Construction And Gel Properties Of Low- Molecular Mass Organogels Based On Monopyrrolotetrathiafulvalene

Tetrathiafulvalene (TTF) has the excellent nature of electron-donating, regularity of the rigid plane as well as can provide effective π-π stacking and S…S interactions, also, many results have shown that TTF and its derivatives can form charge transfer (CT) complexes with various electron acceptors, and the resultant CT complexes exhibit high electrical conductivity. Therefore, TTF and its derivatives have been widely investigated for organic conducting materials. In particular, TTF-based LMOGs have been extensively investigated for the development of organic conducting nanomate-rials and stimuli-responsive materials. In order to construct the highly organized π-conjugated low molecular mass organic gelators (LMOGs), we select monopyrrolo-TTF (MPTTF) as basic skeleton and introduce various of constitutional units in the periphery of the pyrrole ring or TTF, whereby we have synthesized four novel series of LMOGs based on monopyrrolo-TTF and investigate the gelation behaviors, self-assembly structures, melocular arrangement modes as well as the changes of the physical properties after gelation. Based on these points, we have achieved some innovative experiment results, as follows:1. A series of MPTTF-succinamide conjugates and their TCNQ CT complexes have been synthesized and investigated as newLMOGs. The gelation capability of these conjugates is highly dependent on the length of the alkyl chain of the terminal amide. Thus, only the short alkyl chain derivatives la and lb could efficiently gelate cyclo-hexane and methylcyclohexane (MCH). Surprisingly, these gelators react with TCNQ to form stable CT complex gels in both cyclohexane and MCH. The FE-SEM images of the native gels reveal the characteristic gelation morphologies of micropo-rous or fibrous structures, whereas the morphologies of CT complex gels show the fibrillar and globular aggregates in cyclohexane and MCH, respectively. SAXS study of the native gel and the CT complex gel of la in cyclohexane suggests that the mol-ecules maintain rectangular and hexagonal columnar molecular packing models in the gel phase, respectively. The native gels undergo a reversible gel-sol phase transition upon exposure to external stimuli, such as temperature and chemical oxidation/reduction. Alternatively, the corresponding CT complex gels exhibit a complicated response to external stimuli. Chemical oxidation by h results in the destruction of the gel state. However, neither Fe3+nor Cu2+ can induce the collapse of the gel phase. Interestingly, all the gels show an irreversible gel-sol transition on successively tri-ggering with TFA and TEA. The reformation of the gel from the sol state is achieved just by the addition of water, showing the phase-selective gelation of the solvents from their mixtures with water.2. A series of poly (aryl ether) dendrons with a MPTTF unit linked through an acyl hydrazone linkage weredesigned and synthesized as LMOGs. Two of the dendrons could gelate the aromatic solvents and some solvent mixtures, but the others could not gel all solvents tested except for n-pentanol. Asubtle change onthe molecular structure produces a great influence on the gelation behavior. Note that the dendrons could form the stable gel in the DMSO/water mixture without thermal treatment and could also form the binary gel with fullerene (C60) in toluene.The formed gels under go a reversible gel-sol phase transition upon exposure to external stimuli, such as temper-ature and chemical oxidation/reduction. A number of experiments (SEM, FTIR spec-troscopy,’HNMR spectroscopy, and UV-Vis absorption spectroscopy and XRD) revealed that these dendritic molecules self-assembled into elastically interpenetrating one-dimensional fibrillar aggregates and maintain rectangular molecular-packing mode in organogels. The hydrogen bonding, π-π and donor-acceptor interactions were found to be the main driving forces for formation of the gels. Moreover, the gel system exhibited gel-induced enhanced emission (GIEE) property in the visible region in spite of the absence of a conventional fluorophore unit and the fluorescence was effectively quenched by introduction of C60.3. A series of MPTTF-tripeptide conjugates have been synthesized and investigated as new LMOGs. It was found that most of these compounds could immobilize low-polarity solvents readily and the gelation behaviors of these gelators showed a dependence on the amino acid residues. These organogels were thoroughly studied using various techniques including AFM, FE-SEM, CD spectroscopy, FT-IR spect-roscopy,’H NMR, UV-Vis absorption spectroscopy and XRD. The results showed that the cooperative interplay of hydrogen bonding, π-π stacking and S"’S interact-tions were the main driving force for the formation of the gels. Of all the organogels, the aromatic solvent gels, such as toluene gel, exhibited multiple-stimulus response-veness towards heating, shaking, chemical redox activity and the presence of anions, thus leading to reversible sol-gel phase transitions. Most interestingly, gelation in the presence of 2,4,6-trinitrophenol (TNP) in organic solvents could be observed visually with a concomitant color change through donor-acceptor interactions. The strength of the CT interaction between gelators and TNP was proportional to the incubation time and increasing CGC. The gels could function as efficient absorbents for potential application in removal of crystal violet and rhodamine B dyes from water.4. A series of crown-MPTTF-glutamic acid conjuagtes have been synthesized and investigated as new LMOGs. The gelation ability showed that the different groups at the end of the glutamic acid residual would cause these gelators gelate different solvents. In addition, what deserves to be mentioned was that the solvent had played a great influence on the gelation, for example, in DMF-CH3CN mixture, although the MPTTF moiety could be oxidized to MPTTF+by chemical oxidants, the gel state did not show any changes in the whole oxidants response process and decreased the CGC. The FE-SEM images of the native gels and oxidant gels all revealed the characteristic gelation morphologies of three-dimentional network structures with certain chirality. However, SAXS study of the native gel and oxidant gel of gelator 1 in DMF-CH3CN suggested that the molecules maintained hexagonal and rectangular columnar molecular packing models in the gel phase, respectively. But, the gels were all changed into the solution phases after introduced the oxidants. In the other hand, the native gel underwent a reversible gel-sol phase transition upon exposure to external stimuli, such as temperature, ultrasound, K+and F-.