Mixed valence radical cations and intermolecular complexes derived from indenofluorene-extended tetrathiafulvalenes
Journal article, 2014

Engineering of mixed-valence (MV) radical cations and intermolecular complexes based on pi-extended tetrathiafulvalenes (TTFs) is central for the development of organic conductors. On another front, redox-controlled dimerization of radical cations has recently been recognized as an important tool in supramolecular chemistry. Here we show that pi-extended TTFs based on the indenofluorene core, prepared by Horner-Wadsworth-Emmons reactions, undergo reversible and stepwise one-electron oxidations and that the detectable, intermediate radical cation forms remarkably strong intermolecular MV ([neutral.cation]) and pi-dimer ([cation.cation]) complexes with near-infrared radical cation absorptions. The radical cation itself seems to be a so-called Class III MV species in the Robin-Day classification. The formation of MV dimers was corroborated by ESR spectroelectrochemical studies, revealing two slightly different ESR signals upon oxidation, one assigned to the MV dimer and the other to the cation monomer. Crystals of the radical cation with different anions (PF6- , BF4-, and TaF6-) were grown by electrocrystallization. Conductance studies revealed that the salts behave as semiconductors with the hexafluorotantalate salt exhibiting the highest conductance. Using a custom-built ESR spectrometer with sub-femtomole sensitivity, the magnetic properties of one crystal were investigated. While the spin-to-spin interaction between radical cations was negligible, a high cooperativity coupling to the microwave field was observed - as a result of an exceptionally narrow spin line width and high spin density. This could have great potential for applications in quantum computation where crystalline spin ensembles are exploited for their long coherence times.

Author

M. A. Christensen

University of Copenhagen

C. R. Parker

University of Copenhagen

T. J. Sorensen

University of Copenhagen

Sebastian Erik de Graaf

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Device Physics

T. J. Morsing

University of Copenhagen

T. Brock-Nannestad

University of Copenhagen

J. Bendix

University of Copenhagen

M. M. Haley

University of Oregon

P. Rapta

Slovak University of Technology Bratislava

Andrey Danilov

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Device Physics

Sergey Kubatkin

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Device Physics

O. Hammerich

University of Copenhagen

M. B. Nielsen

University of Copenhagen

Journal of Materials Chemistry C

2050-7526 (eISSN)

Vol. 2 48 10428-10438

Subject Categories

Materials Engineering

Other Engineering and Technologies

DOI

10.1039/c4tc02178a

More information

Latest update

9/6/2018 1