Probing Flexibility in Porphyrin-Based Molecular Wires Using Double Electron Electron Resonance

Janet E. Lovett, Markus Hoffmann, Arjen Cnossen, Alexander T. J. Shutter, Hannah J. Hogben, John E. Warren, Sofia I. Pascu, Christopher W. M. Kay, Christiane R. Timmel, Harry L. Anderson

Research output: Contribution to journalArticlepeer-review


A series of butadiyne-linked zinc porphyrin oligomers, with one, two, three, and four porphyrin units and lengths of up to 75 angstrom, have been spin-labeled at both ends with stable nitroxide TEMPO radicals. The pulsed EPR technique of double electron electron resonance (DEER) was used to probe the distribution of intramolecular end-to-end distances, under a range of conditions. DEER measurements were carried out at 50 K in two types of dilute solution glasses: deutero-toluene (with 10% deutero-pyridine) and deutero-o-terphenyl (with 5% 4-benzyl pyridine). The complexes of the porphyrin oligomers with monodentate ligands (pyridine or 4-benzyl pyridine) principally adopt linear conformations. Nonlinear conformations are less populated in the lower glass-transition temperature solvent. When the oligomers bind star-shaped multidentate ligands, they are forced to bend into nonlinear geometries, and the experimental end-to-end distances for these complexes match those from molecular mechanics calculations. Our results show that porphyrin-based molecular wires are shape-persistent, and yet that their shapes can deformed by binding to multivalent ligands. Self-assembled ladder-shaped 2:2 complexes were also investigated to illustrate the scope of DEER measurements for providing structural information on synthetic noncovalent nanostructures.

Original languageEnglish
Pages (from-to)13852-13859
Number of pages8
JournalJournal of the American Chemical Society
Issue number38
Publication statusPublished - 30 Sep 2009


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