Porphyrins metal-connected assemblies

Photophysical Properties of Metal-Connected Assemblies of Porphyrins. 126... 

In a supramolecular approach to fullerene-porphyrin hybrids, the assembly of a rigidly connected dyad, in which a zinc tetraphenylporphyrin, Zn(TPP), is noncovalently linked to a C60 derivative via axial pyridine coordination to the metal, was reported [219-222]. Photo excitation of the dyad Zn-complex led to electron transfer with very long lifetimes of the charge-separated pairs, as revealed by optical spectroscopy and confirmed by time-resolved electron paramagnetic resonance spectroscopy. Accordingly, two different solvent-dependent pathways can be considered for the electron-transfer processes. Either the excitation of the porphyrin chromophore is followed by fast intramolecular electron transfer inside the complex, or alternatively the free porphyrin is excited undergoing intermolecular electron transfer when the acceptor molecules ap-... 

While molecular assembly has proven to be effective for a photoelectric conversion system, coordination reactions are possibly a simple approach for connecting such functional molecules, as presented in the previous section. We applied the stepwise coordination method to prepare a photoelectric conversion system. Since the molecular wire exhibits redox conduction through the wire,11,13 efficient photo-electron transport through the redox sites in the wire is also expected. In this section, we demonstrate the fabrication of a photoelectric conversion system using ITO electrodes modified with M(tpy)2 (M = Co, Fe, Zn) complex wires with a terminal porphyrin moiety as a photosensitizer. The behavior of photo-electron transfer from porphyrin to ITO through the molecular wire was investigated by changing the metal element in the M(tpy)2 moieties.14... 

Abstract The metal-driven construction of multi-porphyrin assemblies, which exploits the formation of coordination bonds between exocyclic donor site(s) on the porphyrins and metal centers, has recently allowed the design and preparation of sophisticated supra-molecular 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 connected through external coordination compounds, have been constructed in recent years. In this review, we summarize recent work in this field from our and other laboratories. The photophysical properties of some ruthenium-mediated assemblies of porphyrins prepared by our group are also described. 

Design Strategy Multi-Porphyrin Assemblies Connected by Exocyciic Coordination to Metal Fragments... 

Linear dimers of perpendicularly arranged porphyrins can also be assembled at a tetrahedral metal center such as Zn(II) or Cu(I), using ditopic, phenanthroline chelates, as shown by Crossley and coworkers. The case of Cu(l) (92), is shown in Figure 51. The phenanthroline ligands are connected to the tetrapyrrolic macrocycles via fused aromatic rings, producing ribbon-like molecules. 

A related class of compounds has been derived by using porphyrins connected to polypyridines such as 2,2 -bipyridine, 1,10-phenantholine and 2,2 6, 2"-terpyridine. These chelating ligands form thermodynamically more stable and inert transition metal complexes than the pyridine ligand, and such porphyrins have been extensively explored for the assembly of photochemically active supramolecular systems, especially by Sauvage et The oblique... 

The case of coplanar exocyclic coordination complexes is illustrated in assemblies 100-112 (Figure 13.58), reported by Callot and coworkers, who take advantage of their previous experience in porphyrin ring derivatization . Obviously, from the numerous assemblies prepared by this methodology, the formation of exocyclic coordination complexes is extremely versatile regarding the combination of metals in both the porphyrin chromophores and the connecting complexes. The characteristic features of the assemblies are the drastic red shifts of the S0-S2 and Sq-Si transitions. The lower energy Sq-Si transitions are... 

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