Browsing by Author "Hemant Kumar Singh"

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Anchoring transition driven by short range ordering in calamitic-discotic composites
(Elsevier, 2015) Srividhya Parthasarathi; D.S. Shankar Rao; Hemant Kumar Singh; B. Singh; S. Krishna Prasad
We report investigations at atmospheric as well as elevated pressures on a host calamitic nematic liquid crystal doped with a discotic material exhibiting a novel anchoring transition (ANT), not present in the pure host. The change over from the substrate-surface determined planar to the homeotropic orientation occurs at a specific temperature that is governed by, as seen from X-ray and Frank bend and splay constants data, the short-range ordering changing from that for a columnar nematic to that of a standard nematic. Applied pressure diminishes the tendency for the orientation change thereby enhancing the range of the planar alignment finally annulling ANT. We ascribe the observed features to the competition between the anchoring energy of the aligning surface and the tendency of the structure to be parallel to the surface creating frustration and leading to ANT. Phase diagrams involving ANT have been constructed at atmospheric as well as elevated pressures. © 2015 Elsevier B.V. All rights reserved.
Effect of alkoxy chain density on the mesogenic properties of aroylhydrazone based liquid crystals: synthesis, characterisation, photophysical and gelation behaviour
(Taylor and Francis Ltd., 2020) Priyanka Kanth; Hemant Kumar Singh; Vijay Kumar; Sachin Kumar Singh; D. S. Shankar Rao; S. Krishna Prasad; Bachcha Singh
Three series of ester linkage containing aroylhydrazone based compounds have been synthesised where density and length of alkoxy chains are varied sequentially at ester end, keeping amide end of the molecule the same to investigate the effect of alkoxy chain density. The series of the compounds with single alkoxy chain at 4- position at ester terminal show nematic mesophase. The series with two alkoxy chains at 3- and 5- positions exhibit columnar rectangular mesophase and the series with three alkoxy chains at 3-, 4- and 5- positions show columnar oblique mesophase. It was observed that increasing the number of alkoxy chains at ester terminal, self-assembly of molecules changes and leads to a change from nematic to columnar mesophase and also significant enhancement in the mesomorphic range. Temperature dependent Raman studies confirm the presence of intermolecular hydrogen bonding which assist the self-assembly and gelation properties of molecules. All the series show similar photophysical properties despite the fact that the series vary in their molecular structures. Representative compounds of each series exhibited gelation in hydrocarbon solvents. FESEM images of the gels showed interwoven network of nanofibers of several micrometres length. These supergelators may be good candidates for applications in electronic devices. © 2020 Informa UK Limited, trading as Taylor & Francis Group.
Effect of regioisomerism on the self-assembly, photophysical and gelation behavior of aroylhydrazone based polycatenars: Synthesis and characterization
(Elsevier B.V., 2019) Priyanka Kanth; Hemant Kumar Singh; Vijay Kumar; Sachin Kumar Singh; D.S. Shankar Rao; S. Krishna Prasad; Bachcha Singh
In this paper we report five series of aroylhydrazone based polycatenars differing from each other in number and position of alkoxy chains on one end of the core; keeping other end the same. A systematic variation in the structures was carried out to understand the effect of position and chain length on the mesophase behavior. In the case of single alkoxy chain at 4-position, there is a transition from Smectic C to Smectic A mesophase during cooling and Smectic A to Smectic C transition in heating cycle in all the homologues except n = 6 & n = 8. In the case of two alkoxy chains at 3-, 5-positions, the compounds are non-mesogenic in nature. On changing the position of alkoxy chains from 3-, 5-positions to 3-, 4-positions, intermolecular forces weaken and these compounds become liquid crystalline and show columnar rectangular mesophase resulting from the effect of regioisomerism. Moving on to the series with three alkoxy chains, it was observed that 2-, 3-, 4-trialkoxy substituted compounds exhibit columnar rectangular mesophase except lower chain length (n = 6 & 8) while 3-, 4-, 5-trialkoxy substituted aroylhydrazones show columnar rectangular mesophase; except n = 10 which shows columnar oblique mesophase. Thus it was established that on increasing density of alkoxy chains around one terminal, mesophase changes from smectic to columnar mesophase. Temperature dependent Raman studies confirm the presence of intermolecular hydrogen bonding. Further, effect of substitution pattern did not show much influence on the photophysical properties of the mesogenic series in solid and solution state. However, the non-mesogenic series showed a different absorption and emission transition from the mesogenic series in solid and solution state. Solid state fluorescence studies show almost similar emission maxima in all the series. However, it was also noticed that non-mesogenic series show maximum red shifted emission maxima in solid state as compared to that of solution. All the series showed good gelation properties with less than 1% CGC (wt%) suggesting the strong ability of molecules to form gel. These H-bonded liquid-crystalline gels have immense potential for applications in emissive displays. © 2019 Elsevier B.V.
Effect of standardized extract of Bacopa monnieri (CDRI-08) on testicular functions in adult male mice
(Elsevier Ireland Ltd, 2017) Shishir Kumar Patel; Shilpi Singh; Hemant Kumar Singh; Shio Kumar Singh
Ethnopharmacological relevance Bacopa monnieri (BM) has been used in India since the time of Rig-Veda for augmentation of learning, memory, brain health etc. Aim of the study The memory augmenting effect of BM is well documented. CDRI-08 is a standardized extract of Bacopa monnieri, but its effect on the male reproductive health has not been investigated. Therefore, the aim of the present study was to examine the effect of CDRI-08 administration on the male reproductive organs with special emphasis on testis in adult mice. Materials and methods CDRI-08, containing at least 55% bacosides (the major constituent of BM), was investigated for its effect on testicular functions in adult Parkes (P) mice. A suspension of CDRI-08 was orally administered in doses of 40 and 80 mg kg−1 body weight day−1 for 28 days and various male reproductive end points were evaluated. Results Compared to control, CDRI-08 treatment caused a significant increase (p<0.05) in spermatogenic cell density (germinal epithelial height: control, 55.03±4.22 vs 40 mg, 67.15±2.65 and 80 mg, 69.93±3.76; and tubular diameter: control, 206.55±2.62 vs 80 mg, 253.23±12.19), PCNA index (control, 59.85±2.09 vs 40 mg, 82.17±1.56 and 80 mg, 84.05±3.51) and in steroidogenic indices in the testis, and in sperm viability (control, 0.67±0.010 vs 80 mg, 0.80±0.04) in cauda epididymidis of the treated mice. On the other hand, however, the same treatment caused a significant decrease (p<0.05) in abnormal sperm morphology (control, 21.72±1.06 vs 40 mg, 10.63±1.50 and 80 mg, 15.86±0.87) in cauda epididymidis, and in lipid peroxidation level in testis of the treated mice compared to controls. Conclusion The results suggest that treatment with CDRI-08 extract improves sperm quality, and spermatogenic cell density and steroidogenic indices in the testis of P mice. © 2016 Elsevier Ireland Ltd
Evolution of Pore Morphometry and Compositional Changes in Immature Raniganj Shale under Heated Environment: Implications for Enhanced Gas Recovery
(American Chemical Society, 2024) Kumar Nilankar; Divyanshoo Singh; Hemant Kumar Singh; Alok Kumar; Khairul Azlan Mustapha
The complexity of pore networks and compositional heterogeneities in shale significantly influences shale gas flow behavior. Thermal treatment in shale reservoirs has enhanced pore connectivity and facilitated gas flow. This study investigates the evolution of pore morphometry and chemical variations in immature Raniganj shale with increasing temperature. By integrating multiple advanced techniques, we aim to improve the precision of two-dimensional/three-dimensional (2D/3D) pore morphometry and mineralogical analysis. Qualitative and quantitative analyses of pore morphometry and surface morphology are conducted on shale samples subjected to temperatures ranging from ambient to 400 °C, using atomic force microscopy (AFM), low-pressure nitrogen (N2) adsorption, and field emission scanning electron microscopy (FE-SEM). Parameters such as surface roughness, fractal dimension, porosity, microcracks, absorbed gas volume, specific surface area, and thermal damage-induced surface area show significant increases, indicating the formation of new macro- and microcracks and the development of pore network connections with pre-existing cracks. The pore size distribution (PSD) reveals a rise in the mesopore and macropore ranges. This research integrates thermogravimetric analysis (TGA), X-ray diffraction (XRD), Rock-Eval pyrolysis, and Fourier transform infrared spectroscopy (FTIR) to analyze the mineralogical and chemical properties of shale and assess the impact of temperature on these attributes. The results indicate that the shale samples are clay-rich and contain significant organic content. The continuous reduction in total organic carbon (TOC) concentration and the breakdown of organic matter above 200 °C can be attributed to hydrocarbon release during devolatilization. Additionally, the observed decline in P-wave velocity and contact angle from 100 to 400 °C suggests an increase in pore volume and the hydrophilic behavior of shale with temperature. The findings of this study provide fundamental insights into the role of thermal environments in enhancing gas recovery from shale formations. They can further improve gas recovery and CO2 storage in shale reservoirs. © 2024 American Chemical Society.
Fabrication of liquid crystal based sensor for detection of hydrazine vapours
(Elsevier B.V., 2014) Rajib Nandi; Sachin Kumar Singh; Hemant Kumar Singh; Bachcha Singh; Ranjan K. Singh
A novel liquid crystal (LC) based sensor to detect trace level amount of hydrazine vapour has been developed. The LC 4′-pentyl-4-biphenylcarbonitrile (5CB) doped with 0.5 wt% 4-decyloxy benzaldehyde (DBA) shows dark to bright optical texture upon exposure of hydrazine vapours as revealed by polarizing optical microscopy under crossed polarizers. The hydrazine interacts with the doped DBA and form diimine compound which disrupt the orientation of aligned 5CB. The interaction between DBA and hydrazine has been also studied by Raman spectroscopy. © 2014 Elsevier B.V. All rights reserved.
Investigation of liquid crystalline property of a new calamitic liquid crystalline system methyl 4-(4ʹ-(4ʹʹ-(decyloxy)benzyloxy) benzylideneamino)benzoate
(Taylor and Francis Ltd., 2017) Rajib Nandi; Hemant Kumar Singh; Sachin Kumar Singh; D. S. Shankar Rao; S. Krishna Prasad; Bachcha Singh; Ranjan K. Singh
A new polar calamitic liquid crystal, methyl 4-(4ʹ-(4ʺ-(decyloxy)benzyloxy) benzylideneamino)benzoate (M3BA) containing ether and Schiff base groups as linker with terminal polar ester group, has been synthesised and mesomorphic properties are studied by differential scanning calorimetry, polarising optical microscopy, density functional theory, temperature-dependent X-ray diffraction and temperature-dependent micro- Raman study. The smectic A (SmA) mesophase with focal conic texture has been observed with wide mesomorphic range. Layer thickness in SmA phase is greater than the optimised length of the molecule, indicating partially bilayer SmA phase. Analysis of Raman marker bands of C–H in-plane bending of phenyl rings, C=C stretching of rings, C=N stretching and C=O stretching shows structural changes at molecular level at Cr → SmA phase transition and provides proper intermolecular interactions responsible for dimeric unit in partially bilayer SmA phase. © 2016 Informa UK Limited, trading as Taylor & Francis Group.
Liquid crystal based sensor system for the real time detection of mercuric ions in water using amphiphilic dithiocarbamate
(Elsevier B.V., 2016) Sachin Kumar Singh; Rajib Nandi; Kirtika Mishra; Hemant Kumar Singh; Ranjan Kumar Singh; Bachcha Singh
We developed a simple, sensitive, label-free and real time detection method for mercuric ions (Hg2+) in water using liquid crystals (LCs). In this system, newly synthesized amphiphilic potassium N-methyl-N-dodecyldithiocarbamate (MeDTC) was doped in 4-cyano-4′-pentyl biphenyl (5CB) LC, which align LC molecules at aqueous interface and polar head group of the amphiphile acts as mecuric ion specific chelating ligand. When this sensor system was incubated in the aqueous solution containing Hg2+ ions, a dark to bright transition of the image of LCs was observed. This was caused due to rapid and stable complex formation between dithiocarbamate chelating group of MeDTC with Hg2+ ions at aqueous interface, which disrupted the orientation of LCs giving bright texture. The limit of detection of the system for aqueous Hg2+ ion is 0.5 μM. This sensor did not respond to other metal ions like Pb2+, Cd2+, Cu2+, Zn2+, Na+, Mg2+ and Ca2+, which are common environmental interference in water. We also demonstrated that this sensor is capable of detecting Hg2+ ions in real water samples (tap water). The very simple and effective procedure reported here should facilitate the development of real time, portable and reliable LC based sensor for mercury pollution control. © 2015 Elsevier B.V. All rights reserved.
Mesomorphic and DFT studies of terminal ester containing salicylaldimines and their copper (II) complexes
(Taylor and Francis Inc., 2017) Hemant Kumar Singh; Sachin Kumar Singh; Vijay Kumar; Priyanka Kanth; Kirtika Mishra; Bachcha Singh
In this article, we report synthesis and characterization of a novel homologous series of butyl 4-(4′-(alkoxy)-2-hydroxybenzylideneamino)benzoates, CnLH (n = 6, 8, 10, 12, 14, 16) and their copper(II) complexes. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and powder X-ray diffraction (XRD) studies. The ligands and their copper(II) complexes exhibit wide range of enantiotropic smectic A mesophase as confirmed by their typical optical texture under polarizing microscope. Thermal stability of the compounds is determined by thermo gravimetric analyses. DFT calculations have been performed using GAUSSIAN-09 program at B3LYP level to obtain the stable electronic structure of the ligand and its copper(II) complex. © 2017 Taylor & Francis Group, LLC.
Mesomorphic, micro-Raman and DFT studies of new calamitic liquid crystals; Methyl 4-[4-(4-alkoxy benzoyloxy)benzylideneamino]benzoates
(Elsevier, 2014) Rajib Nandi; Hemant Kumar Singh; Sachin Kumar Singh; Bachcha Singh; Ranjan K. Singh
The mesomorphic properties of newly synthesized homologous series of calamitic liquid crystals; methyl 4-[4-(4-alkoxy benzoyloxy)benzylideneamino] benzoates, H2n+1CnOC 6H4COOC6H4C(H)N C6H 4COOCH3; n = 6, 8, 10, 12, 14, 16 (MABBAB-n) containing ester and Schiff base groups as linker have been studied by temperature dependent micro-Raman study, differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). All members of this series exhibit enantiotropic smectic A (SmA) mesophase with oily streak and focal conic textures. Analyses of Raman marker bands of phenyl rings, Schiff base and ester groups of MABBAB-10 confirm the phase transitions. The Raman study also gives an evidence of breaking of weak intermolecular hydrogen bonds associated with ester groups and formation of new hydrogen bonds through CN bond at Cr → SmA phase transition. The monomer and dimer were optimized and vibrational assignment of MABBAB-10 was also done with density functional theoretical (DFT) technique to understand the experimental results. © 2014 Elsevier Ltd. All rights reserved.
Microwave-assisted synthesis and mesomorphic investigations of p-substituted aroylhydrazones and their nickel(II) and copper(II) complexes
(Taylor and Francis Ltd., 2015) Sachin Kumar Singh; Vijay Kumar; Rajib Nandi; Hemant Kumar Singh; Ranjan K. Singh; Bachcha Singh
The present study is focused on the development of green microwave process for the synthesis of mesogenic substituted aroylhydrazones and their nickel(II) and copper(II) complexes. The compounds have been synthesised by microwave-assisted as well as thermal methods for comparison purpose. The compounds were structurally characterised by using suitable spectroscopic techniques. The mesomorphic properties were studied by differential scanning calorimetric analysis and polarising optical microscopy. The stable molecular structures of the mesogenic methylidenehydrazinato-nickel(II) complex have been obtained by density functional theoretical method to understand the structural origin responsible for the mesomorphic property. © 2015, Taylor & Francis.
Microwave-assisted synthesis, characterisation and mesomorphic investigations of novel disubstituted aroylhydrazones
(Taylor and Francis Ltd., 2015) Sachin Kumar Singh; Vijay Kumar; Hemant Kumar Singh; Priyanka Kanth; Bachcha Singh
The present study is focused on the development of green microwave process for the synthesis of mesogenic substituted aroylhydrazones and their structure–mesophase relationship study. Two new liquid crystalline series of disubstituted aroylhydrazones with (ABB(OH)H-n) and without lateral hydroxyl group (ABBH-n) (n = 6–16) have been synthesised by microwave-assisted methods. The compounds were structurally characterised by using suitable spectroscopic techniques. The mesomorphic properties of the series of aroylhydrazones were examined using differential scanning calorimetric analysis and polarising optical microscopy. The relationship between structure and mesogenic properties was analysed by comparison of the present series and earlier reports on homostructural series of aroylhydrazones. Thus, the effects of substitution of phenyl rings with ester and ether linking group at both terminals and introduction of hydroxyl group at lateral position on stability of mesophase and their width were investigated. In general, all substituted aroylhydrazone derivatives exhibit SmC mesophase, and substitution of terminal and lateral group has considerably increased the stability and broadened the width of mesophase of the compounds. © 2015 Taylor & Francis.
Molecular approach to phase transitions in a calamitic ester substituted aroylhydrazone liquid crystal
(John Wiley and Sons Ltd, 2016) Rajib Nandi; Sachin Kumar Singh; Hemant Kumar Singh; D.S. Shankar Rao; S. Krishna Prasad; Bachcha Singh; Ranjan K. Singh
Temperature dependent Raman and X-ray diffraction studies of a calamitic ester substituted aryolhydrazone liquid crystal (LC) system; N-[4-(4ʹ-decyloxy)benzoyloxy benzylidene]-Nʹ-[4ʹ-decyloxybenzoyl]hydrazine (DB2H) have been performed to investigate the molecular arrangement and intermolecular interaction environment in LC phase. X-ray diffraction study with the help of density functional theoretical study gives the information of molecular tilt angle in SmC layer. Prominent Raman signatures of crystal I → crystal II, crystal II → SmC and SmC → Isotropic phase transitions were identified in terms of changes in peak position and linewidth as well as Raman intensity. Analysis of Raman marker bands gives evidence of residual intermolecular hydrogen bonds between amide groups responsible for tilting arrangement in SmC phase. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
Multiscale Characterization of Pore Evolution in Lesser Himalayan Black Shale from Krol Formation under Oxic Thermal Heating: Relevance to Untapped Shale Gas Extraction
(American Chemical Society, 2025) Divyanshoo Singh; Kumar Nilankar; Hemant Kumar Singh; Alok Kumar; Vikram Vishal; Khairul Azlan Mustapha
Thermal stimulation under oxic heating has emerged as a transformative approach for enhancing gas recovery from tight shale reservoirs, which is typically challenging due to their complex pore structures, low permeability, and inherent anisotropy. Considering this, an untapped Neoproterozoic shale from the Lesser Himalayan region was heated up to 400 °C to investigate pore structure evolution using a combination of small-angle X-ray scattering (SAXS), low-pressure N2 gas adsorption (LPGA), and field emission scanning electron microscopy (FE-SEM). Given the shale’s fair hydrocarbon generation potential, as indicated by total organic carbon (TOC) and vitrinite reflectance (%VRo) data, understanding its thermal-induced pore structure evolution is critical for enhancing gas extraction efficiency. The outcomes of this study demonstrate that oxic heating significantly alters the pore structure of shale, marked by a progressive shift from micropores to meso- and macropores. SAXS and LPGA analyses reveal a strong positive correlation between pore size distribution (PSD) and thermal treatment. The increased steepness in LPGA-derived BET isotherms and hysteresis loop transition from H4 to H3 confirms the development of larger pores. These substantial changes result from the coalescence and collapse of the adjacent pores during combustion. Along with the expansion of pre-existing pores, new pores were also developed during combustion, which was obvious with the findings of pore area and specific surface area (SSA) derived from SAXS and LPGA analysis. Furthermore, a notable rise in the pore area at 400 °C was also observed, suggesting the breakdown of organic matter and the formation of numerous organic matter pores. This organic matter breakdown was evident with the thermogravimetric analysis (TGA), where a rapid mass loss was observed at 400 °C. The SEM photomicrographs with widened pores, fractures, and numerous finer pores at higher temperatures further supported the above findings. This study highlights the potential of combustion-induced thermal stimulation and suggests that oxic thermal treatment can effectively alter shale microstructure, thereby offering a viable enhancement technique for shale gas recovery. © 2025 American Chemical Society.
Observation of exceptional 'de Vries-like' properties in a conventional aroylhydrazone based liquid crystal
(Royal Society of Chemistry, 2016) Hemant Kumar Singh; Sachin Kumar Singh; Rajib Nandi; D. S. Shankar Rao; S. Krishna Prasad; Ranjan K. Singh; Bachcha Singh
Smectic liquid crystals with 'de Vries-like' properties are characterized by a maximum layer contraction of ≤1% upon transition from the non-tilted SmA phase to the tilted SmC phase. A straight alkoxy chain-terminated conventional aroylhydrazone based liquid crystal N-(4-(tetradecyloxy)-2-hydroxybenzylidene)-4′((4′′(hexadecyloxy)benzyl)oxy)benzohydrazide (BSac-1416) undergoes the SmA-SmC phase transition with a maximum layer contraction of 0.65%. The merits of the de Vries reduction factor, i.e. R and f values for this mesogen, are comparable to, or even lower than, those reported for established perfluorinated and polysiloxane-terminated bona fide de Vries-like materials. © 2016 The Royal Society of Chemistry.
Synthesis and self-assembly of aroylhydrazone based polycatenars: A structure-property correlation
(Elsevier B.V., 2019) Hemant Kumar Singh; Ravindra Kumar Gupta; Sachin Kumar Singh; D.S. Shankar Rao; S. Krishna Prasad; Ammathnadu S. Achalkumar; Bachcha Singh
Two series of aroylhydrazone based polycatenars which differ from each other in terms of the linking groups (semi flexible ester or flexible ether linkage) were synthesized. These hexacatenars were mesogenic and also showed gelation in organic solvents at very low concentration, which is assisted by the intermolecular hydrogen bonding. Both the series of hexacatenars were prepared by varying the peripheral chain length from n-hexyloxy to n-hexadecyloxy chain. In the case of ester based series on moving from n-decyloxy to n-dodecyloxy chain, a transition from columnar rectangular phase to columnar hexagonal phase was noticed. Such behavior was not seen in the case of ether-based hexacatenars, irrespective of the chain length. Representative hexacatenars from each series exhibited gelation at low concentration, but the critical gelation concentration of ester-based hexacatenar was almost half of that observed for ether-based hexacatenar. From these studies we can understand the importance of the linking group, which constitutes very small part of the molecule, but has a significant effect on the type of the self-assembly in bulk as well as in presence of solvents. The presence of semi-flexible ester group provides a bent conformation to the molecule, while the presence of flexible ether group provides a linear shape to the molecule, as evident from the molecular modeling studies. Further the presence of the ester group enhances the extent of intermolecular hydrogen bonding with the solvent that leads to a lower critical gelation concentration in comparison to the ether-based linking group. Such H-bonded liquid crystals have potential in the preparation of liquid crystalline physical gels and related applications. © 2019
Synthesis, characterisation, mesomorphic investigation and temperature-dependent Raman study of a novel calamitic liquid crystal: Methyl 4-(4′-n-alkoxybenzylideneamino)benzoate
(2013) Rajib Nandi; Hemant Kumar Singh; Sachin Kumar Singh; Bachcha Singh; Ranjan K. Singh
A new series of Schiff base calamitic liquid crystal; methyl 4-(4′-n-alkoxybenzylideneamino)benzoate (MABAB), H2n+1CnOC6H4C(H)=NC6H4COOCH3 (n = 6, 8, 10, 12, 14, 16) has been synthesised and characterised by elemental analyses, Fourier transform infrared spectroscopy (FT-IR), 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy. The mesomorphic properties of these compounds were studied by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). All members of the series exhibit enantiotropic smectic A (SmA) mesophase. Temperature-dependent micro-Raman study of one of the members, MABAB-10 has been employed to identify phase transitions and the molecular rearrangement therein. Analysis of Raman marker bands; C-H in-plane bending, C-C stretching of phenyl rings and -C(H)=N- linking group of core confirms the transitions clearly as observed through DSC and POM. An in situ Raman measurement of C-H in-plane bending mode has also been performed to visualise the molecular changes more clearly. The Raman study gives an evidence of induced co-planarity of rings at Cr→SmA phase transition. The density functional theoretical (DFT) optimisation of monomer, dimer and rotational conformer of MABAB-10 also support the induced co-planarity at Cr→SmA phase transition. © 2013 Copyright Taylor and Francis Group, LLC.
Synthesis, characterization and mesomorphic investigations of ester-substituted aroylhydrazones possessing a lateral hydroxyl group
(Elsevier Ltd, 2014) Sachin Kumar Singh; Hemant Kumar Singh; Rajib Nandi; Vijay Kumar; Nicolae Tarcea; Jürgen Popp; Ranjan K. Singh; Bachcha Singh
The synthesis, characterization and investigation of a new liquid crystalline series of ester containing aroylhydrazones with a lateral hydroxyl group, N-[4-(4′-alkoxy)benzoyloxy-2-hydroxy-benzylidene]-N′- [4″-alkoxybenzoyl]hydrazine (Cm,nLH), with the same or different peripheral alkoxy chains, and some of their nickel(II) and copper(II) complexes are described. All the ligands, except those with no terminal chains on either end of the molecule, exhibit an enantiotropic SmC mesophase, as evidenced by polarizing optical microscopy and differential scanning calorimetric studies. It has been found that addition of a lateral hydroxyl group along with ester-substitution to the aroylhydrazone core increases the mesomorphic as well as thermal stability of the ligands. Also, the coordination of Ni2+ and Cu2+ with the aroylhydraozone core inhibits the mesomorphic potential of the ligands. A temperature dependent Raman study of one of the members, C12,12LH (m = n = 12) has been made to identify phase transitions and to understand the molecular rearrangement as a result of changes in intermolecular interactions at the phase transition. DFT calculations have been performed to obtain the stable electronic structure of the ligand (C6,6LH) and its nickel(II) complex. © 2014 Elsevier Ltd. All rights reserved.
Synthesis, characterization, and mesomorphic investigations of calamitic liquid crystals - Methyl 4-(4′-(alkoxy)-2-hydroxybenzylideneamino) benzoates and their copper(ii) and nickel(ii) complexes
(Taylor and Francis Inc., 2013) Hemant Kumar Singh; Sachin Kumar Singh; Vijay Kumar; Bachcha Singh
A new series of Schiff's base mesogenic ligands with a polar methyl ester as an end group, methyl 4-(4′-(alkoxy)-2 hydroxybenzylideneamino) benzoates, CnLH (n = 6, 8, 10, 12, 14, 16) and their copper(II) and nickel(II) complexes have been synthesized. They were characterized by elemental analyses, Fourier transform infrared (FT-IR), 1H and 13C nuclear magnetic resonance, and UV-VIS spectroscopy. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The ligands exhibit an enantiotropic SmA mesophase with a high-temperature range and thermal stability. The square planar copper(II) complexes show enantiotropic SmA mesophase, but the nickel(II) complexes are nonmesogenic in nature. The thermal stability of the compounds was also determined by thermo gravimetric analyses. Density functional theory (DFT) calculations were performed using GAUSSIAN-03 program at B3LYP level to obtain the stable electronic structure of the ligand and their metal complexes. © 2013 Copyright Taylor and Francis Group, LLC.
Synthesis, characterization, and mesomorphic investigations of diester-substituted salicylaldimines and their copper (II) complexes
(Taylor and Francis Inc., 2016) Sachin Kumar Singh; Madan Kumar Singh; Hemant Kumar Singh; Bachcha Singh
A novel homologous series of N-[4-[4′-n-alkoxy)benzoyloxy-2-hydroxybenzylidene)-4-carbethoxy anilines, H2n+1CnOC6H4C(O)OC6H3(OH)C(H)NC6H4COOC2H5 (n = 6, 8, 10, 12, 14, 16) and their copper(II) complexes have been synthesized. All these compounds have been characterized by suitable spectroscopic techniques. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The ligands exhibit wide range of enantiotropic smectic A and nematic phases as confirmed by their typical optical texture under polarizing microscope. The square planar copper(II) complexes of the ligands show only an isotropic phase at higher temperature and no mesogenic nature is observed. DFT calculations have been performed using GAUSSIAN-03 program at B3LYP level to obtain the stable electronic structure of the ligand with decyloxy chain length and its copper(II) complex. © 2016 Taylor and Francis Group, LLC.