Hydrogen-bonded Liquid Crystal Complexes Research Articles

Comments on the thermodynamic and dielectric studies on hydrogen-bonded liquid crystal complexes

A research article titled as “Hydrogen-bonded liquid crystal complexes: A comprehensive study of structure, behaviour and potential applications” has been recently published by Meddeb et al., J. Mol. Liq. 395 (2024) 123838. Authors have reported and analysed thermodynamic and dielectric studies on highly ordered SmB and SmG mesophases in 14OBAF/DABCO complexes. But explanations of the dielectric data reported on the material are flawed based on various facts. Unintended wrong interpretations by the authors in reporting and explaining the thermodynamic and dielectric results are discussed here. Influence of various artefacts on acquired dielectric data has also been discussed in order to avoid such problems in further reports.

Hydrogen-bonded liquid crystal complexes: A comprehensive study of structure, behaviour and potential applications

Intermolecular hydrogen bond (HB) interaction becomes an intensively studied topic in supramolecular chemistry and soft matter science. Herein, a new series of hydrogen-bonded liquid crystals (HBLCs) composed of 3-flurobenzoic acid derivatives (nOBAF) and 1,4-diazabicyclo [2.2.2] octane (DABCO) has been prepared and characterized by Fourier-transform infrared spectroscopy. The thermal behavior was determined by differential scanning calorimetry and observed by polarized optical microscopy. All complexes were found to exhibit smectic G (SmG) and smectic B (SmB) phases over a wide temperature range. Furthermore, it was found that the thermal stability of these mesophases increases with increasing the alkoxy chain length. The complex dielectric permittivity was reported as a function of frequency in the range 1 Hz–10 MHz. Lower frequency process attributed to the collective fluctuations of azimuthal angle and higher frequencies, associated to the soft mode were observed in SmB. In the SmG, additional to the soft mode (106 Hz) a higher frequency mode (105 Hz) was detected for the first time. The experimental results obtained for these complexes were correlated with density functional theory (DFT) calculations. Furthermore, these results suggest that nOBAF/DABCO has the potential to be switchable dielectric materials.

Display device parametric computation through image analysis on supra molecular hydrogen bonded liquid crystal p-n-alkyloxy benzoic acid (where n=10) with pimelic acid

Selection of suitable liquid crystal material for designing a electro-optical display device is a challenging problem. The present article deals with the employment of supra moleccular hydrogen bonded liquid crystal complex p-n-alkyloxy benzoic acid (where n = 10) with pimelic acid in fabricating a display device is explored. This presumes the optical properties luminance, luminance uniformity, contrast modulation and contrast ratio. For such investigation, textural analysis was employed with matlab platform. Information related to the suitability of the mesogens for designing the display devices with the help of their textures. The results obtained in the current study, indicates that supra molecular hydrogen bonded liquid crystal complex p-n-alkyloxy benzoic acid(where n = 10) with pimelic acid (PA:10OBA) shows highly suitable for fabrication of opto-electronic display devices.

Theoretical studies (DFT) on hydrogen bonded liquid crystal derived from 4-amino and 4-dodecyloxy benzoic acids

Hydrogen bonded liquid crystal (HBLC) complex was obtained from the combination of 4-Amino benzoic acid (ABA) and mesogenic 4-(Dodecyloxy) benzoic acid (12OBA). The HBLC molecular structure was optimized by B3LYP/6-311G basis set (d, p). The O-H⋯O bond angle, bond length and electrostatic potential (ESP) had been studied by DFT. The natural bonding orbital (NBO) reveals the intermolecular charge transfers within the molecules, and the monomer I, monomer II and dimer O-H⋯O intermolecular stabilization energy were analysed. Further, the band gap energy for monomer I (4.275 eV), monomer II (4.559 eV) and dimer (4.745 eV) were calculated by Homo-Lumo. Mulliken analysis shows the clear evidence of the charge distribution between the molecules. Thermochemistry properties, O-H⋯O binding energy, collision diameter and chemical parameters were also computed by Gaussian 16 programme. Computational studies were performed to identify the nature of HBLC complex and its possible applications in the field of optoelectronics.

Experimental Observation of Induced Thermoluminescence Nematic Liquid Crystals for Optoelectronic Applications

A new class of intermolecular hydrogen bonded liquid-crystal complex (HBLC) was designed and synthesized from non-mesogenic benzylmalonic acid (BMA) and mesogenic 4n-pentyloxybenzoic acid (5OBA). Intermolecular hydrogen bonds (H-bond) and vibrational functional groups were characterized by using Fourier transform-infrared spectroscopy (FTIR). Textural characterizations and the corresponding transition temperature along with enthalpy values were observed using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The optical absorption and emission bandgap energies were calculated by using ultraviolet-visible (UV-vis) and photoluminescence (PL) spectra. The phase transition temperature, thermal stability factor, and thermal span width were calculated and their impact on the liquid crystal properties are discussed. An interesting feature of the BMA+5OBA HBLC complex was the observation of schlieren textures, and the induced thermoluminescence with parachromic variation in the nematic phase is an alternative tool for the manufacture of opto-electronic devices.

Computation of liquid crystal display device parameters through image analysis in supramolecule MA:nOBA

ABSTRACT In this article, the usage of the hydrogen-bonded liquid crystal complexes dicarboxylic acid (Malonic acid MA): p-n alkoxy benzoic acid (nOBA): abbreviated as MA:nOBA (where n = 10,11,12) towards the applications of liquid crystal display devices is investigated. This involves the measurement of physical parameters of displays: Luminance, Luminance uniformity, Luminance coefficient, Contrast ratio, Transmission of Display, Figure of Merit (Performance of the material) and Chromaticity. Liquid crystal texture analysis on the MATLAB platform is employed for this investigation. Display device parameters computed from the grey level intensities of the liquid crystal textures as a function of temperature and wavelength gives the information about application suitability of the material. Obtained results shows that, hydrogen-bonded liquid crystal complex MA:10OBA has high values of display parameters and make them as is a suitable material for the fabrication of display devices compared to other studied compounds.

Observation of Induced Luminescence and Thermochromism in Achiral Hydrogen Bonded Liquid Crystal Complexes

Abstract A novel hydrogen bonded liquid crystal (HBLC) complexes are obtained from the non-mesogenic (benzylmalonic acid) and mesogenic (p-n-alkyloxybenzoic acid, where n = 6, 7 and 8) compound via intermolecular hydrogen bonds (H-bond). H-bonds are experimentally confirmed by the Fourier transform infrared spectroscopic (FT-IR) studies and the same is validated using density functional theory (DFT). Induced thermochromism is observed by the polarizing optical microscope (POM) and its possible applications are reported. Phase transition temperature and their analogous enthalpy values, stability factor and span width are determined by the differential scanning calorimetry (DSC) studies. Band gap energy is calculated using UV-visible and photoluminescence spectrum. Hyper conjugative stabilization energy and atomic charge distribution is studied by the natural bond orbital (NBO) studies. Mulliken analysis clearly reveals the intermolecular interaction and steric effect of the HBLC complexes. An interesting phenomenon is that the observation of luminescence and thermochromism in the highly fluidity nematic phase. This peculiar behavior is attributed due to the intermolecular H-bonding interaction between the BMA and nOBA compounds and the effect of rotatory motion of the molecules in nematic phase. Luminescence increases when the spacer moiety decreases in the present complexes is also reported. In nematic phase, the molecules are in different degrees of the excited state which is correlated with the hyper conjugative energy through NBO studies.

Thermal and Optical Characterization of Multiple Hydrogen Bonded Liquid Crystals and Its Application in Display Devices

Novel homologous series of phloroglucinol (PG) and 4-n-alkyloxybenzoic acid (nOBA, n = 4 to 12) hydrogen bonded liquid crystal (HBLC) complex have been designed and synthesized. In the self-assembly process, intermolecular interaction between the molecules produce the multiple HBLCs with various shapes and structure. Existences of multiple hydrogen bonds in the PG+nOBA HBLC complex are confirmed by FT-IR spectroscopic method. Textural changes along with that phase transition temperature are identified by polarizing optical microscope (POM). Due to the polymerization, an induced stabilized smectic phase along with re-entrant disordered phase is noticed in the present PG+nOBA HBLC complex. The thermodynamic properties such as enthalpy values, thermal stability and thermal span width are analyzed by differential scanning calorimetry (DSC). An induced re-entrant phenomenon in the present HBLC complex is due to the dipolar aggregation has been discussed. The band gap energy is calculated by UV–Visible spectrometer (UV–Vis) which gives the clear evidence for the existence of band gap energy value (Eg = 3.5 eV) in the present HBLC complex. The desirable band gap in the present HBLC and its display device application is reported in the present communication. The other liquid crystal parameters (thermal stability, tilt angle, etc.) are also discussed.

Synthesis and characterization of hydrogen bonded liquid crystal complexes by 4-octyloxy benzoic acid and some dicarboxylic acids

Hydrogen bonded liquid crystal complexes synthesized from mesogenic 4-octyloxy benzoic acid (8OBA) and some non-mesogenic dicarboxylic acids {HOOC(CH2)nCOOH, n = 4, 7 and 8}; referred as ADA/8OBA (n = 4, Adipic acid), AZA/8OBA (n = 7, Azelaic acid) and SEA/8OBA (n = 8, Sebacic acid) are reported. Thermal and microstructural properties of the binary liquid crystal systems are investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The hydrogen bond formed between the 8OBA and dicarboxylic acid is confirmed by Fourier Transformed Infrared spectroscopy (FTIR) assay. The DSC and POM results infer that the binary complexes exhibit mesogenic smectic and nematic phases. All binary liquid crystal complexes exhibited four phase transition peaks to indicate Cr ↔ SmG ↔ SmC ↔ N ↔ I phase sequence during heating and cooling DSC scans. Similar phase sequence is also observed by POM. Effect of the heating rate on the phase transition temperatures and enthalpy changes is investigated. As the heating rate increased, the phase transition temperature and peak heights are increased, but enthalpy value generally decreased. Thermal stability factor and entropy changes are calculated. The phases and transitions are found to follow regular thermal order.

Theoretical and experimental studies on optically tunable hydrogen bonded liquid crystal complex derived from mesogenic and non-mesogenic aromatic compound

A novel hydrogen bonded liquid crystal (HBLC) complex is synthesized from non-mesogenic benzylmalonic acid (BMA) and mesogenic 4-nonyloxybenzoic acid (9OBA). Structural properties and optimized vibrational frequencies of BMA + 9OBA have been studied by FT-IR spectrum. The weak intermolecular interaction between the molecules is proved by NBO and Mulliken charge distribution analysis. The optical and thermal properties are investigated by POM, DSC, UV-Visible and PL techniques. The present HBLC complex exhibits schlieren textures of nematic, broken focal conic texture of smectic C and multicolored mosaic texture of smectic G phases respectively which is not observed in the pure mesogen (9OBA). The HBLC complex geometry is optimized by DFT method at the level of B3LYP basis set 6311G (d, p). The electronic properties of HBLC complex such as, NBO, HOMO-LUMO, ESP and Mulliken charge distribution are also studied. A noteworthy observation is brought out by identifying the presence of photoluminescence in nematic phase due to the variation in intermolecular interaction of the mesophase. The utility of the same complex is discussed. The phase width, thermal stability factor, tilt angle, phase transition temperature and its enthalpy values are reported.

Study of variation in thermal width of nematic and induced smectic ordering phase of citric acid (CA) and 4-heptyloxybenzoic acid (7OBA) hydrogen bonded liquid crystal complexes

Hydrogen-bonded liquid crystals (HBLCs) have been derived from nonmesogenic citric acid (CA) and mesogenic 4-heptyloxybenzoic acid (7OBA) yielding a highly ordered smectic C (Sm C) phase along with the new smectic X (Sm X) phase which has been identified as fingerprint-type texture. Optical (polarizing optical microscopy), thermal (differential scanning calorimetry) and structural (Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy) properties are studied. A noteworthy observation is that the intermolecular H-bond (between CA and 7OBA) influences on its melting point and clearing temperature of the HBLCs which exhibits lower value than those of the individual compounds. A typical extended mesophase region has been observed in the present complex while varying the mixture ratio (1:1 to 1:3) than those of individual compounds. The change in the ratio of the mesogenic compound in the mixture alters thermal properties such as enthalpy value and thermal span width in nematic (N) region of HBLC complex. Optical tilt angle measurement of CA+7OBA in Sm C phase has been discussed to identify the molecular position in the mesophase.

Analysis of optical and thermal properties of double hydrogen bonded liquid crystal binary mixtures

ABSTRACTEighteen binary mixtures are prepared from three thermotropic double hydrogen bonded liquid crystal complexes formed by Mesaconic Acid (ME) and various alkyloxy benzoic acids, namely ME + 5BAO, ME + 11BAO and ME + 12BAO where 5BAO, 11BAO and 12BAO represents pentyloxy benzoic acid, undecyloxy benzoic acid and dodecyloxy benzoic acid respectively. Two sets of binary mixtures (ME + 12BAO with ME + 5BAO and ME + 11BAO with ME + 5BAO) are formed by varying their molar ratio in steps of 0.1 to 0.9 which leads to the formation of eighteen binary mixture complexes. Existence of different energy bands in the binary mixtures is identified from the analysis of Fourier Transform Infrared Spectroscopy (FTIR). Phases such as nematic and smectic C are observed in all the binary mixtures which are confirmed through Polarizing Optical Microscopy (POM). Transition temperatures corresponding to the individual mesophases are further verified using Differential Scanning Calorimetry (DSC). Phase diagram of two sets of binary mixtures are constructed with the aid of POM and DSC data. Optical tilt angle measurement; a primary order parameter; is calculated in smectic C phase of the binary mixtures and the resultant data obtained is fitted to critical exponent value is in concurrence with the Mean Field theory predicted value. Thermal studies such as stability factor, order of phase transitions and specific heat capacity value of the mesophases are extracted from the DSC thermograms.

Induced Smectic X Phase Through Intermolecular Hydrogen-Bonded Liquid Crystals Formed Between Citric Acid and p-n-(Octyloxy)Benzoic Acid

Hydrogen-bonded liquid crystal (HBLC) is synthesized from citric acid (CA) and 4-(octyloxy)benzoic acid (8OBA) with different mole ratios. Fourier transform infrared spectroscopy (FT-IR) confirms the presence of hydrogen bond between CA and 8OBA. Nuclear magnetic resonance (NMR) spectroscopic studies validate the intermolecular complementary, cyclic type of hydrogen bond, and molecular environment in the designed HBLC complex. Powder X-ray diffraction analysis reveals the monoclinic nature of liquid crystal complex in solid phase. Liquid crystal parameters such as phase transition temperature and enthalpy values for the corresponding mesogenic phases are investigated using a polarizing optical microscope (POM) and differential scanning calorimetry (DSC). It is observed that the change in chain length and steric hindrance while increasing the mole ratio in HBLC complex induces a new smectic X (Sm X) along with higher-order smectic G (Sm G) phases by quenching of smectic C (Sm C). From the experimental observations, induced Sm X phase has been identified as a finger print texture. Also, Sm G is a multi-colored mosaic texture in 1:1, 1:2, and 1:3 mol ratios. The optical tilt angle, thermal stability factor, and enhanced thermal span width of CA + 8OBA complex are discussed.

Observation of induced new smectic phase in supramolecular hydrogen bonded liquid crystals between mesogenic and non-mesogenic aliphatic compounds

ABSTRACTPresent supramolecular hydrogen bonded liquid crystal (HBLC) complex is obtained between mesogenic 4-nonyloxybenzoic acid (9OBA) and non-mesogenic citric acid (CA). A phase transition temperature and enthalpy values are calculated by differential scanning calorimetry (DSC) and phase behaviour are identified by polarizing optical microscope (POM). The liquid crystal parameters and structure are characterized by POM, DSC, FT-IR, NMR and optical tilt angle studies. The DSC and POM reveals the smectic and nematic phase transitions in the present complex. The molecular structure of HBLC complex is elucidated by Proton Nuclear Magnetic Resonance (1H NMR). The noteworthy in the present complex is the nematic and Smectic C phase is separated by a Smectic X phase which shows the finger print textures. The Smectic X phase is estimated by varying the mole ratio of the CA+9OBA from 1:1 to 1:3. Molecular tilt with respect to the director the Smectic X and Smectic C phase data are fitted to a power law equation in the optical tilt angle studies and it follows the Mean Field Theory. The 1:2 mole ratio of CA+9OBA shows monotropic Smectic C phase. Another creditable observation is that while the mole ratio of 9OBA mesogenic compound increases the nematic range also increases in the present HBLC complex.

Experimental investigation on the effect of mesogenic ratio in hydrogen-bonded liquid crystal complexes

ABSTRACTHydrogen-bonded liquid crystal complex (HBLC) is synthesized from mesogenic 4-hexyloxy benzoic acid (6OBA) and aliphatic non-mesogenic citric acid (CA). The presence of intermolecular hydrogen bond in the HBLC complex is confirmed by FTIR spectrum. Phase transition temperature and enthalpy values are identified using different techniques. Induced highly ordered smectic G phase has been noticed in the present HBLC complex. Thermal span width and thermal stability factor of the individual mesogenic phase are discussed. The complexes are synthesized in different mole ratios, and their corresponding influence on the phase transitions is also discussed.

Optical, Thermal Studies on Binary and Ternary Hydrogen-Bonded Liquid Crystal Complexes

Hydrogen-bonded ferroelectric liquid crystalline (HBFLC) complexes are synthesized from binary mixtures of l-(+)-tartaric acid with 4-dodecyloxybenzoic acid and cholesteryl acetate. A ternary complex has been obtained from l-(+)-tartaric acid, 4-dodecyloxybenzoic acid, and cholesteryl acetate. Fourier transform infrared spectroscopy (FTIR) studies confirm the formation of an intermolecular hydrogen bond in the binary as well as the ternary complex. The l-(+)-tartaric acid does not show any mesomorphic behavior, but the hydrogen-bonded binary and ternary complexes are exhibiting the nematic phase along with tilted smectic phases. Phase transition properties of HBFLC mixtures have been investigated by means of differential scanning calorimetry (DSC) and polarizing optical microscope (POM). The DSC and POM clearly reveal the existence of nematic and smectic phases in the HBFLC mixtures. The optical tilt angle of binary and ternary mixtures for smectic C* phase and thermal stability factors of the mesogenic phases have been discussed. The noteworthy observation is that there is a significant reduction of phase transition temperatures with enhanced phase width, lowering melting temperature, and clearing point in the HBFLC ternary complex.

Inductive effect for the phase stability in hydrogen bonded liquid crystals, x-(p/m)BA:9OBAs

A new series of hydrogen bonded liquid crystal (HBLC) complexes, made up with substituted benzoic acids (BAs) and nonyloxy benzoic acid, viz., x-(p/m)BA:9OBAs are reported for x = F, Cl, Br and –CH3 substituted at para (p) or meta (m) positions of BA moiety. Proton nuclear magnetic resonance (1H-NMR) spectrum confirms the HBLC complex. Infra red (IR) spectrum confirms linear, double and complementary type of hydrogen bonding (HB) between x-(p/m)BAs and 9OBA. The liquid crystal (LC) phases are characterised by polarisation optical microscopy (POM) and differential scanning calorimetry (DSC) techniques. x-(p/m)BA:9OBA exhibit N, C and G LC phase variance. HB induces tilted phases and enhances LC phase stability. The influence of configuration, size, electronegativity, electron directing capacity and inductive nature of substituent (x) is investigated for the stability of LC phases. An overview of the LC phase data indicates predominant ‘negative inductive effect’ in HBLCs with electron withdrawing substituents. Inductive effect operates effectively for para substitutions. Results are discussed in the wake of reports in other HBLCs.

Conformational studies of intermolecular hydorgen bonding through induced crystal G phase in nBA:7HB

This paper exploits the physical investigation on liquid crystal complexes obtained by self-organisation of p-n-alkyl benzoic acid (nBA) mesogens with non-mesogenic materials heptyl p-hydroxy benzoate (7HB). Intermolecular interactions of the molecules result the hydrogen bond between the proton donor (COOH) of nBA and proton acceptor (OH) of 7HB. The formation of hydrogen bond is attributed to the quenching of the nematic phase and inducement of crystal G phase in liquid crystal complex. A comparative study of phase abundance is presented with respect to the pure nBAs and other hydrogen bonded liquid crystal complexes of nBAs. Thermal and phase behaviour of the complexes are determined by polarising optical microscope (POM), differential scanning calorimetry (DSC) and image moments approach. Intermolecular interactions which result the hydrogen bond in complexes are investigated using Fourier transform infrared (FTIR) spectroscopy. Molecular structure of the liquid crystal complexes in the solid phase was elucidated using powder X-ray diffraction and proton nuclear magnetic resonance (1HNMR).

Design, synthesis and characterization of a linear hydrogen bonded homologous series exhibiting reentrant smectic C ordering

Design, synthesis and characterization of seven linear hydrogen bonded liquid crystal complexes derived from mesogenic p–n-decyloxy benzoic acid and p–n-alkyl benzoic acids designated as 10OØn (where n varied from ethyl to octyl) are reported. FTIR studies confirm the hydrogen bond formation in all these complexes. The phase transition temperatures and their corresponding enthalpy values are experimentally deduced from Differential Scanning Calorimetry (DSC) studies. POM and DSC data are further utilized for the construction of 10OØn phase diagram. Two Odd–even effects have been evinced, one in enthalpy values and the other in corresponding transition temperatures across the isotropic to nematic phase transition. An interesting result is the observation of re-entrant smectic ordering, designated as smectic CR in three higher ordered mesogens. A new smectic ordering, smectic X, has been observed which is sandwiched between traditional smectic C and re-entrant smectic CR. Magnitudes of optical tilt angle in smectic C, smectic X and smectic CR are experimentally found to attain saturation with decrement of temperature in the corresponding phase. The occurrence of smectic X and smectic CR are discussed with relation to the molecular chemical structure. The optical filtering action in smectic C and re-entrant smectic CR phases have been analyzed.

Induction of Liquid Crystalline Phases and Influence of Chain Length of Fatty Acids in Linear Hydrogen-Bonded Liquid Crystal Complexes

A novel series of linear hydrogen-bonded liquid crystals (HBLCs), viz., Py14BA:nFAs synthesized from nonmesogenic moieties, such as an N(p-n-pyridene carboxaldehyde), p-n-tetradecyl aniline, and the long-chain-bearing aliphatic acids (nFAs for n = 10, 12, 14, 16, and 18), are reported. The chemical stability, purity of the sample, and the presence of hydrogen bonding (HB) are confirmed by polarized thermal microscopy and 1H NMR and IR spectroscopy. The LC phase abundance is characterized by polarized optical microscopy (POM) and differential scanning calorimetry (DSC) techniques. Py14BA:nFAs are found to exhibit BF liquid crystalline phase variance. The Iso–SmBcryst and SmBcryst–SmF transitions are found to be of first-order nature. Phase diagram for Py14BA:nFAs infers the induction and enhancement of LC phase stability. The growth of tilted LC phases due to HB interaction is discussed. Analysis of the influence of chain length (n) on LC phase stability, viz., ΔTLC and ΔTTilt, suggests for a tunable molecular pair potential given by U12(n) = [A × eαn − 1]. The tilted LC phase stability is found to grow with a relative exponential strength in Py14BA:nFA series.