Liquid‐Crystalline Phase Behavior in a Zwitterionic Tetraazapentacene

Abstract

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.

Room‐Temperature Redox‐Active Liquid Crystals Composed of Tetraazanaphthacene Derivatives

“…Moreover, upon the addition of the strong base 1,8‐diazabicycloundec‐7‐ene (DBU), a mixture of 1a and 2a generates a TANC radical anion by the disproportionation of an electron from the FFV to the TANC framework. To the best of our knowledge, for an N ‐heteroacene framework, only a smectic LC state based on dipole moments has been reported 23. However, this is the first report on the formation of the columnar LC state of 1a and 2a at room temperature through self‐organization.…”

N1-(5-Fluoro-2,4-dinitrophenyl)-N2-phenyl-4-(trifluoromethyl)benzene-1,2-diamine

“…Disappointingly, after 4 h, we obtained a mixture of N 1 -(5-ethoxy-2,4-dinitrophenyl)-N 2 -phenyl-4-(trifluoromethyl)benzene-1,2-diamine (5) (38%) and the desired N 1 -(5-fluoro-2,4-dinitrophenyl)-N 2 -phenyl-4-(trifluoromethyl)benzene-1,2-diamine (6) (51%) which required chromatographic separation (n-hexane/DCM) (Scheme 2). Our interest in difluorodinitrobenzene 1 stems from its use as a starting point in the synthesis of biscyanine azaacenes such as the hexaazaanthracene 2 [20,21] and the tetraazapentacene 3 [22][23][24][25] ( Figure 1) that followed a modification of Nietzki's classical preparation of tetraazapentacene from 1,2-diaminobenzenes and the considerably less reactive 1,5-dichloro-2,4-dinitrobenzene [26]. A key initial step in preparing asymmetrically-substituted biscyanine tetraazaacene analogues [23] is the selective displacement of one fluorine by N 1 -aryl/alkyl 1,2-benzenediamines and this is typically achieved at 0-20 °C in solvents such as EtOH or MeOH in the presence of either triethylamine or pyridine (1 equiv) or additional N 1 -aryl/alkyl 1,2-benzenediamine (1 equiv).…”

“…Our interest in difluorodinitrobenzene 1 stems from its use as a starting point in the synthesis of biscyanine azaacenes such as the hexaazaanthracene 2 [20,21] and the tetraazapentacene 3 [22][23][24][25] ( Figure 1) that followed a modification of Nietzki's classical preparation of tetraazapentacene from 1,2-diaminobenzenes and the considerably less reactive 1,5-dichloro-2,4-dinitrobenzene [26].…”

“…General structure of biscyanines 2 and 3 prepared from difluorodinitrobenzene 1[20][21][22][23][24][25].…”

Regiospecific synthesis of 5,7-disubstituted quinoxalino[2,3-b]phenazines

“…1 A 5,7-bisoctadecyl derivative has shown interesting high temperature liquid crystalline properties. 2,3 These studies were made possible by an improved high yielding and regiospecific synthesis of the 5,7-disubstitued isomers. We now wish to report the full synthetic details.…”