Calixarene Functionalized Supramolecular Liquid Crystals and Their Diverse Applications

Abstract

Liquid crystals are considered to be the fourth state of matter with an intermediate order and fluidity in comparison to solids and liquids. Calixarenes are among one of the most versatile families of building blocks for supramolecular chemistry due to their unique vaselike structure that can be chemically engineered to have different shapes and sizes. During the last few decades, calixarenes have drawn much attention in the field of supramolecular chemistry due to their diverse applications in the fields of ion and molecular recognition, ion-selective electrodes for catalysis, drug delivery, gelation, organic electronics and sensors, etc. Imbuing liquid crystallinity to the calixarene framework leads to functionalized calixarene derivatives with fluidity and order. Columnar self-assembly of such derivatives in particular enhance the charge migration along the column due to the 1D stacking due to the enhanced π-π overlap. Considering limited reports and reviews on this new class of calixarene based liquid crystals, a comprehensive account of the synthesis of calixarene liquid crystals along with their mesomorphic behavior and potential applications are presented in this review.

Figure 1

Schematic diagram showing conventional and nonconventional molecular shapes used for the stabilization of LC phases.

Figure 2

Schematic diagram showing mesophases stabilized by conventional liquid crystals: (a) calamitic LC phases and (b) discotic LC phases.

Figure 3

Basic molecular structures of calixarene and resorcinarene cores and their self-assembly on functionalization.

Scheme 1. Bowl-Shaped Liquid Crystalline Derivatives of Calixarene

Figure 4

Graphical representation of the thermal behavior of bowl-shaped liquid crystalline derivatives (1d–1g, 3e–3h) (considered the cooling scan).

Scheme 2. Calixarene Based Liquid Crystalline Derivatives

Figure 5

CPK model of compound 3f showing the hollow side view. Reproduced with permission from ref (43). Copyright 1990 Taylor & Francis.

Scheme 3. Synthesis of Calix[4]resorcinarene Derived from Cinnamaldehyde (5a–5c)

Figure 6

Graphical representation of the thermal behavior of octasubstituted resorcinarene alkyl arm functionalized derivatives (5a–5c) (considered the cooling scan).

Scheme 4. Synthesis of Liquid Crystalline Resorcinarene Derivatives (6a–6d)

Figure 7

Graphical representation of the thermal behavior of octasubstituted resorcinarene alkyl arm functionalized derivatives 6a–6d (considered the cooling scan).

Scheme 5. Synthesis of Tungsten Oxo Calix[4]arene Derivatives (7a, 7b)

Figure 8

(a) Graphical representation of the thermal behavior of tungsten oxo calix[4]arene derivatives 7a and 7b. (b) Rearrangement of bowl-shaped calixarene linked tungsten core into columnar structure (7a, 7b). Reproduced from ref (48). Copyright 1993 American Chemical Society.

Figure 9

Structure of the azobenzene based calix[4]arene (8) and N-n-butylformamide (a). Schematic representation of the stacking calix[4]arenes by forming a 2:1 complex with N-n-butylformamide in the mesophase (b). Optical texture of the B_h phase stabilized by the host–guest complex in 2:1 ratio (c). Reproduced from ref (49). Copyright 1995 American Chemical Society.

Figure 10

Structures of calix[4]arenes reported by Oh et al. (a). Presentation of molecular organization of compound 10 and C6Azo in the form of a mixed monolayer on a water surface (b). Reproduced with permission from ref (50). Copyright 2001 The Royal Society of Chemistry.

Figure 11

Structures of perfluorooctylazobenzene (11a) or octylazobenzene (11b) functionalized O-octacarboxymethylated calix[4]arene derivatives.

Scheme 6. Synthesis of Lower Rim Azocalix[4]arene Derivatives (12a–12d)

Figure 12

Graphical representation of the thermal behavior of azocalix[4]arene derivatives (12a–12d) (considered the heating scan).

Figure 13

Polarized optical textures: (A) focal conic for compound 12a at 85 °C; (B) schlieren type for compound 12a at 175 °C; (C) rodlike domains obtained for SmC for compound 12c at 97 °C; (D) rodlike domains obtained for SmC for compound 12b; (E) nematic droplets for compound 12b at 200 °C; (F) needlelike pattern of SmC obtained for compound 12d at 92 °C. Reproduced with permission from ref (52). Copyright 2013 The Royal Society of Chemistry.

Scheme 7. Azo-Ester Linked Lower Rim Substituted Calixarene Derivatives (13a–13e and 14a–14e)

Figure 14

Graphical representation of the thermal behavior of azo-ester linked lower rim substituted calixarene derivatives (13d, 13e and 14d, 14e) (considered the cooling scan).

Scheme 8. Structures of LC Calixarenes Reported by Shinkai and Co-workers

Figure 15

Schematic representation of the phase transitions of cone-shaped calix[4]arenes. In K, the molecular motion of the aliphatic chains is frozen, whereas in M it is allowed. Reproduced with permission from ref (55). Copyright 1993 CSJ Publisher.

Figure 16

Graphical representation of the thermal behavior of cone-shaped calix[4]arenes derivatives (16a–16e) (considered the heating scan).

Scheme 9. Synthesis of Calixarene Schiff Base Derivatives (17a–17e and 18a–18e)

Figure 17

Compound 17c nematic phase at 185 °C (a). SmA phase at 139 °C (b). SmC phase at 88 °C (c). Compound 18c nematic phase at 176 °C (d). SmA phase at 130 °C. (e) SmC phase at 90 °C (f). Reproduced with permission from ref (56). Copyright 2010 Springer.

Figure 18

Graphical representation of the thermal behavior of Schiff base calixarene derivatives (17a–17e and 18a–18e) (considered the heating scan).

Scheme 10. Synthetic Route of Schiff Base Molded Calix[4]arene Derivatives (19–21)

Figure 19

Graphical representation of the thermal behavior of Schiff base calixarene derivatives (19, 20, 21, and Zn/20) (considered the heating scan).

Figure 20

Proposed arrangements of compounds 19 and 20 in SmA phase (a) and compound 21 in nematic phase (b). Reproduced with permission from ref (58). Copyright 2017 Wiley.

Scheme 11. Synthetic Route of Schiff Base Ester Calixarene Derivatives (22a–22m and 23a–23m)

Figure 21

Graphical representation of the thermal behavior of Schiff base ester calixarene derivatives (a) 22a–22m and (b) 23a–23m (considered the heating scan).

Scheme 12. Synthetic Route of Lower Rim Substituted Calixarene Derivatives (24a–24g)

Figure 22

Graphical representation of the thermal behavior of Schiff base derivatives (24a–24g) (considered the cooling scan).

Scheme 13. Preparation of Lower Rim Substituted Schiff Base Ester Derivatives (25a–25d)

Figure 23

Graphical representation of the thermal behavior of Schiff base ester derivatives (25a–25d) (considered the cooling scan).

Figure 24

Photomicrographs of 25a at 93.1 °C (a), 25b at 84.2 °C (b), 25c at 76.4 °C (c), and 25d at 66.6 °C (d) on heating from the solid crystalline state as seen under cross polarizers. Reproduced with permission from ref (61). Copyright 2020 The Royal Society of Chemistry.

Scheme 14. Preparation of Lower Rim Substituted Schiff Base Ester Derivatives (26a–26d and 27a–27d)

Figure 25

Graphical representation of the thermal behavior of quinoline armed thiacalix[4]arene derivatives (26a–26d and 27a–27d) (considered the cooling scan).

Figure 26

Distribution of parent calixarene linked quinoline derivative (27d) in nematodes (Caenorhabditis elegans) (5 μM). (a) Nematode exposed with aqueous THF solution in the blue filter; (b) nematode exposed with aqueous THF solution in green filter; (c, d) nematode exposed with compound 27d in THF solvent. Reproduced with permission from ref (62). Copyright 2022 Elsevier.

Figure 27

Structures of calix[4]arenes and 4-n-alkoxybenzoic acids and schematic representation of stacking calix[4]arenes to form Col phase (for chain length 12 and above). Reproduced with permission from ref (63). Copyright 1995 Elsevier.

Figure 28

Graphical representation of the thermal behavior of calix[4]arene derivatives (M₁₀, M₁₂, M₁₄, M₁₆, and M₁₈) (considered the heating scan).

Scheme 15. Synthetic Route for Oligophenylenevinylene Functionalized Calixarene Derivatives (29)

Scheme 16. Synthesis of Bowl-Shaped Calixarene Derivatives Bearing trans-Cinnamic Acid Derivatives (30a–30f and 31a–31f)

Figure 29

Graphical representation of the thermal behavior of bowl-shaped calixarene derivatives bearing trans-cinnamic acid: 30a–30f (a) and 31a–31f (b) (considered the cooling scan).

Scheme 17. Synthesis of Tetraoligophenylene Substituted Luminescent Calix[4]arene Derivatives (32/8–32/11, 33a–33e, and 34/8–34/16)

Figure 30

(a) Graphical representation of the thermal behavior of tetraoligophenylene substituted luminescent calix[4]arene derivatives (32/9, 32/10, and 34/8–34/16) (considered the cooling scan). (b) Phase diagram showing the smectic phase in the 34/n compounds series versus the tail alkoxy carbon number n = 9–16 measured from the second heating cycle. Reproduced from ref (66). Copyright 2006 American Chemical Society.

Figure 31

Some representative polarized optical microscope textures (magnification 200×): (a) 34/11 at 168 °C, mosaic and lancet texture with some homeotropic area; (b) 34/14 at 148 °C, mosaic texture; (c) 34/15 at 153 °C, grasslike and fanlike texture; (d) 31/9 at 150 °C, mosaic texture. Reproduced from ref (66). Copyright 2006 American Chemical Society.

Scheme 18. Synthetic Route of Calix[4]resorcinarene and Calix[8]arene Based Derivatives (35, 36)

Figure 32

Structural formula of calix[4]resorcinarene derivative (35) and LC dendrimer.

Scheme 19. Synthesis of Octahomotetracalix[4]arene Derivatives (37a–37c and 38a–38c)

Figure 33

Graphical representation of the thermal behavior of octahomotetracalix[4]arene derivatives (38a–38c and 38a/EN–38c/EN) (considered the cooling scan).

Figure 34

Schematic representation of the proposed conformational change of 38 with 1,2-ethylenediamine. Reproduced from ref (69). Copyright 2006 American Chemical Society.

Scheme 20. Synthetic Route of Amphiphilic Calixarene Derivatives (39a, 39b; 40a, 40b)

Figure 35

(a) Chemical structure of amphiphilic oxyethylated calix[4]arene. (b) Molecular model of 9CO16; gas phase energy minimized structure optimized by MM method with MM2 force field; Chem3D program. Reproduced with permission from ref (71). Copyright 2010 Elsevier.

Scheme 21. Synthesis Route of Supramolecular Amide Linked Calixarene Derivatives (42–44)

Figure 36

Graphical representation of the thermal behavior of gallic-calixarene derivatives (42–44) (considered the cooling scan).

Figure 37

Schematic representations of the columnar self-assembly of compounds 42 and 43 (a). Textures of compounds 42 and 43 under POM on cooling at 70 °C (b, c). Reproduced with permission from ref (72). Copyright 2015 Elsevier.

Scheme 22. Synthesis of Calix[4]resorcinarene Molded Schiff Base Amide Derivatives (45a–45f)

Figure 38

Graphical representation of the thermal behavior of Schiff base functionalized resorcin[4]arene derivatives (45a–45f) (considered the cooling scan).

Figure 39

Nematic textures of compound 45e at 50 °C (a) and compound 45c at 70 °C (b). Reproduced with permission from ref (73). Copyright 2021 Taylor & Francis.

Scheme 23. Structures of exo-Calix[4]arene Derivatives

Figure 40

Graphical representation of the thermal behavior of exo-calix[4]arene derivatives (46a, 46b, and 47a–47e) (considered the cooling scan).

Scheme 24. Preparation of Thiadiazole Linked Azo Calixarene Based Supramolecular Compounds (48a–48f)

Figure 41

Graphical representation of the thermal behavior of supramolecular calix[4]arene substituted with 1,3,4-thiadiazole derivatives (48a–48f) (considered the cooling scan).

Figure 42

POM texture images of compound 48a at 142.6 °C (a), compound 48f at 112.9 °C (b), compound 48e at 121.2 °C (c), and compound 48c at 133.8 °C (d), obtained on heating from the solid crystalline state. Reproduced with permission from ref (76). Copyright 2019 The Royal Society of Chemistry.

Scheme 25. Synthetic Route of Oxadiazole Linked Schiff Base Calixarene Derivatives (49a–49f)

Figure 43

Graphical representation of the thermal behavior of supramolecular calix[4]arene LCs based on oxadiazole derivatives (49a–49f) (considered the cooling scan).

Figure 44

POM texture image of Col_h phase in compound 49c at 131.3 °C (a), compound 49d at 136.6 °C (b), compound 49e at 124.8 °C (c), and compound 49f at 104.2 °C (d), on heating condition as seen under cross polarizers. Reproduced with permission from ref (77). Copyright 2018 Elsevier.

Scheme 26. Synthetic Route of Oxadiazole and Thiadiazole Linked Calixarene Derivatives (50a, 50b; 51a, 51b)

Figure 45

Graphical representation of the thermal behavior of supramolecular calix[4]arene LCs based on oxadiazole and thiadiazole derivatives (50a, 50b; and 51a, 51b) (considered the cooling scan).

Figure 46

AFM images of the aggregates of compound 50b (a) and compound 51b (b) in pure dodecane (scale bar 1 mm). Images showing solutions of compound 50b (c1) and compound 10d (d1) in daylight. Images showing the formation of gels in daylight and UV light of compound 50b (c2 and c3) and compound 51b (d2 and d3). Reproduced with permission from ref (78). Copyright 2019 The Royal Society of Chemistry.

Scheme 27. Synthetic Route of Thiadiazole Linked Thiacalixarene Derivatives (52a–52d)

Figure 47

Graphical representation of the thermal behavior of thiadiazole linked calixarene derivatives (52a–52d) (considered the cooling scan).

Figure 48

(a, b) Images showing solutions of compound 52c (a1) and compound 52d (b1) in daylight. Gels in daylight and UV light of compound 52c (a1–a3) and compound 52d (b1–b3). Reproduced from ref (79). Copyright 2019 American Chemical Society.

Scheme 28. Synthetic Route of Thiadiazole Linked Calixarene Derivatives (53a–53d)

Figure 49

Graphical representation of the thermal behavior of thiadiazole linked calixarene derivatives (53a–53d) (considered the cooling scan).

Scheme 29. Synthetic Routes of Cholesterol Linked Calix[4]arene Derivatives (54a, 54b; 55a, 55b)

Figure 50

Graphical representation of the thermal behavior of calix[4]arene–cholesterol oligomeric LCs (54a, 54b; and 55a, 55b) (considered the cooling scan).

Figure 51

POM images obtained for the Col phase of compounds 54a (a), 54b (b), 55a (c), and 55b (d) obtained at 80 °C on cooling the isotropic melt. Reproduced with permission from ref (84). Copyright 2015 Elsevier.

Scheme 30. Preparation of Cholesterol Linked Calix[4]arene Derivatives (56a, 56b)

Figure 52

Graphical representation of the thermal behavior of calix[4]arene–cholesterol derivatives with Schiff base bridges (56a, 56b) (considered the cooling scan).

Figure 53

Schematic representation of (a) columnar layered molecular arrangements, (b) their dimensions, and (c) the complexation models. Reproduced with permission from ref (85). Copyright 2016 Elsevier.

Scheme 31. Synthetic Route of Calix[4]resorcinarene Linked Cholesterol Derivatives (57a, 57b; 58a, 58b)

Figure 54

Graphical representation of the thermal behavior of calix[4]resorcinarene–cholesterol LCs (57a, 57b; 58a, 58b) (considered the cooling scan).

Figure 55

Mesomorphic texture of Col_h phase obtained under POM on cooling for compounds 57a, 57b, 58a, and 58b at 75, 90, 170, and 160 °C (500×) (a–d). Reproduced with permission from ref (86). Copyright 2017 Elsevier.

Scheme 32. Synthesis Route of Calixarene Linked Discotic Triphenylene Derivatives (59a, 59b)

Scheme 33. Synthesis Route of Thiacalix[4]triphenylene Derivatives (60a, 60b)

Figure 56

Graphical representation of the thermal behavior of calixarene linked discotic triphenylene derivatives (59a, 59b; 60a, 60b) (considered the heating scan).

Scheme 34. Synthetic Route of Triphenylene Linked Amide Based Calixarene Derivatives (61)

Scheme 35. Synthetic Route of Triphenylene Linked Hydrazone Based Calixarene Derivatives (62)

Figure 57

Textures of columnar phase of triads 61 and 62 under POM on cooling at 45 °C (400×) (a, b). Reproduced with permission from ref (91). Copyright 2012 Elsevier.

Figure 58

Graphical representation of the thermal behavior of symmetrical triads of triphenylene–calix[4]arene–triphenylene columnar LCs (61, 62) (considered the cooling scan).

Scheme 36. Synthetic Route of Novel Triads of Triphenylene–Calix[4]arene–Triphenylenes (63a, 63b)

Figure 59

Graphical representation of the thermal behavior of symmetrical triads of triphenylene–calix[4]arene–triphenylene columnar LCs (63a, 63b) and their complexes (63a+Ag⁺, 63b+Ag⁺) (considered the cooling scan).

Figure 60

Two kinds of schematic representation of the columnar layered molecular arrangement for triads of triphenylene–calixarene–triphenylenes 63a and 63b before and after complexation. Reproduced with permission from ref (92). Copyright 2013 Elsevier.

Scheme 37. Synthetic Route of Calixarene Linked Azide–Triphenylene Derivatives (64a, 64b)

Figure 61

Fanlike textures of columnar phase in compounds 64a and 64b (a, b) were obtained with polarized optical microscopy on cooling at 90 °C (400×). Reproduced with permission from ref (93). Copyright 2014 Elsevier.

Figure 62

Graphical representation of the thermal behavior of calixarene linked discotic triphenylene columnar LCs (64a, 64b) (considered the cooling scan).

Scheme 38. Synthetic Route of Calix[4]resorcinarene–Triphenylene Oligomers (65–68)

Figure 63

Mesomorphic columnar hexagonal textures of compounds 65 (a) and 66/67 (b) and distorted lamellar type columnar phase of compound 68 (c) obtained under POM on cooling at 70 °C (500×). Reproduced with permission from ref (94). Copyright 2017 Taylor & Francis.

Figure 64

Graphical representation of the thermal behavior of calix[4]resorcinarene–triphenylene oligomer columnar LCs (65–68) (considered the cooling scan).

Figure 65

Two possible schematic representations of the hexagonal columnar phase and lamellar columnar structure for compound 65. Reproduced with permission from ref (94). Copyright 2017 Taylor & Francis.

Scheme 39. Synthetic Route of Thiacalixarene Linked Triphenylene Derivatives (69a–69d)

Figure 66

Graphical representation of the thermal behavior of thiacalixarene linked triphenylene based room temperature columnar LCs (69a–69d) (considered the cooling scan).

Scheme 40. Synthetic Route of Chalcone Linked Calixarene Derivatives (70a–70d)

Figure 67

Graphical representation of the thermal behavior of chalcone–biphenyl amine functionalized supramolecular columnar LCs (70a–70d) (considered the cooling scan).