Photophysical properties of metal-mediated assemblies of porphyrins

The metal-driven construction of multi-porphyrin assemblies, which exploits the formation of coordination bonds between peripheral basic site(s) on the porphyrins and metal centers, has recently allowed the design and preparation of sophisticated supramolecular architectures whose complexity and function begin to approach the properties of naturally occurring systems. Within this framework, meso-pyridyl/phenyl porphyrins (PyPs), or strictly related chromophores, can provide geometrically well-defined connections to as many as four metal centers by coordination of the pyridyl peripheral groups. Several discrete assemblies of various nuclearities, in which the pyridylporphyrins are linkers binding metalloporphyrins and/or coordination compounds, have been constructed in recent years. In this review, we summarize recent work from our laboratories on metal-mediated multi-porphyrin assemblies and their photophysical properties. The review is organized as follows: after a brief summary of relevant concepts on energy and electron transfer processes and their implications in charge separation and the antenna effect (Section 2), the main assembling strategies leading to side-to-face and metal-mediated assemblies are synthetically reviewed (Section 3). The photophysical studies leading to the identification and kinetic characterization of the photoinduced energy and/or electron transfer processes within the supramolecular structures are surveyed in Section 4.