Effects of Substituent Chains on the Mesomorphism of the Schiff’s Bases of p-Aminocinnamic Acid Esters

Abstract

Compounds of the general structure

are known to form variously smectic and nematic mesophases (1,2). Leclercq, Billard and Jacques (4) have presented thermodynamic data on fifteen derivatives of the above structure. Very little work has been presented on the effect of various substituent groups on the order-disorder magnitude (entropy) of various transitions in these or other nematogenic series. The availability of the data of Leclercq et al. (4), Table I, permits a preliminary consideration of the following questions for the lower members of the series:

• 1. Which end of the molecule controls predominantly the order-disorder of the solid → smectic, smectic → nematic and nematic → isotropic liquid changes?

• 2. To what extent is pure geometric size a controlling factor in the above transitions?

• 3. To what extent does the polarity of the substituent groups control transition entropies and types?

• 4. What effect does an increase in molecular thickness have on transition entropy and mesophase type?