Novel Molecular Building Blocks Based on the Boradiazaindacene Chromophore: Applications in Fluorescent Metallosupramolecular Coordination Polymers

We designed and synthesized novel boradiazaindacene (Bodipy) derivatives that are appropriately functionalized for metal-ion-mediated supramolecular polymerization. Thus, ligands for 2-terpyridyl-, 2,6-terpyridyl-. and bipyridyl-functionalized Bodipy dyes were synthesized through Sonogashira couplings. These fluorescent building blocks are responsive to metal ions in a stoichiometry-dependent manner. Octahedral coordinating metal ions such as Zn-II result in polymerization at a stoichiometry corresponding to two terpyridyl ligands to one Zn-II ion. However, at increased metal ion concentrations, the dynamic equilibria are re-established in such a way that the monomeric metal complex dominates. The position of equilibria can easily be monitored by H-1 NMR and fluorescence spectroscopies. As expected, although open-shell Fe-II ions form similar complex structures, these cations quench the fluorescence emission of all four functionalized Bodipy ligands.