ORGANIC HYDROGEN-BONDED DIELECTRICS - QUANTUM PARAELECTRICITY BASED ON TAUTOMERIZATION OF 9-HYDROXYPHENALENONE DERIVATIVES

Dielectric properties based on tautomerization in 9-hydroxyphenalenone derivatives were examined. While the 5-methyl derivative 2 exhibits an antiferroelectric transition at 41 K, such a phase transition was not observed in 5-bromo derivative 3 down to 4.2 K. Suppression of the phase transition in the latter may be interpreted in terms of quantum paraelectricity based on proton-tunneling along the hydrogen bond. The reason for the appearance of antiferroelectric ordering coupled with the phase transition in 2 may be ascribed to reduction of the tunneling frequency due to symmetry breaking caused by the methyl group. The present system can be regarded as zero-dimensional hydrogen-bonded system and is interesting in reference to inorganic hydrogen-bonded dielectrics.