## 3 Results and Discussion
### Thermotropic Liquid Crystalline Phase Behavior
The first transition in the cooling cycle can be identified as the transition from the isotropic liquid into the liquid crystalline phase (I \(\longrightarrow\) LC) since the second transition in each DSC trace has too high enthalpy values to be a transition from a crystalline solid-state to another crystalline solid-state. The transition enthalpies of the second transitions, ranging from 12 to 19 kJ mol\({}^{-1}\), are smaller than the reference values from a liquid crystalline phase to a crystalline solid-state transition (30-50 kJ mol\({}^{-1}\)), however, they are much higher than the values for transitions from LC to LC or LC to an isotropic liquid (4-6 kJ mol\({}^{-1}\))[23]. This indicates that the second transitions can be assigned to a transition from a liquid crystalline phase to a crystalline solid-state (LC \(\longrightarrow\) Cr\({}^{\prime\prime}\)). The enthalpy of the third transition is smaller compared to the \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Salt**} & **Clearing Points** & **Melting Points** \\  & **T\({}_{\text{c}}\)** [\({}^{\circ}\)C] & **T\({}_{\text{m}}\)** [\({}^{\circ}\)C] \\ \hline
**1d** & 108.8 & 86.1 \\
**1e** & 131.0 & 87.1 \\
**1f** & 133.0 & 82.0 \\
**2d** & 107.9 & 60.0 \\
**2e** & 132.8 & 71.4 \\
**2f** & 146.9 & 76.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Clearing [T\({}_{\text{c}}\)] and Melting [T\({}_{\text{m}}\)] points of the salts **1d-f** and **2d-f** with [T\({}_{\text{2}}\)N\({}^{-}\)] as the counterion extracted from the second cooling cycle from the DSC curves. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Salt**} & **T [\({}^{\circ}\)C] a** & \(\triangle\)**H [k] mol\({}^{-1}\)]** & **Transition** \\ \hline \multirow{3}{*}{**1d**} & 108.8 & 4.2 & Iso-LC (SmA) \\  & 86.1 & 15.1 & LC (SmA)–Cr\({}^{\prime\prime}\) \\  & –10.9 & - & Cr\({}^{\prime\prime}\)–Cr\({}^{\prime}\) \\ \hline \multirow{3}{*}{**1e**} & 131.0 & 8.7 & Iso-LC (SmA) \\  & 87.1 & 15.3 & LC (SmA)–Cr\({}^{\prime\prime}\) \\  & 25.3 & 4.5 & Cr\({}^{\prime\prime}\)–Cr\({}^{\prime}\) \\ \hline \multirow{3}{*}{**1f**} & 133.0 & 4.4 & Iso-LC (SmA) \\  & 82.0 & 12.0 & LC (SmA)–Cr\({}^{\prime\prime}\) \\  & 36.4 & 9.3 & Cr\({}^{\prime\prime}\)–Cr\({}^{\prime}\) \\ \hline \multirow{3}{*}{**2d**} & 107.9 & 1.8 & Iso-LC (SmA) \\  & 60.0 & 18.7 & LC (SmA)–Cr\({}^{\prime\prime}\) \\  & 4.4 & 8.0 & Cr\({}^{\prime\prime}\)–Cr\({}^{\prime}\) \\ \hline \multirow{3}{*}{**2e**} & 132.8 & 4.0 & Iso-LC (SmA) \\  & 71.4 & 19.7 & LC (SmA)–Cr\({}^{\prime\prime}\) \\  & 28.9 & 6.6 & Cr\({}^{\prime\prime}\)–Cr\({}^{\prime}\) \\ \hline \multirow{3}{*}{**2f**} & 146.9 & 4.7 & Iso-LC (SmA) \\  & 76.5 & 18.3 & LC (SmA)–Cr\({}^{\prime\prime}\) \\ \cline{1-1}  & 46.7 & 15.5 & Cr\({}^{\prime\prime}\)–Cr\({}^{\prime}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Transition temperatures (T), enthalpies (\(\triangle\)H) and the phase transition of the salts **1d-f** and **2d-f** obtained from the DSC traces upon cooling with 10 \({}^{\circ}\)C min\({}^{-1}\). second transition and led to the assumption that a transition from a crystalline solid-state to another crystalline solid-state (Cr\"\(\longrightarrow\) Cr\") takes place. The salts were further analyzed by POM to identify and confirm the liquid crystalline phases. Two transitions could be observed during the POM analysis for each salt by heating and cooling the samples at 10 \({}^{\circ}\)C min\({}^{-1}\). The following discussion will concentrate on the cooling events. When cooling the samples from the isotropic liquid, a change from the dark isotropic liquid phase into a birefringent phase has been observed for every salt, whereby the new structure was formed very slowly over a wide temperature range. Furthermore, a second structure change has been observed when cooling the salts further, which was very fast. The first transition from the isotropic liquid into the birefringent mesophase (I \(\longrightarrow\) LC) is illustrated in the supporting information S10.