Design and Self-Assembling Behaviour of Calamitic Reactive Mesogens with Lateral Methyl and Methoxy Substituents and Vinyl Terminal Group

Smart self-organising systems attract considerable attention in the scientific community. In order to control and stabilise the liquid crystalline behaviour, and hence the self-organisation, the polymerisation process can be effectively used. Mesogenic units incorporated into the backbones as functional side chains of weakly cross-linked macromolecules can become orientationally ordered. Several new calamitic reactive mesogens possessing the vinyl terminal group with varying flexible chain lengths and with/without lateral substitution by the methyl (methoxy) groups have been designed and studied. Depending on the molecular structure, namely, the type and position of the lateral substituents, the resulting materials form the nematic, the orthogonal SmA and the tilted SmC phases in a reasonably broad temperature range, and the structure of the mesophases was confirmed by X-ray diffraction experiments. The main objective of this work is to contribute to better understanding of the molecular structure–mesomorphic property relationship for new functional reactive mesogens, aiming at further design of smart self-assembling macromolecular materials for novel sensor systems.


Introduction
Functional self-assembling systems' build-up from the organic molecules attract considerable attention from the scientific community due to their extraordinary properties that can be utilised for smart applications [1][2][3]. Some soft organic materials with definite molecular structure can exhibit the liquid crystalline (LC), i.e., self-assembling, behaviour, that can be changed, tuned and controlled by an external stimulus: applied electric/magnetic field, mechanical stress and irradiation by UV or visible light [3][4][5]. A tremendous number of materials, mixtures and composites possessing the LC behaviour have been designed and investigated during the last decades, many of which already respond to the demands of specific applications, such as various display and opto-electronic devices. Nevertheless, the information gained so far is still insufficient for the effective applicability of LC materials for further smart applications, the reason being that the control and prediction of the LC properties requires further efforts to assure the stability of the target LC mesophases and other specific properties.
In order to stabilise the liquid crystalline behaviour, and hence the self-organisation, the polymerisation process can be effectively used [6][7][8][9]. Mesogenic units, also called

Materials and Methods
This section contains a detailed description of the synthesis and confirmation of the molecular structures obtained for all of the designed reactive mesogens. Additionally, it provides the description of the experimental techniques used for the characterisation of the mesomorphic, thermal and structural properties.

Design and Synthesis
All starting materials and reagents were purchased from local ditributors of Sigma-Aldrich (Merck), Acros Organics or Fluorochem. Solvents used for the syntheses were "p.a." purity grade. 1 H NMR spectra were recorded on Varian VNMRS 300; deuteriochloroform (CDCl3) was used as solvent and the signal of solvent served as the internal standard. Chemical shifts (δ) are given in ppm and spin-spin coupling constants (J) are given in Hz. Column chromatography was carried out using Merck Kieselgel 60 (60−100 μm). The purity of final compounds was checked by HPLC analysis (high-pressure pump ECOM Alpha; column WATREX Biospher Si 100, 250×4 mm, 5 μm; detector WATREX UVD 250) and were found to be > 99.8 %.
Newly designed reactive mesogens have been synthesised according to the synthetic route described in Figure 2. First, benzoyl chloride 1 and hydroxy-esters 2a-d were synthesised following the procedures from the literature [17]. The reaction of benzoyl chloride 1 with appropriate hydroxy-ester 2a-d and the subsequent deprotection of hydroxyl by means of aqueous ammonia yielded hydroxy-esters 3a-d. In the next step, acids 4a and 4b, which were synthesised as recently described [17], were reacted with hydroxy-esters 3a-c in a DCC-mediated reaction, resulting in reactive mesogens denoted as UKHG, UKHM, UVHG and UVHGET (see Figure 2).

Materials and Methods
This section contains a detailed description of the synthesis and confirmation of the molecular structures obtained for all of the designed reactive mesogens. Additionally, it provides the description of the experimental techniques used for the characterisation of the mesomorphic, thermal and structural properties.

Design and Synthesis
All starting materials and reagents were purchased from local ditributors of Sigma-Aldrich (Merck), Acros Organics or Fluorochem. Solvents used for the syntheses were "p.a." purity grade. 1 H NMR spectra were recorded on Varian VNMRS 300; deuteriochloroform (CDCl 3 ) was used as solvent and the signal of solvent served as the internal standard. Chemical shifts (δ) are given in ppm and spin-spin coupling constants (J) are given in Hz.
Newly designed reactive mesogens have been synthesised according to the synthetic route described in Figure 2. First, benzoyl chloride 1 and hydroxy-esters 2a-d were synthesised following the procedures from the literature [17]. The reaction of benzoyl chloride 1 with appropriate hydroxy-ester 2a-d and the subsequent deprotection of hydroxyl by means of aqueous ammonia yielded hydroxy-esters 3a-d. In the next step, acids 4a and 4b, which were synthesised as recently described [17], were reacted with hydroxy-esters 3a-c in a DCC-mediated reaction, resulting in reactive mesogens denoted as UKHG, UKHM, UVHG and UVHGET (see Figure 2). Synthesis of UTHH8 reactive mesogen was started from hydroxyester 3d, which was originally esterified with 4-formylbenzoic acid (5). Aldehyde 6 was then oxidized to benzoic acid 7 using potassium permanganate in pyridine. In the final step, acid 7 was esterified with 10-undecenol by means of DCC coupling.

-{[2-(Hexyloxy)-2-oxoethoxy]carbonyl}phenyl 4-hydroxybenzoate (3a)
Benzoyl chloride 1 (4.0 g, 18.64 mmol) dissolved in toluene (20 mL) was added dropwise to the stirred mixture of 2a (5.20 g, 18.55 mmol) and dry pyridine (8 mL) in toluene (70 mL). The reaction mixture was stirred for 6 h and then refluxed for 30 min. The resulting cooled mixture was filtered, and the filtrate was washed with diluted hydrochloric acid (100 mL, 5%) and water (100 mL). The separated organic layer was dried with anhydrous magnesium sulphate. After the evaporation of the solvent, the residue was dissolved in tetrahydrofuran (50 mL) and cooled to −20 • C. To this precooled solution, concentrated aqueous ammonia (10 mL, 25%, 64.19 mmol) was added, with constant stirring. The reaction mixture was stirred and let warm to room temperature, and the progress of the hydrolysis was monitored by TLC. After ca. 45 min, the resulting mixture was poured into water (100 mL) and neutralised with hydrochloric acid. The organic layer was separated, and the aqueous layer was extracted with diethylether (2 × 50 mL). Combined organic lay-ers were washed with water (50 mL) and dried over anhydrous sodium sulphate. Solvent was removed under reduced pressure and the oily residue was purified by chromatography on silica (dichloromethane:acetone (96:4)). Yield = 5.96 g (80%) of viscous liquid 3a.
Polymers 2021, 13, x 4 of Figure 2. General scheme for synthesis of new reactive mesogens with vinyl terminal group possessing the lateral substitution on the molecular core by the methyl and methoxy groups.
Synthesis of UTHH8 reactive mesogen was started from hydroxyester 3d, which w originally esterified with 4-formylbenzoic acid (5). Aldehyde 6 was then oxidized to be zoic acid 7 using potassium permanganate in pyridine. In the final step, acid 7 was est ified with 10-undecenol by means of DCC coupling.

4'-{[2-(Hexyloxy)-2-oxoethoxy]carbonyl}phenyl 4-hydroxybenzoate (3a)
Benzoyl chloride 1 (4.0 g, 18.64 mmol) dissolved in toluene (20 mL) was added dro wise to the stirred mixture of 2a (5.20 g, 18.55 mmol) and dry pyridine (8 mL) in tolue (70 mL). The reaction mixture was stirred for 6 h and then refluxed for 30 min. The resu ing cooled mixture was filtered, and the filtrate was washed with diluted hydrochlo acid (100 mL, 5%) and water (100 mL). The separated organic layer was dried with anh drous magnesium sulphate. After the evaporation of the solvent, the residue was d solved in tetrahydrofuran (50 mL) and cooled to −20 °C. To this precooled solution, co centrated aqueous ammonia (10 mL, 25%, 64.19 mmol) was added, with constant stirrin The reaction mixture was stirred and let warm to room temperature, and the progress the hydrolysis was monitored by TLC. After ca. 45 min, the resulting mixture was pour into water (100 mL) and neutralised with hydrochloric acid. The organic layer was sep rated, and the aqueous layer was extracted with diethylether (2 × 50 mL). Combined o ganic layers were washed with water (50 mL) and dried over anhydrous sodium sulpha Solvent was removed under reduced pressure and the oily residue was purified by ch matography on silica (dichloromethane:acetone (96:4)). Yield = 5.96 g (80%) of viscous l uid 3a. 1 9.89 mmol) and hydroxy-ester 3d (3.66 g, 9.88 mmol) was dissolved in tetrahydrofuran (50 mL) and cooled to 0 • C. Dicyclohexylcarbodiimide (DCC) (2.18 g, 10.35 mmol) and 4-(N,N-dimethylamino)pyridine (DMAP) (0.30 g, 2.46 mmol) were added, and the mixture was stirred for 3 h at room temperature. Precipitated N,N'-dicyclohexylurea was filtered off, and the resulting filtrate was washed with HCl (20 mL, 1:15) and water. The organic layer was dried with anhydrous sodium sulphate. Removal of the solvent under reduced pressure yielded benzoate 6 (4.72 g, 95%), which was utilised in the further step without additional purification. 1 (7) The solution of potassium permanganate (1.55 g, 9.81 mmol) in water (20 mL) at ca. 50 • C was added in two portions with a 15 min interval to the agitated solution of 4-formylbenzoate 6 (4.70 g, 9.35 mmol) in pyridine (50 mL), cooled to −10 • C by the ice-salt bath. After the last addition, the mixture was kept overnight at −20 • C and then it was slowly added to the mixture of the concentrated HCl (50 mL) in the ice-cold water (100 mL). The resulting suspension was neutralised by an additional amount of the concentrated HCl (ca. 18 mL) and filtered through the suction with a pad of celite. Filtered solid was boiled with acetone (100 mL) and filtered again. Macerate was dried with anhydrous sodium sulphate. The evaporation of acetone yielded crude 7, which was crystallised from hexane. Yield = 4.36 g (90%). 1  Ester 3a (1.0 g, 3.28 mmol) and acid 4a (1.31 g, 3.27 mmol) were dissolved in dry dichloromethane (50 mL) and cooled to 2-8 • C. Then, N,N -dicyclohexylcarbodiimide (DCC) (0.71 g, 3.40 mmol) and 4-(N,N-dimethylamino)pyridine (DMAP) (0.1 g, 0.82 mmol) were added. The mixture was stirred for six hours and then filtered. The resulting filtrate was evaporated, and the residue was purified by column chromatography (silica gel, dichloromethane:acetone, 99.7:0.3) and recrystallised from hexane to obtain 2.04 g (91%) of UKHG. 1

Experimental Methods and Techniques
The sequence of mesophases was determined by the observation of the characteristic textures and their changes in a polarising optical microscope (POM), Nikon Eclipse E600POL (Nikon, Tokyo, Japan). Planar cells (bookshelf geometry) of 12 µm thickness (glasses with indium tin oxide transparent electrodes (5 × 5 mm 2 ) were supplied by Military University of Technology (Warsaw, Poland)). The cells were filled with the studied material in the isotropic phase by means of capillary action. The texture observation on the samples with homeotropic alignment, e.g., free-standing films (FSF), was also performed; while preparing the FSF, the liquid crystalline material was mechanically spread over a circular hole (diameter 3 mm) in a metal plate placed in the hot stage. The heating/cooling stage Linkam LTS E350 (Linkam, Tadworth, UK) with a TMS 93 temperature programmer was used for the temperature control, which allows temperature stabilisation within ±0.1 K.
The phase transition temperatures were determined by differential scanning calorimetry (DSC) using a Perkin-Elmer DSC8000 calorimeter (PerkinElmer, Shelton, CT, USA). The samples of about 4-8 mg, hermetically sealed in aluminium pans, were placed into the calorimeter chamber filled with nitrogen. The calorimetric measurements were performed on cooling/heating runs at a rate of 5 K min −1 for the precise evaluation of the phase transition temperatures. The kinetics of the phase transition temperatures was studied with heating/cooling rates of 1, 2, 3, 5, 10, 20, 30, 40 and 50 K min −1 . The temperature and enthalpy change values were calibrated on the extrapolated onset temperatures and enthalpy changes of the melting points of water, indium and zinc.
X-ray diffraction (XRD) measurements were performed to determine the structural properties of the smectic mesophases. Experiments in the small diffraction angle range allowed the determination of the smectic layer spacing, d. A Bruker D8 Discover system was used (parallel beam of CuK α radiation, λ = 1.54 Å, formed by Goebel mirror, Anton Paar DCS 350 heating stage, scintillation detector), and the temperature stability was 0.1 K. Samples were prepared in the form of thin films on a heated surface. The smectic layer thickness was determined using Bragg's law: nλ = 2d sinθ, where n is a positive integer and θ is the angular position of the diffraction peak.

Results and Discussion
This section contains the experimental results obtained on several reactive mesogens with different molecular structure by POM, DSC and XRD techniques, together with the related discussion of the obtained results in terms of the molecular structure-mesomorphic property relationship.

Mesomorphic Behaviour
For the newly designed reactive mesogens, the sequences of mesophases were determined from the characteristic textures and their changes observed in a polarising optical microscope. The representative textures obtained by POM on planar samples and freestanding films are presented in Figure 3.  The phase transition temperatures and transition enthalpies were evaluated from DSC measurements, and the results are summarised in Table 1. The DSC plots of the second heating/cooling runs for the selected reactive mesogens are shown in Figure 4. The phase transition temperatures and transition enthalpies were evaluated from DSC measurements, and the results are summarised in Table 1. The DSC plots of the second heating/cooling runs for the selected reactive mesogens are shown in Figure 4. Table 1. Sequence of phases (PH) determined by POM, melting points (m.p.) and clearing points (c.p.) ( • C) measured upon heating, phase transition temperatures ( • C) measured upon cooling (10 K min −1 ) and respective enthalpy values ∆H (J · g −1 ) determined by DSC for the reactive mesogens. Symbol "-" represents if the phase does not exist.  For the UKHM mesogen with the methyl group as a lateral substituent and a branched terminal chain which is sterically unfavourable to create mesophases, the liquid crystalline behaviour was not detected. Nevertheless, it can potentially be utilised as a specific co-monomer for the design of the complex macromolecular materials. All the For the UKHM mesogen with the methyl group as a lateral substituent and a branched terminal chain which is sterically unfavourable to create mesophases, the liquid crystalline behaviour was not detected. Nevertheless, it can potentially be utilised as a specific comonomer for the design of the complex macromolecular materials. All the other mesogens clearly possess the liquid crystalline behaviour over a reasonably broad temperature range. The richest mesomorphic behaviour was detected for the UKHG reactive mesogen with the methyl lateral substituent in Y-position (see Figure 1). The nematic, the SmA and the SmC phases were clearly found upon cooling from the isotropic (Iso) phase. The non-substituted UTHH8 reactive mesogen exclusively possesses the smectic phases, namely the orthogonal SmA and the tilted SmC phases. Figure 3a-c shows the homeotropic textures of the detected smectic mesophases for the UTHH8 reactive mesogen obtained on the FSF.
It can be concluded that the lateral substitution placed at the Y-position on the specific molecular core (see Figure 1), in combination with the appropriate length of the chain far from the polymerisable vinyl group, makes the nematic phase favourable upon cooling from the isotropic phase. This is fully confirmed by two UVHG and UVHGET reactive mesogens which possess the nematic and the SmA phase upon cooling, while the tilted SmC phase was not detected for those two materials. While comparing those two mesogens with the lateral methoxy group, the shorter chain placed far from the polymerisable vinyl group results in an extension of the SmA phase temperature range upon cooling, while the melting point is found almost unaffected. The texture of the N-SmA phase transition for UVHG mesogen obtained on the planar sample is presented in Figure 3f. It was easy to obtain a very homogeneous alignment in the SmA phase for the UVHG reactive mesogen (see Figure 3g). The textures observed on the planar samples are presented in Figure 3d,e for the fan-shaped SmA phase and for the broken fan-shaped SmC phases. The tilted SmC phase was found to be fully monotropic (i.e., overcooled as it appears upon cooling only) for both UKHG and UTHH8 reactive mesogens. However, it can be expected that under definite conditions, the tilted SmC phase can be stabilised and even extended for the foreseen respective macromolecular materials after the polymerisation.
For the UKHG reactive mesogen, the kinetics of the phase transitions was checked using DSC measurements under several cooling rates, as presented in Figure 5, where a clear situation regarding the behaviour of the melting point is shown.
Polymers 2021, 13, x 11 of 18 temperature range. The richest mesomorphic behaviour was detected for the UKHG reactive mesogen with the methyl lateral substituent in Y-position (see Figure 1). The nematic, the SmA and the SmC phases were clearly found upon cooling from the isotropic (Iso) phase. The non-substituted UTHH8 reactive mesogen exclusively possesses the smectic phases, namely the orthogonal SmA and the tilted SmC phases. Figure 3a-c shows the homeotropic textures of the detected smectic mesophases for the UTHH8 reactive mesogen obtained on the FSF. It can be concluded that the lateral substitution placed at the Y-position on the specific molecular core (see Figure 1), in combination with the appropriate length of the chain far from the polymerisable vinyl group, makes the nematic phase favourable upon cooling from the isotropic phase. This is fully confirmed by two UVHG and UVHGET reactive mesogens which possess the nematic and the SmA phase upon cooling, while the tilted SmC phase was not detected for those two materials. While comparing those two mesogens with the lateral methoxy group, the shorter chain placed far from the polymerisable vinyl group results in an extension of the SmA phase temperature range upon cooling, while the melting point is found almost unaffected. The texture of the N-SmA phase transition for UVHG mesogen obtained on the planar sample is presented in Figure 3f. It was easy to obtain a very homogeneous alignment in the SmA phase for the UVHG reactive mesogen (see Figure 3g). The textures observed on the planar samples are presented in Figure 3d,e for the fan-shaped SmA phase and for the broken fan-shaped SmC phases. The tilted SmC phase was found to be fully monotropic (i.e., overcooled as it appears upon cooling only) for both UKHG and UTHH8 reactive mesogens. However, it can be expected that under definite conditions, the tilted SmC phase can be stabilised and even extended for the foreseen respective macromolecular materials after the polymerisation.
For the UKHG reactive mesogen, the kinetics of the phase transitions was checked using DSC measurements under several cooling rates, as presented in Figure 5, where a clear situation regarding the behaviour of the melting point is shown.  For this study, only the data from the second cooling runs were used. It has been found that the stability of all the mesophases slightly depends on the rate of cooling, which is quite obvious. While increasing the cooling rate, the Iso-N and N-SmA phase transition temperatures slightly decreased, and the stability of the phases increased, upon heating, the situation was the opposite (see Figure 6). However, the transition to the solid crystal (Cr) phase shows a clear sign of super-cooling [34,51], being more pronounced For this study, only the data from the second cooling runs were used. It has been found that the stability of all the mesophases slightly depends on the rate of cooling, which is quite obvious. While increasing the cooling rate, the Iso-N and N-SmA phase transition temperatures slightly decreased, and the stability of the phases increased, upon heating, the situation was the opposite (see Figure 6). However, the transition to the solid crystal (Cr) phase shows a clear sign of super-cooling [34,51], being more pronounced especially at cooling rates higher than 40 K. This effect is also related to the monotropic character of the lower temperature range of the SmA phase. especially at cooling rates higher than 40 K. This effect is also related to the monotropic character of the lower temperature range of the SmA phase.

Structural Properties
For three reactive mesogens exhibiting the smectic phases, the small-angle X-ray scattering measurements were performed in order to confirm the mesophase identification and to determine the smectic layer spacing. The results, namely the temperature dependence of the layer spacing, d, for UTHH8 (a), UVHG (b) and UKHG (c) reactive mesogens are presented in Figure 7. All studied materials exhibit a slight increase of d values in the SmA phase upon cooling, which results from the growing orientational order of the molecules and increasing number of all-trans molecular conformers. At the SmA-SmC phase transition, a typical drop in d values appears, caused by the tilting of the molecules with respect to the smectic layer normal in the SmC phase. Upon further cooling towards crystallisation, the tilt angle saturates and the layer spacing starts to increase due to the same factors as described above for the SmA phase (see Figure 7a for UTHH8 reactive mesogen).
For the calculation of the length of the reactive mesogen molecules in the energyoptimised conformation, the MOPAC/AM1 model was used. The resulting molecular structures with the principal axis of minimum moment of inertia, e.g., the long molecular axis, are shown in Table 2. Taking into account the most extended conformer, the length of the molecule, L, is found to be slightly higher than 42 Å for four of the studied materials; naturally, molecules of the UVHGET reactive mesogen with the short terminal chain are considerably shorter, L = 37.7 Å, than that for the other materials. For three reactive mesogens exhibiting the orthogonal SmA phase, namely UTHH8, UVHG and UKHG, the layer spacing was found to be slightly lower than the lengths of the respective most extended conformers, which can be explained by the non-perfect orientational order of the molecules in the smectic layers. We compared the non-substituted UTHH8 reactive mesogen with its substituted analogues, UVHG and UKHG, having the bulky methoxy and methyl lateral substituents, respectively. From the comparison, it can be concluded that the lateral substitution on the molecular core close to the alkyl chain with polymerisable vinyl group has only a minor impact on the resulting molecular shape. This might be because the layer spacing in the orthogonal SmA phase remains almost the same for those three reactive mesogens [40].

Structural Properties
For three reactive mesogens exhibiting the smectic phases, the small-angle X-ray scattering measurements were performed in order to confirm the mesophase identification and to determine the smectic layer spacing. The results, namely the temperature dependence of the layer spacing, d, for UTHH8 (a), UVHG (b) and UKHG (c) reactive mesogens are presented in Figure 7. All studied materials exhibit a slight increase of d values in the SmA phase upon cooling, which results from the growing orientational order of the molecules and increasing number of all-trans molecular conformers. At the SmA-SmC phase transition, a typical drop in d values appears, caused by the tilting of the molecules with respect to the smectic layer normal in the SmC phase. Upon further cooling towards crystallisation, the tilt angle saturates and the layer spacing starts to increase due to the same factors as described above for the SmA phase (see Figure 7a for UTHH8 reactive mesogen).
For the calculation of the length of the reactive mesogen molecules in the energyoptimised conformation, the MOPAC/AM1 model was used. The resulting molecular structures with the principal axis of minimum moment of inertia, e.g., the long molecular axis, are shown in Table 2. Taking into account the most extended conformer, the length of the molecule, L, is found to be slightly higher than 42 Å for four of the studied materials; naturally, molecules of the UVHGET reactive mesogen with the short terminal chain are considerably shorter, L = 37.7 Å, than that for the other materials. For three reactive mesogens exhibiting the orthogonal SmA phase, namely UTHH8, UVHG and UKHG, the layer spacing was found to be slightly lower than the lengths of the respective most extended conformers, which can be explained by the non-perfect orientational order of the molecules in the smectic layers. We compared the non-substituted UTHH8 reactive mesogen with its substituted analogues, UVHG and UKHG, having the bulky methoxy and methyl lateral substituents, respectively. From the comparison, it can be concluded that the lateral substitution on the molecular core close to the alkyl chain with polymerisable vinyl group has only a minor impact on the resulting molecular shape. This might be because the layer spacing in the orthogonal SmA phase remains almost the same for those three reactive mesogens [40].

Summary of the Results and Conclusions
Several new calamitic reactive mesogens, with vinyl terminal group with different length of flexible chains and with/without lateral substitution by the methyl and methoxy groups placed on the molecular core, have been designed and synthesised. Depending on the molecular structure, the reactive mesogens exhibit the nematic, orthogonal SmA and tilted SmC phases in a reasonably broad temperature range. The structure of the smectic mesophases has been confirmed by XRD measurements. The calculated length of the most extended conformer correlates well with the smectic layer spacing obtained experimentally. Lateral substitution by a bulky methoxy group on the molecule core deteriorated the arrangement of the molecules (UVHG and UVHGET), and only nematic and orthogonal SmA phases were detected. The lateral substitution by the methyl group on the molecular 42

Summary of the Results and Conclusions
Several new calamitic reactive mesogens, with vinyl terminal group with different length of flexible chains and with/without lateral substitution by the methyl and methoxy groups placed on the molecular core, have been designed and synthesised. Depending on the molecular structure, the reactive mesogens exhibit the nematic, orthogonal SmA and tilted SmC phases in a reasonably broad temperature range. The structure of the smectic mesophases has been confirmed by XRD measurements. The calculated length of the most extended conformer correlates well with the smectic layer spacing obtained experimentally. Lateral substitution by a bulky methoxy group on the molecule core deteriorated the arrangement of the molecules (UVHG and UVHGET), and only nematic and orthogonal SmA phases were detected. The lateral substitution by the methyl group on the molecular 37

Summary of the Results and Conclusions
Several new calamitic reactive mesogens, with vinyl terminal group with different length of flexible chains and with/without lateral substitution by the methyl and methoxy groups placed on the molecular core, have been designed and synthesised. Depending on the molecular structure, the reactive mesogens exhibit the nematic, orthogonal SmA and tilted SmC phases in a reasonably broad temperature range. The structure of the smectic mesophases has been confirmed by XRD measurements. The calculated length of the most extended conformer correlates well with the smectic layer spacing obtained experimentally. Lateral substitution by a bulky methoxy group on the molecule core deteriorated the arrangement of the molecules (UVHG and UVHGET), and only nematic and orthogonal SmA phases were detected. The lateral substitution by the methyl group on the molecular

Summary of the Results and Conclusions
Several new calamitic reactive mesogens, with vinyl terminal group with different length of flexible chains and with/without lateral substitution by the methyl and methoxy groups placed on the molecular core, have been designed and synthesised. Depending on the molecular structure, the reactive mesogens exhibit the nematic, orthogonal SmA and tilted SmC phases in a reasonably broad temperature range. The structure of the smectic mesophases has been confirmed by XRD measurements. The calculated length of the most extended conformer correlates well with the smectic layer spacing obtained experimentally. Lateral substitution by a bulky methoxy group on the molecule core deteriorated the arrangement of the molecules (UVHG and UVHGET), and only nematic and orthogonal SmA phases were detected. The lateral substitution by the methyl group on the molecular core had a very positive effect on the self-assembling behaviour (UKHG), and rich mesomorphic behaviour (N-SmA-SmC) was observed. While comparing the mesomorphic behaviour for UKHG and UVHG reactive mesogens differing by the substituent type only (i.e., CH 3 and CH 3 O, respectively), it is possible to conclude that the presence of a bulky methoxy group makes the tilted smectic phase unfavourable. However, a lateral methyl substitution in combination with a branched terminal chain (UKHM) fully suppressed the self-assembling behaviour of the resulting material with a given type of molecular core. The kinetics of the phase transitions for UKHG reactive mesogen has been studied in dependence on the heating/cooling rate of DSC runs. The resulting phase diagrams for the UKHG reactive mesogen clearly demonstrated a noticeable difference in the phase transition temperatures on the heating/cooling DSC rate. The Iso-N and N-SmA phase transition temperatures slightly decreased while increasing the cooling rate.
The reactive mesogens reported here with a functional vinyl terminal group can be further used as reactive mesogens, i.e., both the monomers and co-monomers, for the design of the smart self-assembling macromolecular materials, such as siloxane-based polymers, co-polymers and elastomers, exhibiting self-assembling behaviour favourable for various applications, including smart sensors [4,[52][53][54][55] as well as tunable liquid crystal micro-lens array [56], dynamic focusing micro-lens array [57] and spatial modulators for working in THz aimed for photonics and telecommunications systems [58].