LAUSR

The introduction of functional groups into the mesoposition of dipyrromethanes, boron-dipyrromethenes (BODIPYs) and porphyrinoids, is of fundamental importance in designing such dye systems for material sciences or photomedicine. One route that has proven to be particularly useful in this respect is the nucleophilic aromatic substitution (SNAr) on porphyrinoids and their precursors carrying electron-withdrawing substituents. To further expand this methodology, the potential of the 4-fluoro-3-nitrophenyl and the 3,4,5-trifluorophenyl moieties for the synthesis of functionalized dipyrromethanes, BODIPYs, and porphyrinoids has been evaluated. The 3,4,5-trifluorophenyl moiety proved not to be applicable in the SNAr with nucleophiles. The introduction of the 4-fluoro-3-nitrophenyl group, however, allowed fast and efficient SNAr with various amine nucleophiles. The synthesized 4-amino-3-nitrophenyl-substituted dipyrromethanes were successfully applied in the synthesis BODIPYs and were tested in the synthesis of ‘trans’-A2B2 porphyrins and A2B corroles. Furthermore, the dipyrromethanes after oxidation to the dipyrromethenes were found to be suitable ligands for metal ions giving access to functionalized ruthenium(II) metal complexes. Introduction Porphyrins and the related cyclic tetrapyrroles are fundamentally important components in essential biological processes.[1] The special characteristics of porphyrins and corroles such as their conformational flexibility,[2] which can be modified through peripheral substitution,[3] inner core modifications,[4] and the incorporation of metal centers,[5] enable diverse applications. They are characterized by intensive electronic absorption and emission, a low HOMO-LUMO gap, and the option to vary their redox properties via metalation.[6] Porphyrins and their metal complexes are used as catalysts,[7] in light-harvesting complexes, and as components of electronic sensors.[8] Metal complexes of corroles have found application as catalysts in the oxidation of hydrocarbons.[9] Due to their inherent properties, porphyrins and corroles have also found application in photomedicine, e.g. as photosensitizers in photodynamic therapy (PDT). Both compound classes show a strong absorbance at wavelengths with a deep light propagation in human tissue (red to near infrared region) while being harmless to the organism in their ground state.[10,11] Through light-excitation and the subsequent photophysical and chemical processes, tetrapyrrole-based dyes give eventually rise to reactive oxygen species which damage the diseased tissue in PDT by oxidation.[12] Boron-dipyrromethenes (BODIPYs) are well established as fluorescence-imaging dyes in diagnostics[13] and share many characteristics with porphyrins and corroles, such as their intense color and fluorescence.[14] One subject of current research is to improve the BODIPY structure towards absorption at higher wavelengths and specifically to increase excited triplet state formation for an application in PDT.[15] This can e.g. be done by modifying the BODIPY backbone with halogen atoms[16,17,18] or through use of heavy-atom free BODIPYanthracene dyads.[19] Dipyrromethanes are of wide interest in organic synthesis and are commonly employed as building blocks for the selective synthesis of meso-substituted porphyrinoids as well as mesosubstituted BODIPYs.[20,21,22] Specifically, BODIPYs are easily available from dipyrromethanes via a three-step one-pot synthesis.[23,24] The stability of meso-substituted dipyrromethanes strongly depends on the substitution in the meso-position. Electron-withdrawing substituents in this position stabilize the dipyrromethane against decomposition.[25] In addition, electron-withdrawing substituents render the dipyrromethane, or the final porphyrinoid, susceptible to SNAr (whereas it is known that porphyrins in general are also ______________________________________________ [a] Benjamin F. Hohlfeld, Prof. Dr. Mathias Christmann, Dr. Arno Wiehe, Institut für Chemie u. Biochemie, Freie Universität Berlin Takustr. 3, 14195 Berlin, Germany [b] Benjamin F. Hohlfeld, Prof. Dr. Nora Kulak, Institut für Chemie und Biochemie, Freie Universität Berlin, Fabeckstr. 34/36, 14195