Involvement of C-60 fullerene monomers and aggregates in the photoconductivity of ultrathin bilayer lipid membranes

Due to its hydrophobic character, the hydrocarbon core of ultrathin phospholipid bilayer membranes lends itself to the insertion of fullerenes. When doped with C-60 these membranes are photoconducting, the photoconductivity being affected by the presence of quenchers of the excited triplet state such as oxygen. The photoconductivity involves trans-membrane electron transfer; its dependence on C-60 concentration and on the excitation wavelength suggests the participation of small aggregates in the membrane. As derived from time-resolved triplet absorption and fluorescence quenching measurements, the suggested mechanism makes more precise (i) the role of the aggregates which might act as a collecting antenna for the benefit of the monomers, and (ii) the role of the monomers which have a much higher yield of photoinduced triplet state formation than the aggregates.