Liquid-crystalline phase behavior in a zwitterionic tetraazapentacene

A 5,7-dioctadecylquinoxalinophenazine zwitterion 1 has been investigated to determine its thermal phase behavior. A combination of differential scanning calorimetry (DSC), variable temperature low- and high-angle X-ray diffraction (XRD), and deuterium solid-state NMR spectroscopy were used to characterize the different phases of the tetraazapentacene 1. This molecule is found to exist in a variety of crystalline solid phases between room temperature and 167 °C. with different room-temperature phases resulting from crystallization from solution compared with cooling from the melt. Interestingly, the molecule exhibits liquid-crystalline behavior at high temperatures, between 167 °C and 186 °C, above which it becomes an isotropic fluid. The presence of liquid-crystalline behavior in a zwitterionic system opens up the potential for the use of these or related molecules in optoelectronic switching.