Electrogenerated Chemiluminescence: XXXIII . The Production of Excited States by Direct Heterogeneous Electron Transfer from Semiconductor Electrodes

Abstract

Electrogenerated chemiluminescence (ECL) arising from direct electron transfer from semiconductor electrodes to solution species was examined. The reduction of the oxidized forms of several luminescent species [, thianthrene, 9,10‐diphenylanthracene, and rubrene] on several n‐type semiconductor electrodes (, , , , ) was investigated. Only for reduction of rubrene radical cation on and was unequivocal evidence found for production of an excited state (triplet) by direct heterogeneous electron transfer at potentials where homogeneous redox processes producing excited states were not possible. Current interruption techniques were employed to study the emission decay and an unusual emission at open circuit following a cathodic potential step was found. A model for direct triplet generation based on reduction via surface states within the bandgap region and quenching of excited states by the electrode is proposed and constraints on the experimental observation of direct excited state formation are suggested.