An attempt to analyze the orientation behavior of ionic liquids through observation of electron transfer reactions

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Rotational re-orientations of solvent molecules take place during the activation processes of most chemical reactions, since the dipole moments of a molecule in the ground state and in the transition state are usually different. On the other hand, electronic relaxation that forms the transition state from the grounds state should be very rapid. However, such an electronic relaxation cannot be achieved unless much slower solvent rotational relaxation is achieved. Therefore, activation energy is strongly related to the easiness of the re-orientation (rotational relaxation) of solvent molecules. However, such a rotational relaxation is rapid (10^<-12> s) for ordinary molecular liquids with small viscosity. On the other hand, ionic liquid, that has relatively large viscosity and the movement of the component ions of which are largely restricted because of the electrostatic interactions, is expected to be an excellent candidate for the observation of slow rotational relaxation during the chemical activation process. We attempted to observe changes of the activation energy of a reaction that corresponds to the slow orientation relaxation of the component ions of ionic liquids.