# Synthesis, Characterization, and Self-Assembly of a Tetrathiafulvalene (TTF)-Triglycyl Derivative
## 3 Results and Discussion
### Gelation Properties  
The gelation ability of TTF-triglycyl derivative **14** was studied for a number of anhydrous solvents of different nature (i.e., apolar, polar aprotic, polar protic) using the standard heating-cooling treatment. Materials that did flow upon inversion of the vial upside-down were initially classified as gels. One of the gels was used later as a model example to demonstrate its viscoelastic nature by oscillatory rheological measurements (see below). Compound **14** was found to be soluble in methanol, ethanol, isopropanol, dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran, whereas it resulted insoluble in diethyl ether, acetonitrile, _n_-hexane, and cyclohexane. In contrast, opaque gels were obtained in 10 solvents at concentrations varying between 5 \(\pm\) 1 and 50 \(\pm\) 10 g/L (Table 1).  
These gels remained stable for at least two months when stored in sealed vials at RT. Their color varied from bright orange to dark orange-brown depending on the solvent (Figure 2a). The supramolecular gels showed typical thermoreversibility (Figure 2b), and their opaque appearance suggested the presence of aggregates larger than the wavelength of visible light (\(\lambda\) = 380-780 nm), which was in agreement with electron microscopy (see below). Further investigations were carried out using only some selected gels as representative materials.  
As mentioned in the introduction, it is well established that the redox TTF core in this type of LMW also provides both S\(\cdots\)S and \(\pi\)\(\cdots\)\(\pi\) interactions during molecular aggregation, whereas the peptide chain drives molecular aggregation via hydrogen bonding [73; 74]. Comparison of Fourier transform infrared (FT-IR) spectra of solid TTF derivative **14** with that of the xerogel (i.e., prepared by freeze-drying the corresponding organogel) and **14** in solution (i.e., below the CGC) showed only very small frequency shifts (i.e., red-shift \(\Delta\
u\) \(\sim\) 5 cm\({}^{-1}\)) for characteristic bands such as C=O stretching (\(\sim\)1641 cm\({}^{-1}\)), N-H amide I (br \(\sim\) 3280 cm\({}^{-1}\)), and N-H amide II (bending vibration) (\(\sim\)1553 cm\({}^{-1}\)) (Figure S2). These values suggest that **14** may also be aggregated in the solid state and in solution via  
\begin{table}
\begin{tabular}{c c c c} \hline
**Solvent 2** & **CGC (g/L)** & **Gelation Time (min)** & \(T_{\text{gel}}\) (\({}^{\circ}\)C)** \\ \hline Acetone & 40 \(\pm\) 10 & 60 \(\pm\) 10 & 36 \(\pm\) 3 4 [FOOTNOTE:4]Footnote 4: Gels were obtained upon a heating–cooling cycle (see Experimental Section). The use of anhydrous solvents was found to be very critical to obtain the lowest possible critical gelation concentration (CGC) values. In general, the use non-anhydrous solvents either inhibited the gelation or raised the CGC up to 3–4 times in comparison to anhydrous solvents. Error values were calculated from three randomized experiments. 2 Solvent volume = 1 mL. \\
1,4-Dioxane & 50 \(\pm\) 10 & 60 \(\pm\) 10 & 51 \(\pm\) 3 \\ Ethyl acetate & 5 \(\pm\) 1 & 10 \(\pm\) 2 & 47 \(\pm\) 2 \\ Toluene & 9 \(\pm\) 1 & 90 \(\pm\) 10 & 41 \(\pm\) 2 \\ Xylene 3  & 8 \(\pm\) 1 & 90 \(\pm\) 10 & 46 \(\pm\) 2 \\ \hline \end{tabular}
\end{table}
Table 1: Gelation ability of TTF–triglycyl derivative **14**, critical gelation concentration (CGC), gelation time, and _gel_-to-_sol_ transition temperature (\(T_{\text{gel}}\)). 1 similar intermolecular hydrogen-bonding pattern between amide groups, most likely in the parallel \(\beta\)-sheet conformation [79], as well as van der Waals interactions between the alkyl chains.