The photoelectrochemical reduction of pyrene in acetonitrile solution

Abstract

The reduction of pyrene (Py) at a mercury channel electrode is studied in acetonitrile solution, both in the dark and under conditions where the pyrene radical anion (Py −.) is photoexcited, using a wavelength of 501.7 nm. In the dark a reversible one-electron process occurs forming the radical anion. However, upon photoexcitation of the electrogenerated radical anion, photocurrents are observed, and the precise electrode mechanism is shown to be: ▪ The photocurrent arising from further reduction of Py, since rapid homogeneous reactions of Py −2 give electroinactive products. With this scheme an “effective” second order decay of Py − is observed, rate = −k eff[Py − ] p2 where k eff is proportional to k 3 I/ k f. k eff has been evaluated from analysis of the limiting current-flow rate behaviour at the channel electrode at the channel electrode. This was found to be 4.0 ± 0.1 × 10 3 mol−1 dm 3 s −1 at a light intensity of 0.30 W cm −2 and a pyrene concentyration of 2.97 mM.