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Article

Photoinduced Phase Transitions of Imine-Based Liquid Crystal Dimers with Twist–Bend Nematic Phases

by
Yuki Arakawa
* and
Yuto Arai
Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580, Aichi, Japan
*
Author to whom correspondence should be addressed.
Materials 2024, 17(13), 3278; https://doi.org/10.3390/ma17133278
Submission received: 30 May 2024 / Revised: 26 June 2024 / Accepted: 27 June 2024 / Published: 3 July 2024
(This article belongs to the Special Issue Structural and Physical Properties of Liquid Crystals)
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Abstract

:
Photoisomerizable molecules in liquid crystals (LCs) allow for photoinduced phase transitions, facilitating applications in a wide variety of photoresponsive materials. In contrast to the widely investigated azobenzene structure, research on the photoinduced phase-transition behavior of imine-based LCs is considerably limited. We herein report the thermal and photoinduced phase-transition behaviors of photoisomerizable imine-based LC dimers with twist–bend nematic (NTB) phases. We synthesize two homologous series of ester- and thioether-linked N-(4-cyanobenzylidene)aniline-based bent-shaped LC dimers with an even number of carbon atoms (n = 2, 4, 6, 8, and 10) in the central alkylene spacers, namely, CBCOOnSBA(CN) and CBOCOnSBA(CN), possessing oppositely directed ester linkages, C=OO and OC=O, respectively. Their thermal phase-transition behavior is examined using polarizing optical microscopy and differential scanning calorimetry. All dimers form a monotropic NTB phase below the temperature of the conventional nematic (N) phase upon cooling. Remarkably, the NTB phases of CBCOOnSBA(CN) (n = 2, 4, 6, and 8) and CBOCOnSBA(CN) (n = 6 and 8) supercool to room temperature and vitrify without crystallization. In addition, the phase-transition temperatures and entropy changes of CBCOOnSBA(CN) are lower than those of CBOCOnSBA(CN) at the same n. Under UV light irradiation, the NTB and N phases transition to the N and isotropic phases, respectively, and reversibly return to their initial LC phases when the UV light is turned off.

Graphical Abstract

1. Introduction

Photoisomerizable building blocks coupled with liquid crystals (LCs) have attracted considerable attention for a variety of applications such as optical storage [1,2,3,4], photomobile materials [5,6,7,8], photoalignments [9,10], and adhesion [11,12]. In particular, the azobenzene (Ph–N=N–Ph) structure is well-known for its mesogenic and reversible trans–cis isomerization abilities. The trans isomer, stable under ambient temperature, transforms into the cis isomer upon UV light irradiation [13], and the generated cis isomer reverts to the initial trans isomer upon irradiation with visible light or by heating. This trans-to-cis isomerization disorders the molecular arrangements in LC phases. Consequently, LC phases, such as nematic (N) [1,14], blue (BP) [15], layered smectic (Sm) [16], and columnar phases, [17] in trans azobenzenes transition to isotropic (Iso) phases, which reversibly return to the initial LC phases. However, some LC phases rearrange into other LC and chiral Iso phases [18,19,20,21]. Even solid crystals of certain azobenzenes can liquefy to the Iso phase [11,22]. These phenomena are known as the photoinduced (or light-induced) phase transitions for LCs. Additionally, photoisomerization of the azobenzene structures follows the Weigert effect. Upon irradiation with linearly polarized light, the molecular anisotropic polarization direction (long axis) of azobenzene becomes normal to that of the exposed light, thus inducing a change in the shape and surface of LC materials for the applications mentioned above.
Similarly, the rigid and anisotropic imine-based N-benzylideneaniline (Ph–CH=N–Ph) structure is a commonly used building block for LC molecules [23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43]. Similar to that of azobenzene, the –CH=N– imine bond in the N-benzylideneaniline structure undergoes reversible trans–cis isomerization upon irradiation with UV light [44,45,46]. The trans-to-cis isomerization of the imine bond requires more energy (~50–60 kcal mol−1) [46,47,48] than that of azobenzene (<~50 kcal mol−1) [7]. As a notable difference, the imine bond shows remarkably faster thermal back-relaxation from cis-to-trans forms than the azo bond. The energy barrier for the thermal back-relaxation of imine bonds (~16 kcal mol−1) is lower than those of azobenzene (~23 kcal mol−1) and structurally similar stilbene Ph–CH=CH–Ph (42 kcal mol−1), resulting in a short half-life of the cis isomer of the imine at ambient temperature [45,46]. Accordingly, the cis state of imine molecules can be detected by UV–visible spectroscopy only at low temperatures below –70 °C and not at ambient temperatures [45,46]. An advantage of N-benzylideneaniline over azobenzene is its transparency in the visible region, which is crucial for practical applications. However, the current research on the photoisomerization behaviors of N-benzylideneaniline-based LCs is considerably limited [49,50,51,52,53,54]. In the presence of N-benzylideneaniline-based molecules, the LC phases reversibly transition to Iso phases upon UV light irradiation [53,54]. Kawatsuki and Kondo et al. investigated the photoisomerization of N-benzylideneaniline-based LC polymers for photoreorientation and adhesion applications [49,50,51,52,53]. Hu and Yu recently reported a solid-to-liquid phase transition of N-benzylideneaniline with asymmetric alkyl chain substitution [54]. In addition to the photoisomerizability, Terentjev et al. demonstrated the applicability of the bond exchangeable ability of N-benzylideneaniline embedded in LC elastomers [55]. Therefore, the use of N-benzylideneaniline for LCs has been continuously increasing.
Over the last decade, the helical twist–bend nematic (NTB) phase for bent molecules has gained widespread interest in LC science [56,57,58]. The NTB phase exhibits heliconical structures with pitches in the range of several to tens of nanometers, generated by the precession of bent molecules [59,60,61]. The heliconical structures of the NTB phase form pseudo-layers, making the physical properties of this phase more similar to those of layered Sm phases than to the conventional N phase [62,63,64,65]. The majority of the NTB phase is observed for bent LC dimers composed of two mesogenic arms linked via a central spacer with an odd number of total atoms along the spacer [66,67,68,69,70,71]. The molecular biaxialities of the bent dimers can be associated with NTB phase induction [72]. Twist–bend nematogenic bent dimers are also useful for photonic applications with wavelength or color tunability [73,74]. The photoinduced phase-transition behavior of the NTB phase has been evaluated for azobenzene-based LC dimers [75,76]. Under moderate UV irradiation, the NTB phase transitions to the conventional N phase, exhibiting reversibility when the light is switched on and off [75]. Owing to the Weigert effect, the molecular and helical axes of the NTB phase can be oriented perpendicular to the polarization direction of the polarized linear light [76]. However, to the best of our knowledge, the photoinduced phase-transition behaviors of the LC phases for imine-based LC dimers have not been reported to date.
We herein report the synthesis and thermal and photoinduced phase-transition behaviors for the N and NTB phases of N-benzylideneaniline-based LC dimers. We synthesized two new homologous series of oppositely directed ester- and thioether-linked N-(4-cyanobenzylidene)aniline- and 4-cyanobiphenyl-based dimers [CBCOOnSBA(CN) and CBOCOnSBA(CN)] with even-numbered alkylene spacers (n = 2, 4, 6, 8, and 10) and total odd number of atoms to obtain bent molecular shapes (Figure 1c). The series differs in the ester linkage directions, viz., C=OO or OC=O for CBCOOnSBA(CN) and CBOCOnSBA(CN), respectively. We previously reported two homologous series of oppositely directed ester- and thioether-linked cyanobiphenyl LC dimers, CBCOOnSCB and CBOCOnSCB, as given in Figure 1a [33,77]. These dimers exhibit the NTB phases, which can be stably cooled to the ambient temperature and vitrified; however, their phase-transition behaviors, helical pitches, and viscoelastic properties differ substantially owing to the ester directions [33,77,78,79]. Furthermore, thioether-linked N-(4-cyanobenzylidene)aniline- and 4-cyanobiphenyl-based bent dimers, CBSnSBA(CN) (Figure 1b) exhibit stable and vitrifiable NTB phases [34]. In this context, we designed N-(4-cyanobenzylidene)aniline-containing LC dimers with thioether and oppositely directed ester linkages for new twist–bend nematogens to elucidate their thermal and photoinduced phase-transition behaviors. The thermal phase-transition behavior was evaluated using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). Additionally, POM was used to analyze the photoinduced phase transitions via UV irradiation of the LC phases.

2. Materials and Methods

All chemicals were commercially available and used as received. The synthetic scheme for the two homologous series is outlined in Scheme 1. The molecular structures were characterized by 1H and 13C nuclear magnetic resonance (NMR) spectroscopies using JEOL JNM-ECS400 (400 and 100 MHz for 1H and 13C NMR, respectively) or JEOL JNM-ECX500 (500 and 125 MHz for 1H and 13C NMR, respectively) spectrometers. The synthetic procedures and characterization data are provided in Supporting Information. The thermal phase transitions and phase identification were evaluated by POM using an Olympus BX50 optical microscope equipped with a Linkam temperature controller (LK-600PM). For planar and uniaxial alignment observation, polyimide surface cells with thicknesses of 1 and 7 µm were obtained from EHC Co., Ltd. (Hachioji-shi, Japan). The phase-transition temperatures and associated enthalpy changes were determined using a Shimadzu DSC-60 Plus at a rate of 10 °C min−1 under a nitrogen gas flow rate of 50 mL min−1 and liquid nitrogen (Liq. N2) was added for cooling. Indium was used for calibration. The photoinduced phase-transition behavior was observed using POM upon UV light irradiation. The 365-nm UV light from the outer light source (Asahi Spectra LAX-C100) was reflected by a dichroic half mirror inserted in an Olympus BX53M optical microscope, which was exposed to the LC samples in the non-treated glass cells with two pieces of commercial glass on a Mettler Toledo HS82 hot-stage system. The UV light intensity (approximately 3 mW cm−2) was monitored at each sample height using an Ushio UIT-201 digital UV intensity meter equipped with an Ushio photodetector UVD-365PD. The UV–visible absorption spectra for both homologous series with n = 6 were recorded in tetrahydrofuran (THF) using a JASCO V-630 UV–visible spectrophotometer.

3. Results and Discussion

3.1. Thermal Phase Transitions

The melting temperatures (Tm) upon heating, Iso–N phase transition (TIN), N–NTB phase-transition (TNNTB), glass transition (Tg), and crystallization (TCr) temperatures upon cooling, along with their associated enthalpy changes (ΔH) for CBCOOnSBA(CN) are listed in Table 1. Upon heating, the shorter spacer CBCOOnSBA(CN) homologs (n = 2, 4, and 6) did not exhibit LC phases, whereas longer spacers (n = 8 and 10) formed the conventional N phase. All the CBCOOnSBA(CN) homologs exhibited NTB and N phases upon cooling. The NTB phase was identified by blocky (Figure 2a), striped (Figure 2b), focal-conic-like, or rope-like (Figure 2c) textures in the non-treated glass cells as shown for n = 6, 8, and 10, respectively. Specifically, blocky textures were often observed beneath the N–NTB phase transition, as shown in Figure 2a. Shearing the cells led to striped textures along the shear direction, as shown in Figure 2b. This behavior is attributed to the Helfrich–Hurault mechanism of the pseudo-layered NTB phase [63,80].
The optical texture of the NTB phase of CBCOO2SBA(CN) was not as regular in the non-treated glass cells, as shown in Figure 3a. POM using uniaxially rubbed planar alignment cells with 1- and 7-µm thicknesses show lines or thin stripes growing along the rubbing direction, as shown in Figure 3b,c, respectively. The stripes for a 7-µm-thick cell were wider and clearer than those for a 1-µm-thick one, which could be attributed to the Helfrich–Hurault-like instability of the pseudo-layer nature of the NTB phase [80]. The stripes of CBCOO2SBA(CN) were relatively thinner and more ambiguous than those of typical stripes, which could be attributed to its high viscoelastic properties, as observed for the structurally similar cyanobiphenyl dimer CBCOO4SCB, exhibiting similar textural behaviors [79].
The N–NTB phase-transition peaks of all the CBCOOnSBA(CN) dimers were detected by DSC, as shown in Figure 4. The shapes of the N–NTB phase-transition peaks suggest that they are first-order for shorter spacer CBCOOnSBA(CN) dimers (n < 8), which could be attributed to the strong molecular biaxiality (molecular bend) of these dimers owing to the small bond angle of the C–C(=O)–O ester linkage and the shorter spacer, as reported previously [33,77,78,79]. The rigidity of the C–C(=O)–O ester linkage may also help to enhance their molecular biaxiality for the shorter spacer in terms of narrower plausible conformation distributions.
The phase-transition results for CBOCOnSBA(CN) are listed in Table 2. Upon heating, the CBOCOnSBA(CN) homologs (n = 4, 6, 8, and 10) showed the N phase, whereas CBOCO2SBA(CN) did not exhibit the LC phase. All the homologs exhibited the NTB and N phases upon cooling, similar to the CBCOOnSBA(CN) homologs. The NTB phase was characterized by typical blocky, striped, and focal-conic-like and rope-like textures in the non-treated glass cells for n = 4, 6, and 8, respectively, as shown in Figure 5, which are similar to those of CBCOOnSBA(CN). Figure 6 shows the DSC curves for CBCOOnSBA(CN) upon cooling. The shorter-spacer CBOCOnSBA(CN) dimers (n = 2 and 4) crystallized from the conventional N phase during DSC, and the crystallization peaks cover the N–NTB phase-transition peaks upon cooling in Figure 6. Therefore, their TNNTB values were determined by POM. Figure 6 reveals the NTB phase of CBOCOnSBA(CN) with n = 6 and 8 vitrified at approximately 10 °C. CBCOO10nSBA(CN) crystallized from the NTB phase.
The TIN, TNNTB, and Tg values of CBCOOnSBA(CN) and CBOCOnSBA(CN) upon cooling are plotted as a function of temperature in Figure 7a and Figure 7b, respectively. Notably, the TIN values of CBCOOnSBA(CN) are remarkably lower than those of CBOCOnSBA(CN), which is similar to the difference in those of previously reported CBCOOnSCB and CBOCOnSCB [33,77]. This behavior could be attributed to a more bent molecular shape of CBCOOnSBA(CN) or a more anisotropic one of CBOCOnSBA(CN) [33,77]. The Ar–C–O bond angle in the COO ester linkage (109°) is smaller than that of Ar–O–C in the OCO-ester linkage, similar to Ar–O–C in the ether linkage. The smaller Ar–C–O bond angle results in a more bent molecular shape for CBCOOnSBA(CN) compared to that for CBOCOnSBA(CN). The more rigid COO ester than OCO facilitates the stronger biaxiality of CBCOOnSBA(CN) than that of CBOCOnSBA(CN) [33,77]. The entropy changes (ΔSIN/R) at the I–N phase transition upon cooling scaled by the gas constant (R = 8.31 J K−1 mol−1), which are indicators of the molecular biaxiality [81], are plotted as a function of n in Figure 8. The ΔSIN/R values are remarkably lower for CBCOOnSBA(CN) than that for CBOCOnSBA(CN), indicating the stronger biaxiality or considerably more molecular bending of CBCOOnSBA(CN).
In contrast, the TNNTB values of both the homologous series are comparable. A bent geometry is advantageous, whereas a more linear molecular shape more likely to stabilize the conventional N phase. Inducing the NTB phase in CBOCOnSBA(CN) requires more supercooled conditions from the N phase upon cooling compared with inducing this phase in the more bent CBCOOnSBA(CN) [34,82]. Accordingly, the TNNTB values of more linear CBOCOnSBA(CN) are comparable to those of more bent CBCOOnSBA(CN), in contrast to the trend observed for TIN values between both series. Table 1 and Table 2 reveal that the TNNTB/TIN values used to indicate the supercooling degree of the NTB phase formation from TIN [83] are lower for CBOCOnSBA(CN) (0.82–0.85) than those for CBCOOnSBA(CN) (0.88–0.95).
The TIN and TNNTB values of CBCOOnSBA(CN) decrease with decreasing n values from 10 to 4 and marginally increase at n = 2. This reduction could be ascribed to the enhanced effective molecular biaxiality or molecular bend for the shorter n and is partly supported by the ΔSIN/R trend, which decreases with descending n. The exception for n = 2 could be attributed to its high rigidity owing to its short spacers.
However, the trends of TIN and TNNTB values as a function of n for CBOCOnSBA(CN) differ from those for CBCOOnSBA(CN). Specifically, the TIN and TNNTB values of CBOCOnSBA(CN) are comparable or marginally increase with decreasing n and suddenly decrease at the shortest spacer (n = 2). These trends resemble those of the structurally similar cyanobiphenyl-based CBOCOnSCB [77] and ether-linked CBOnOCB [84]. The bond angle of Ar–O–C in the OCO-ester is similar to the ~118° bond angle in ether. Therefore, trends for n of OCO-ester-linked dimers are similar to those of ether-linked ones in terms of the molecular shape (bend). The TIN and TNNTB values of the OCO-ester-linked and ether-linked dimers with shorter spacers are expected to be compensated by molecular anisotropy and flexibility owing to the Ar–O–C ether bond. More anisotropy increases TIN, whereas more flexibility is likely to widen the conformations and distort the effective molecular bent shape of OCO-linked dimers compared to those of the more bent COO-linked dimers.

3.2. Photoinduced Phase Transitions

The UV–visible spectra of n = 6 for both series before UV irradiation recorded in dilute THF solutions are shown in Figure 9. These spectra are similar, exhibiting two main absorption peaks. A main band was observed at approximately 370 nm, attributed to the π–π* transition of the benzylideneaniline moiety [34]. Because of the presence of the thioether linkage and cyano group, the absorption wavelengths from the π–π* transitions are red-shifted compared to around 310 nm of typical benzylideneanilines [85,86]. In addition, a peak at approximately 265 nm in their spectra may be ascribed to the σ–π* transition of the benzylideneaniline moiety [85,86] and the π–π* transition of the cyanobiphenyl moiety [87]. These results agree with those of previously reported thioether-linked N-benzylideneaniline-based LC dimers [34].
The photoinduced phase transitions of CBCOOnSBA(CN) and CBOCOnSBA(CN) were examined by irradiating UV light (365 nm and approximately 3 mW cm−2) to the N and NTB phases of these dimers. This applied wavelength of the light source is appropriate as the UV–visible absorption is observed at approximately 370 nm for the π–π* transition of the benzylideneaniline moiety in both dimers. The optical textures of the LC phases of CBCOO6SBA(CN) when the UV light is turned on and off are shown in Figure 10. Upon UV irradiation, the birefringent N phase texture changed to the dark textures of the Iso phase, and the birefringent texture recovered after turning off the UV light, shown in Figure 10a,b, indicating a reversible photoinduced phase transition between the N and Iso phases. However, UV irradiation turned the blocky textures of the NTB phase into the marble texture of the N phase, which then reversibly returned to the initial NTB phase texture after the UV irradiation was turned off, as shown in Figure 10c,d. This behavior revealed a reversible photoinduced phase transition between the NTB and N phases. These photoinduced phase transition behaviors are similar to those observed for azobenzene-based twist–bend nematogenic dimers [75,76]. To the best of our knowledge, this is the first report of photoinduced phase transitions in imine-based LC dimers. However, the temperature ranges for the transitions under UV light were strictly limited to 1 °C below the corresponding N or Iso phases. Similar azobenzene-based dimers exhibited photoinduced phase transitions within wider temperature ranges (~10 °C) using the same UV irradiation source. This difference could be ascribed to the energies of the isomerization process, as described in Section 1. The energy barrier of the trans-to-cis isomerization for the imine bond is higher than that of the azo bond [46,47,48], which may prevent the imine bond isomerization at lower temperatures and narrow the possible photoinduced phase-transition temperature ranges. Additionally, the cis-to-trans relaxation of the imine bond is remarkably faster owing to its lower energy barrier (~16 kcal mol−1) compared to that of azobenzene (23 kcal mol−1) [45]. We also recorded the UV-visible spectra of the samples in a THF solution subjected to UV irradiation for 1–15 min at room temperature. No changes were observed in the UV–visible spectra, indicating that the N-benzylideneaniline moieties exist in the trans form after UV irradiation, which agrees with the previously reported results [45,46]. One possibility is that the N–Iso and NTB–N phase transitions of the imine-based dimers upon UV–light irradiation might have been caused by the heat generated during the UV irradiation, considering their limited temperature windows. However, the texture changed reversibly soon after switching on and off the light. In addition, extending the UV irradiation time caused neither further changes in textures nor expansion of the area. Therefore, the phase transitions upon UV irradiation could have been driven by the photoisomerization of the imine bond. Owing to the limitations of the apparatus, we could not use incident light higher than approximately 3 mW cm−2. High-intensity light may expand the temperature range of photoinduced phase transitions and lead to the NTB–Iso phase transition, as observed for an azobenzene dimer [75].

4. Conclusions

We synthesized two homologous series of N-(4-cyanobenzylidene)aniline and cyanobiphenyl-based LC dimers with thioether and inverse ester linkages (COO and OCO, respectively). The dimers formed a monotropic NTB phase below the temperature of the conventional N phase. Remarkably, the NTB phases of certain CBCOOnSBA(CN) and CBOCOnSBA(CN) homologs were stably supercooled to ambient temperatures and vitrified. The LC phase-transition temperatures (TIN and TNNTB) and associated entropy changes (ΔSIN) of the CBCOOnSBA(CN) homologs were lower than those of the CBOCOnSBA(CN) homologs at the same n, which could be attributed to the more bent molecular geometry of the CBCOOnSBA(CN). UV irradiation transformed the NTB and N phases of the dimers into the N and Iso phases, respectively. These phases reversibly returned to their initial phases after turning off the UV light. This study successfully demonstrates the photoinduced phase transitions of N-benzylideneaniline-based LC dimers with the NTB phases, which show a remarkable potential for photomobile LC materials.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/ma17133278/s1.

Author Contributions

Conceptualization, Y.A. (Yuki Arakawa); Methodology, Y.A. (Yuki Arakawa); Validation, Y.A. (Yuki Arakawa); Formal analysis, Y.A. (Yuki Arakawa); Investigation, Y.A. (Yuki Arakawa) and Y.A. (Yuto Arai); Resources, Y.A. (Yuki Arakawa); Data curation, Y.A. (Yuki Arakawa); Writing—Original Draft Preparation, Y.A. (Yuki Arakawa); Writing—Review and Editing, Y.A. (Yuki Arakawa) and Y.A. (Yuto Arai); Visualization, Y.A. (Yuki Arakawa); Supervision, Y.A. (Yuki Arakawa); Project Administration, Y.A. (Yuki Arakawa); Funding Acquisition, Y.A. (Yuki Arakawa). All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by JSPS KAKENHI Grant number 20K15351.

Data Availability Statement

Data are presented in the article and Supplementary Materials.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Tazuke, S.; Kurihara, S.; Ikeda, T. Amplified image recording in liquid crystal media by means of photochemically triggered phase transition. Chem. Lett. 1987, 16, 911–914. [Google Scholar] [CrossRef]
  2. Eich, M.; Wendorff, J.H.; Reck, B.; Ringsdorf, H. Reversible digital and holographic optical storage in polymeric liquid crystals. Makromol. Chem. Rapid Commun. 1987, 8, 59–63. [Google Scholar] [CrossRef]
  3. Ikeda, T.; Tsutsumi, O. Optical switching and image storage by means of azobenzene liquid-crystal films. Science 1995, 268, 1873–1875. [Google Scholar] [CrossRef]
  4. Rochon, P.; Batalla, E.; Natansohn, A. Optically induced surface gratings on azoaromatic polymer films. Appl. Phys. Lett. 1995, 66, 136–138. [Google Scholar] [CrossRef]
  5. Finkelmann, H.; Nishikawa, E.; Pereira, G.G.; Warner, M. A new opto-mechanical effect in solids. Phys. Rev. Lett. 2001, 87, 015501. [Google Scholar] [CrossRef]
  6. Yu, Y.; Nakano, M.; Ikeda, T. Directed bending of a polymer film by light. Nature 2003, 425, 145. [Google Scholar] [CrossRef]
  7. Mahimwalla, Z.; Yager, K.G.; Mamiya, J.I.; Shishido, A.; Priimagi, A.; Barrett, C.J. Azobenzene photomechanics: Prospects and potential applications. Polym. Bull. 2012, 69, 967–1006. [Google Scholar] [CrossRef]
  8. Lugger, S.J.; Ceamanos, L.; Mulder, D.J.; Sánchez-Somolinos, C.; Schenning, A.P.H.J. 4D printing of supramolecular liquid crystal elastomer actuators fueled by light. Adv. Funct. Mater. 2023, 8, 2201472. [Google Scholar] [CrossRef]
  9. Ichimura, K.; Suzuki, Y.; Seki, T.; Hosoki, A.; Aoki, K. Reversible change in alignment mode of nematic liquid crystals regulated photochemically by command surfaces modified with an azobenzene monolayer. Langmuir 1988, 4, 1214–1216. [Google Scholar] [CrossRef]
  10. Fukuhara, K.; Nagano, S.; Hara, M.; Seki, T. Free-surface molecular command systems for photoalignment of liquid crystalline materials. Nat. Commun. 2014, 5, 3320. [Google Scholar] [CrossRef]
  11. Akiyama, H.; Kanazawa, S.; Okuyama, Y.; Yoshida, M.; Kihara, H.; Nagai, H.; Norikane, Y.; Azumi, R. Photochemically reversible liquefaction and solidification of multiazobenzene sugar-alcohol derivatives and application to reworkable adhesives. ACS Appl. Mater. Interfaces 2014, 6, 7933–7941. [Google Scholar] [CrossRef]
  12. Wu, Z.; Ji, C.; Zhao, X.; Han, Y.; Müllen, K.; Pan, K.; Yin, M. Green-light-triggered phase transition of azobenzene derivatives toward reversible adhesives. J. Am. Chem. Soc. 2019, 141, 7385–7390. [Google Scholar] [CrossRef]
  13. Hartley, G.S. The cis-form of azobenzene. Nature 1937, 140, 281. [Google Scholar] [CrossRef]
  14. Tsutsumi, O.; Shiono, T.; Ikeda, T.; Galli, G. Photochemical phase transition behavior of nematic liquid crystals with azobenzene moieties as both mesogens and photosensitive chromophores. J. Phys. Chem. B 1997, 101, 1332–1337. [Google Scholar] [CrossRef]
  15. Wen, Y.; Zheng, Z.; Wang, H.; Shen, D. Photoinduced phase transition behaviours of the liquid crystal blue phase doped with azobenzene bent-shaped molecules. Liq. Cryst. 2012, 39, 509–514. [Google Scholar] [CrossRef]
  16. Ikeda, T. Photomodulation of liquid crystal orientations for photonic applications. J. Mater. Chem. 2003, 13, 2037–2057. [Google Scholar] [CrossRef]
  17. Yamamoto, T.; Nishiyama, I.; Yokoyama, H.H. Novel photoinduced phase transition observed in three-dimensional liquid-crystalline phase of azobenzene compound. Chem. Lett. 2007, 36, 1108–1109. [Google Scholar] [CrossRef]
  18. Hori, R.; Furukawa, D.; Yamamoto, K.; Kutsumizu, S. Light-driven phase transition in a cubic-phase-forming binary system composed of 4′-n-Docosyloxy-3′-nitrobiphenyl-4-carboxylic acid and an azobenzene derivative. Chem. Eur. J. 2012, 18, 7346–7350. [Google Scholar] [CrossRef]
  19. Alaasar, M.; Poppe, S.; Dong, Q.; Liu, F.; Tschierske, C. Isothermal chirality switching in liquid-crystalline azobenzene compounds with non-polarized light. Angew. Chem. Int. Ed. 2017, 56, 10801–10805. [Google Scholar] [CrossRef]
  20. Wang, M.; Hu, W.; Wang, L.; Guo, D.Y.; Lin, T.H.; Zhang, L.; Yang, H. Reversible light-directed self-organized 3D liquid crystalline photonic nanostructures doped with azobenzene-functionalized bent-shaped molecules. J. Mater. Chem. C 2018, 6, 7740–7744. [Google Scholar] [CrossRef]
  21. Alaasar, M.; Cai, X.; Kraus, F.; Giese, M.; Liu, F.; Tschierske, C. Controlling ambidextrous mirror symmetry breaking in photosensitive supramolecular polycatenars by alkyl-chain engineering. J. Mol. Liq. 2022, 351, 118597. [Google Scholar] [CrossRef]
  22. Norikane, Y.; Hirai, Y.; Yoshida, M. Photoinduced isothermal phase transitions of liquid-crystalline macrocyclic azobenzenes. Chem. Commun. 2011, 47, 1770–1772. [Google Scholar] [CrossRef]
  23. Goldmacher, J.; Barton, L.A. Liquid crystals. I. Fluorinated anils. J. Org. Chem. 1967, 32, 476–477. [Google Scholar] [CrossRef]
  24. Castellano, J.A.; Goldmacher, J.E.; Barton, L.A.; Kane, J.S. Liquid crystals. II. Effects of terminal group substitution on the mesomorphic behavior of some benzylideneanilines. J. Org. Chem. 1968, 33, 3501–3504. [Google Scholar] [CrossRef]
  25. Kitamura, T.; Mukoh, A.; Isogai, M.; Inukai, T.; Furukawa, K.; Terashima, K. Synthesis and some properties of low melting ferroelectric liquid crystals of benzylidene anilines. Mol. Cryst. Liq. Cryst. 1986, 136, 167–173. [Google Scholar] [CrossRef]
  26. Date, R.W.; Imrie, C.T.; Luckhurst, G.R.; Seddon, J.M. Smectogenic dimeric liquid crystals. The preparation and properties of the α, ω-bis (4-n-alkylanilinebenzylidine-4′-oxy) alkanes. Liq. Cryst. 1992, 12, 203–238. [Google Scholar] [CrossRef]
  27. Blumstein, A.; Blumstein, R.B.; Clough, S.B.; Hsu, E.C. Oriented polymer growth in thermotropic mesophases. Macromolecules 1975, 8, 73–76. [Google Scholar] [CrossRef]
  28. Niori, T.; Sekine, T.; Watanabe, J.; Furukawa, T.; Takezoe, H. Distinct ferroelectric smectic liquid crystals consisting of banana shaped achiral molecules. J. Mater. Chem. 1996, 6, 1231–1233. [Google Scholar] [CrossRef]
  29. Paul, M.K.; Saha, S.K.; Kalita, G.; Bhattacharya, B.; Sarkar, U. Low-temperature nematic phase in azo functionalised reactive hockey stick mesogens possessing lateral methyl group. Dyes Pigm. 2020, 173, 107233. [Google Scholar] [CrossRef]
  30. Yeap, G.Y.; Ha, S.T.; Lim, P.L.; Boey, P.L.; Ito, M.M.; Sanehisa, S.; Youhei, Y. Synthesis, physical and mesomorphic properties of Schiff’s base esters containing ortho-, meta- and para-substituents in benzylidene-4′-alkanoyloxyanilines. Liq. Cryst. 2006, 33, 205–211. [Google Scholar] [CrossRef]
  31. Kosaka, Y.; Kato, T.; Uryu, T. Synthesis and the smectic mesophase of copolymers containing a mesogenic (carbazolylmethylene) aniline group as the electron donor and a (4’-nitrobenzylidene) aniline group as the electron acceptor. Macromolecules 1994, 27, 2658–2663. [Google Scholar] [CrossRef]
  32. Fritsch, L.; Lavayen, V.; Merlo, A.A. Photochemical behaviour of Schiff base liquid crystals based on isoxazole and isoxazoline ring. A kinetic approach. Liq. Cryst. 2018, 45, 1802–1812. [Google Scholar] [CrossRef]
  33. Arakawa, Y.; Komatsu, K.; Inui, S.; Tsuji, H. Thioether-linked liquid crystal dimers and trimers: The twist-bend nematic phase. J. Mol. Struct. 2020, 1199, 126913. [Google Scholar] [CrossRef]
  34. Arakawa, Y.; Ishida, Y.; Komatsu, K.; Arai, Y.; Tsuji, H. Thioether-linked benzylideneaniline-based twist-bend nematic liquid crystal dimers: Insights into spacer lengths, mesogenic arm structures, and linkage types. Tetrahedron 2021, 95, 132351. [Google Scholar] [CrossRef]
  35. Perju, E.; Marin, L. Mesomorphic behavior of symmetric azomethine dimers containing different chromophore groups. Molecules 2021, 26, 2183. [Google Scholar] [CrossRef]
  36. Cruickshank, E.; Walker, R.; Strachan, G.J.; Goode, C.H.; Majewska, M.M.; Pociecha, D.; Gorecka, E.; Storey, J.M.; Imrie, C.T. The influence of the imine bond direction on the phase behaviour of symmetric and non-symmetric liquid crystal dimers. J. Mol. Liq. 2023, 391, 123226. [Google Scholar] [CrossRef]
  37. Chakraborty, A.; Bhattacharjee, D.; Alapati, P.R.; Bhattacharjee, A. Theoretical investigation of N (pn alkyloxy benzylidene) pn alkyl aniline Schiff-based liquid crystal molecule. Phys. Rev. B Condens. Matter 2024, 681, 415857. [Google Scholar] [CrossRef]
  38. Omar, A.Z.; El-Atawy, M.A.; Alsubaie, M.S.; Alazmi, M.L.; Ahmed, H.A.; Hamed, E.A. Synthesis and computational investigations of new thioether/azomethine liquid crystal derivatives. Crystals 2023, 13, 378. [Google Scholar] [CrossRef]
  39. Katariya, K.; Patil, J.; Nakum, K.; Nada, S.; Hagar, M.; Soni, R. Biphenyl based Schiff base derivatives of 6-aminocoumarin: Design, synthesis, mesomorphic properties and DFT studies. J. Mol. Struct. 2024, 1311, 138395. [Google Scholar] [CrossRef]
  40. Martínez, D.; Schlossarek, T.; Würthner, F.; Soberats, B. Isothermal phase transitions in liquid crystals driven by dynamic covalent chemistry. Angew. Chem. Int. Ed. 2024, 63, e202403910. [Google Scholar] [CrossRef] [PubMed]
  41. Chakraborty, A.; Bhattacharjee, D.; Bhattacharjee, A. Exploring odd-even sensitivity in m.OnO.m liquid crystal compounds: A comprehensive study using DFT analysis. J. Mol. Liq. 2024, 403, 124800. [Google Scholar] [CrossRef]
  42. Soni, R.; Nakum, K.J.; Katariya, K.D.; Gergis, M.; Hagar, M.; Sharma, V.S. Biphenyls embedded Schiff base-bis esters: Self-assembling behaviour, impact of additional aromatic ring and ester linkage and their DFT investigations. Liq. Cryst. 2024. [Google Scholar] [CrossRef]
  43. Rabari, M.; Bhatt, M.; Prajapati, A.K. Symmetrical liquid crystalline dimers containing azo and azomethine linkages: Synthesis, characterisation, mesomorphic study and DFT studies. Liq. Cryst. 2024. [Google Scholar] [CrossRef]
  44. Kuhn, R.; Weitz, H.M. Photochemistry of triphenylformazan. Chem. Ber. 1953, 86, 1199–1212. [Google Scholar] [CrossRef]
  45. Fischer, E.; Frei, Y. Photoisomerization equilibria involving the C=N Double bond. J. Chem. Phys. 1957, 27, 808–809. [Google Scholar] [CrossRef]
  46. Maeda, K.; Fischer, E. Photoformation of “Z”(cis) isomers in diaryl- and triaryl-Azomethines, Part II. 1 electronic and NMR spectra of methyl derivatives of benzylideneaniline (C6H5—CH= N—C6H5). Isr. J. Chem. 1977, 16, 294–298. [Google Scholar] [CrossRef]
  47. Gahl, C.; Brete, D.; Leyssner, F.; Koch, M.; McNellis, E.R.; Mielke, J.; Carley, R.; Grill, L.; Reuter, K.; Tegeder, P.; et al. Coverage- and temperature-controlled isomerization of an imine derivative on Au(111). J. Am. Chem. Soc. 2013, 135, 4273–4281. [Google Scholar] [CrossRef] [PubMed]
  48. Chakraborty, A.; Chakraborty, S.; Ganguly, T. Photoisomerization within a novel synthesized photoswitchable dyad: Experimental and theoretical approaches. Ind. J. Phys. 2013, 87, 1113–1120. [Google Scholar] [CrossRef]
  49. Kawatsuki, N.; Matsushita, H.; Kondo, M.; Sasaki, T.; Ono, H. Photoinduced reorientation and polarization holography in a new photopolymer with 4-methoxy-N-benzylideneaniline side groups. APL Mater. 2013, 1, 022103. [Google Scholar] [CrossRef]
  50. Kawatsuki, N.; Matsushita, H.; Washio, T.; Kozuki, J.; Kondo, M.; Sasaki, T.; Ono, H. Photoinduced orientation of photoresponsive polymers with N-benzylideneaniline derivative side groups. Macromolecules 2014, 47, 324–332. [Google Scholar] [CrossRef]
  51. Kawatsuki, N.; Miyake, K.; Kondo, M. Facile fabrication, photoinduced orientation, and birefringent pattern control of photoalignable films comprised of N-Benzylideneaniline side groups. ACS Macro Lett. 2015, 4, 764–768. [Google Scholar] [CrossRef]
  52. Kondo, M.; Kojima, D.; Ootsuki, N.; Kawatsuki, N. Photoinduced exfoliation of a polymeric N-benzylideneaniline liquid-crystalline composite based on a photoisomerization-triggered phase transition. Macromol. Chem. Phys. 2021, 222, 2100097. [Google Scholar] [CrossRef]
  53. Kondo, M.; Uematsu, T.; Ootsuki, N.; Okai, D.; Adachi, H.; Kawatsuki, N. Photoinduced phase transition of N-benzylideneaniline liquid crystalline polymer and applications of photodismantlable adhesives. React. Funct. Polym. 2022, 174, 105247. [Google Scholar] [CrossRef]
  54. Hu, J.; Yu, H. Photoinduced solid-to-liquid transition of an N-benzylideneaniline derivative towards smart glass. New J. Chem. 2024, 48, 4690–4698. [Google Scholar] [CrossRef]
  55. Lin, X.; Gablier, A.; Terentjev, E.M. Imine-based reactive mesogen and its corresponding exchangeable liquid crystal elastomer. Macromolecules 2022, 55, 821–830. [Google Scholar] [CrossRef]
  56. Dozov, I. On the spontaneous symmetry breaking in the mesophases of achiral banana-shaped molecules. Europhys. Lett. 2001, 56, 247–253. [Google Scholar] [CrossRef]
  57. Cestari, M.; Diez-Berart, S.; Dunmur, D.A.; Ferrarini, A.; de La Fuente, M.R.; Jackson, D.J.; Lopez, D.O.; Luckhurst, G.R.; Perez-Jubindo, M.A.; Richardson, R.M.; et al. Phase behavior and properties of the liquid-crystal dimer 1’’,7’’-bis(4-cyanobiphenyl-4’-yl) heptane: A twist-bend nematic liquid crystal. Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 2011, 84, 031704. [Google Scholar] [CrossRef]
  58. Panov, V.P.; Balachandran, R.; Nagaraj, M.; Vij, J.K.; Tamba, M.G.; Kohlmeier, A.; Mehl, G.H. Microsecond linear optical response in the unusual nematic phase of achiral bimesogens. Appl. Phys. Lett. 2011, 99, 261903. [Google Scholar] [CrossRef]
  59. Chen, D.; Porada, J.H.; Hooper, J.B.; Klittnick, A.; Shen, Y.; Tuchband, M.R.; Korblova, E.; Bedrov, D.; Walba, D.M.; Glaser, M.A.; et al. Chiral heliconical ground state of nanoscale pitch in a nematic liquid crystal of achiral molecular dimers. Proc. Natl. Acad. Sci. USA 2013, 110, 15931–15936. [Google Scholar] [CrossRef]
  60. Borshch, V.; Kim, Y.K.; Xiang, J.; Gao, M.; Jákli, A.; Panov, V.P.; Vij, J.K.; Imrie, C.T.; Tamba, M.G.; Mehl, G.H.; et al. Nematic twist-bend phase with nanoscale modulation of molecular orientation. Nat. Commun. 2013, 4, 2635. [Google Scholar] [CrossRef]
  61. Zhu, C.; Tuchband, M.R.; Young, A.; Shuai, M.; Scarbrough, A.; Walba, D.M.; Maclennan, J.E.; Wang, C.; Hexemer, A.; Clark, N.A. Resonant carbon K-edge soft X-ray scattering from lattice-free heliconical molecular ordering: Soft dilative elasticity of the twist-bend liquid crystal phase. Phys. Rev. Lett. 2016, 116, 147803. [Google Scholar] [CrossRef]
  62. Salili, S.M.; Kim, C.; Sprunt, S.; Gleeson, J.T.; Parri, O.; Jákli, A. Flow properties of a twist-bend nematic liquid crystal. RSC Adv. 2014, 4, 57419–57423. [Google Scholar] [CrossRef]
  63. Challa, P.K.; Borshch, V.; Parri, O.; Imrie, C.T.; Sprunt, S.N.; Gleeson, J.T.; Lavrentovich, O.D.; Jákli, A. Twist-bend nematic liquid crystals in high magnetic fields. Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 2014, 89, 060501. [Google Scholar] [CrossRef]
  64. Kumar, M.P.; Kula, P.; Dhara, S. Smecticlike rheology and pseudolayer compression elastic constant of a twist-bend nematic liquid crystal. Phys. Rev. Mater. 2020, 4, 115601. [Google Scholar] [CrossRef]
  65. Merkel, K.; Loska, B.; Arakawa, Y.; Mehl, G.H.; Karcz, J.; Kocot, A. How do intermolecular interactions evolve at the nematic to twist–bent phase transition? Int. J. Mol. Sci. 2022, 23, 11018. [Google Scholar] [CrossRef]
  66. Henderson, P.A.; Imrie, C.T. Methylene-linked liquid crystal dimers and the twist-bend nematic phase. Liq. Cryst. 2011, 38, 1407–1414. [Google Scholar] [CrossRef]
  67. Mandle, R.J.; Davis, E.J.; Archbold, C.T.; Voll, C.C.; Andrews, J.L.; Cowling, S.J.; Goodby, J.W. Apolar bimesogens and the incidence of the twist–bend nematic phase. Chem. Eur. J. 2015, 21, 8158–8167. [Google Scholar] [CrossRef]
  68. Jansze, S.M.; Martínez-Felipe, A.; Storey, J.M.; Marcelis, A.T.; Imrie, C.T. A twist-bend nematic phase driven by hydrogen bonding. Angew. Chem. Int. Ed. 2015, 54, 643–646. [Google Scholar] [CrossRef]
  69. Dawood, A.A.; Grossel, M.C.; Luckhurst, G.R.; Richardson, R.M.; Timimi, B.A.; Wells, N.J.; Yousif, Y.Z. On the twist-bend nematic phase formed directly from the isotropic phase. Liq. Cryst. 2016, 43, 2–12. [Google Scholar] [CrossRef]
  70. Arakawa, Y.; Komatsu, K.; Tsuji, H. Twist-bend nematic liquid crystals based on thioether linkage. New J. Chem. 2019, 43, 6786–6793. [Google Scholar] [CrossRef]
  71. Mandle, R.J. A ten-year perspective on twist-bend nematic materials. Molecules 2022, 27, 2689. [Google Scholar] [CrossRef] [PubMed]
  72. Tomczyk, W.; Longa, L. Role of molecular bend angle and biaxiality in the stabilization of the twist-bend nematic phase. Soft Matter 2020, 16, 4350–4357. [Google Scholar] [CrossRef]
  73. Xiang, J.; Li, Y.; Li, Q.; Paterson, D.A.; Storey, J.M.; Imrie, C.T.; Lavrentovich, O.D. Electrically tunable selective reflection of light from ultraviolet to visible and infrared by heliconical cholesterics. Adv. Mater. 2015, 27, 3014–3018. [Google Scholar] [CrossRef] [PubMed]
  74. Liu, B.; Yuan, C.L.; Hu, H.L.; Wang, H.; Zhu, Y.W.; Sun, P.Z.; Li, Z.Y.; Zheng, Z.G.; Li, Q. Dynamically actuated soft heliconical architecture via frequency of electric fields. Nat. Commun. 2022, 13, 2712. [Google Scholar] [CrossRef]
  75. Paterson, D.A.; Xiang, J.; Singh, G.; Walker, R.; Agra-Kooijman, D.M.; Martíne-Felipe, A.; Gao, M.; Storey, J.M.D.; Kumar, S.; Lavrentovich, O.D.; et al. Reversible isothermal twist–bend nematic–nematic phase transition driven by the photoisomerization of an azobenzene-based nonsymmetric liquid crystal dimer. J. Am. Chem. Soc. 2016, 138, 5283–5289. [Google Scholar] [CrossRef] [PubMed]
  76. Feng, C.; Feng, J.; Saha, R.; Arakawa, Y.; Gleeson, J.; Sprunt, S.; Zhu, C.; Jákli, A. Manipulation of the nanoscale heliconical structure of a twist-bend nematic material with polarized light. Phys. Rev. Res. 2020, 2, 032004. [Google Scholar] [CrossRef]
  77. Arakawa, Y.; Komatsu, K.; Feng, J.; Zhu, C.; Tsuji, H. Distinct twist-bend nematic phase behaviors associated with the ester-linkage direction of thioether-linked liquid crystal dimers. Mater. Adv. 2021, 2, 261–272. [Google Scholar] [CrossRef]
  78. Tang, W.; Deng, M.; Kougo, J.; Ding, L.; Zhao, X.; Arakawa, Y.; Komatsu, K.; Tsuji, H.; Aya, S. Extreme modulation of liquid crystal viscoelasticity via altering the ester bond direction. J. Mater. Chem. C 2021, 9, 9990–9996. [Google Scholar] [CrossRef]
  79. Aya, S.; Tang, W.; Kong, X.; Arakawa, Y.; Komatsu, K.; Tsuji, H. Nontrivial ultraslow dynamics under electric-field in nematics of bent-shaped molecules. Phys. Chem. Chem. Phys. 2023, 25, 297–303. [Google Scholar] [CrossRef]
  80. Zhou, J.; Tang, W.; Arakawa, Y.; Tsuji, H.; Aya, S. Viscoelastic properties of a thioether-based heliconical twist–bend nematogen. Phys. Chem. Chem. Phys. 2020, 22, 9593–9599. [Google Scholar] [CrossRef]
  81. Luckhurst, G.R. Liquid crystal dimers and oligomers: Experiment and theory. Macromol. Symp. 1995, 96, 1–26. [Google Scholar] [CrossRef]
  82. Arakawa, Y.; Ishida, Y.; Tsuji, H. Ether- and thioether-linked naphthalene-based liquid-crystal dimers: Influence of chalcogen linkage and mesogenic-arm symmetry on the incidence and stability of the twist–bend nematic phase. Chem. Eur. J. 2020, 26, 3767–3775. [Google Scholar] [CrossRef]
  83. Mandle, R.J.; Goodby, J.W. Molecular flexibility and bend in semi-rigid liquid crystals: Implications for the heliconical nematic ground state. Chem. Eur. J. 2019, 25, 14454–14459. [Google Scholar] [CrossRef]
  84. Arakawa, Y.; Komatsu, K.; Shiba, T.; Tsuji, H. Phase behaviors of classic liquid crystal dimers and trimers: Alternate induction of smectic and twist-bend nematic phases depending on spacer parity for liquid crystal trimers. J. Mol. Liq. 2021, 326, 115319. [Google Scholar] [CrossRef]
  85. Jaffé, H.H.; Yeh, S.J.; Gardner, R.W. The electronic spectra of azobenzene derivatives and their conjugate acids. J. Mol. Spectrosc. 1958, 2, 120–136. [Google Scholar] [CrossRef]
  86. Knöpke, L.R.; Spannenberg, A.; Brückner, A.; Bentrup, U. The influence of substituent effects on spectroscopic properties examined on benzylidene aniline-type imines. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2012, 95, 18–24. [Google Scholar] [CrossRef] [PubMed]
  87. Shah, A.; Sannaikar, M.S.; Inamdar, S.R.; Duponchel, B.; Douali, R.; Singh, D.P. Photoluminescence modulation in the graphene oxide dispersed 4-n-octyl-4’-cyanobiphenyl molecular system. J. Lumin. 2020, 226, 117509. [Google Scholar] [CrossRef]
Materials 17 03278 g001
Figure 1. Molecular structures of (a) CBCOOnSCB, CBOCOnSCB, [33,77] (b) CBSnSBA(CN) [34] from our previous study, and (c) CBCOOnSBA(CN) and CBOCOnSBA(CN) in the present study.
Figure 1. Molecular structures of (a) CBCOOnSCB, CBOCOnSCB, [33,77] (b) CBSnSBA(CN) [34] from our previous study, and (c) CBCOOnSBA(CN) and CBOCOnSBA(CN) in the present study.
Materials 17 03278 g001
Materials 17 03278 sch001
Scheme 1. Synthesis of CBCOOnSBA(CN) and CBOCOnSBA(CN), where n = 2, 4, 6, 8, and 10.
Scheme 1. Synthesis of CBCOOnSBA(CN) and CBOCOnSBA(CN), where n = 2, 4, 6, 8, and 10.
Materials 17 03278 sch001
Materials 17 03278 g002
Figure 2. Optical textures observed in the NTB phases in a non-treated glass cell upon cooling CBCOOnSBA(CN): (a) blocky texture for n = 6, (b) striped texture for n = 8, and (c) rope-like and focal-conic-like textures for n = 10.
Figure 2. Optical textures observed in the NTB phases in a non-treated glass cell upon cooling CBCOOnSBA(CN): (a) blocky texture for n = 6, (b) striped texture for n = 8, and (c) rope-like and focal-conic-like textures for n = 10.
Materials 17 03278 g002
Materials 17 03278 g003
Figure 3. Optical textures of the NTB phase of CBCOO2SBA(CN) in (a) non-treated and uniaxially rubbed planar alignment glasses with cell thicknesses of (b) 1 and (c) 7 µm.
Figure 3. Optical textures of the NTB phase of CBCOO2SBA(CN) in (a) non-treated and uniaxially rubbed planar alignment glasses with cell thicknesses of (b) 1 and (c) 7 µm.
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Materials 17 03278 g004
Figure 4. DSC curves of CBCOOnSBA(CN) upon cooling at a rate of 10 °C min−1.
Figure 4. DSC curves of CBCOOnSBA(CN) upon cooling at a rate of 10 °C min−1.
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Materials 17 03278 g005
Figure 5. Optical textures of the NTB phase of CBOCOnSBA(CN) in a non-treated glass cell upon cooling: (a) blocky texture for n = 4, (b) striped texture for n = 6, and (c) rope-like texture for n = 8. The blocky texture of (a) CBOCO4SBA(CN) was recorded in a supercooled region that did not crystallize.
Figure 5. Optical textures of the NTB phase of CBOCOnSBA(CN) in a non-treated glass cell upon cooling: (a) blocky texture for n = 4, (b) striped texture for n = 6, and (c) rope-like texture for n = 8. The blocky texture of (a) CBOCO4SBA(CN) was recorded in a supercooled region that did not crystallize.
Materials 17 03278 g005
Materials 17 03278 g006
Figure 6. DSC curves of CBOCOnSBA(CN) upon cooling at a rate of 10 °C min−1.
Figure 6. DSC curves of CBOCOnSBA(CN) upon cooling at a rate of 10 °C min−1.
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Materials 17 03278 g007
Figure 7. TIN, TNNTB, Tg, and TCr values as a function of n for (a) CBCOOnSBA(CN) and (b) CBOCOnSBA(CN) upon cooling.
Figure 7. TIN, TNNTB, Tg, and TCr values as a function of n for (a) CBCOOnSBA(CN) and (b) CBOCOnSBA(CN) upon cooling.
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Materials 17 03278 g008
Figure 8. ΔSIN/R values as a function n for CBCOOnSBA(CN) (red circles) and CBOCOnSBA(CN) (blue squares) upon cooling.
Figure 8. ΔSIN/R values as a function n for CBCOOnSBA(CN) (red circles) and CBOCOnSBA(CN) (blue squares) upon cooling.
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Materials 17 03278 g009
Figure 9. Non-normalized UV–visible spectra of CBCOO6SBA(CN) (red solid line) and CBOCO6SBA(CN) (blue dashed line) in THF solution.
Figure 9. Non-normalized UV–visible spectra of CBCOO6SBA(CN) (red solid line) and CBOCO6SBA(CN) (blue dashed line) in THF solution.
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Materials 17 03278 g010
Figure 10. POM images under UV irradiation for CBCOO6SBA(CN). Turning UV (a) on and (b) off at 106.0 °C and turning UV (c) on and (d) off at 85.6 °C in a non-treated glass cell.
Figure 10. POM images under UV irradiation for CBCOO6SBA(CN). Turning UV (a) on and (b) off at 106.0 °C and turning UV (c) on and (d) off at 85.6 °C in a non-treated glass cell.
Materials 17 03278 g010
Table 1. Values of Tm upon heating, TIN, TNNTB, Tg, and TCr upon cooling at a rate of 10 °C min–1 and their associated ΔH for CBCOOnSBA(CN).
Table 1. Values of Tm upon heating, TIN, TNNTB, Tg, and TCr upon cooling at a rate of 10 °C min–1 and their associated ΔH for CBCOOnSBA(CN).
nTm (°C)ΔH TIN (°C)ΔH ΔSIN TNNTB (°C)ΔH Tg or TCr (°C)ΔH
(kJ mol–1)(kJ mol–1)(kJ mol–1)(kJ mol–1)
2170.1182.93I95.00.270.05N50.910.06NTB24.63-G
4124.7068.26I84.90.120.06N59.240.24NTB13.7-G
6124.3780.67I102.00.380.12N82.010.8NTB16.54-G
890.3250.3I115.60.930.29N91.16-NTB19.95-G
10108.8479.99I115.71.430.44N90.26-NTB60.7524.97Cr
Table 2. Values of Tm upon heating, TIN, TNNTB, Tg, and TCr upon cooling at a rate of 10 °C min–1 and their associated ΔH for CBOCOnSBA(CN).
Table 2. Values of Tm upon heating, TIN, TNNTB, Tg, and TCr upon cooling at a rate of 10 °C min–1 and their associated ΔH for CBOCOnSBA(CN).
nTm (°C)ΔH TIN (°C)ΔHΔSIN TNNTB (°C)ΔH Tg or TCr (°C)ΔH
(kJ mol–1)(kJ mol–1)(kJ mol–1)(kJ mol–1)
2156.4736.59I139.41.390.41N66-NTB a104.327.1Cr
4142.143.66I161.71.500.42N88.5-NTB a94.6533.8Cr
6108.838.28I160.82.130.59N93.75-NTB8.31-G
8111.3340.47I156.82.830.79N91.84-NTB7.44-G
10113.8743.44I150.73.390.96N86.17-NTB68.9430.3Cr
a Determined by POM.
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Arakawa, Y.; Arai, Y. Photoinduced Phase Transitions of Imine-Based Liquid Crystal Dimers with Twist–Bend Nematic Phases. Materials 2024, 17, 3278. https://doi.org/10.3390/ma17133278

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Arakawa Y, Arai Y. Photoinduced Phase Transitions of Imine-Based Liquid Crystal Dimers with Twist–Bend Nematic Phases. Materials. 2024; 17(13):3278. https://doi.org/10.3390/ma17133278

Chicago/Turabian Style

Arakawa, Yuki, and Yuto Arai. 2024. "Photoinduced Phase Transitions of Imine-Based Liquid Crystal Dimers with Twist–Bend Nematic Phases" Materials 17, no. 13: 3278. https://doi.org/10.3390/ma17133278

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