Supramolecular Organogels Based on N-Benzyl, N′-Acylbispidinols

The acylation of unsymmetrical N-benzylbispidinols in aromatic solvents without an external base led to the formation of supramolecular gels, which possess different thicknesses and degrees of stability depending on the substituents in para-positions of the benzylic group as well as on the nature of the acylating agent and of the solvent used. Structural features of the native gels as well as of their dried forms were studied by complementary techniques including Fourier-transform infrared (FTIR) and attenuated total reflection (ATR) spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and small-angle X-ray scattering and diffraction (SAXS). Structures of the key crystalline compounds were established by X-ray diffraction. An analysis of the obtained data allowed speculation on the crucial structural and condition factors that governed the gel formation. The most important factors were as follows: (i) absence of base, either external or internal; (ii) presence of HCl; (iii) presence of carbonyl and hydroxyl groups to allow hydrogen bonding; and (iv) presence of two (hetero)aromatic rings at both sides of the molecule. The hydrogen bonding involving amide carbonyl, hydroxyl at position 9, and, very probably, ammonium N-H+ and Cl− anion appears to be responsible for the formation of infinite molecular chains required for the first step of gel formation. Subsequent lateral cooperation of molecular chains into fibers occurred, presumably, due to the aromatic π−π-stacking interactions. Supercritical carbon dioxide drying of the organogels gave rise to aerogels with morphologies different from that of air-dried samples.


4ae*HCl in nitrobenzene
To a suspension of 70 mg (0.27 mmol) of bispidine 3a in 2.5 ml of nitrobenzene was added dropwise a solution of 39 mg (0.27 mmol) of 2-thiophenecarbonyl chloride in 2.5 mL of nitrobenzene. Then the mixture was refluxed (210 °C) under vigorous stirring for 3.5 hours. Highly viscous and dense amber gel was formed after 2 days at room temperature. Figure S1. Photo of 4ae*HCl in nitrobenzene.

4ae*HCl in ethoxybenzene
To a suspension of 70 mg (0.27 mmol) of bispidine 3a in 2.5 mL of ethoxybenzene was added dropwise a solution of 39 mg (0.27 mmol) of 2-thiophenecarbonyl chloride in 2.5 mL of ethoxybenzene. Then the mixture was stirred at 80 °C for 3.5 hours. Highly viscous and dense colourless gel was formed after 1 hour at room temperature.

4ae*HCl in mesitylene
To a suspension of 70 mg (0.27 mmol) of bispidine 3a in 2.5 mL of mesitylene was added dropwise a solution of 39 mg (0.27 mmol) of 2-thiophenecarbonyl chloride in 2.5 mL of mesitylene. Then the mixture was stirred at 80 °C for 3.5 hours. Loose colourless gel was formed after 1 hour at room temperature. Figure S3. Photo of 4ae*HCl in mesitylene.

4ab*HCl in nitrobenzene.
To a suspension of 70 mg (0.27 mmol) of bispidine 3a in 2.5 mL of nitrobenzene was added dropwise a solution of 47.1 mg (0.27 mmol) of 4-chlorobenzoyl chloride in 2.5 mL of nitrobenzene. Then the mixture was stirred at 80 °C for 3.5 hours. A precipitate was formed. Figure S4. Photo of 4ab*HCl in nitrobenzene.

4ab*HCl in ethoxybenzene
To a suspension of 70 mg (0.27 mmol) of bispidine 3a in 2.5 mL of ethoxybenzene was added dropwise a solution of 47.1 mg (0.27 mmol) of 4-chlorobenzoyl chloride in 2.5 mL of ethoxybenzene. Then the mixture was stirred at 80 °C for 3.5 hours. Loose colourless gel was formed after 1 hour at room temperature.

4ab*HCl in mesitylene.
To a suspension of 70 mg (0.27 mmol) of bispidine 3a in 2.5 mL of mesitylene was added dropwise a solution of 47.1 mg (0.27 mmol) of 4-chlorobenzoyl chloride in 2.5 mL of mesitylene. Then the mixture was stirred at 80 °C for 3.5 hours. Loose colourless gel was formed after 1 hour at room temperature.   Figure S8. Dependence of viscosity of benzene@4ce*HCl on shear rate. Table S2. Dependence of the loss and storage moduli on angular frequency benzene@4ce*HCl.