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Photoinduced processes in the self-assembled bis- porphyrins and fullerene complexes

In the past decade, many self-assembled bis- porphyrins and fullerene complexes have been built because of their potential application in artificial photosynthesis. In this study we explored how different geometry and flexibility of bis-porphyrin hosts (molecular tweezers) affects both the complexation process with fullerene derivatives and the photo-reactivity of the complex (Figure 1). Both molecular tweezers are composed of a norbornane bridge that connects zinc metalated porphyrin rings. The difference is in the arms bearing porphyrin rings having rigid [5]polynorbornane linkers or flexible propyl chains. Their complexation with bispyridinofullerene has been characterized with spectrophotometric and spectrofluorimetric analysis and the derived association constants are of the order of 104 M-1 for rigid and 106 M-1 for flexible tweezers. A photophysical investigation of the complexes, performed by steady-state and time resolved optical spectroscopy, showed that an electron transfer process from the bis-porphyrin host to the fullerene guest occurs in both cases, with a slightly longer lifetime of the charge- separated state for the complex with the more flexible host.

bis-porphyrins ; fullerene ; self-assembly ; photoinduced processes

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