Anomalous luminescence of a bicapped [60]fullerene–γ-cyclodextrin complex at an oxide-covered aluminium cathode

Abstract

A bicapped [60]fullerene–γ-cyclodextrin complex has been prepared in an aqueous boric acid–caesium borate buffer. It is shown that this water-soluble complex generates an anomalous [60]fullerene specific blue–green emission at the cathodically polarized aluminium/aluminium oxide interface but not at the zirconium/zirconium oxide and tantalum/tantalum oxide interfaces. A mechanistic pathway for the formation of this emission is proposed: the cathodic polarization of the aluminium/aluminium oxide interface injects a hot electron from the conduction band edge of the aluminium oxide to the higher acceptor levels 2t_2g and/or 4a_g of [60]fullerene. The relaxation of these acceptor levels to the 5t_1u level (LUMO) of [60]fullerene initiates the intense emission peaking at around 445 nm. Further, use of this cathodic electroluminescence (EL) for the recognition of [60]fullerene from its mixtures with higher fullerenes is proposed.