Paired Electrochemical Reactions of a Fluorene-Based Conjugated Polymer

Bipolar electrochemistry using a wireless electrode driven by an external electric field from feeder electrodes is attractive because electrochemical oxidation and reduction takes place simultaneously on the same surface of the bipolar electrode with a potential slope between both poles. The redox ability of parent polymer P1 containing fluorenol moiety to form P2 (fluorenone) and P3 (fluorene), which is accompanied by a drastic color change, is expected to exhibit a multi-colored gradient film by the application of a potential slope on the bipolar electrode according to the bipolar polymer reaction. A BDD plate (3 × 3 cm²) covered with P1 was placed between driving stainless electrodes (1 × 4 cm²) in a bipolar cell and a constant current (0.1 mA/cm²) was passed between them in 5 mM Et₄NOTs/i-PrOH. After the electrolysis, the emission color of the polymer film under UV-irradiation was a gradation with yellow-blue-dark orange from the cathodic pole to the anodic pole. The gradient polymer film was peeled off from the BDD plate with scotch tape, and divided into three pieces for PL measurements. The PL spectra corresponded well to those of P1-P3. Previous reports on the bipolar electrolysis for producing gradient materials focused only on anodic reaction with sacrificial cathodic reaction or vice versa. This paired bipolar electrolysis successfully provided a new class of composition-gradient polymer film.