互変異性過程を内包する水素結合系結晶の結晶内ダイナミックス

抄録

9-Hydroxyphenalenones exhibit a dynamical disorder due to a tautomeric process or a reorientational motion in the solid state depending on the crystal environment. Both 5-methyl and 5-bromo derivatives undergo a rapid tautomerization in crystals along the symmetrical double-well potential of the hydrogen bond. While the tautomerization of 5-methyl derivative was quenched at 41K due to the antiferroelectric phase transition, 5-bromo derivative does not show any transition down to 4K, because the antiferroelectric transition is suppressed due to the “quantum fluctuation” caused by the tunnelling effect on the proton transfer along the hydrogen bond. On the other hand, the unique dielectric behavior of 9-hydroxyphenalenone in phase II was interpreted in terms of the motion of the domain walls between left-and right-directed molecules based on the reorientational motion in crystals.