Browsing by Author "Singh, Sachin K."

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    Exploring a solid polymorphism and phase transitions in 4-cyano-4′-pentylbiphenyl (5CB) and rGO-doped 5CB using temperature dependent Raman spectroscopy
    (Elsevier B.V., 2025) Khoja, Ummer Bashir; Patel, Chandan B.; Tripathi, Pankaj Kumar; Kumar, Rajesh; Mishra, Soni; Singh, Sachin K.; Singh, Ranjan K.; Vikram, Kunwar
    Raman spectroscopy is used to examine the temperature-dependent phase transition behaviour of the liquid crystalline system 4-cyano-4′-pentylbiphenyl (5CB) and its nanocomposite with reduced graphene oxide (5CB@rGO) over the temperature range of −160 °C to 90 °C. First time, such a broad temperature range study of 5CB and 5CB@rGO has been reported. The structural and intermolecular interaction characteristics of the liquid crystal 5CB and its behaviour in the presence of reduced graphene oxide (rGO) are examined in depth by the temperature-induced Raman spectra and DFT calculations. To assess the phase transitions in 5CB and 5CB@rGO, the significant bands associated with the polar C[tbnd]N group and phenyl rings were thoroughly examined. A new crystal-crystal (solid polymorphism) phase transition is investigated first time, occurring between −120 °C and −100 °C. Another significant new crystal-crystal phase transition in 5CB and 5CB@rGO is also exposed, taking place between −20 °C and −10 °C. Differential scanning calorimeter (DSC) measurements confirm this new phase transition in 5CB and temperature sensitivity fairly matches Raman analysis. To evaluate the structural as well as change in intermolecular interactions in each phase, the detailed DFT study is performed on the 5CB molecule to establish the spectra-structure relation. The detailed spectra-structure correlation is discussed in this study. The spectra-structure correlation and change in spectral parameters are used to investigate the structure and intermolecular interaction of each phase. © 2025 Elsevier B.V.
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    Probing the mesophase formation in thermotropic liquid crystal HBDBA using temperature-dependent Raman spectroscopy and DFT method
    (Elsevier B.V., 2024) Patel, Chandan Bhai; Pandey, Satyabratt; Singh, Sachin K.; Vikram, K.; Singh, Ranjan K.
    Liquid crystalline properties of the synthesized liquid crystal (LC) N-(o-hydroxybenzylidene)-N′-(4-n-alkoxybenzylidene) azines (HBDBA) are probed thoroughly using the comprehensive array of techniques e.g. differential scanning calorimetry (DSC), differential thermal analysis (DTA), polarizing optical microscopy (POM), temperature-dependent Raman spectroscopy and density functional theory (DFT) method. In this study, intricate molecular interactions crucial for mesophase formation of liquid crystalline system HBDBA and molecular rearrangement that occurs during LC transitions are unravelled comprehensively. Remarkably, at the Cr → SmA phase transition, the peak position, linewidth, and intensity of signature Raman bands are prominently changed. A thorough analysis of Raman marker bands and DFT calculation confirm the disruption of intramolecular hydrogen bonds in HBDBA at the Cr → SmA transition. The conclusion of the present study enriches the understanding of the underlying mechanisms of mesophase formation and intricate molecular interactions and arrangement at the molecular level of the thermotropic LC. © 2024 Elsevier B.V.
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    Spectroscopic study of coordination of Cu2+ with liquid crystal HBDBA: An investigation at ultra trace level
    (Elsevier B.V., 2024) Patel, Chandan Bhai; Nayak, Monalisha; Pandey, Satyabratt; Prakash, Om; Singh, Sachin K.; Singh, Ranjan K.
    The present work describes the synthesis and characterization of a copper complex with a liquid crystal compound called N-(o-hydroxybenzylidene)-N'-(4-n-alkoxybenzylidene) azines (HBDBA). The FTIR/ Raman spectroscopy and DFT calculations were employed to confirm the coordination of Cu2+ ion with HBDBA. On complex formation several changes in the Raman and FTIR spectra were observed. The linewidth and peak position of few Raman/ IR bands changed and few new bands in the Raman and IR spectra appeared. The experimentally observed bands of HBDBA molecule and its Cu2+- complex are assigned with the help of DFT. In the next part a concentration-dependent study has been done to detect ultra-trace amount (∼10–8 M) of Cu2+ ion binding with HBDBA using Raman and fluorescence spectroscopy. The result suggests that HBDBA can be used to detect Cu2+ ions in trace amount. © 2024
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    Substituted Aroylhydrazone Based Polycatenars: Tuning of Liquid Crystalline Self-Assembly
    (Wiley-Blackwell, 2018) Singh, Hemant K.; Pradhan, Balaram; Singh, Sachin K.; Nandi, Rajib; Rao, Doddamane S. Shankar; Prasad, Subbarao K.; Achalkumar, Ammathnadu S.; Singh, Bachcha
    A systematic investigation on mesomorphic properties of two new classes of substituted-aroylhydrazones having semi-flexible ester (ester based polycatenars) and flexible ether linker (ether based polycatenars) with variable alkoxy chain length (n=6, 8, 10, 12, 14, 16) are described. The members of each series with six soft alkoxy chains formed columnar self-assembly as confirmed by differential scanning calorimetry analysis, polarized optical microscopy and powder X-ray diffraction studies. For the ester based polycatenar scaffolds, the mesophase of lower alkoxy chain members exhibited columnar oblique phase which further transformed to columnar hexagonal phase with the increase in the chain length and thus showing a mesophase crossover phenomenon. In the case of ether based polycatenars, the presence of ether link provides significant stabilization of the columnar oblique phase for all the members except the lower homologues. The driving forces for the appearance of columnar self-assembly are the intermolecular hydrogen-bonding interactions between the amide groups (-C=O⋅⋅⋅H-N-) of aroylhydrazone core, which was confirmed by the temperature dependent IR studies. In addition, both the series of compounds exhibit good gelation properties, which is assisted by the intermolecular hydrogen bonding. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim