The synthesis and mesomorphic properties of novel ester derivatives of three series heterocyclic 1,3-oxazepinediones and the 1,3-oxazepandione moiety (a-c) are described. All structures were elucidated by physical measurements and the bonding characteristics of the resulting compounds were substantiated by Fourier transform infrared spectroscopy spectroscopy. Their molecular structures are supported by the H-1 and C-13 NMR spectra along with two-dimensional COSY, HMQC, and HMBC.A structure-property relationship has been established and mesogenic properties were found to be dependent on the type of rings within the molecular core. Compounds1a--7a not mesogenic exhibited Cr-I upon heating and cooling, while the series compounds 1b--7b were not mesogenic and only exhibited the transition of Cr-1-Cr-2 upon cooling and heating. In compounds 1c--7c, the SmA observed in compounds 1c-3c with short terminal alkyl chains during heating and cooling. However, the nematic phases were formed in compounds 4c--7c. The nematic phase presence increases with the length of the terminal alkyl chain. Theoretical studies are presented in this study and are in agreement with our results.