meso-Tetrakis(pentafluorophenyl)porphyrin-Derived Chromene-Annulated Chlorins

The synthesis of mono- and bis-chromene-annulated meso-(pentafluorophenyl)chlorins from meso-tetrakis(pentafluorophenyl)porphyrins by an OsO4-mediated dihydroxylation reaction, followed by an intramolecular nucleophilic aromatic substitution reaction, is described. The reaction sequence is applicable to the free base systems as well as their Zn(II), Ni(II), Pd(II), and Pt(II) complexes. The optical properties (UV–vis and fluorescence spectra) of the (metallo)chlorin-like chromophores that possess slightly red-shifted optical spectra compared to the corresponding 2,3-dihydroxychlorins are reported. Molecular modeling and 1H–19F-HOESY NMR spectroscopy provide indications for the conformation of the chromene-annulated chromophores. Using 1H–1H COSY and 19F–19F QF-COSY NMR spectra, we interpret the 1H and 19F NMR spectra of the porphyrins and chlorins, thus providing a refined reference point for the use of 19F NMR spectroscopy as a diagnostic tool in the analysis of meso-pentafluorophenyl-substituted porphyr...