Solvent effects on the intramolecular spin exchange in biradicals at room temperature

Abstract

Solvent effects on intramolecular electron spin exchange 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 were 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, the exchange integral (J) and the characteristic time of an intramolecular movement (τ _eff), have been compared with solvent viscosity and polarity parameters (macroscopic level) and the 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 the solvent and different sites of the biradicals was found, in some cases even surpassing the other effects.

Keywords:

• Molten salts
• Molecular dynamics
• Molecular liquids
• Polarizable potentials

Acknowledgement

V.A.T. would like to thank ASEA Uninet for a scholarship.