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Chlorophyll a (Chl a) in hydrocarbon solution with a small amount of dioxane or water shows red-shifted absorption bands at 686 nm and at 700 nm (dioxane) and at 745 nm (water), indicative of self-organized aggregate structures in solution. To study the relationship between the structure and spectral properties of the aggregates, several one-dimensional model structures of Chl a−dioxane and Chl a−water aggregates were computed by the molecular mechanics method. Three overall structures ranging from stick to a ring shape were energetically favored for the dioxane system. All these structures contain structural heterogeneity that consists of repeating dimers that further form tetramer substructures. For the Chl a−water system a one-dimensional homogenous helical structure was obtained. By using the model structures, the transition energies and fluorescence excitation polarizations were computed. Exciton theory with dipole−dipole interaction approximation and semiempirical quantum mechanical CI calculations ...

The vast range of possible applications for fullerenes makes them interesting compounds, either as materials or as substances able to confer on other materials their physicochemical properties. Porous polymer membranes were modified by the incorporation of C60 concomitantly with amphipathic molecules (phospholipids). These membranes had the same photoconducting properties, by electron transfer, as those already described for bilayer lipid membranes incorporating C60. They present the advantage of an uncomparably greater mechanical stability in comparison with their ultrathin homologues.

Information processing on a molecular scale will hopefully be achieved by assemblies composed of molecules acting either as electronic components or as electron wires. A face to face porphyrin tetramer is designed here as a candidate for an electron wire. We present evidence from direct electric measurement for the electric conduction of such molecules embedded in an ultrathin membrane which spatially organize them. According to energetic considerations issued from electrochemical and spectroscopic data, an intramolecular charge shift following photoexcitation and photooxidation is more probable than transient formation of a biradical ion pair.

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.