Artificial light-harvesting systems by use of metal coordination

Construction of artificial light-harvesting systems by metal coordination is reviewed. Light absorbing dyes include porphyrin, phthalocyanine, perylenebisimide and polypyridyl metal complexes. The supramolecular assemblies are obtained by ligand coordination to metal ions in the center or exterior of the chromophores. Supermolecules of discrete structures even in the solution phase are focused on, and methodologies to acquire large association constants are discussed. Complementary or multitopic coordination to the Zn2+ ion gives satisfactory results in obtaining stable and discrete supramolecular structures while maintaining the singlet excited state, Fast energy transfers among the chromophore units are analyzed satisfactorily to examine the properties of light-harvesting antennae. Use of transition-metal ions provides strong coordination, but intersystem crossing of the singlet excited state to the triplet becomes significant. Photophysical properties of such triplet excited species are reported in a limited number of cases and their properties are discussed in view of the light-harvesting antenna function. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).