## 3 Results and Discussion
### Thermotropic Liquid Crystalline Phase Behavior
The mesophase after a full transition is shown in Figure 2 for the salts **1d-f** and **2d-f**, showing typical liquid crystalline textures. The hypothesis, from the DSC traces, that the first transition refers to the I \(\longrightarrow\) LC transition and the second to a LC \(\longrightarrow\) Cr\" transition can be verified by the POM analysis (data reported in the supporting information S11 for LC \(\longrightarrow\) Cr\" transition). However, following the LC \(\longrightarrow\) Cr\" transition, no Cr\" \(\longrightarrow\) Cr\" transition could be observed by POM. As the mesophases are reversibly formed during heating and cooling, the compounds can be classified as enantiotropic ionic liquid crystals. The structure of the compounds likely leads to the conclusion that the perfluoroalkyl chains and the alkyl chains will segregate from one another, as previously observed for similar systems [10; 15; 16]. Indeed, the long perfluoroheptyl chain introduces a certain structural stiffness conferring stability to the thermotropic LC phase. Comparing the salts from this work with the previous work with only \(N\)-methylated pyridinium salts [10], we can assume that the additional alkyl chain in this compound tends to stress self-aggregation in the mesophase due to the van der Waals interactions between the molecules driving the formation of LC phases. As reported in previous studies, micro-segregation is involved in the formation of smectic-like phases [24]. By comparing the textures observed by POM of these salts to pictures from literature, it is reasonable to hypothesize a smectic A (SmA) phase for all the salts; in fact, the defects look like SmA batonnets growing into focal conic textures [25]. Discussing the mesophase range with respect to the structural variables, it can be clearly seen that the mesophase range increases with the increasing alkyl chain length within the series, as shown in Figure 3. By comparing the regioisomers with each other, salts **2d-f** have a wider mesophase range than the **1d-f** samples, indicating a higher stability of the liquid crystalline phase. The different behavior between the regioisomers can be explained by the different linkage of the pyridinium ring and the resulting effect of charge delocalization due to the distortion of the linearity. When the pyridinium ring is linked to the C(5) of the 1,2,4-oxadiazole (**2d-f**), the conjugation of the system increased compared to the pyridinium linked to the C(3) of the 1,2,4-oxadiazole (**1d-f**), resulting in a higher effect of charge delocalization for the compounds **2d-f**. The enhanced positive charge delocalization increases the size of the polar head and affects the extent of the charge dispersion favoring a higher anion mobility. This is supported by the lower transition temperatures for **2d-f** and thus the wider mesophase range. Figure 3: Comparison of the mesophase range of the salts **1d-f** and **2d-f**. Figure 2: Optical textures of the salts (**a**) **1d** at 106.4 \({}^{\circ}\)C, **1e** at 130.7 \({}^{\circ}\)C, **1f** at 132.0 \({}^{\circ}\)C and (**b**) **2d** at 107.0 \({}^{\circ}\)C, **2e** at 130.2 \({}^{\circ}\)C, **2f** at 132.4 \({}^{\circ}\)C observed by polarized optically microscopy analysis under crossed polarizers showing the mesophase after the 1 st transition from the isotropic liquid to the liquid crystalline phase (I \(\longrightarrow\) LC (SmA)) upon cooling with 10 \({}^{\circ}\)C min\({}^{-1}\). Abbreviation: I, isotropic phase; LC, liquid crystalline phase; SmA, smectic A phase.