Transmembrane electron transport mediated by photoexcited fullerenes

Experiments were caried out to confirm the existence of nanoampere mm-2 currents photoinduced in bilayer lipid membranes (≈40 A width) containing C60 or C70 fullerenes and to explore possible mechanism of electron transport in these model light harvesting and conversion systems. Thermodynamic considerations indicate the electron transfer occurs via reduction of fullerene triplets. This supported by triplet quenching experiments. No photocurrent change was observed when an ionic gradient was imposed on the membrane or when its ionic permeability was modified. This is consistent with an eletron-hopping mechanism. The following parameters were varied: membrane thickness, fullerenes concentration, applied membrane potential, light intensity and intermittency. The results indicate that electron transport is mediated by fullerene aggregates that span the membrane and that light excitation can either enhance or diminish fullerene aggregation and electron transfer, according to its intensity.