Electronic Delocalization in the Radical Cations of Porphyrin Oligomer Molecular Wires

• DOI: 10.1021/jacs.7b05386
• Publication Date: 2017-07-05T17:31:41Z
• Authors: Martin D. Peeks; Claudia E. Tait; Patrik Neuhaus; Georg M. Fischer; Markus Hoffmann; Renée Haver; Arjen Cnossen; Jeffrey R. Harmer; Christiane R. Timmel; Harry L. Anderson
• Keywords: Oligomer; Radical ion

The radical cations of a family π-conjugated porphyrin arrays have been investigated: linear chains N = 1-6 porphyrins, 6-porphyrin nanoring and 12-porphyrin nanotube. were generated in solution by chemical electrochemical oxidation, probed vis-NIR-IR EPR spectroscopies. exhibit strong NIR bands at ∼1000 nm 2000-5000 nm, which shift to longer wavelength with increasing oligomer length. Analysis the IR spectra indicates that polaron is delocalized over 2-3 units oligomers. Some vibrational are strongly intensified on Fano-type antiresonances observed when activated vibrations overlap electronic transitions. solution-phase Gaussian lineshapes linewidths proportional N-0.5, demonstrating room temperature spin hops rapidly whole chain time scale hyperfine coupling (ca. 100 ns). Direct measurement couplings through electron-nuclear double resonance (ENDOR) frozen (80 K) distribution for all oligomers, except nanotube, spread about 4-6 porphyrins. These experimental studies cyclic give consistent picture, supported DFT calculations multiparabolic modeling reorganization energy 1400-2000 cm-1 2000 charge transfer between neighboring sites, placing system Robin-Day class III.