Self-assembly And Photophysical Properties Of Low Molecular Weight Gelators Based On Triphenylbenzene Derivatives

The concept of supramolecular chemistry through organogelators has proved to be successful and continue to be of great interest not only for basic research and applications in separation technology, catalysis, templates, cosmetics, fluorescent imaging, light harvesting systems, drug delivery, but also for the growth of nanoscale molecular electronics and related fields. Organogels are expected to be useful for novel functional soft materials with well-defined nanostructures assemblies.Herein, we synthesized several organogelators based on triphenylbenzene derivatives and investigated their gel morphologies by mean of SEM. By the investigation of FT-IR, UV-vis, XRD, and 1H NMR, the molecular interactions and the stacking mode in the self-assembled gel systems could be obtained. The introduction of the functional groups in the gel could make the organogels show unique optical properties which have potential applications in optical nanomaterials. Furthermore, using a composite organogel approach, a perylene dye chromism and fluorescence emission could be modulated. The main results were outlined as follows:(1) Two-component gelation between 1,3,5-tris(4-amidobutanoic acid)phenyl benzene, a small discotic molecule bearing H-bonding donor, and 4-(4-alkoxybenzoyloxy)- 4'-stilbazole derivatives was reported. Self-assembly of these complex systems induced the gelation of alcoholic solvents. SEM study revealed that twisted and entangled supramolecular rods or tapes as well as sheet-like structures were generated in the gel phases. Based on XRD analysis, FT-IR and 1H NMR temperature- dependent studies the hierarchical growth of these nanostructures is attributed to the columnar-type packing of the complexes facilitated by cooperative hydrogen bonding,π-stacking and van der Walls interactions. Gelation of complexes resulted in weak emission enhancement due probably to the planarization of the core segments in the self-assemblies. (2) The composite organogels based on 1,3,5-tris(4-dodecyloxybenzoylamino) phenylbenzene (DBAPB), a known gelator, and N,N'-di(octadecyl)-perylene- 3,4,9,10-tetracarboxylic diimide (C18PTCDI), a non-gelator dye, have been achieved leading to the controllable color and emitting color changes. SEM images and XRD patterns revealed that the packing of the DBAPB-based gelator could almost be maintained in the composite gels. The temperature-dependent UV-vis absorption and fluorescence excitation and emission spectra illustrated that the optical properties of the composite gels could be controlled by the content of C18PTCDI as well as the temperature in the gel phases. When the content of C18PTCDI was 1 mol %, C18PTCDI could be isolated as unimolecules in the composite gel, which was yellow and gave bright greenish-yellow emission under 365 nm light. For the mixed systems containing 2-10 mol % of C18PTCDI, the fresh gels, which were obtained after cooling the hot solutions for a short time, were yellow and showed greenish-yellow emission under 365 nm illumination. However, the corresponding stable composite gels, which were obtained via prolonging the cooling time, were red and emitted weak red emission excited by UV light due to the formation of C18PTCDI aggregates. The reversible color and emitting color changes could be realized in the gel phases in a narrow temperature range. Moreover, the excitation energy of DBAPB could be transferred to C18PTCDI in the composite gels, leading to the obvious emission quenching of the former.(3) We have designed a family of achiral C3-symmetrical discotic molecules consisting of triphenylbenzene core linked to three N-phenylbenzamide moieties using a cyano-substituted vinylene as the spacers. It is found that CN-DBAPPB3 can self-assembled into organogels exhibiting helical fibers in benzaldehyde, in which the gelators was packed into layered microstructures, or nanorods composed of lots of 1D hexagonal aggregates in 1,4-dioxane. Notably, benzaldehyde gel can emit greenish-yellow light, and 1,4-dioxane gel can emit greenish-blue light under UV irradiation due to the formation ofπ-aggregates in benzaldehyde gel instead of in 1,4-dioxane one. It suggested that solvent has great effect on the molecular packing of gelators, which further tuned the emitting light. In addition, a simple precipitation method was applied to generate organic spherical nanoparticles of CN-DBAPPBn in the mixture of THF/H2O, and aggregation-induced emission, which is different from that in gel systems, was detected for the nanoparticles compared with the isolated species in solution. Therefore, the synthesized C3-symmetrical discoticπ-conjugated molecules with controllable fluorescence can be used as functional soft materials applied in sensors or optoelectronic devices and related fields.