Hydrogen Bonded Ferroelectric Liquid Crystals Research Articles

Detailed analysis of induced smectic phases and paramorphic effect of double hydrogen bonded ferroelectric liquid crystals

A novel double hydrogen bonded ferroelectric liquid crystal (HBFLC) complex was isolated from (R)-(+)-Methylsuccinic acid (RMSA) and 4-Nonyloxybenzoic acid (9OBA). The presence of hydrogen bond between proton donor (RMSA) and proton acceptor (9OBA) molecules were characterized by FT-IR spectroscopy. Mesomorphic behavior and its phase transition temperature of the HBFLC complex (1:1 and 1:2 ratio) were studied by differential scanning calorimeter (DSC), polarized optical microscope (POM) and identified smectic A*, smectic C* and smectic G* phases by quenching of nematic. MSA + 9OBA HBFLC complex has strong dipole moment which is vertical to the lengthy molecular axis provide a pathway to the insight of smectic mesophases. Sm C* phase revealed paramorphic effect due to refractive index changes in the H-bond layers and leads violet to red color textures. Stabilization of the smectic phase by dipole-dipole interaction in the HBFLC complex was reported using density functional theory (DFT) analysis. Stability of the phase increase while increasing the mesogenic ratio in the present HBFLC complex was also discussed. The structure of the MSA + 9OBA HBFLC complex was optimized by B3LYP theory with the basis set of 6311-G (d, p). In natural bond orbital analysis, it was found that the high stabilization energy specified the intermolecular interaction among the molecules.

Optical modulation studies of multiwall carbon nanotube dispersed in hydrogen bonded ferroelectric liquid crystal mixture for electro-optic devices

Structural, optical and electrical properties of multiwall carbon nanotubes (MWCNT) dispersed liquid crystalline (LC) mixture is extensively studied for electro-optic devices. A small amount of (0.1%) MWCNT is dispersed in cholesteryl stearate (CHS) and 4-dodecyloxybenzoic acid (12OBA) and its mixture is further characterized. Hydrogen bond between the mesogenic compounds are confirmed using FT-IR. Surface morphology and MWCNT dispersion in hydrogen bonded ferroelectric liquid crystal (HBFLC) mixture is established by SEM studies. Optical studies of the mixture using polarizing optical microscope (POM) is recognized by the induced smectic blue phase and smectic A* mesogenic phases. Transition temperatures and its corresponding enthalpy values of induced mesophases are analyzed by differential scanning calorimetry (DSC). An interesting observation of optical modulation in the present MWCNT dispersed HBFLC mixture is reported using dielectric studies. Textural modification with respect to external stimulus (bias voltage) in the present HBFLC mixture is reported. Further the field induced phase transitions and improved dielectric permittivity due to the dispersion of MWCNT is also reported.

Investigation on Induced Non-Tilted Smectic A* and Thermochromic Effect in Tilted Smectic C* Phase of Linear Double Hydrogen Bonded Ferroelectric Liquid Crystals

Linear double hydrogen bonded ferroelectric liquid crystal (HBFLC) complexes are derived from non-mesogenic (R)-(+)-methylsuccinic acid and mesogenic 4-n-alkyloxybenzoic acids. Fourier transform infrared (FT-IR), polarizing optical microscope (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies are used to verify the existence of intermolecular hydrogen bonds in the synthesized HBFLC complexes. An induced orthogonal non-tilted smectic A* phase and a noteworthy observation of a thermally tuned thermochromic phenomenon are analyzed by using textural and thermal studies. Due to increasing elastic viscous force, the induced hexagonal higher- order smectic G* phase is reported in the lower alkyloxy carbon mesogens whereas the same is not observed in the individual compounds. Based on the temperature and change in the alkyloxy chain length, the induced thermochromic effect is discussed. Quenching of the nematic phase by an induced orthogonal phase is observed. Other liquid crystal parameters, such as the melting point, the phase transition temperature, the texture and the enthalpy, are reported.

Optical, thermal and electrical investigations in two homologous series of hydrogen bonded ferroelectric liquid crystals

Two novel series of complimentary hydrogen bonded ferroelectric liquid crystals (HBFLC) comprising of 14 mesogens are synthesised by mixing (R)-(+)-2-(Benzyloxy) propionic acid (BPA) with various alkyloxy/alkyl benzoic acids. First series yielded eight HBFLC mesogens namely (R)-(+)-2-(Benzyloxy) propionic acid mixing with various benzoic acids viz., pentyloxy benzoic acid (BPA + 5BAO), hexyloxy benzoic acid (BPA + 6BAO), heptyloxy benzoic acid (BPA + 7BAO), octyloxy benzoic acid (BPA + 8BAO), nonyloxy benzoic acid (BPA + 9BAO), decyloxy benzoic acid (BPA + 10BAO), undecyloxy benzoic acid (BPA + 11BAO) and dodecyloxy benzoic acid (BPA + 12BAO) respectively. The second series yielded six HBFLC mesogens namely (R)-(+)-2-(Benzyloxy)propionic acid mixing with various benzoic acids viz., propyl benzoic acid (BPA + 3BA), butyl benzoic acid (BPA + 4BA), pentyl benzoic acid (BPA + 5BA), hexyl benzoic acid (BPA + 6BA), heptyl benzoic acid (BPA + 7BA) and octyl benzoic acid (BPA + 8BA) respectively. The molecular structure of entire 14 mesogens is represented by ball and stick model. Phase identification is made by textural studies of various phases through Polarizing Optical Microscopy (POM), enthalpy values and phase transition temperatures are elucidated from Differential Scanning Calorimetry (DSC) studies. The homologues of the first series BPA + nBAO exhibited smectic B*and smectic G* phases while only smectic G* phase is observed in BPA + nBA. Formation of hydrogen bond in the synthesised mesogens is confirmed by FTIR spectra. Phase diagrams for both the series are constructed from POM and DSC studies. Dielectric relaxation studies in smectic B* and smectic G* phases are performed on selected mesogens.

Investigations on smectic X* and re-entrant smectic C* orderings in hydrogen bonded ferroelectric liquid crystals

Two homologous series of hydrogen bonded ferroelectric liquid crystal (HBFLC) series have been isolated. One mole of ferroelectric Dextro tartaric acid (DTA) is mixed with 2 mol of p-n-alkyloxy benzoic acid (BAO) to obtain homologues of DTA + nBAO. Eight mesogens are isolated by varying the carbon number from pentyloxy to dodecyloxy viz., DTA + 5BAO to DTA + 12BAO. Similarly 1 mol of ferroelectric Dextro tartaric acid (DTA) is mixed with 2 mol of p-n- alkyl benzoic acid (BA) to obtain homologues of DTA + nBA. Seven mesogens are isolated by varying the carbon number from pentyl to dodecyl viz., DTA + 3BA to DTA + 8BA. Spectroscopic characterization (FTIR, 1H and 13CNMR) for all the 14 mesogens indicate the formation of hydrogen bond in HBFLC. Optical textures are recorded in various phases. An interesting observation is the finding of parachromatism in cholesteric phase. In addition to the conventional phases, two new smectic orderings viz., smectic X* and re-entrant smectic C* have been characterized. The textures of smectic X* exhibits a worm like textures while that of smectic C* is broken focal conic and the transition from smectic X* to re-entrant smectic C*. Smectic X* is observed to be sandwitched between cholestric and smectic C*. The x-ray study of smectic X* confirm it to be a smectic ordering. Measurments of tilt angle, light filtering and dielectric relaxation studies have been performed in this new smectic ordering. A new smectic ordering labeled as re-entrant smectic C* has been identified and characterized. Data of dielectric relaxation, magnitude of tilt angle in this phase confirm this phase is distinctly different from conventional smectic C*. Re entrant Smectic C* and Smectic X* are observed in higher homologues of DTA + nBAO where ‘n’ varies from 8 to 12.

Exploration of Induced Blue Phases and Orthogonal Smectic Batonnets in Hydrogen-Bonded Ferroelectric Nanoliquid Crystalline Complexes for Optoelectronic Devices

A novel blue phase hydrogen-bonded ferroelectric liquid crystal (HBFLC) series has been synthesized from cholesteryl stearate (CHS) and p-n-alkyloxybenzoic acid (nOBA, where n = 2 to12). Blue phase (BP) liquid crystalline complex is a high potent material for next-generation optoelectronic devices. The structural, optical, and thermal properties of present HBFLC complexes have been characterized by X-ray diffraction techniques (XRD), Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), polarizing optical microscope (POM), and differential scanning calorimetry (DSC) techniques. The band gap energy of the present HBFLC complex (4.6 eV) is estimated by UV-Visible spectrometer. X-ray diffraction and scanning electron microscope (SEM) studies which confirm the monoclinic nature and morphology of the present complex. Phase diagram of the present CHS + nOBA is constructed from DSC data and the same is discussed. The lower homologous of CHS + nOBA HBFLC (n = 2 to 6) complex shows BPsm1, BPsm2, BPsm3 while higher homologous (n = 7 to 12) exhibiting orthogonal smectic A* (SmA*) character with blue phases. A noteworthy observation is that the identification of extended thermal span of smectic blue phases and induced SmA* phase in the present HBFLCs. Another important observation is that the widest BP range is reported in the present hydrogen-bonded ferroelectric nanoliquid crystalline (HBFNLC) complex which is more suitable for photonic devices. In addition, LC parameters such as, phase width, thermal stability factor, phase transition temperature with enthalpy value, and the origination of orthogonal phases in CHS + nOBA HBFLC complex is also reported.

Experimental and computational (DFT) studies on induced orthogonal smectic A∗ phase in hydrogen-bonded ferroelectric liquid crystals

Hydrogen-bonded ferroelectric liquid crystals (HBFLC) are designed and synthesized from nonmesogenic chiral proton donor compound of (R)-([Formula: see text])-Methylsuccinic acid (MSA) and mesogenic proton acceptor compound of 4-undecyloxybenzoic acid (11OBA) in a different mole ratio. Intermolecular hydrogen bonds (H-bond) between the nonmesogenic and mesogenic compounds have been confirmed through experimental Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) computational studies. The steric hindrance and inductive effects of the present complex and its influence on the structure are discussed. A rich phase polymorphism in the liquid crystalline complex has been studied using polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The chiral phases observed in the present complex are due to the presence of lone pair (n) to anti-bonding ([Formula: see text]) transition symmetry which is validated by DFT studies. A noteworthy observation of induced smectic A[Formula: see text](Sm A[Formula: see text]) by quenching of traditional phase (nematic) has been identified and the reason for the same has been discussed by DFT studies. The unusual phase order of Sm A[Formula: see text], smectic C[Formula: see text](Sm C[Formula: see text]) and smectic G[Formula: see text][Formula: see text](Sm G[Formula: see text]) mesogenic phases are observed. The other liquid crystalline parameters are evaluated by experimental and theoretical calculations and the same has been compared. Increased tilt angle in liquid crystal (LC) molecules has been theoretically analyzed by natural bond orbital (NBO) studies. Stability of the HBFLC phases and its origination mechanism have been discussed with the help of highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) energies.

Observation of paramorphic phenomenon and non-tilted orthogonal smectic phases in hydrogen bonded ferroelectric liquid crystals for photonic applications

A new class of hydrogen bonded ferroelectric liquid crystals (HBFLC) have been designed and synthesized by intermolecular hydrogen bonds between mesogenic 4-decyloxybenzoic acid (10OBA) and non-mesogenic (R)-(+)-Methylsuccinic acid (MSA) which have been confirmed through experimental and theoretical studies. Further, Mulliken population analysis clearly reveals that the existence of hydrogen bonds, strength and dynamic properties. Textural observation and its corresponding enthalpy values are analyzed by polarizing optical microscope (POM) and differential scanning calorimetry (DSC) respectively. Paramorphic changes in Sm C* phase due to the change of refractive index, which clearly reveal that the complex could be used for filtering action in photonic devices. The transition from lone pair to π* with large stabilization energy evidently exposes the chiral phases in the present HBFLC complex. Intermolecular interaction is analyzed by using natural bond orbital (NBO) studies. The highest energy in the HOMO-LUMO shows the stable phase in the HBFLC complex. Molecular structure of the HBFLC complex possesses the monoclinic which has been evinced through x-ray analysis. The randomly oriented bunch of homogeneous molecules in Sm A* phase of the HBFLC complex is reported.

A detailed study of hydrogen bonded ferroelectric mesogens formed between alkyl and alkyloxy benzoic acids with carbamyl glutamic acid

ABSTRACTA new ferroelectric homologous series of hydrogen-bonded ferroelectric liquid crystals is designed and synthesised with 14 compounds comprising two homologous series. The hydrogen bond is formed between dicarboxylic acid, viz. Carbamyl glutamic acid (CGA) with p-n-alkyl/alkyloxy benzoic acids (BA/BAO) and is confirmed by Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) studies. These two series referred as the CGA+nBAO and the CGA+nBA yields 14 mesogenic homologues and the mesogenic nature is detected by optical textures through polarising microscope which is confirmed through Differential Scanning Calorimetry (DSC). CGA+nBAO series exhibit cholesteric, smectic X*, smectic C* and smectic G* phases while CGA+nBA exhibits cholesteric and smectic G*phases. The enthalpy values of the corresponding temperatures are elucidated. Odd–even effect is evinced at smectic C* to smectic G* phase transition temperatures of CGA+nBAO series. The order of the individual phase transition and thermal stability factor of the phases is also calculated. Optical tilt angle in smectic C* phase is obtained by optical extinction method. Dielectric relaxation and their corresponding frequency shift observed in different ferroelectric phases are measured and a dielectric molecular modelling is presented. Crystallisation kinetic study of smectic G* phase in CGA+nBAO is computed. An interesting phenomenon – ‘Parachromatism’ – is elaborated.

Structural and thermo-optic studies on linear double hydrogen bonded ferroelectric liquid crystal homologous series

ABSTRACTA novel series of supramolecular hydrogen bonded ferroelectric liquid crystal (HBFLC) is formed through hydrogen bonding interaction between nonmesogenic dextro-levo tartaric acid (DLTA) and mesogenic p-n-alkyloxy benzoic acids (nBAO, where n = 7 to 12). The formation of hydrogen bond in the complex is confirmed through Fourier transform infrared spectroscopy (FTIR) studies. Optical and thermal behaviors for mesomorphic phases of individual complex in the series are meticulously studied by means of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Computation of the enthalpy values in the homologous series of complex during both heating and cooling cycles is proved that thermal equilibrium exhibited by the complex system. Extended thermal span width and rich liquid crystallinity is observed in the present complex due to the presence of aromatic ring with chiral center. Thermal stability factor and thermal equilibrium are also discussed. Presence of alkyloxy chain on either side of chiral molecules hinder the abundant reduction in phase transition temperature and lowered melting point compared to the individual mesogens. Optical tilt angle for smectic C* phase is determined and the same is fitted to a power law.

Thermal analysis of hydrogen-bonded ferroelectric liquid crystals

Thirty-six hydrogen-bonded ferroelectric liquid crystal (HBFLC) binaries derived from N-carbamoyl-l-glutamic acid (CGA) and p-n-alkyloxy/alkyl benzoic acids (nBAO/nBA) are synthesized and characterized. Hydrogen bonding in HBFLC is evidenced through Fourier transform infrared spectra. Proposed molecular environment is verified by proton nuclear magnetic resonance (1H NMR) investigation. Optical textures are recorded and the corresponding mesophases are identified by polarizing optical microscopy. From differential scanning calorimetry curves, transition temperatures and enthalpy values are experimentally deduced for 36 binaries, and further order of the transition is also calculated. Phase diagrams of four series, namely CGA + 5BAO and CGA + 5BA, CGA + 6BAO and CGA + 6BA, CGA + 7BAO and CGA + 7BA & CGA + 8BAO and CGA + 8BA, are constructed, and phase variance along with the percentage possession of individual phase is estimated. Optical tilt angle in smectic X* phase exhibited by the binaries is determined and fitted to a power law whose exponent is in good agreement with mean field theory prediction. Specific heat in smectic X* phase pertaining to nine molar proportions of CGA + 5BAO and CGA + 6BAO is discussed with respect to isotropic to smectic X* transition.

Binary Mixtures of Hydrogen-Bonded Ferroelectric Liquid Crystals: Thermal Span Enhancement in Smectic X* Phase

Abstract Thermotropic hydrogen-bonded ferroelectric binary liquid crystal mixtures comprising of N-carbamyl-l-glutamic acid (CGA) and p-n-alkyloxy benzoic acids (BAO) are investigated. Variation in the molar proportion of X and Y (where X=CGA+5BAO and Y=CGA+9BAO, CGA+10BAO, CGA+11BAO, and CGA+12BAO) comprising of four series yielded 36 binary mixtures. Optical and thermal properties of these mixtures are meticulously studied in the present article. In addition to the traditional phases, a novel smectic ordering namely smectic X* is observed in all the four series. The aim of the investigation is to obtain abundance occurrence of smectic X* with a large thermal span, and hence, the proportions of the binary mixtures are so chosen that the prelude task is accomplished. Optical tilt angle in smectic X* and smectic C* phases is experimentally determined, and a theoretical fit is performed. Phase diagrams of the four series are constructed from the data obtained from the differential scanning calorimetry and correlated with the phases recorded by the polarising optical microscope studies. Thermal stability factor and thermal equilibrium are also premeditated.

Thermal Analysis, Calorimetric and Electrical Polarization Studies in Smectic X* Phase of Hydrogen-Bonded Ferroelectric Liquid Crystals

Intermolecular hydrogen-bonded ferroelectric liquid crystals are isolated and characterized. Formation of hydrogen bond is evinced by Fourier Transform Infra-Red (FTIR) studies. Phases are confirmed by polarizing optical microscopic (POM) studies and further confirmed by Differential Scanning Calorimetry (DSC) thermograms. Phase diagram is constructed from POM and DSC data and the order of transition possessed by the individual phases are evaluated from the Cox parameter. Summation of the enthalpy values exhibited by the individual complexes both in heating and cooling cycles are compared to verify the thermal equilibrium exhibited by the system. Mono variant smectic X* phase observed in two complexes are confirmed to be smectic ordering from the tilt angle, helix, and spontaneous polarization measurements. Enhancement of smectic X* thermal range is noticed through the phase diagram of the binary mixtures. Unwinding of the helix is measured from helical pitch measurements. From dielectric studies, the threshold values for two field-induced phase transitions E1 and E2 are measured. Electric field–temperature (E–T) phase diagram is constructed from the threshold field values obtained with respect to the temperature variation. Further, molecular modeling is proposed for the observed electric field-induced phase transitions.

Electrical and Optical Studies of Hydrogen Bonded Ferroelectric Liquid Crystals Dispersed with MWCNT

Two hydrogen bonded ferroelectric liquid crystals (HBFLC) are dispersed with multi-walled carbon nanotubes (MWCNT) for achieving better thermal and electrical performance. Interesting feature of the present communication is the enhancement in the enthalpy value pertaining to isotropic-nematic transition in MWCNT doped liquid crystals compare to its pure counter parts. Dielectric relaxations studies are carried out in the pure and the MWCNT doped systems. It is observed that doping of MWCNT elevated the activation energies considerably. Optical shuttering action in one of the complex dispersed with MWCNT are discussed.

Design and characterization of hydrogen bonded ferroelectric liquid crystals: A study of light modulation in nematic and smectic orderings

A novel series of hydrogen bonded ferroelectric liquid crystals (HBFLC) have been isolated. Phase transition temperatures obtained by differential scanning calorimetry (DSC) and textural observations elicited by polarizing optical microscope (POM) studies are discussed. Phase diagram is constructed from the above data. Salient feature of the present work is observation of a light modulation due to field induced transitions (FiT) in nematic and smectic C* phases. Tilt angle measurements in various FiT of smectic C* phase are discussed. One of the mesogens in nematic phase behaves like an optical modulator; helical pitch measurements support the above observation.

Design, Synthesis and Characterization of Hydrogen-Bonded Ferroelectric Liquid Crystals

A novel series of hydrogen-bonded ferroelectric liquid crystals has been isolated. A hydrogen bond was formed between chiral ingredient (S)-(+)-6-methoxy-α-methyl-2-naphthaleneacetic acid (Nap) and mesogenic p-n alkyloxy benzoic acids. A phase diagram was constructed from the transition temperatures obtained by differential scanning calorimetry (DSC) and polarizing optical microscopic (POM) studies. Thermal and dielectric properties exhibited by these complexes, namely, Nap + nBA (where n = 6 to 11), are discussed. A phase diagram of the present hydrogen-bonded series was compared with that of the free alkyloxy benzoic acids (nBA). Nap + nBA series exhibits cholesteric, smectic C*, smectic G*, and smectic F* phases. Dielectric relaxations were studied in selected members of the homologous series that exhibits cholesteric and smectic GF* phases. Dielectric studies indicate multiple relaxation processes in the cholesteric phase and a single relaxation process in smectic G*, smectic F* phase. Activation energies calculated from the respective Cole–Cole plots are discussed.

A study of field induced transitions (FiT) in the nematic phase of an inter hydrogen bonded ferroelectric liquid crystal

A novel series of hydrogen bonded ferroelectric liquid crystals (HBFLC) have been isolated. Hydrogen bond is formed between non mesogen chiral ingredient (S)-1, 2–cholo-3-(4-hydroxy) phenyl propionic acid and mesogenic p-n alkoxy benzoic acids. Phase diagram is constructed from the transition temperatures obtained by differential scanning calorimetry (DSC) and polarizing optical microscopic (POM) studies. Thermal and electrical properties exhibited by a hydrogen bonded complex namely (S)-1,2–cholo-3-(4-hydroxy)phenyl propionic acid with octyloxy benzoic acid (CTy + 8BA) are discussed. Observation of dielectric hysteresis in CTy + 8BA makes it more suitable for device applications. Salient feature of the present work is observation of a field induced transitions in nematic phases pertaining to the above complex designated as FiT. This phenomenon has been confirmed by optical textures of POM, helicoidal measurements, optical intensity and dielectric studies. Four threshold electrical field values are noticed which in turn contributed to four new phases (E 1, E 2, E 3 and E 4) induced by electric field and helical pitch measurements supports the above observation. FiT is reversible in the sense that when applied field is removed the original texture is restored.

Tilt Angle, Spontaneous Polarization and LF Dielectric Relaxation Investigations in the Chiral Nematic and Smectic-C* Phases of a Hydrogen Bonded Ferroelectric Liquid Crystal (HBFLC)—11 bpa

Investigations of tilt angle, spontaneous polarization and Low frequency (5 Hz - 10 MHz) dielectric relaxations are reported in a chiral hydrogen bonded liquid crystal, HBFLC, viz., 11 bpa. Isotropic to chiral nematic (IN*) and chiral nematic to chiral smectic-C (N*SmC*) phase transition temperatures determined by dielectric method agree with reports of TM and DSC. Temperature variation of order parameter (viz., primary order parameter tilt θ (T) and secondary order parameter spontaneous polarization P S (T) relevant to SmC* phase) studied through critical exponents β 1 and β 2 agree with Mean-Field predictions. Influence of hydrogen bonding on the growth of relevant order parameters is discussed. Dielectric dispersion revealed a collective motion (i.e., Goldstone mode GM) around ∼ 100 Hz. Other two higher frequency relaxation processes (viz., Type–I and –II) observed in the N* and SmC* phases are explained on the basis of a molecular dipole model. The influence of bias field on G.M. is studied in SmC* phase. The off-centred non-Debye's dispersion is studied through the Cole-Davidson theory. HF relaxations of Type-I and –II are explained as reorientation of dipole distinctly configured on the molecular frame. Soft mode relaxation in SmC* phase follows ferroelectric Curie-Weiss law. Arrhenius shift of relaxation frequency fR reveals higher activation energy for Type-II and lower energy for Type-I reorientation. The influence of hydrogen bonding on ferroelectricity in LCs is studied in terms of phase stability, tilt angle and polarization in SmC* phase in the wake of reports in other FE materials.

Influence of hydrogen bonding on phase abundance in ferroelectric liquid crystals

The synthesis and characterization of five hydrogen-bonded ferroelectric liquid crystal complexes (HBFLCs) prepared from mesogenic p-n-alkoxy benzoic acids and non-mesogenic propionic/butyric acids with different chiral centres are reported. Complementary intermolecular hydrogen bonding is confirmed through IR study. HBFLCs are found to exhibit chiral nematic (N*), smectic C* (SmC*) and smectic G* (monotropic) phases in their cooling profiles during polarizing thermal microscopy and differential scanning calorimetry. Phase coexistence regions are observed above the IN* transition. The chiral nematic to smectic C* transition is found to be of first order. The temperature variation of spontaneous polarization exhibited by these HBFLC complexes in their SmC* phase is presented. The effect of non-covalent interaction imparted by the soft hydrogen bonding in these LC complexes on enhanced or induced thermal stability of tilted LC phases is discussed.