Hexakis Porphyrinato Benzenes. A New Class of Porphyrin Arrays H. A. M. Biemans, ² A. E. Rowan,* ,‡ A. Verhoeven, ‡ P. Vanoppen, § L. Latterini, § J. Foekema, ‡ A. P. H. J. Schenning, ² E. W. Meijer, ² F. C. de Schryver, § and R. J. M. Nolte ‡ Contribution from the Department of Organic Chemistry, NSR Center, UniVersity of Nijmegen, The Netherlands, the Department of Macromolecular and Organic Chemistry, EindhoVen UniVersity of Technology, The Netherlands, and the Department of Chemistry, Katholieke UniVersiteit of LeuVen, Belgium ReceiVed May 4, 1998 Abstract: A new type of porphyrin array has been synthesized by the coupling of six porphyrin moieties to a central benzene core via an ether linkage. The resulting porphryin supermolecule has a diameter up to 80 Å and a mass of 8500 daltons. In solution, the six porphyrins around the central benzene ring arrange themselves into three sets of offset overlapping dimers, which are rapidly interconverting at room temperature. Solution UV-vis and fluorescence studies, however, indicate that there are no electronic interactions between the individual porphyrin molecules. Upon spreading a chloroform solution of these porphyrin molecules on a surface, they self-assemble to form ring-shaped architectures on a micrometer scale. Near-field scanning optical microscopy studies reveal that the porphyrin moieties within the rings have an ordered arrangement with respect to their position in the ring after the sample has been annealed at 80 °C for 2 days. Introduction The design and construction of novel porphyrin architectures, in particular well-defined porphyrin arrays, is an area of increasing current interest. 1-3 These porphyrin assemblies are of fundamental importance not only as models for the study of the energy and electron-transfer functions of the light-harvesting antenna and the photosynthetic reaction centers but also as building blocks for the construction of functional molecular devices, i.e., molecular scale wires, switches and photovoltaic devices, etc. 1,4 In the case of the natural antenna systems, the function and properties of the chromophoric arrays are controlled by the spatial arrangement and orientation of the molecules, which themselves are held in a specific architecture through predominantly noncovalent interactions within a protein and carotenoid scaffold. The resulting assemblies, which can consist of up to several hundred porphyrins, are able to transfer energy over large distances with a very high efficiency. 5,6 More recently, the crystal structure of the light-harvesting antenna LH2 of a purple photosynthetic bacterium was resolved. 6 In this antenna complex, the bacteriochlorophyll chromophores are arranged into two sets of rings which are formed by the self- assembly of nine identical components. The first step toward mimicking the properties of such systems is the development of techniques which enable the construction of well-defined multichromophore arrays. 7 In earlier work, we have been focused in particular on the design of cyclic arrays of porphyrins for the study of through- space electron transfer and of simple synthetic architectural mimics of the antenna complex LH2. 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