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Synthesis, complexation process and photo- reactivity of the self-assembled bis-porphyrins and fullerenes complexes

Self-assembled bis-porphyrins and fullerene coordination complexes continue to attract attention because of their potential application in artificial photosynthesis. In this study we wanted to explore 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. We have synthesized molecular tweezers composed of a norbornane bridge that, with flexible propyl chains, connects zinc metalated porphyrin rings. Its complexation with bispyridinofulleren and the photoinduced processes of the complex have been compared to a more rigid host. For synthetic purposes, modern green chemistry methodologies, microwave irradiation and high-speed vibrational milling, have been employed. The formation of the complexes in solution has been characterized with spectrophotometric and spectrofluorimetric analysis and the derived association constants are of the order of 10^4 M^-1 for rigid and 10^6 M^-1 for flexible tweezers. A photophysical investigation of the complexes 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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