Directional electron transfer at the interface of two dielectric materials plays a key role in organic photovoltaics. We approach this problem using donor-acceptor dyads (A or B) deposited on a water-dodecane interface. The dyads, synthesized in the group of Dr. A. Efimov (TUT, Finland), consist of a covalently bound porphyrin donor and a fullerene acceptor coupled to two hydrophilic arms to orient the dyad perpendicular to the interface. Surface Second Harmonic Generation (SSHG) with pump-probe technique allows us to directly probe the interfacial electron-transfer dynamics. The biphasic SSHG kinetics measured with dyad A is tentatively attributed to the charge separation (CS) and recombination (CR). Both the CS and CR appear slower at the interface compared to bulk solution in benzonitrile. The CS dynamics therefore indicate a relatively low dielectric constant of the interface. Possibility to change the polarities of both the donor and acceptor media separately, as well as the orientation of the dyad, can yield interesting insights into the partial solvent stabilization of the ions and further measurements are on the way.
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Physical Chemistry Department - Sciences II - University of Geneva
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