Synthesis, Characterization, and Investigation of Mesomorphic Properties of a New 2,5-Bis-(4-alkanoyloxybenzylidene)cyclopentan-1-one.

A new set of cyclopentanone chalcone esters 2,5-bis-(4-alkanoyloxybenzylidene)cyclopentan-1-one (B2-B10) has been synthesized and monitored by TLC. Structures of these compounds were determined by spectroscopic techniques (FTIR, H NMR, and mass spectrometry). Differential scanning calorimetry (DSC) and polarized optical microscopy were used to evaluate their transition temperatures and mesophase properties (POM) throughout heating and cooling scans. The thermal data indicate that the compounds B5-B10 have mesomorphic properties with thermal stabilities; the data also reveal that the compounds B6-B10 are monotropic, whereas B5 is enantiotropic. B6, B7, and B9 only have a nematic phase, but B8 and B10 have a smectic phase followed by a nematic phase, and B5 only has a smectic phase. In addition, the study reveals that the inclusion of an acyl group as a terminal chain had the opposite effect on isotropization temperatures for compounds B6, B8, and B10, resulting in an increase in transition temperatures and a decrease in mesophase stability. The lack of a smectic phase in B7 and B9 compounds could be attributed to the narrow phase temperature range, which makes examination difficult, or to the molecules' lack of lateral attraction.