Photoinduced Processes in a Supramolecular Assembly Based on a Bis(Acridinium-Porphyrin) Receptor and a Tetra-pyridyl Free-Base Porphyrin Guest

Photoinduced processes occurring in non-covalent arrays based on porphyrins are of high interest for their relevance to energy and electron transfer reactions that take place in natural photosynthetic centers [1]. A novel bis(acridinium-porphyrin) tweezer (Figure 1) has been designed as a multi-responsive array containing two Zn(II) porphyrins, as coordinating sites, and two acridinium units, as elements that can modify their chemical and electronic features following chemical or redox stimuli. The association of acridinium units and porphyrins in the same molecular or supramolecular structure has led to systems characterized by fast photoinduced electron transfer reactions between the porphyrin donor and the acridinium acceptor [2]. In order to explore the potentiality of the bis(acridinium-porphyrin) conjugate as a receptor for photoactive hosts, its coordination with a tetra-pyridyl porphyrin (5,10,15,20-tetra(4?-pyridyl)porphyrin, TPYP, Figure 1) has been analyzed. Herein we report on the study of the complexation process and on the characterization of the complex pattern of photoinduced events that occur within the adduct, performed by means of spectrophotometric and spectrofluorimetric analysis and ultrafast transient absorption measurements.