Oligoporphyrins are promising substrates for photophysical"] studies related to light-induced charge separation. However, their redox behavior[" has attracted little attention. Our finding, that tetratolylporphyrin can be reduced in successive electron-transfer steps to a hexa-anion, prompted us to consider oligo-and polyporphyrins with a view to their charge-storage capability. Their syntheses are often tedious, but here we describe a straightforward approach to alkyland aryl-substituted dipyrromethanes 1 a-c, which can be readily transformed into the phenylene-bridged trisporphyrin 3. The interaction between the porphyrin chromophores in 3, in the analogous bisporphyrin 2, and in the tetratolylporphyrinato zinc complexes Zn-4 have been examined by electron absorption spectroscopy. In addition, the considerable charge-storage capacity of the title structures has been investigated using cyclic voltammetry.The utility of porphyrins has been limited by their tedious synthesis via the [2 + 2]-cyclization of dipyrr~methanes[~] of type Id (with R, = alkyl). We show here that 2,T-linked dipyrromethanes la-c (with R, = H) are accessible in up to 60 YO yield through a one-pot condensation reaction between pyrrol and different aryl-or alkyl-aldehydes (Scheme 1).Scheme 1. Synthesis of 2,2'-dipyrromethanes.
Wie wir kurzlich zeigten, konnen Porphyrine durch elektrochemische oder chemische Reduktion reversibel in hochgeladene Anionen iiberfuhrt werden; so ist der Zinkkomplex 1 a des meso-Tetraarylporphyrins 2a in der Lage, sukzessiv sechs Elektronen unter Bildung eines Hexaanions aufzunehmen'). Es stellt sich die Frage, ob die hohe Redoxaktivitat des Porphyrin-x-Systems in hoherrnolekularen Analoga mit mehreren Porphyrin-Einheiten erhalten bleibt.
Five grams of a mixture of C60/C70 can be separated in 24 hours by gel permeation chromatography on polystyrene gel. The mobile phase can be completely recovered, and the method can be scaled up by a simple increase in the inner diameter of the column.
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