Coumarin Derivatives: Synthesis, Characterization, Mesomorphic Behavior and Thermal Conductivity.

Abstract

Two series of new derivatives Coumarin dimer based on liquid crystals were synthesized. The preparation of these liquid crystalline compounds included alkylation reactions (54a-54b), alkylation reactions (55a-55i), and the preparations of chalcones (Claisen-Schmidt condensation) (56a-56r). The structure of all the prepared liquid crystalline compounds were clarified by elemental microanalysis, CHN/O, FT-IR, 1H-NMR and 13C-NMR techniques. The liquid crystal properties (DSC) and (POM) and the measurement of the transition temperatures of the prepared compounds and related enthalpy values were studied through differential calorimetry (DSC) and the use of polarized light microscopy (POM) to study the quality of phases. The first series of Coumarin derivatives (57a-57i) were prepared from the reaction of Coumarin (53) with chalcones (56a-56i). The terminal chains are either odd or even equivalence. The results showed a compound (57a, 57g, 57f) that does not show a liquid crystal phase. It only showed a crystal isotropic transition which was shown by polarized light microscopy and differential calorimeter. Compounds (57b-57e) and compounds (57h,57i) with increasing carbon atoms in alkyl terminal chains showed (enantiotropic) nematic phase by heating and cooling except for compound (57i) that showed monotropic nematic phase through heating. The second series of Coumarin derivatives (58a-58i) were prepared by reacting Coumarin (53) with chalcones (56j-56r) and the terminal chains are either odd or even valent. The results showed that the compounds (58b, 58f, 58g) did not show a liquid crystal phase, only showed a crystal-isotropic transition. Compounds (58a, 58c, 58d, 58e, 58h, 58i) showed a nematic phase through heating and cooling. The Photoluminescence (PL) of the two series-prepared compounds was measured and the compounds emission photoluminescence in the visible region, the blue region, and the red region. The thermal conductivity of the prepared compounds was measured and the compounds were thermally conductive.