Direct evidence for the effect of lateral hydrogen bonding on the smectic phase

In order to reduce the number of hydrogen bonds in biamide derivatives, one amide group in N-(4-cetyloxybenzoyl)-N'-(4'-nitrobenzoyl) hydrazine (C16-NO2) was replaced by a Schiff base group, forming N-(4-cetyloxybenzoyl)-N'-(4'-nitrobenzylidene) hydrazine (C16-Sch). Computational study on the molecular structure at B3LYP/6-311+G** level revealed that the molecular geometry of C16-NO2 could be well retained by C16-Sch. In addition, C16-Sch exhibited the same mesophase structure (SmA(1)) as C16-NO2, and the hydrogen bonding was demonstrated to be still interacting in the mesophase. However, compared to C16-NO2, the mesophase stability of C16-Sch is dramatically decreased by the reduction of the number of hydrogen bonds, providing direct evidence that intermolecular hydrogen bonding plays an important role in stabilising the smectic phase.