Porphyrin-based self-assembled arrays with light-driven functionalities

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. Among the possible non-covalent interactions which can be exploited to build self-assembled structures, coordination bonds between the nitrogen atom of a pyridinic fragment and a metal ion (either the central metal atom of a porphyrin such as zinc(II) or a metal ion which acts as a bridge) are the most versatile for the creation of a variety of architectures with promising properties in different fields, ranging from optoelectronics to artificial photosynthesis to photocatalysis. We have been exploring photoactive multi-phorphyrinic assemblies for several years and the main results will be here presented. In particular, two types of structures will be discussed: i) tweezer-like porphyrinic arrays, which are able to coordinate photoactive guests and ii) coordination cages which have been designed as size-controlled nanoreactors for the uptake of guests with light-induced functionalities. Spectrophotometric and spectrofluorimetric analysis allowed to characterize the absorption and emission features of the single components and to determine the binding constants in solution. The photoinduced processes occurring in the assembled systems were identified by means of detailed photophysical investigations, with temporal resolution down to hundreds of femtoseconds.