A series of mesogenic derivatives of o-carborane was synthesized, their properties were analyzed by thermal, optical and XRD methods, and results were compared with those of isostructural p-carborane and benzene analogues. Comparative analysis revealed lower nematic phase stability and enhanced smectic behavior, including SmC, in the o-carborane derivatives relative to the isosteric p-carborane analogues. The effect of o-carborane on the electrooptical properties was assessed for biphenyl derivative 1[B]a in the 6CHBT nematic host giving the extrapolated Δε = 11.0, and a moderate increase of the elastic constants Kii. Complete analysis of the dielectric results for o-carborane and p-carborane analogues 1[B]a and 1[A]a was performed using the Maier–Meier formalism augmented by DFT computational methods.

A series of bent-core derivatives of 6-oxoverdazyl 1[12] was synthesized and mesogenic properties were investigated in the pure form and in binary mixtures. Results demonstrate that the effectiveness of the C(3) substituent in nematic phase stabilization follows the order: COOMe > m-FC6H4 > Ph > thienyl > o-FC6H4, which is consistent with steric parameters established with DFT computational methods and opposite to the order of the appearance of a re-entrant isotropic phase. The effect of alkyl chain elongation on mesogenic properties and the effect of C(3) substituent on electronic absorption spectra are also investigated.

A series of p-substituted phenylhydrazones of trifluoroacetaldehyde (1) was synthesized and the azo-hydrazo (1–2) tautomeric equilibrium was investigated experimentally using correlation analysis and computationally with DFT methods. Investigation revealed strong impact of the substituent and solvent polarity on the tautomeric ratio (1/2). Calculations also revealed that acidity of the azo tautomers is similar to that of malonate esters.

Bent-core mesogens containing 6-oxoverdazyl radical as the angular central unit exhibit rich polymorphism that includes isotropic–isotropic transition, re-entant isotropic (Ire), and a novel 3D tetragonal (Tet) phases. Surprisingly, the paramagnetic Tet phase interacts linearly with applied electric field and exhibits photoinduced ambipolar charge transport (μ ≈ 10–3 cm2 V–1 s–1). Magnetic analysis showed gradual increase of antiferromagnetic interactions upon cooling.

A series of six 6-oxoverdazyl (1[10]) substituted with a total of three 3,4,5-tri(decyloxy)phenyl and/or 3,4,5-tri(decylsulfanyl)phenyl groups was investigated by thermal, XRD, spectroscopic, magnetic and photovoltaic methods. The compounds exhibit columnar hexagonal (1[10]c, Colh), columnar hexagonal ordered (1[10]b, Colh(o)), columnar hexagonal 3D (1[10]a, 1[10]e and 1[10]f, Colh(3D)) or a sequence of two phases (1[10]b, Colh–Colh(3D)). The mesophase structure and stability and also thermochromism were investigated as a function of the number and distribution of decyloxy and decylsulfanyl substituents in the molecule. Thermal analysis demonstrated that the presence of the 3,4,5-tri(decyloxy)phenyl substituent in the C(3) position increases the phase stability. Spectroscopic analysis showed that only all-decyloxy derivative 1[10]b exhibits a hypsochromic shift upon Colh(o) formation, while all other compounds in the series show a modest bathochromic shift in the columnar phase relative to the isotropic phase. Magnetization investigation of 1[10]d demonstrated the paramagnetic behavior of isolated spins in isotropic and columnar phases. Negligible photocurrent was detected for 1[10]d in the columnar phase.

Two series of polar compounds 3[n] and 4[n] with longitudinal dipole moments ranging from 10 to 17 D were synthesized and investigated as additives to two nematic hosts, ClEster and CinnCN. Compounds 3[n] do not exhibit liquid crystalline behavior and have limited compatibility with nematic hosts, but still are effective additives for increasing dielectric anisotropy, Δε, of liquid crystalline host materials. On the other hand, esters 4[n] typically exhibit nematic behavior and form stable solutions in ClEster up to 5 mol%. In this concentration range, the binary solutions exhibit a linear dependence of dielectric parameters and the extrapolated Δε values range from <18 (4[3]l, μ = 11.3 D) to 70 (4[3]c, μ = 14.1 D and 4[3]k, μ = 17.2 D). Analysis of the dielectric data with the Maier–Meier formalism using DFT-calculated α and μ parameters gave apparent order parameter values Sapp in a range of 0.51–0.68 and Kirkwood parameters g in a range 0.55–0.78 for esters 4[n].

Substituted closo-carbaborate–pyridinium zwitterions were prepared in 35–50% yield by reacting 1-amino-closo-1-carbaborates with 4-alkoxypyrylium triflates. Two of the new materials, 1[6]d and 2[10]b, exhibit a high temperature SmA phase, whose stability is driven by dipolar interactions. Solution studies in a nematic host, ClEster, demonstrated high positive dielectric anisotropy of these new compounds (Δε ≈ +50) resulting from a longitudinal molecular dipole moment of about 20 D.

Two isomerically pure 1,12-difunctionalized derivatives of o-carborane, 12-iodo-1-vinyl (1b) and 12-iodo-1-phenyl (1c), are conveniently obtained on a practical scale in yields of 22% and 32%, respectively, by monoiodination of the corresponding o-carborane derivatives (4b and 4c) followed by separation of the regioisomers by crystallization (1b) and chromatography (1c). Subsequent functional group transformations gave access to other derivatives, including two liquid-crystalline compounds, in which o-carborane is a linear structural element. Regioselectivity of substitution on the carborane cage and on the benzene ring correlates with the inductive effect parameter of the substituent. The preparation of analogous derivatives of m-carborane was also investigated.

Replacement of the B− atom in the monocarbaborate anion, 1[10] or 1[12], and the N+ atom in the pyridinium cation [Pyr] of a liquid crystalline ion pair with C atoms leads to an isoelectronic and isosteric non-ionic binary liquid crystalline mixture of carborane (2[10] or 2[12]) and benzene ([Ph]) derivatives lacking coulombic interactions. A comparison of mesogenic properties of ion pairs, 1[10]c–[Pyr]c and 1[12]c–[Pyr]c, with their analogous non-ionic mixtures, 2[10]c–[Ph]c and 2[12]c–[Ph]c, shows a 181 K higher clearing temperature, Tc, for the ion pair. This corresponds to a DFT-calculated difference in association energy ΔΔHa = 24.5 kcal mol−1 in a typical dielectric medium (ε = 2.5). Pure compounds and binary mixtures were characterized using thermal, optical, and XRD methods.

Transformations of functional groups OCOPh, OCH2Ph, I, NO2, and CO2Me in Blatter’s radical derivatives 1–5 were investigated in order to develop synthetic tools for incorporation of the benzo[1,2,4]triazinyl system into complex molecular architectures. Thus, basic hydrolysis of OCOPh or Pd-catalyzed debenzylation of OCH2Ph gave phenol functionality, which was acylated and alkylated. Pd-catalyzed Suzuki, Negishi, Sonogashira, and Heck C–C cross-coupling reactions of iodo derivatives 1c, 1d, and 2d were also successful and efficient. Reduction of NO2 in 1e led to aniline derivative 1t, which was reductively alkylated with hexanal and coupled to l-proline. Selected benzo[1,2,4]triazinyl radicals were characterized by EPR and electronic absorption spectroscopy, and the results were analyzed in tandem with DFT computational methods. Lastly, the mechanism for formation of the 1,4-dihydrobenzo[1,2,4]triazine ring was investigated using the B3LYP/6-31G(2d,p) method.

Two series of related three-ring nematoges with Δε > 0 and containing 12-vetex carborane (A), 10-vertex carborane (B), bicyclo[2.2.2]octane (C), cyclohexane (D) and benzene (E) were prepared and investigated as additives to 6-CHBT nematic host and in the pure form (series 2). Dielectric results were analyzed with the Maier–Meier relationship to gain an understanding of behavior of additives in nematic solutions. Molecular parameters for each nematogen were obtained at the B3LYP/6-31G(d,p) level of theory in the host’s dielectric medium, and dielectric data was used as the only experimental parameter to calculate apparent order parameter Sapp and the Kirkwood factor g. The results demonstrated that compounds in series 1 stabilize the nematic phase (high Sapp) of the host more than additives in series 2 (low Sapp), and carbocycles C and D are more effective (higher Sapp) than carborane analogues A and B (lower Sapp). The method provides insight into behavior of additives in nematic solutions and is useful for comparative analysis of a series of compounds or a series of hosts.

The [closo-1-CB9H10]− anion is a member of an extensive family of σ-aromatic closo-boranes that possess impressive stability and functionalization characteristics. In contrast to its bigger, more extensively studied brother, the [closo-1-CB11H12]− anion, convenient access to the [closo-1-CB9H10]− anion has only been recently established, and researchers have only begun to develop and understand its fundamental chemistry.The geometrical and electronic properties of the [closo-1-CB9H10]− anion make it an attractive structural element of novel classes of either zwitterionic or ionic liquid crystals suitable for electro-optical and ion transport applications, respectively. Such materials require a 1,10-difunctionalized [closo-1-CB9H10]− anion that permits for the formation of molecules of elongated shape. The covalent attachment of an onium fragment or the use of a counterion compensates for the negative charge. This Account highlights the progress made in the advancement and understanding of the fundamental chemistry of the [closo-1-CB9H10]− anion. We also describe the development of 1,10-difunctionalized derivatives as key intermediates in the preparation of new classes of liquid crystalline materials.We obtained the first isomerically pure 1,10-difunctionalized derivative of the [closo-1-CB9H10]− anion, iodo acid [closo-1-CB9H8-1-COOH-10-I]−, from decaborane through the Brellochs reaction. Functional group transformation of the C(1)-carboxyl group led to a 1-amino derivative and, subsequently, to a synthetically valuable 1-dinitrogen derivative. The latter exhibits reactivity typical for PhN2+ and undergoes diazocoupling and Gomberg–Bachmann arylation reactions. The B(10)-iodine participated in Negishi alkylation and Buchwald–Hartwig amination reactions, leading to 10-hexyl and 10-amino carboxylic acids, respectively. We converted the 10-amino carboxylic acid to a 10-dinitrogen acid [closo-1-CB9H8-1-COOH-10-N2], which proved to be synthetically valuable in the preparation of 10-pyridinium and 10-sulfonium zwitterionic acids and their liquid crystalline esters. We investigated several intermediates using structural, spectroscopic, and kinetic methods.

Transformations of functional groups, such as OCH2Ph, OCOPh, NO2 and I, in 1,3,5-triphenyl-6-oxoverdazyls 1a–1e were investigated in order to expand the range of synthetic tools for incorporation of the verdazyl system into more complex molecular architectures and to increase spin delocalization. Thus, Pd-catalyzed debenzylation of the OCH2Ph group or basic hydrolysis of the OCOPh group gave the phenol functionality, which was acylated, but could not be alkylated. Orthogonal deprotection of diphenol functionality was also demonstrated in radical 1c. Pt-catalyzed reduction of the NO2 group led to the aniline derivative, which was acylated. Attempted C–C coupling reactions to iodophenyl derivatives 1e and 5e were unsuccessful. Selected verdazyl radicals were characterized by EPR and electronic absorption spectroscopy, and results were analyzed with the aid of DFT computational methods.

1,3,5-Triphenyl-6-oxoverdazyl radicals 1[n], in which each phenyl group is substituted with three alkylsulfanyl groups (n = 6, 8, 10), exhibit a monotropic columnar rectangular (Colr) phase below 60 °C. Detailed analysis of 1[n] revealed a broad absorption band in the visible region with maxima at 540 and 610 nm and redox potentials E1/20/+1 = +0.99 V and E1/20/–1 = −0.45 V vs SCE. Photovoltaic studies of 1[8] demonstrated a hole mobility of 1.52 × 10–3 cm2 V–1 s–1 in the mesophase with an activation energy of 0.06 ± 0.01 eV. Magnetization studies of 1[8] revealed nearly ideal paramagnetic behavior in either the solid or fluid phase above 200 K and weak antiferromagnetic interactions at low temperatures.

6-Oxoverdazyls 1b[n], substituted with three 3,4,5-trialkoxyphenyl groups (n = 8 and 10), exhibit a columnar hexagonal phase (Colh) below 130 °C. They display reversible color change from red to green at the transition to the isotropic phase. XRD and magnetization data do not support dimerization of the radicals in the mesophase.

The apparent ionization constants pKa′ for series of carboxylic acids [closo-1-CB9H8-1-COOH-10-X]− (1) and [closo-1-CB11H10-1-COOH-12-X]− (2), where X = H, I, n-C6H13, +NMe3, +N2, +SMe2, OC5H11, were measured in EtOH/H2O (1/1, v/v) at 24 °C. Correlation analysis of the pKa′ values using Hammett substituent constants σp(X) gave the reaction constant ρ = 0.87 ± 0.04 for series 1 and ρ = 1.00 ± 0.09 for series 2. These values are higher than for derivatives of PhCH═CHCOOH (ρ = 0.70 ± 0.09 in 55% EtOH) and correspond to 56% and 65% efficiencies in transmission of electronic effects by [closo-1-CB9H10]− (E) and [closo-1-CB11H12]− (F), respectively, as compared to benzene (A). Experimental results were supported with DFT calculations of relative acidity for series of acids derived from A, E, and F in aqueous medium.

A new class of nematics with high dielectric anisotropy (Δε) for display applications has been developed and characterized by thermal and dielectric methods in mixtures with 3 nematic hosts: ClEster, 6-CHBT, and ZLI-1132. The key structural element is the zwitterionic derivative of the [closo-1-CB9H10]− anion substituted at the B(10) position with either pyridinium (3) or sulfonium (4) groups. The zwitterions increase the longitudinal molecular electric dipole moment by 8 D (4) or 12 D (3) and give rise to the extrapolated Δε in the range of 22 (4a)–113 (3c). The sulfonium derivatives 4 have higher solubility in nematic hosts, lower tendency to aggregate, and lower impact on host's viscosity than pyridinium 3. This, in part, is attributed to facile epimerization at the sulfur center in 4 and existence of the trans/cis equilibrium. Experimental results are augmented with DFT calculations and analyzed using the Maier–Meier relationship.

A comparative study of the reactivity of dinitrogen acids [closo-1-CB9H8-1-COOH-10-N2] (3[10]) and [closo-1-CB9H8-1-COOH-6-N2] (3[6]) was conducted by diazotization of a mixture of amino acids [closo-1-CB9H8-1-COOH-6-NH3] (1[6]) and [closo-1-CB9H8-1-COOH-10-NH3] (1[10]) with NO+BF4− in the presence of a heterocyclic base (pyridine, 4-methoxypyridine, 2-picoline, or quinoline). The 10-amino acid 1[10] formed an isolable stable 10-dinitrogen acid 3[10], while the 6-dinitrogen carboxylate 3[6]− reacted in situ, giving products of N-substitution at the B6 position with the heterocyclic solvent (4[6]). The molecular and crystal structures for pyridinium acid 4[6]a were determined by X-ray crystallography. The electronic structures and reactivity of the 6-dinitrogen derivatives of the {1-CB9} cluster were assessed computationally at the B3LYP/6-31G(d,p) and MP2/6-31G(d,p) levels of theory and compared to those of the 10-dinitrogen, 2-dinitrogen, and 1-dinitrogen analogues.

Replacement of a C–C fragment with an N+–B− fragment leads to pairs of isosteric non-polar/polar nematics with a difference in the calculated molecular dipole moment of about 12 D. Contrary to the expectations, the uniform increase of the dipole moment does not affect phase stability equally, and a strong dependence on the substituent structure is observed. For one of the polar derivatives (5b, µ = 20 D) a record high dielectric anisotropy (Δε = 113) was measured in dilute nematic solutions.

Amino acid [closo-1-CB9H8-1-COO-10-NH3]− (4) was prepared by amination of iodo acid [closo-1-CB9H8-1-COOH-10-I]− (1) with LiHMDS in a practical and reproducible manner. The apparent dissociation constants, pK2 = 5.6 and pK1 > 11, were measured for 4[NMe4] in 50% aq. EtOH. Diazotization of 4 with NO+PF6− under mildly basic conditions afforded stable dinitrogen acid [closo-1-CB9H8-1-COOH-10-N2] (5). Activation parameters (ΔH⧧ = 33.9 ± 1.4 kcal mol−1 and ΔS⧧ = 10 ± 3.5 cal mol−1 K−1) for thermolysis of its methyl ester [closo-1-CB9H8-1-COOMe-10-N2] (11) in PhCN were established, and the heterolysis of the B−N bond is believed to be the rate-determining step. Electrochemical analysis showed a partially reversible reduction process for 11 (E1/2red = −1.03 V) and 5− (E1/2red = −1.21 V), which are more cathodic than reduction of [closo-1-CB9H9-1-N2] (17). The dinitrogen acid 5 was reacted with pyridine and N,N-dimethylthioformamide, to form pyridine acid 6 and protected mercapto acid 7, respectively, through a boronium ylide intermediate 18. Compound 7 was converted to sulfonium acid 8. The molecular and crystal structures for 5 [C2H9B9N2O2 monoclinic, P21/n, a = 7.022(2) Å, b = 11.389(4) Å, c = 12.815(4) Å, β = 96.212(5)°; V = 1018.8(6) Å3, Z = 4,], 6 [C7H14B9NO2, monoclinic, P21/n, a = 14.275(4) Å, b = 12.184(3) Å, c = 30.538(8) Å, β = 95.377(4)°; V = 5288(3) Å3, Z = 16], and 8 [C7H19B9O2S, monoclinic, P21/c, a = 15.988(5) Å, b = 19.377(6) Å, c = 9.655(3) Å, β = 98.348(5)°; V = 2959.4(16) Å3, Z = 8] were determined by X-ray crystallography and compared with results of density functional theory (DFT) and MP2 calculations. Electronic structures of 5, 6, and related species were elucidated with electronic spectroscopy and assessed computationally at the B3LYP/6-31G(d,p), MP2/6-31G(d,p), and ZINDO//MP2 levels of theory.

The dinitrogen derivative [closo-1-CB9H9-1-N2] (1) was prepared from amine [closo-1-CB9H9-1-NH3] (2) and reacted with three types of nucleophiles: activated arenes (phenolate and aniline), divalent sulfur compounds (Me2S and Me2NCHS), and pyridine, giving products of substitution at Ccage. The reaction of 1 with pyridine gave all four isomers 11a−11d, indicating the Gomberg−Bachmann mechanism, which involves radical anion [closo-1-CB9H9]−• (26). The radical and also closed-shell electrophilic aromatic substitution mechanisms were probed with the aid of DFT and MP2 computational methods and compared to those of phenylation of pyridine. Overall, experimental results supported by computational analysis suggest two mechanisms for the substitution of the N2 group in 1: (i) thermal heterolytic cleavage of the Ccage−N bond and the formation of electrophilic carbonium ylide [closo-1-CB9H9] (19) and (ii) electron-transfer-induced homolytic cleavage of the Ccage−N bond and the formation of 26. Decomposition of 1 in MeCN is believed to proceed by the nonradical mechanism involving formation of the ylide 19 as the rate-determining step with experimental activation parameters △H‡ = 38.4 ± 0.8 kcal mol−1 and △S‡ = 44.5 ± 2.5 cal mol−1 K−1. The electron-transfer-induced formation of 26 is consistent with the relatively high reduction potential of 1 (Epc = −0.54 V), which is more cathodic than that of PhN2+ by 0.38 V. Transformations of the phenol 8a and the Me2NCHS adduct 10 were demonstrated by O-methylation of the former and hydrolysis of 10 followed by S-alkylative cyclization. Direct products and their derivatives were investigated by UV−vis spectroscopy and analyzed with the ZINDO computational method.

Several members of two homologous series of symmetric bent-shaped compounds with either m-carborane or adamantane (1[n] or 2[n], n = 9–13) in the central position were synthesized and investigated by optical, calorimetric, X-ray diffraction, and electro-optical methods. Results show that the two shortest members of the m-carborane series, 1[9] and 1[10], exhibit an intercalated lamellar B6 phase. The adamantane derivatives 2[9]–2[13] display a monotropic weakly birefringent soft crystalline or crystalline phase with homochiral domains. Neither phase undergoes polarization switching in an electric field.

Six series of structurally similar compounds containing 12- and 10-vertex p-carborane (A and B), bicyclo[2.2.2]octane (C), and benzene (D) were prepared and their mesogenic and dielectric properties investigated. Comparative analysis showed that all carborane derivatives form significantly less stable mesophases than their carbocyclic analogs, however they exhibit a relatively high shielding ability for lateral fluorination. Depression of the clearing temperature upon fluorination of series 1, 3, and 5 is approximately constant for each series A–D and correlates with the diameter of the ring (the slope = 14.8 °C Å−1 and R2 = 0.997). Compounds in series 2 (X = F) were used as low concentration additives to a nematic host, 6-CHBT. Dielectric parameters were extrapolated to pure additives and analyzed using the Maier–Meier equation. The Kirkwood factors g and apparent order parameters Sapp that are required to reproduce the extrapolated dielectric values follow the trend in the size of ring . The smallest g (0.47) and the largest Sapp (6.3) are obtained for carborane 2A, and the largest g (0.69) and the smallest Sapp (0.7) are obtained for the terphenyl derivative 2D. The increase of Sapp in the series D→A corresponds to the increasing disorder of the nematic solution with increasing size of ring .

Three structurally similar esters containing carborane (1A), bicyclo[2.2.2]octane (1B), and benzene (1C) were prepared and their mesogenic properties investigated. All esters exhibited chiral nematic phases, and only 1B showed rich smectic behavior. The esters were used as additives to three structurally different nematic hosts. The resulting cholesteric pitch p was measured as a function of concentration and temperature. The calculated helical twisting power βM followed the order 1A < 1B ≤ 1C, and the temperature dependence of βM was ≥0 for all mixtures except for 1C in host I. These results are discussed in terms of size and conformational properties of each ring system A–C and the role of their “biaxiality” in chirality transfer. The observed trends in βM are consistent with non-specific solute–solvent interactions in which the chiral additive breaks the uniaxial symmetry imposed by the phase and differentiates energy of the chiral conformers of the host.

6-Oxoverdazyls 1b[n], substituted with three 3,4,5-trialkoxyphenyl groups (n = 8 and 10), exhibit a columnar hexagonal phase (Colh) below 130 °C. They display reversible color change from red to green at the transition to the isotropic phase. XRD and magnetization data do not support dimerization of the radicals in the mesophase.

Substituted closo-carbaborate–pyridinium zwitterions were prepared in 35–50% yield by reacting 1-amino-closo-1-carbaborates with 4-alkoxypyrylium triflates. Two of the new materials, 1[6]d and 2[10]b, exhibit a high temperature SmA phase, whose stability is driven by dipolar interactions. Solution studies in a nematic host, ClEster, demonstrated high positive dielectric anisotropy of these new compounds (Δε ≈ +50) resulting from a longitudinal molecular dipole moment of about 20 D.

Several members of two homologous series of symmetric bent-shaped compounds with either m-carborane or adamantane (1[n] or 2[n], n = 9–13) in the central position were synthesized and investigated by optical, calorimetric, X-ray diffraction, and electro-optical methods. Results show that the two shortest members of the m-carborane series, 1[9] and 1[10], exhibit an intercalated lamellar B6 phase. The adamantane derivatives 2[9]–2[13] display a monotropic weakly birefringent soft crystalline or crystalline phase with homochiral domains. Neither phase undergoes polarization switching in an electric field.

Replacement of a C–C fragment with an N+–B− fragment leads to pairs of isosteric non-polar/polar nematics with a difference in the calculated molecular dipole moment of about 12 D. Contrary to the expectations, the uniform increase of the dipole moment does not affect phase stability equally, and a strong dependence on the substituent structure is observed. For one of the polar derivatives (5b, µ = 20 D) a record high dielectric anisotropy (Δε = 113) was measured in dilute nematic solutions.

A new class of nematics with high dielectric anisotropy (Δε) for display applications has been developed and characterized by thermal and dielectric methods in mixtures with 3 nematic hosts: ClEster, 6-CHBT, and ZLI-1132. The key structural element is the zwitterionic derivative of the [closo-1-CB9H10]− anion substituted at the B(10) position with either pyridinium (3) or sulfonium (4) groups. The zwitterions increase the longitudinal molecular electric dipole moment by 8 D (4) or 12 D (3) and give rise to the extrapolated Δε in the range of 22 (4a)–113 (3c). The sulfonium derivatives 4 have higher solubility in nematic hosts, lower tendency to aggregate, and lower impact on host's viscosity than pyridinium 3. This, in part, is attributed to facile epimerization at the sulfur center in 4 and existence of the trans/cis equilibrium. Experimental results are augmented with DFT calculations and analyzed using the Maier–Meier relationship.

A series of mesogenic derivatives of o-carborane was synthesized, their properties were analyzed by thermal, optical and XRD methods, and results were compared with those of isostructural p-carborane and benzene analogues. Comparative analysis revealed lower nematic phase stability and enhanced smectic behavior, including SmC, in the o-carborane derivatives relative to the isosteric p-carborane analogues. The effect of o-carborane on the electrooptical properties was assessed for biphenyl derivative 1[B]a in the 6CHBT nematic host giving the extrapolated Δε = 11.0, and a moderate increase of the elastic constants Kii. Complete analysis of the dielectric results for o-carborane and p-carborane analogues 1[B]a and 1[A]a was performed using the Maier–Meier formalism augmented by DFT computational methods.

A series of six 6-oxoverdazyl (1[10]) substituted with a total of three 3,4,5-tri(decyloxy)phenyl and/or 3,4,5-tri(decylsulfanyl)phenyl groups was investigated by thermal, XRD, spectroscopic, magnetic and photovoltaic methods. The compounds exhibit columnar hexagonal (1[10]c, Colh), columnar hexagonal ordered (1[10]b, Colh(o)), columnar hexagonal 3D (1[10]a, 1[10]e and 1[10]f, Colh(3D)) or a sequence of two phases (1[10]b, Colh–Colh(3D)). The mesophase structure and stability and also thermochromism were investigated as a function of the number and distribution of decyloxy and decylsulfanyl substituents in the molecule. Thermal analysis demonstrated that the presence of the 3,4,5-tri(decyloxy)phenyl substituent in the C(3) position increases the phase stability. Spectroscopic analysis showed that only all-decyloxy derivative 1[10]b exhibits a hypsochromic shift upon Colh(o) formation, while all other compounds in the series show a modest bathochromic shift in the columnar phase relative to the isotropic phase. Magnetization investigation of 1[10]d demonstrated the paramagnetic behavior of isolated spins in isotropic and columnar phases. Negligible photocurrent was detected for 1[10]d in the columnar phase.

Two series of polar compounds 3[n] and 4[n] with longitudinal dipole moments ranging from 10 to 17 D were synthesized and investigated as additives to two nematic hosts, ClEster and CinnCN. Compounds 3[n] do not exhibit liquid crystalline behavior and have limited compatibility with nematic hosts, but still are effective additives for increasing dielectric anisotropy, Δε, of liquid crystalline host materials. On the other hand, esters 4[n] typically exhibit nematic behavior and form stable solutions in ClEster up to 5 mol%. In this concentration range, the binary solutions exhibit a linear dependence of dielectric parameters and the extrapolated Δε values range from <18 (4[3]l, μ = 11.3 D) to 70 (4[3]c, μ = 14.1 D and 4[3]k, μ = 17.2 D). Analysis of the dielectric data with the Maier–Meier formalism using DFT-calculated α and μ parameters gave apparent order parameter values Sapp in a range of 0.51–0.68 and Kirkwood parameters g in a range 0.55–0.78 for esters 4[n].