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Veeraprakash B, Kesava Reddy M, Das BB, Lobo NP, Ramanathan KV, Narasimhaswamy T. Effortless Extraction of Structural and Orientational Information from 13C- 1H Dipolar Couplings for Thiophene Mesogens. J Phys Chem B 2023; 127:10912-10922. [PMID: 38063349 DOI: 10.1021/acs.jpcb.3c06176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2023]
Abstract
Five molecular mesogens containing phenyl rings and thiophene are subjected to a detailed 13C NMR investigation. The first mesogen contains only phenyl rings, while the other four have thiophene with substitution at position 2 or 3. Two of these also have a spacer inserted between the thiophene and the rest of the core unit. The mesophase properties evaluated by complementary techniques reveal an enantiotropic nematic phase for all the cases and smectic C as well as Crystal J for a few mesogens. In addition to solution 13C NMR, the samples were studied using 1D and 2D solid-state 13C NMR experiments in the liquid crystalline phase. The chemical shifts and 13C-1H dipolar couplings obtained in the mesophase provided cutting-edge information about the molecular structure and orientation of the thiophene mesogens. Accordingly, dramatic differences in these parameters are noted for the mesogens, and consequently, the identification of 2- and 3-substituted thiophene mesogens is accomplished by a simple visual examination of the 2D spectra. Furthermore, for mesogens with a spacer between thiophene and the rest of the core, 13C chemical shifts and 13C-1H dipolar couplings showed remarkable variation, which was directly reflected in the order parameters. For instance, the order parameter (Szz) of thiophene in 2- and 3-substituted mesogens in which the spacer is absent is ∼0.63 whereas for those with spacer, it is reduced to ∼0.14-0.18. In comparison, the mesogen in which the core unit is made up of phenyl rings alone that is used to benchmark the characteristics of thiophene ordering showed an order parameter of ∼0.85. The study unambiguously demonstrates the supremacy of 13C NMR in extracting the structural and orientational information on mesogens in which thiophene is a constituent of the core unit.
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Affiliation(s)
- Bathini Veeraprakash
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | | | - Bibhuti B Das
- Department of Physics, Indian Institute of Science, Bangalore 560012, India
| | - Nitin P Lobo
- Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS), CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | | | - Tanneru Narasimhaswamy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
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2
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Kumar AVNA, Zoghaib WM, Chalapathy PV, Srinivasulu M, Madhumohan MLN, Rani GP, Potukuchi DM. Collective modes, relaxations, de Vries behavior and field influence in SmA and SmC* deVr phases of chiral liquid crystal dimer C-10Bms with siloxy spacer. Eur Phys J E Soft Matter 2023; 46:89. [PMID: 37782358 DOI: 10.1140/epje/s10189-023-00326-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Accepted: 07/18/2023] [Indexed: 10/03/2023]
Abstract
Investigations in chiral liquid crystal dimer with trisiloxy unit on spacer unit, viz. C-10Bms, are reported with respect to its resolved dipole moment. Occurrence of SmA and SmC*deVr LC phases was characterized by POM and DSC. Relatively enhanced thermal range of LC phases in dimer configuration was detailed. Tilt angle, hysteresis, polarization, collective modes and other low-frequency relaxations were investigated. Primary order parameter revealed validity of critical field model. Moderate tilt for viewing angle and electro-clinic response for switch speed in dimer were addressed. Hysteresis in SmC*deVr ensued storage capability for memories. Slightly higher activation energy Ea was attributed to siloxy chain on spacer. Goldstone and Soft modes were identified in SmC*deVr phase. Field influence on Goldstone mode was analyzed. Equivalence of thermal/Arrhenius and field activation energies was observed. Curie-Weiss law for SM revealed strong collective ferroelectric response. Temperature and field trends of dielectric relaxation parameters were addressed in terms of chiral center-based out-of-phase dipole moment. Figure of merit parameters in SmC*deVr estimated by dielectric loss revealed its relative performance far below the SmA-SmC*deVr phase transition.
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Affiliation(s)
- A V N Ashok Kumar
- Department of Physics, University College of Engineering, Jawaharlal Nehru Technological University:Kakinada, Kakinada, 533003, India
| | - W M Zoghaib
- Department of Chemistry, College of Sciences, Sultan Qaboos University, Al-Khoud, Muscat, Oman
| | - P V Chalapathy
- Department of Physics, University College of Engineering, Jawaharlal Nehru Technological University:Kakinada, Kakinada, 533003, India
| | - M Srinivasulu
- Department of Chemistry, Manipal Institute of technology, Manipal Academy of Higher Education, Manipal, 576104, India
| | - M L N Madhumohan
- Department of Physics, Vignan Foundation for Science, Technology and Research, Vadlamudi, 522213, India
| | - G Padmaja Rani
- Department of Physics, University College of Engineering, Jawaharlal Nehru Technological University:Kakinada, Kakinada, 533003, India
| | - D M Potukuchi
- Department of Physics, University College of Engineering, Jawaharlal Nehru Technological University:Kakinada, Kakinada, 533003, India.
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3
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Veeraprakash B, Shanavas AKJ, Reddy GSM, Lobo NP, Ramanathan KV, Narasimhaswamy T. Molecular Conformations of Shape Anisometrically Variant Mesogens in Liquid Crystalline Phase Studied by 13 C NMR Spectroscopy. Chemphyschem 2023:e202300353. [PMID: 37725408 DOI: 10.1002/cphc.202300353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Revised: 09/19/2023] [Accepted: 09/19/2023] [Indexed: 09/21/2023]
Abstract
Mesogens that vary in shape anisometry have been investigated by 13 C solid-state NMR in the liquid crystalline phase to inspect the conformations. The molecules examined comprise of (i) rod-like mesogen with three-phenyl ring core and terminal hexyloxy chains, (ii) three-ring core linked to the fourth phenyl ring via a spacer, and (iii) trimesic acid connected to three side arms core units through a spacer. The order parameter (Szz ) values for the phenyl rings of the rod-like mesogen are 0.65-0.68, while the mesogen with a three-ring core linked to a phenyl ring via spacer showed dissimilarity. Consequently, for the core unit phenyl rings, Szz is ~0.70, and the terminal phenyl ring showed a low value of 0.12. For the trimesic acid based mesogen, the Szz value for the side arm phenyl rings is ~0.53, and for the central phenyl ring, a very low value of 0.11 is witnessed. By considering the ordering of the rod-like mesogen as a yardstick and employing the ratios of Szz values of the phenyl rings, the average conformations of other mesogens are arrived. Accordingly, for the trimesic acid based mesogen, a tripod-like conformation instead of λ shape is proposed in the liquid crystalline phase.
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Affiliation(s)
- Bathini Veeraprakash
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai, 600020, India
| | - Abdul K J Shanavas
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai, 600020, India
| | - Goddeti S M Reddy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai, 600020, India
| | - Nitin P Lobo
- Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS), CSIR-Central Leather Research Institute, Adyar, Chennai, 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| | | | - Tanneru Narasimhaswamy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai, 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
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4
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Reddy MG, Lobo NP, Ramanathan KV, Narasimhaswamy T. Molecular Order of Topologically Variant Flexible Mesogens by 13C Nuclear Magnetic Resonance. Langmuir 2020; 36:12620-12631. [PMID: 32993293 DOI: 10.1021/acs.langmuir.0c02182] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
13C nuclear magnetic resonance investigations in the nematic phase of mesogens comprising a rod-like core with three phenyl rings connected to a fourth phenyl ring via a flexible spacer are reported. The molecules are abbreviated as monomer, dimer, and trimer as they comprised one, two, and three pairs of core and spacer combinations linked to ring IV, respectively. Hot-stage optical polarizing microscopy and differential scanning calorimetry studies confirmed that all of them exhibit an enantiotropic nematic phase with additional monotropic or enantiotropic smectic mesophases. Large values of 13C-1H dipolar couplings of the order of 11 kHz are observed for all the cases for the terminal carbon C1 of the core unit. These high values indicated that the corresponding CH vector is collinear with the long axis of the molecule, which itself is aligned parallel to the magnetic field. In contrast, the terminal carbon of the ring IV (C19/C17) exhibits a relatively smaller value in the range of 2.0-2.5 kHz, reflecting the divergent local dynamics at different sections of the mesogens. The orientational order parameters of the phenyl rings computed from the 13C-1H dipolar couplings have been used to obtain the conformation of the mesogens in the nematic phase. It is concluded that the dimer and trimer exhibit C2 and C3 symmetry with the ring IV connected by spacers tilted away from the symmetry axis by 35.9 and 90° for the two cases, respectively. This leads to the interesting tripod-like molecular shape for the trimer in the nematic phase rather than the planar representation of the λ shape.
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Affiliation(s)
- Mandadhi Guruprasad Reddy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - Nitin P Lobo
- Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS) CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | | | - Tanneru Narasimhaswamy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
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Knapkiewicz M, Rachocki A, Bielejewski M, Sebastião PJ. NMR studies of molecular ordering and molecular dynamics in a chiral liquid crystal with the SmC_{α}^{*} phase. Phys Rev E 2020; 101:052708. [PMID: 32575273 DOI: 10.1103/physreve.101.052708] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Accepted: 04/30/2020] [Indexed: 05/08/2023]
Abstract
Molecular dynamics of the antiferroelectric liquid crystal 4'-(octyloxy)biphenyl-4-carboxylate2-fluoro-4-[(octyl-2-yloxy)carbonyl]phenyl (abbreviated as D16) was investigated using different nuclear magnetic resonance (NMR) techniques. D16 molecules form a smectic-C_{α}^{*} phase (SmC_{α}^{*}) in an extremely wide temperature range (∼10 °C). Due to a small tilt of the molecules, this phase is characterized by short switching times, important for new photonic applications. The proton spin-lattice relaxation times were measured in isotropic (Iso), smectic-A (SmA), and SmC_{α}^{*} phases over a wide frequency range of five decades, with conventional and fast field-cycling NMR techniques. This approach allowed a comparison of the essential processes of molecular dynamics taking place in these phases. On the basis of NMR relaxometry measurements, we present a description of the motional behavior of liquid crystal molecules forming SmC_{α}^{*}. Pretransitional effects were observed in wide temperature ranges in both the isotropic and SmA phases in D16. The ^{1}H fast field-cycling NMR measurements were supplemented with NMR diffusometry and ^{19}F NMR spectroscopy.
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Affiliation(s)
- Magdalena Knapkiewicz
- Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznan, Poland
| | - Adam Rachocki
- Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznan, Poland
| | - Michał Bielejewski
- Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznan, Poland
| | - Pedro J Sebastião
- Center of Physics and Engineering of Advanced Materials, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
- Department of Physics, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
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Gradišek A, Cifelli M, Wojcik M, Apih T, Dvinskikh S, Gorecka E, Domenici V. Study of Liquid Crystals Showing Two Isotropic Phases by 1H NMR Diffusometry and 1H NMR Relaxometry. Crystals 2019; 9:178. [DOI: 10.3390/cryst9030178] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In this work, we report a study of two thermotropic liquid crystalline samples showing a not common mesophase behavior. The samples, namely a di-benzyloxy biphenyl derivative labelled 9/2 RS/RS, and a bimesogenic liquid crystal labelled L1, show a direct transition between two isotropic phases followed, at lower temperatures, by the optically isotropic, 3D structured, cubic phase. These systems have been investigated by means of 1H NMR diffusometry and 1H NMR relaxometry in order to characterize their isotropic–isotropic’–cubic mesophase behavior, mainly on the dynamic point of view. In particular, the temperature trend of the self-diffusion coefficients measured for both samples allowed us to significantly distinguish between the two isotropic phases, while the temperature dependence of the 1H spin-lattice relaxation time (T1) did not show significant discontinuities at the isotropic–isotropic’ phase transition. A preliminary analysis of the frequency-dependence of 1H T1 at different temperatures gives information about the main motional processes active in the isotropic mesophases.
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Santhosh Kumar Reddy Y, Lobo NP, Narasimhaswamy T. Effect of alkyl chain and linking units on mesophase transitions and molecular order of rod-like thiophene mesogens:13C NMR investigation. NEW J CHEM 2018. [DOI: 10.1039/c7nj03525j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
This study provides insight into the influence of alkyl chains and linking units on the mesophase properties of thiophene-based mesogens and on the orientational constraints of the core and terminal alkyl chain.
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Affiliation(s)
| | - Nitin P. Lobo
- Inorganic & Physical Chemistry
- CSIR-Central Leather Research Institute
- Chennai 600020
- India
| | - T. Narasimhaswamy
- Polymer Science & Technology
- CSIR-Central Leather Research Institute
- Chennai 600020
- India
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Affiliation(s)
- Valentina Domenici
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Pisa, Italy
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9
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Abstract
Thiophene-based rodlike molecules constructed from a three phenyl ring core and terminal dialkoxy chains recognized as forked mesogens are synthesized, and their mesophase properties as well as the molecular order are investigated. The synthesized forked mesogens would serve as model compounds for tetracatenar or biforked mesogens. On the basis of the position of the thiophene link with the rest of the core, 2-substituted and 3-substituted mesogens are realized in which the length of the terminal alkoxy chains is varied. The mesophase properties are evaluated using a hot-stage polarizing microscope and differential scanning calorimetry. For both homologues, the appearance of either nematic phase alone or in conjunction with smectic C phase is noticed depending on the length of the terminal alkoxy chains. The existence of layer ordering characteristic of the smectic C phase is confirmed for a representative mesogen using variable-temperature powder X-ray diffraction. High-resolution solid-state (13)C NMR measurements of C12 homologues of the two series reveal orientational order parameters of all rings of the core as well as terminal chains in the liquid crystalline phase. For both homologues, because of the asymmetry of ring I, the order parameter value is higher in contrast to ring II, ring III, and the thiophene ring. The chemical shifts and (13)C-(1)H dipolar couplings of OCH2 carbons of the terminal dodecyloxy chains provide contrasting conformations, reflecting the orientational constraints. Furthermore, the investigations also reveal that the mesophase range and the tendency for layer ordering are higher for 3-substituted mesogens compared to 2-substituted homologues.
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Affiliation(s)
- K Rajasekhar Reddy
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
| | - Nitin P Lobo
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
| | - T Narasimhaswamy
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
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Gradišek A, Domenici V, Apih T, Novotná V, Sebastião PJ. 1H NMR Relaxometric Study of Molecular Dynamics in a “de Vries” Liquid Crystal. J Phys Chem B 2016; 120:4706-14. [DOI: 10.1021/acs.jpcb.6b02224] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Anton Gradišek
- Jožef Stefan Institute, Jamova
39, SI-1000 Ljubljana, Slovenia
| | - Valentina Domenici
- Dipartimento di Chimica e Chimica Industriale, via Moruzzi 13, 56124 Pisa, Italy
| | - Tomaž Apih
- Jožef Stefan Institute, Jamova
39, SI-1000 Ljubljana, Slovenia
| | - Vladimíra Novotná
- Institute
of Physics, Academy of Sciences of the Czech Republic, Na Slovance
2, 182 21 Prague, Czech Republic
| | - Pedro J. Sebastião
- Center
of Physics and Engineering of Advanced Materials, Instituto Superior
Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
- Department
of Physics, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
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Westphal E, Gallardo H, Caramori GF, Sebastián N, Tamba MG, Eremin A, Kawauchi S, Prehm M, Tschierske C. Polar Order and Symmetry Breaking at the Boundary between Bent-Core and Rodlike Molecular Forms: When 4-Cyanoresorcinol Meets the Carbosilane End Group. Chemistry 2016; 22:8181-97. [DOI: 10.1002/chem.201503901] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Indexed: 12/21/2022]
Affiliation(s)
- Eduard Westphal
- Institute of Chemistry, Organic Chemistry; Martin Luther University Halle-Wittenberg, Kurt-Mothes-Strasse 2; 06120 Halle/Saale Germany
- Department of Chemistry; Federal University of Santa Catarina; 88040-900 Florianópolis Brazil
| | - Hugo Gallardo
- Department of Chemistry; Federal University of Santa Catarina; 88040-900 Florianópolis Brazil
| | | | - Nerea Sebastián
- Department of Nonlinear Phenomena, Institute for Experimental Physics; Otto von Guericke University Magdeburg, Universitätsplatz 2; 39106 Magdeburg Germany
| | - Maria-Gabriela Tamba
- Department of Nonlinear Phenomena, Institute for Experimental Physics; Otto von Guericke University Magdeburg, Universitätsplatz 2; 39106 Magdeburg Germany
| | - Alexey Eremin
- Department of Nonlinear Phenomena, Institute for Experimental Physics; Otto von Guericke University Magdeburg, Universitätsplatz 2; 39106 Magdeburg Germany
| | - Susumu Kawauchi
- Department of Organic & Polymeric Materials; Tokyo Institute of Technology, O-okayama, Meguro-ku; Tokyo 152-8552 Japan
| | - Marko Prehm
- Institute of Chemistry, Organic Chemistry; Martin Luther University Halle-Wittenberg, Kurt-Mothes-Strasse 2; 06120 Halle/Saale Germany
| | - Carsten Tschierske
- Institute of Chemistry, Organic Chemistry; Martin Luther University Halle-Wittenberg, Kurt-Mothes-Strasse 2; 06120 Halle/Saale Germany
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12
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Abstract
Three-ring mesogens with a core comprising thiophene linked to one phenyl ring directly and to the other via flexible ester are synthesized with terminal alkoxy chains to probe the mesophase properties and find the molecular order. The phenyl thiophene link in the core offers a comparison of the mesophase features with the molecular shape of the mesogen. The synthesized mesogens display enantiotropic polymesomorphism and accordingly nematic, smectic A, smectic C and smectic B mesophases are perceived depending upon the terminal chain length. For some of the homologues, monotropic higher order smectic phases such as smectic F and crystal E are also witnessed. The existence of polymesomorphism are originally observed by HOPM and DSC and further confirmed by powder X-ray diffraction studies. For the C8 homologue, high resolution solid state (13)C NMR spectroscopy is employed to find the molecular structure in the liquid crystalline phase and using the 2D SLF technique, the (13)C-(1)H dipolar couplings are extracted to calculate the order parameter. By comparing the ratio of local order of thiophene as well as phenyl rings, we establish the bent-core shape of the mesogen. Importantly, for assigning the carbon chemical shifts of the core unit of aligned C8 mesogen, the (13)C NMR measured in mesophase of the synthetic intermediate is employed. Thus, the proposed approach addresses the key step in the spectral assignment of target mesogens with the use of (13)C NMR data of mesomorphic intermediate.
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Affiliation(s)
- B Veeraprakash
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
| | - Nitin P Lobo
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
| | - T Narasimhaswamy
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
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13
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Kesava Reddy M, Varathan E, Lobo NP, Roy A, Narasimhaswamy T, Ramanathan KV. Monolayer to interdigitated partial bilayer smectic C transition in thiophene-based spacer mesogens: X-ray diffraction and (13)C nuclear magnetic resonance studies. Langmuir 2015; 31:10831-10842. [PMID: 26366989 DOI: 10.1021/acs.langmuir.5b02327] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Mesophase organization of molecules built with thiophene at the center and linked via flexible spacers to rigid side arm core units and terminal alkoxy chains has been investigated. Thirty homologues realized by varying the span of the spacers as well as the length of the terminal chains have been studied. In addition to the enantiotropic nematic phase observed for all the mesogens, the increase of the spacer as well as the terminal chain lengths resulted in the smectic C phase. The molecular organization in the smectic phase as investigated by temperature dependent X-ray diffraction measurements revealed an interesting behavior that depended on the length of the spacer vis-a-vis the length of the terminal chain. Thus, a tilted interdigitated partial bilayer organization was observed for molecules with a shorter spacer length, while a tilted monolayer arrangement was observed for those with a longer spacer length. High-resolution solid state (13)C NMR studies carried out for representative mesogens indicated a U-shape for all the molecules, indicating that intermolecular interactions and molecular dynamics rather than molecular shape are responsible for the observed behavior. Models for the mesophase organization have been considered and the results understood in terms of segregation of incompatible parts of the mesogens combined with steric frustration leading to the observed lamellar order.
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Affiliation(s)
- M Kesava Reddy
- Department of Chemistry, S. V. University , Tirupati, 517502, India
| | | | - Nitin P Lobo
- Department of Physics, Indian Institute of Science , Bangalore, 560012, India
| | - Arun Roy
- Soft Condensed Matter, Raman Research Institute , Bangalore, 560080, India
| | | | - K V Ramanathan
- NMR Research Centre, Indian Institute of Science , Bangalore, 560012, India
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14
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Reddy MG, Lobo NP, Varathan E, Easwaramoorthi S, Narasimhaswamy T. Intramolecular charge transfer interactions and molecular order of rod like mesogens. RSC Adv 2015. [DOI: 10.1039/c5ra22261c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Photophysical studies, VT-XRD and13C solid state NMR investigation of three ring based dimethylamino mesogens reveal intramolecular charge transfer, smectic Admesophase and molecular order.
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Affiliation(s)
- M. Guruprasad Reddy
- Polymer Laboratory
- CSIR-Central Leather Research Institute
- Chennai
- India-600020
| | - Nitin P. Lobo
- Chemical Physics Laboratory
- CSIR-Central Leather Research Institute
- Chennai
- India-600020
| | - E. Varathan
- Chemical Laboratory
- CSIR-Central Leather Research Institute
- Chennai
- India-600020
| | - S. Easwaramoorthi
- Chemical Laboratory
- CSIR-Central Leather Research Institute
- Chennai
- India-600020
| | - T. Narasimhaswamy
- Polymer Laboratory
- CSIR-Central Leather Research Institute
- Chennai
- India-600020
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