Synthesis, characterization and self-assembly of new cholesteryl-substitued sym-tetrazine: Fluorescence, gelation and mesogenic properties

Abstract

Fluorescent liquid crystalline organogels have been considered as proper candidates for low-energy consumption electronic displays particularly for portable flexible electronics. Herein, we synthesized novel fluorescent symmetric 3,6-bis(4-(cholesterylester)phenyl)-1,2,4,5-tetrazine (sym-Tetrazine; DCh-Tz) liquid crystalline low molecular weight organogelator (LMWO). The molecular structure of the prepared sym-Tetrazine was characterized by different spectroscopic methods, including 1H/13C NMR and FT-IR spectra. The new oganogelator, sym-tetrazine, was synthesized via an addition reaction of hydrazine monohydrate with 4-cyanobenzoic acid to give the corresponding dihydrotetrazine. The product of the addition reaction was subjected to an oxidation reaction to give 3,6-bis(4-carboxyphenyl)-tetrazine to interact with cholesterol affording the desired DCh-Tz. It was proved to possess fairly high gelation capability to generate nanofibers in various alcohols, such as 1,6-dihydroxyhexane, n-octanol and n-butanol. The mesogenic phases of the prepared cholesterylester s-tetrazine were studied by POM and DSC. The photophysical properties of the new fluorescent and thermoreversible low molecular weight organogelator from cholesterylester s-tetrazine were discussed. Both of UV-Vis absorption and fluorescence spectra showed a solvatochromic and solvatofluorochromic activities, respectively. The supramolecular self-assembly of the synthesized cholesterylester s-tetrazine occurred via van der Waals and π-stack interaction forces to result in the gelation of various organic solvents. A dried xerogel of the cholesterylester s-tetrazine was studied by scanning electron microscopy (SEM) to show fiber-like nano-scaled scaffolds. Both of cytotoxicity and antimicrobial properties were explored to prove the use the current DCh-Tz for other potential applications, such as bioimaging and drug delivery systems.