Isomeric porphyrin phenanthrenequinones: synthesis, NMR spectroscopy, electrochemical properties, and in situEPR/ENDOR studies of the o-semiquinone anion radicals

Abstract

Porphyrin quinones are attractive model compounds for mimicking natural electron transfer processes. While the overwhelming majority of studies have been performed with porphyrin p-quinones the isomeric porphyrin o-quinones have been mostly neglected. Using phenanthrene-9,10-quinones as the acceptor component we have prepared several porphyrin o-quinones (1, 2, 5, 6) and show that a facile and simple variation of ΔG_ET can be achieved by using the in situ formed semiquinones for metal chelatization. Additionally, detailed NMR studies show that for asymmetrically substituted porphyrins a complete assignment of the ¹H- and ¹³C-chemical shifts is possible. Complete NMR assignments were necessary for an unambiguous structure determination.