| Autor: |
Wang R; Department of Chemistry, Duke University , Durham, North Carolina 27708, United States., Brugh AM; Center for Photochemical Sciences and Department of Chemistry, Bowling Green State University , Bowling Green, Ohio 43403, United States., Rawson J; Department of Chemistry, Duke University , Durham, North Carolina 27708, United States., Therien MJ; Department of Chemistry, Duke University , Durham, North Carolina 27708, United States., Forbes MDE; Center for Photochemical Sciences and Department of Chemistry, Bowling Green State University , Bowling Green, Ohio 43403, United States. |
| Abstrakt: |
Spin and conformational dynamics in symmetric alkyne-bridged multi[copper(II) porphyrin] structures have been studied in toluene solution at variable temperature using steady-state electron paramagnetic resonance (EPR) spectroscopy. Comparison of the dimer EPR spectra to those of Cu porphyrin monomers shows evidence of an isotropic exchange interaction (J avg ) in these biradicaloid structures, manifested by a significant line broadening in the dimer spectra. The extent line broadening depends on molecular structure and temperature, suggesting J avg is modulated by conformational dynamics that impact the torsional angle distribution between the porphyrin-porphyrin least-squares planes. Computational simulation of the experimental EPR spectra, using a developed algorithm for J modulation in flexible organic biradicals, supports this hypothesis. Comparison of ethyne and butadiyne alkyne bridges reveals remarkable sensitivity to orbital interactions between the spacer and the metal, reflected in measurements of J avg as a function of temperature. The results suggest orbital symmetry relationships may be more important than recognized in design of optimized molecular spintronic devices. |
