Distorted fused porphyrin–phthalocyanine conjugates: synthesis and photophysics of supramolecular assembled systems with a pyridylfullerene

Abstract

In the current work, we report on the synthesis and photophysical features of supramolecular hybrid systems that are based on newly fused porphyrin–phthalocyanine (P–Pc) conjugates and a pyridylfullerene. The ZnP–ZnPc conjugate was synthesized in three steps starting with a Diels–Alder reaction between β-vinylporphyrin and fumaronitrile. The resulting mixture of isomeric adducts was then dehydrogenated to yield the corresponding benzo[b]porphyrin-2¹,2²-dicarbonitrile. In the final step, cyclotetramerization with 4-tert-butylphthalonitrile, in the presence of zinc acetate, afforded the bis-metalated conjugate. Selective demetallation of ZnP led to the H₂P–ZnPc conjugate. For both conjugates steric hindrance is the inception to a bent configuration, which does, however, not preclude enlargement of the π-conjugated system, that is, the porphyrins and the phthalocyanines. The two conjugates coordinate N-(4-pyridyl)fullero[c]pyrrolidine giving rise to the corresponding supramolecular porphyrin–phthalocyanine–fullerene systems. Photophysical measurements corroborate a sequential deactivation in the excited state, namely an initial intramolecular energy transfer from ZnP or H₂P to ZnPc followed by an intramolecular charge transfer to yield ZnP–(ZnPc)˙⁺–(C₆₀)˙⁻ and H₂P–(ZnPc)˙⁺–(C₆₀)˙⁻, respectively.