Construction Of Π-conjugated Low Molecular Mass Organogels With Fluorescence Sensing Abilities

Low molecular mass organogels are a kind of "jelly" soft materials with orderedmicrostructures induced by the weak intermolecular interactions, such as hydrogenbonding, π-π interactions, van der Waals force, hydrophilic/hydrophobic effects andelectrostatic interactions, etc. Organogels usually show the different physicochemicalproperties from those in solution phases. For example, the aggregate-induced enhanced emission, efficient intermolecular energy transfer and electron transfer.Moreover, the introduction of some functional groups would make the gel possessintelligent response ability to the external stimuli. These smart response gel systemscould be caused the changes of the optical, electrical, chemical properties andmolecular conformation by the external stimuli, meaning that the storage, transfer andprocessing of chemical information. Therefore, it is a significant work to construct thenew gel system responded to the external stimuli for their applications in informationprocessing and transmission, and supermolecular devices.Herein, we have designed and synthesized some π-conjugated low molecular massorganogelators containing amide and urea and studied their self-assembled behaviors,photophysical properties and the fluorescence sensing ability for the anions and nitrocompounds. Some creative results have been obtained, and the main results areoutlined as follows:(1) A new dendritic gelator containing carbazole as repeating unit and amidemoieties as bridge have been synthesized. It was found that it could form gels inDMSO and some DMSO mixed solvents. The results showed that the H-bonding andπ–π interactions were the main driving forces for the gel formation, and the t-butyland amide units played key roles in the gelation process. Interestingly, significantaggregation-induced emission enhancement was observed during gelation process,and we found that the gel could be destroyed in the presence of F–, accompanied bythe emission enhancement, while other halogen anions can not induce gel-sol transformation. The results illustrated that the dendritic gel could selectively recognizeF–.1H NMR test results shown that the interactions between F–and amide bond wasthe reason that lead to the gel-sol phase transition. This work provides a strategy todesign novel dendritic gelators with expected functions.(2) Three urea-substituted t-butyl carbazole derivatives bridged by phenyl grouphad been synthesized, and their self-assembling and anion sensing properties wereinvestigated. We found that the gel formed by t-butyl carbazole derivative witho-bis-urea structure could be destroyed by H－2PO4and AcO－. On the other hand,, thegel of p-bis-urea t-butyl carbazole could selectively recoginize H2PO－4. It suggeststhat the molecular configuration of gelators strongly influences on their sensingproperties.(3) Two cyano styrene small molecular gelators with phenothiazine units had beendesigned and synthesized. It was found that they could form supramolecular gel intoluene/cyclohexane and some other mixed solvents, and self-assembled into3-Dnetworks consisting of lots of fibers with diameters from a few nanometers to tens ofnanometers. From the results of FT-IR, UV-vis and fluorescence emission spectra, wedeemed that H-bonding and π–π interactions were the main driving force for the gelformation. Moreover, the energy levels of HOMO and LUMO of the two moleculeswere estimated by the electrochemical method, meaning that the two oligomers weretypical electron-rich compounds, which suggested that the thin film materials mighthave potential applications to detect aromatic nitro compounds. In fact, gel nanofiberfilm based on phenothiazine derivatives exhibited the good fluorescence sensingability for DNT and TNT.(4) In order to investigate the effect of molecular structure on the ability of gelation,three triphenylamine-functionalized bis(β-diketone)s derivatives have beensynthesized. The results showed that the compound containing acyclopentane-1,3-dione moiety exhibited better gelation ability than the compoundswithout the cyclopentane-1,3-dione moiety. It was because that thecyclopentane-1,3-dione moiety could balance the intermolecular π-π interactions. Thisresult demonstrated that the introduction of alicyclic ring into the conjugatedmolecules could favor molecule as gelator. This study generates a wealth ofknowledge to the design of new rigid π-gelators with intriguing photonic andelectronic properties. On the other hand, we also found that the gelator allowed selective recognition of F–in solution and in gel, which made it good fluorescencechemosensor for F~－.