EFFECT OF MOLECULAR-STRUCTURE ON MESOMORPHISM .7. ENHANCEMENT OF SMECTIC-ISOTROPIC TRANSITION-TEMPERATURES IN BINARY-MIXTURES OF A NEW LIQUID-CRYSTAL SERIES - 4-NITROPHENYL 4'-N-ALKOXYBENZOATES

The homologous series of 4-nitrophenyl 4'-n-alkoxybenzoates has been synthesized and transition temperatures have been determined. All members of this series with three carbons or more in the alkoxy chain exhibit liquid crystalline behavior. The familiar odd-even alternation in mesophase-isotropic temperatures was found. A method for determining mesophase-isotropic temperatures in strongly supercooled samples is described. This series of nitro esters exhibits marked nonlinear thermal behavior in selected binary mesophase systems. Maxima in mesophase-isotropic transition temperatures have been determined for mixtures of each of the 4-nitrophenyl 4'-alkoxybenzoates with 4-heptyloxybenzylidene-4'-butylaniline and with 4-octyloxy-benzylidene-4'-butylaniline. These maxima occur at or very near 50:50 mole percent composition of the binary mixtures. A plot of the maxima vs. alkoxy chain length of the nitro esters exhibits an odd-even alternation. In mixtures of 4-substituted-phenyl 4'-decycloxybenzoates, enhanced Sa mesophases were found for the nitro ester when mixed with methyl and methoxy esters; linear, ideal mixture behavior was found for the nitro ester when mixed with trifluoromethyl and cyano esters. A π molecular complex is proposed to account for this nonideal solution behavior. © 1978, American Chemical Society. All rights reserved.