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.