules, an electrochemical reaction is a straightforward strategy due to its mild reaction conditions and reaction controllability. To date, electrochemical post-functionalization of CPs in the film state has been explored.2,3 Although this electrochemical reaction can realize the C–H functionalization with a simple protocol, the yield is not high owing to the detachment of polymer films during electrolysis. Given these challenges, there is a rising interest in another electrochemical post-functionalization approaches such as the use of redox mediators to functionalize dissolved polymer precursors.

Nevertheless, there have been a few reports on electrochemical post-functionalization in a homogeneous state because of inefficient electron transfer at the limited reaction field of the working electrode (Figure 1 (a)). To enhance the efficiency, indirect electrolysis is a suitable approach (Figure 1 (b)).4 In this method, redox mediators (i.e., triphenylamine derivatives) are activated at an electrode, facilitating the electron transfer between the activated mediators and dissolved CPs (Figure 1 (b)). In this study, we aimed to achieve electrochemical post-functionalization in a homogeneous state through indirect electrochemical polymer reactions such as anodic phosphonylation.

To investigate the electron transfer between redox mediators and CPs, we preformed cyclic voltammetry measurements of polyfluorene (PFO) and tris(2,4-dibromophenyl)amine (Ar3N) (Figure 1 (c)). Comparing the voltammograms, the oxidation current of the mediators was increased and the reduction current was decreased in the presence of CPs. This behavior indicates that the electron transfer occurred between the PFO and the mediator. The indirect anodic phosphonylation of PFO was carried out using triethyl phosphite as a nucleophile (Figure 1 (d)), and then we obtained phosphonylated PFO (PFO-Phos(Et)) (yield: 56%, degree of substitution: 0.58). In this presentation, the more detailed results and discussion will be explained.

References

(1) Qiu, Z.; Hammer, B. A. G.; Müllen, K. Conjugated Polymers – Problems and Promises. Prog. Polym. Sci.
2020, 100, 101179.

(2) Taniguchi, K.; Kurioka, T.; Shida, N.; Tomita, I.; Inagi, S. Postfunctionalization of the Main Chain of Poly(3-Hexylthiophene) via Anodic C–H Phosphonylation. Polym. J.
2022, 54 (10), 1171–1178.

(3) Kurioka, T.; Inagi, S. Electricity‐Driven Post‐Functionalization of Conducting Polymers. Chem. Rec.
2021, 21 (9), 2107–2119.

(4) Francke, R.; Little, R. D. Redox catalysis in organic electrosynthesis: basic principles and recent developments. Chem. Soc. Rev.
2014, 43, 2492–2521.

Figure 1