Study of the Effects of Decreasing Molecular Rigidity on Mesomorphism

Abstract

A Chalconyl homologous series: RO-C6H4-CH=CH-CO-C6H4-OC14H29(n) (meta) is synthesized and studied with a view to understand and establish the effect of molecular structure on Liquid crystal behaviour by reducing molecular rigidity through diminishing of a phenyl ring and a central carboxy or vinyl carboxy group from a molecule. Novel series consists of thirteen homologues (C1to C18). First member (C1) homologue is nonliquid crystal and the rest of the homologues (C2to C18) are enantiotropically ( C2to C5) nematogenic or monotropically (C6to C18) nematogenic plus smectogenic of low mesophaselengths and low transition temperatures ( 38°C to 76°C). Transition temperatures were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Cr-N/I, N-I, I-N, N-Sm transition curves behaved in normal manner in a phase diagram. N-I and I-Sm transition curves exhibited odd-even effect. Textures of nematic phase are threaded or schlieren and that of the smectic phase are of the type A or C. Analytical, spectral and thermal data supported molecular structure of homologues. Thermal stability ( N-I/ I-N) of series for nematic is 67.5°C and that of the smectic is very low. Group efficiency order derived on the basis of thermal stability is as under. –Cl with –C6H4.COO- > -OC14H29(n) without –C6H4.COO-with reference to central bridge –CH=CH-CO-.

Mesomorphic properties of liquid crystalline compounds with chalconyl central linkage in two phenyl rings

“…Doshi et al reported chalconyl-ester linking group-based homologues series [25][26][27][28][29][30][31]. Previously, our research group also reported homologues series based on chalconyl-ester and chalconyl-vinyl ester central group with reference to two or three phenyl rings, respectively [32][33][34][35][36][37][38][39][40][41][42][43][44][45].…”

“…The variations in the LC property and the degree of mesomorphism from homologue to homologue in the same series or from series to series for the same homologue are attributed to the changing magnitudes of molecular rigidity and flexibility due to changing molecular polarity and polarisability and other related parameters concerning the suitable magnitudes of intermolecular cohesions and closeness. The mesogenic properties of the presently investigated homologous series-1 are compared with structurally similar series-X [43] and -Y [49], as shown in Figure 6.…”