Can the molecule involved in a CT interaction reorient itself in the crystal lattice? Phase transition and glass transition in trans-stilbene-TCNQ

The heat capacity of the title compound has been measured below room temperature by adiabatic calorimetry. A structural phase transition and a glass transition, both probably related to the intramolecular crankshaft motion, were detected at 273 K and 250 K, respectively. The degree of charge transfer (CT) was determined from IR spectroscopy as approximately 0.2e−. Since the central CC moiety of the stilbene molecule has a significant density in the HOMO, the observation of the phase and glass transitions means that the part involved in the CT interaction reorients itself in the crystal lattice above the glass transition temperature.