An infrared spectroscopic study of the phase transitions of crystalline aromatic donor—acceptor complexes involving a pseudoplastic state

Variable temperature i.r. spectroscopic studies of weak π-donor-π-acceptor complexes in the crystalline state indicate that the complexes undergo order—disorder transitions, the disorder being caused by molecular motion. Thermodynamic data on the phase transitions along with the spectral data suggest that the high-temperature crystalline forms of the complexes are likely to be pseudoplastic.