Photoinduced energy and electron transfer processes in a supramolecular system combining a tetrapyrenylporphyrin derivative and arene-ruthenium metalla-prisms.

A supramolecular system, consisting of a tetrapyrenylporphyrinic core surrounded by arene-ruthenium prisms, has been assembled and characterized by means of electrochemical and photophysical techniques. The photophysical study shows that quantitative energy transfer from the peripheral pyrenyl units towards the central porphyrin core is operative in the tetrapyrenylporphyrinic system. Interestingly, encapsulation of the pyrenyl units into the ruthenium cages affects the photophysics of the central porphyrin component, since its emission quantum yield is reduced in the supramolecular array. Femtosecond transient absorption analysis evidenced a complex interplay of deactivation pathways, including energy and electron transfer processes from the porphyrin to the metalla-prisms, associated with different conformations of the system allowed by the flexibility of the linkers. Moreover, the non-emissive arene-ruthenium cages present a peculiar excited-state dynamics, here disentangled for the first time by means of transient absorption investigations.