Liquid crystalline imidazolium salts bearing 5-phenylpyrimidine: dependence of mesomorphic properties on spacer lengths, terminalN-alkyl group and counterions

Towards room temperature ionic liquid crystals: linear versus bent imidazolium phenylpyrimidines

“…17 One possible reason for the observation of SmC phases of compounds p-5(10,8) and p-5 (12,8) might be that, for these particular spacer and chain length combinations, the ''SmC promoting effect'' of phenylpyrimidines, reported by Lemieux, 4,8a seems to overrule any other mesophase-controlling effects. The finding that compound p-5 (10,8) has a lower melting point as compared to compound p-5(8,8) (entries 6 and 7) might be explained as follows. In the case of p-5 (10,8) the melting transition from Cr to SmC presumably requires less energy as compared to the melting transition from Cr to SmA in the case of p-5(8,8).…”

“…Following our previously established procedure, enamine 9 12 was submitted to condensation with dodecanamidine 10a 13 to give 3-(2-dodecylpyrimidin-5-yl)phenol 11. 10,14 Subsequent etherification with 1,9-dibromononane gave bromide 12, which was alkylated with N-methylimidazole 13a to yield the desired bent 5-phenylpyrimidine 4 (Scheme 3).…”

“…8,9 Despite ample precedence of ionic liquid crystals containing biphenyls as calamitic units, 3 the corresponding phenylpyrimidines 3 (Scheme 2) have only been rarely employed for such purposes. 10 We have recently reported the mesomorphic properties of 5-phenylpyrimidines 3 with a tethered imidazolium moiety with respect to chain lengths, tether lengths and counter ions. 10 Although N-methylimidazolium bromides 3 (n ¼ 12, m ¼ 4-9) displayed broad mesophase ranges (SmA), the high clearing temperatures affected the thermal stability considerably and led to decomposition after repetitive heating/cooling cycles.…”

“…10 We have recently reported the mesomorphic properties of 5-phenylpyrimidines 3 with a tethered imidazolium moiety with respect to chain lengths, tether lengths and counter ions. 10 Although N-methylimidazolium bromides 3 (n ¼ 12, m ¼ 4-9) displayed broad mesophase ranges (SmA), the high clearing temperatures affected the thermal stability considerably and led to decomposition after repetitive heating/cooling cycles. In addition melting points were relatively high, thus limiting the potential applications of these novel materials.…”

Key Developments in Ionic Liquid Crystals

“…One of the molecular design tools to accomplish this is based on a reduction of the symmetry that results in a decreased melting temperature. The authors selected a suitable approach for this purpose and used a geometry of the target calamitic 2-phenylpyrimidine via a meta -substitution, rather than the typical para -substitution [ 134 , 135 ]. The results showed that, indeed, this approach is successful and that meta -substitution at the phenyl ring resulted in room temperature mesophases with sufficient thermal stability.…”