Non-symmetrical three and two-core ring mesogens based on quinoxaline and benzimidazole derivatives: Supramolecular layers through amphoteric donating/accepting H-bonds

• Published in: Journal of molecular structure 2019-03, Vol.1180, p.399-405
• Main Authors: de Oliveira, André H., Silva, Welisson P., da Silva, Jordan K., Freitas, Júlio.C.O., de Souza, Miguel A.F., Cristiano, Rodrigo, Menezes, Fabrício G.
• Format: Article
• Language: English
• Subjects: Benzimidazole; Quinoxaline; Self-assembly; Smectic mesophase; Soft materials; Spherulitic packing
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2018.12.007

Self-assembly-based molecular structures have proven to be highly relevant to the development of soft materials. This work reports the synthesis, thermal behavior and computational analysis of two novel heterocyclic compounds with a non-symmetrical shape bearing a single long alkyl (C12) chain. The compounds 2-(4-dodecyloxy-phenyl)-1H-benzoimidazole, 1, with three-ring core mesogen with a more linear shape, and 1-dodecyl-1,4-dihydro-quinoxaline-2,3-dione, 2, with a condensed two-ring core with a more compact discotic shape, were obtained in good yields and investigated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC) analysis. Benzimidazole derivative 1 was found to present liquid crystalline property, with a mesophase range from 85 to 177 °C, as verified by POM and DSC, with a smectogenic polymorphism assigned as a SmB and a more organized unidentified SmX phase. On the other hand, although quinoxaline 2 did not show liquid crystal behavior, POM analysis indicated an interesting spherulitic packing pattern, typical of a columnar arrangement of the molecules by possible H-bond interactions. Computational results indicated that combining intermolecular hydrogen bonds and hydrophobic interactions lead to a non-planar lamellar model for benzimidazole 1, consistent with the smectic packing found in the liquid crystalline phase and a twist-type packing for compound 2, which is consistent with a spherulitic model. [Display omitted] •Novel non-symmetrical heterocycles-based mesogens were synthesized.•Benzimidazole 1 presented smectogenic polymorphism from 85 to 177 °C.•Quinoxaline2 presented spherulitic packing possibly due intermolecular H-bonds.•Self-assembly of compounds 1 and 2 were proposed base on theoretical calculations.