To verify the possibility of producing several different orga- nogelators starting from compound 1 we produced compounds
8–12 reacting 1 with the five different organic azides 3–7 (Scheme
1, for details see the ESI†).7
The five azides chosen possess different substituents with peculiar electronic and steric requirements and represent, in our opinion, a convincing test to demonstrate the efficiency of the substituted triazine moiety as a gelating scaffold. It is already possible to highlight that the overall yield and the efficiency of this synthesis is higher with respect to the previous approach
(Fig. 1).4
The gelling ability is correlated with the minimum amount of compound necessary to gel the solvent. As Table 1 shows, this quantity is generally dependent on the chemical derivatization of
1 and, for a given gelator, on the solvent used.
Fig. 2 Gel of compound 11 in toluene (left) and gel of compound 12 in cyclohexane (right).
Notwithstanding the differences shown by the five compounds, it has been always possible to obtain stable gels choosing among a limited number of different solvents. Most gels are transparent as is shown by the transparent gel of compound 11 in toluene (Fig. 2 left); furthermore the non- transparent gels of compound 12 (Fig. 2, right) showed a thixo- tropic behavior, reforming the original gel less than half an hour after shaking.
The gelling ability is, for a given compound, dependent on solvent polarity and on its p-stacking and H-bonding properties. For the derivative 12 a p-stacking solvent decreases the gelling ability (see toluene vs. cyclohexane), while solvent polarity favours gelation, demonstrating that solvophobic segregation of the alkyl chains definitely plays a role. However, when the solvent is too strong a competitor for H-bonds, as in the case of isopropanol, the gelating efficiency of 12 is drastically lowered, giving an indication of the driving force provided by this latter interaction.
参考资料:雅虎翻译