Electrochemiluminescence of rubrene at a zinc oxide electrode

Abstract

The electrochemiluminescence ( ecl of rubrene at a zinc oxide electrode has been studied with regard to the possibility of the formation of excited species via a heterogeneous electron-transfer reaction. Electrochemiluminescence has actually been observed, the spectrum of which coincides with the fluorescence spectrum of rubrene. However, the emitted light does not occur at potentials where rubrene radical cations are reduced but at potentials where radical anions are formed at the ZnO electrode. From this fact it is concluded that the emission observed originates from homogeneous electron transfer between radical cations and anions but not from formation of excited species via heterogeneous electron transfer. On the base of an energy diagram derived from the flat-band potential of ZnO in contact with a non-aqueous electrolyte and from electrochemical and photochemical data of rubrene the underlying processes are discussed qualitatively.