We report that the use of a boron trifluoride‐diethyl ether complex (BFEE) as an electrolyte greatly improves the current efficiency in the anodic chlorination of poly(3‐hexylthiophene) (P3HT) compared to the conventional electrochemical post‐functionalization method using an acetonitrile (MeCN) solution. The oxidation potential of P3HT is successfully decreased, whereas that of a chloride ion (Cl−) can be significantly increased in BFEE, as evidenced by cyclic voltammetry. Given these findings, we investigated the anodic chlorination of P3HT films in the presence of Cl− as a nucleophile in BFEE and a mixed solution of BFEE/MeCN, thereby suppressing undesirable oxidation of Cl−. Characterization and optoelectronic property studies of the obtained chlorinated P3HT were carried out.

The post‐polymerization modification of selenophene‐containing (co)polymers is presented based on the electrochemical polymer reaction (ECPR). Selenophene‐ or thiophene‐containing (co)polymers, which are known to be promising materials in optoelectronic devices, were synthesized through Kumada catalyst transfer polymerization to give their homopolymers and block‐ or statistical copolymers with various side chains. Each of the series of polymers was subjected to post‐modification through the ECPR, and the reaction efficiencies were systematically compared. Selenophene‐containing polymers were successfully modified with better ECPR reaction efficiencies than their thiophene analogues. Moreover, the dramatic inhibiting effect of a branched side chain on the ECPR was observed and rationalized, which was very unexpected. Based on the basic tendency observed here, we have finally demonstrated the selective modification of a single segment of a rod−rod block copolymer for the first time.

C−H functionalization of π-conjugated polymers is a straightforward approach to changing their optoelectronic properties and aggregation behavior; however, the functionalization methodologies and applicable precursor polymers remain limited. Here, we demonstrated the electrochemical aromatic C−H chlorination of π-conjugated polymers using aluminum chloride (AlCl 3 ). AlCl 3 facilitated the anodic oxidation of precursor polymers in acetonitrile (MeCN), and the AlCl 3 /MeCN system exhibited greater oxidation tolerance than other electrolyte systems. Given these discoveries, we achieved anodic chlorination of poly(3hexylthiophene) with high current efficiency and expanded applicable precursor polymers such as poly(p-phenylene) derivatives and poly(9,9-dioctylfluorene) (PFO). The regioselectivity of the chlorination of PFO was clarified on the basis of detailed nuclear magnetic resonance studies of the chlorinated PFO. The optoelectronic properties and aggregation behavior of the precursor polymers were substantially changed after chlorination.

Electrochemical doping of conducting polymers (CPs) generates polarons (radical ionic species) and bipolarons (ionic species) in their backbone via multi‐electron transfer between an electrode and the CP. In the electrochemical polymer reaction (ePR), these generated ionic species are regarded as reactive intermediates for further transformation of the chemical structures of CPs. This electrochemical post‐functionalization can easily be used to control the degree of reactions by turning a power supply on/off, as well as tuning the applied electrode potential, which leads to fine‐tuning of the various properties of the CPs, such as the HOMO/LUMO level and PL properties. This Account summarizes recent developments in the electrochemical post‐functionalization of CPs. In particular, we focus on reaction design for the ePR, with respect to the preparation and structure of the precursor polymers, applicable functional groups, efficient reaction conditions, and electrolytic methodologies.

We herein report that the regioselective anodic fluorination of S-alkyl benzothioate and its derivatives in various aprotic solvents using Et3N·nHF (n = 3–5) and Et4NF·nHF (n = 3–5) as supporting electrolyte and a fluorine source successfully provided the corresponding α-fluorinated products in moderate yields. Dichloromethane containing Et4NF·4HF was found to be the most suitable combination as electrolytic solvent and supporting salt as well as fluorine source for the anodic fluorination. The electrochemical fluorination of cyclic benzothioates such as benzothiophenone was also achieved.