Solvent Effects on the Intramolecular Spin Exchange in Biradicals at Room Temperature

van Anh Tran (1) , Kenneth Rasmussen (1) , Günter Grampp (1) , Alexander Kokorin (2)

1 Institute of Physical and Theoretical Chemistry
2 N. N. Semenov Institute of Chemical Physics

Solvent effects on intramolecular electron spin exchange (IMSE) in biradicals have been investigated in various solvents by electron spin resonance (ESR) spectroscopy at room temperature. Biradicals containing different radical fragments and bridges of different length and composition have been used. Interactions between solvent molecules and biradicals were found to take place at the radical fragment as well as at the functional group in the connecting bridge and have been proved to have an influence on the intramolecular spin exchange. The experimentally measured parameters, exchange integral (J) and characteristic time of an intramolecular movement (τ_eff), have been compared with solvent viscosity and polarity parameters (macroscopic level) and longitudinal solvent relaxation time (microscopic level). The dependencies on viscosity and polarity were in good agreement with reported results. In addition, strong evidence of hydrogen bonding between solvent and different sites of the biradicals was found, in some cases even surpassing the other effects.

Mots clés: Physical Sciences

van Anh Tran, Kenneth Rasmussen, Günter Grampp, Alexander Kokorin. Solvent Effects on the Intramolecular Spin Exchange in Biradicals at Room Temperature. Molecular Physics, 2008, 105 (15-16), pp.2119-2125. ⟨10.1080/00268970701651714⟩. ⟨hal-00513144⟩