Porphyrin-fullerene dyads are promising candidates for organic photovoltaic devices. The electron-transfer (ET) properties of the molecular devices depend significantly on the mutual position of the donor and acceptor. Recently, a new type of molecular isomerism (akamptisomerism) has been discovered. In the present study, we explore how photoinduced ET can be modulated by passing from one akamptisomer to another. To this aim, four akamptisomers of the quinoxalinoporphyrin-[60]fullerene complex are selected for computational study. The most striking finding is that, depending on the isomer, the porphyrin unit in the dyad can act as either electron donor or electron acceptor. Thus, the stereoisomeric diversity allows one to change the direction of ET between the porphyrin and fullerene moieties. To understand the effect of akamptisomerism on the photoinduced ET processes, a detailed analysis of initial and final states involved in the ET is performed. The computed rate for charge separation is estimated to be in the region of 1-10 ns-1 . The formation of a long-living quinoxalinoporphyrin anion radical species is predicted.

Institució Catalana de Recerca i Estudis Avancats 08010 Barcelona Spain

Institut de Química Computacional i Catàlisi and Departament de Química Universitat de Girona C Maria Aurèlia Capmany 69 17003 Girona Spain

Institute of Organic Chemistry and Biochemistry Academy of Sciences of the Czech Republic Flemingovo nám 2 166 10 Prague Czech Republic

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