Supramolecular porphyrin-DABCO array in single- and double-stranded polynorbornenes.

Zinc-porphyrin-appended norbornene derivative 6, the corresponding dimer 7, coherently aligned single-stranded polynorbornene 5, and zinc-porphyrin-linked double-stranded polymeric ladderphane 3 have been used for complexation with 1,4-diazabicyclo[2.2.2]octane (DABCO) to generate an array of porphyrin-DABCO supramolecular scaffolds. The stoichiometries of the complex formation are analyzed in detail by (1)H NMR spectroscopy as well as absorption and emission spectroscopic methods. Bidentate ligand DABCO is found to form with 7, 5, and 3 to give 2-to-1 porphyrin-DABCO sandwich structures. Monomer 6, on the other hand, forms a 2-to-1 porphyrin-DABCO sandwich structure at high concentration (20 mM), but a 1-to-1 porphyrin-DABCO complex at low concentration (10(-6) M). Time-resolved fluorescence decays revealed a similar behavior for the 2-to-1 porphyrin-DABCO sandwich structures that are formed from 3, 5, and 7.