Molecular Crystals and Liquid Crystals, Vol.652, No.1, 1-9, 2017
Molecular flexibility operated mesomorphism by end groups in azoester series
A novel azoester homologous series, RO-C6H4-COO-C6H4-N = N-C6H4-OC7H15 (n) (para) has been synthesized and studied with a view to understanding and establishing the effects of molecular structure on mesomorphic properties with reference to tthe flexible terminal chain. The novel azoester series consists of thirteen (C-1-C-18) members. Mesomorphism commences from C-5 homologue. C-1-C-4 homologues are nonmesomorphic, C-5 homologue is only nematogenic and C-6-C-18 homologues are smectogenic and nematogenic. All mesogenic homologues are enantiotropically mesomorphic. Transition temperatures and textures were determined by polarizing optical microscopy (POM) and a heating stage. Cr-M/I transition curve follows a zigzag path of rising and falling values and behaves in a normal manner. The Sm-N and N-I transition curves of a phase diagram behave in the normal established manner except for a small deviation for the higher homologues (C-14 and C-16). An odd-even effect is exhibited by Sm-N and N-I transition curves. Analytical spectral and thermal data support the molecular structures. Smectic and nematic thermal stabilities are 93.62 degrees C and 114.3 degrees C, respectively. Smectic and nematic mesophas elengths range from 12.0 degrees C to 18.0 degrees C and 11.0 degrees C to 31.0 degrees C. The series is predominantly nematogenic and partly smectogenic and of middle order melting type. Group efficiency order derived for smectic and nematic. Smectic and nematic: -OCH3 > -OC4H9 > -OC7H15 (n).