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Friebel P, Galimberti DR, Savoini M, Cattaneo L. Unveiling Low THz Dynamics of Liquid Crystals: Identification of Intermolecular Interaction among Intramolecular Modes. J Phys Chem B 2024; 128:596-602. [PMID: 38189643 PMCID: PMC10801680 DOI: 10.1021/acs.jpcb.3c07947] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Revised: 12/15/2023] [Accepted: 12/18/2023] [Indexed: 01/09/2024]
Abstract
Liquid crystals have found a wide area of application over the last few decades, proving to be excellent materials for tunable optics from visible to near-infrared frequencies. Currently, much effort is devoted to demonstrating their applicability at THz frequencies (1-10 THz), where tremendous advances of broadband and intense sources have been achieved. Yet, a detailed understanding of THz-triggered dynamics in liquid crystals is incomplete. Here, we perform broadband THz time domain spectroscopy on 4-cyano-4'-alkyl-biphenyl (nCB) and 5-phenylcyclohexanes (PCH5) across mesophases. Density functional theory calculations on isolated molecules capture the majority of the response. In particular, the pronounced modes around 4.5 and 5.5 THz mainly originate from bending modes of the cyano group. In contrast, the broad response below 3 THz, linked to modes of the alkyl chain, disagrees with the single molecule calculation. Here, we identify a clear intermolecular character of the response, supported by dimer and trimer calculations.
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Affiliation(s)
- Patrick Friebel
- Max
Planck Institute for Nuclear Physics, Saupfercheckweg 1, Heidelberg 69117, Germany
| | - Daria Ruth Galimberti
- Institute
for Molecules and Materials, Radboud University, Heyendaalsweg 135, Nijmegen 6526 AJ, The Netherlands
| | - Matteo Savoini
- Institute
for Quantum Electronics, ETH Zürich, Auguste-Piccard-Hof 1, Zürich 8093, Switzerland
| | - Laura Cattaneo
- Max
Planck Institute for Nuclear Physics, Saupfercheckweg 1, Heidelberg 69117, Germany
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2
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Li Y, Zhang W, Bishop C, Huang C, Ediger MD, Yu L. Surface diffusion in glasses of rod-like molecules posaconazole and itraconazole: effect of interfacial molecular alignment and bulk penetration. SOFT MATTER 2020; 16:5062-5070. [PMID: 32453335 DOI: 10.1039/d0sm00353k] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The method of surface grating decay has been used to measure surface diffusion in the glasses of two rod-like molecules posaconazole (POS) and itraconazole (ITZ). Although structurally similar antifungal medicines, ITZ forms liquid-crystalline phases while POS does not. Surface diffusion in these systems is significantly slower than in the glasses of quasi-spherical molecules of similar volume when compared at the glass transition temperature Tg. Between the two systems, ITZ has slower surface diffusion. These results are explained on the basis of the near-vertical orientation of the rod-like molecules at the surface and their deep penetration into the bulk where mobility is low. For molecular glasses without extensive hydrogen bonds, we find that the surface diffusion coefficient at Tg decreases smoothly with the penetration depth of surface molecules and the trend has the double-exponential form for the surface mobility gradient observed in simulations. This supports the view that these molecular glasses have a similar mobility vs. depth profile and their different surface diffusion rates arise simply from the different depths at which molecules are anchored. Our results also provide support for a previously observed correlation between the rate of surface diffusion and the fragility of the bulk liquid.
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Affiliation(s)
- Yuhui Li
- School of Pharmacy, University of Wisconsin-Madison, Madison, WI 53705, USA.
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3
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Sims MT, Abbott LC, Goodby JW, Moore JN. Shape segregation in molecular organisation: a combined X-ray scattering and molecular dynamics study of smectic liquid crystals. SOFT MATTER 2019; 15:7722-7732. [PMID: 31509149 DOI: 10.1039/c9sm01527b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Temperature-dependent X-ray scattering studies have been carried out on 4-undecyloxy-4'-cyanobiphenyl (11OCB) and 4-(12,12-dimethyltridecyloxy)-4'-cyanobiphenyl (t-Bu-11OCB) in the smectic A phase, from which their layer spacings and translational order parameters were obtained. Marked differences between the layer structures of the two compounds were demonstrated, showing that the addition of the t-Bu group results in a higher translational order parameter and wider layer spacing for t-Bu-11OCB than 11OCB. Fully atomistic MD simulations of both compounds run for >1000 ns demonstrated the spontaneous formation of smectic mesophases from isotropic starting geometries, and experimental trends in order parameters and absolute layer spacings were shown to be replicated well. Further analysis showed that both the aromatic head-groups and the alkyl tail-groups exhibit interdigitation in the simulated smectic phases of both compounds, and the difference in the layer structures between 11OCB and t-Bu-11OCB could be attributed mainly to a shape segregation effect arising from the addition of the bulky t-Bu end-group to the alkyl chain.
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Affiliation(s)
- Mark T Sims
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
| | - Laurence C Abbott
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
| | - John W Goodby
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
| | - John N Moore
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
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4
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Affiliation(s)
- Michael P. Allen
- Department of Physics, University of Warwick, Coventry, UK
- H. H. Wills Physics Laboratory, Royal Fort, Bristol, UK
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5
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Boyd NJ, Wilson MR. Validating an optimized GAFF force field for liquid crystals: TNI predictions for bent-core mesogens and the first atomistic predictions of a dark conglomerate phase. Phys Chem Chem Phys 2018; 20:1485-1496. [DOI: 10.1039/c7cp07496d] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Atomistic simulations of bent core mesogens provide excellent TNI predictions and show the formation of a dark conglomerate phase.
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Gürbulak O, Cebe E. Molecular dynamics simulations on the adsorption of 4-n-octyl-4′-cyanobiphenyl (8CB) at the air/water interface. J DISPER SCI TECHNOL 2017. [DOI: 10.1080/01932691.2017.1380530] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- Oğuz Gürbulak
- Department of Physics, Faculty of Science, Ege University, Izmir, Turkey
| | - Emine Cebe
- Department of Physics, Faculty of Science, Ege University, Izmir, Turkey
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7
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Roscioni OM, Muccioli L, Zannoni C. Predicting the Conditions for Homeotropic Anchoring of Liquid Crystals at a Soft Surface. 4-n-Pentyl-4'-cyanobiphenyl on Alkylsilane Self-Assembled Monolayers. ACS APPLIED MATERIALS & INTERFACES 2017; 9:11993-12002. [PMID: 28287693 DOI: 10.1021/acsami.6b16438] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We have studied, using atomistic molecular dynamics simulations, the alignment of the nematic liquid-crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) on self-assembled monolayers (SAMs) formed from octadecyl- and/or hexyltrichlorosilane (OTS and HTS) attached to glassy silica. We find a planar alignment on OTS at full coverage and an intermediate situation at partial OTS coverage because of the penetration of 5CB molecules into the monolayer, which also removes the tilt of the OTS SAM. Binary mixtures of HTS and OTS SAMs instead induce homeotropic (i.e., perpendicular) alignment. A comparison with the existing experimental literature is provided.
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Affiliation(s)
- Otello Maria Roscioni
- Dipartimento di Chimica Industriale "Toso Montanari" Università di Bologna , viale Risorgimento 4, IT-40136 Bologna, Italy
| | - Luca Muccioli
- Dipartimento di Chimica Industriale "Toso Montanari" Università di Bologna , viale Risorgimento 4, IT-40136 Bologna, Italy
| | - Claudio Zannoni
- Dipartimento di Chimica Industriale "Toso Montanari" Università di Bologna , viale Risorgimento 4, IT-40136 Bologna, Italy
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8
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Sadati M, Ramezani-Dakhel H, Bu W, Sevgen E, Liang Z, Erol C, Rahimi M, Taheri Qazvini N, Lin B, Abbott NL, Roux B, Schlossman ML, de Pablo JJ. Molecular Structure of Canonical Liquid Crystal Interfaces. J Am Chem Soc 2017; 139:3841-3850. [PMID: 28177227 DOI: 10.1021/jacs.7b00167] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Numerous applications of liquid crystals rely on control of molecular orientation at an interface. However, little is known about the precise molecular structure of such interfaces. In this work, synchrotron X-ray reflectivity measurements, accompanied by large-scale atomistic molecular dynamics simulations, are used for the first time to reconstruct the air-liquid crystal interface of a nematic material, namely, 4-pentyl-4'-cyanobiphenyl (5CB). The results are compared to those for 4-octyl-4'-cyanobiphenyl (8CB) which, in addition to adopting isotropic and nematic states, can also form a smectic phase. Our findings indicate that the air interface imprints a highly ordered structure into the material; such a local structure then propagates well into the bulk of the liquid crystal, particularly for nematic and smectic phases.
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Affiliation(s)
| | | | | | | | - Zhu Liang
- Department
of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States
| | - Cem Erol
- Department
of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States
| | | | | | | | - Nicholas L. Abbott
- Department
of Chemical and Biological Engineering, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States
| | | | - Mark L. Schlossman
- Department
of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States
| | - Juan J. de Pablo
- Argonne National Laboratory, Argonne, Illinois 60439, United States
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9
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Ramezani-Dakhel H, Sadati M, Rahimi M, Ramirez-Hernandez A, Roux B, de Pablo JJ. Understanding Atomic-Scale Behavior of Liquid Crystals at Aqueous Interfaces. J Chem Theory Comput 2016; 13:237-244. [DOI: 10.1021/acs.jctc.6b00844] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | | | | | | | | | - Juan J. de Pablo
- Argonne National
Laboratory, Argonne, Illinois 60439, United States
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10
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Purcell SM, Tesa-Serrate MA, Marshall BC, Bruce DW, D'Andrea L, Costen ML, Slattery JM, Smoll EJ, Minton TK, McKendrick KG. Reactive-Atom Scattering from Liquid Crystals at the Liquid-Vacuum Interface: [C 12mim][BF 4] and 4-Cyano-4'-Octylbiphenyl (8CB). LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:9938-9949. [PMID: 27603521 DOI: 10.1021/acs.langmuir.6b02440] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Two complementary approaches were used to study the liquid-vacuum interface of the liquid-crystalline ionic liquid 1-dodecyl-3-methylimidazolium tetrafluoroborate ([C12mim][BF4]) in the smectic A (SmA) and isotropic phases. O atoms with two distinct incident translational energies were scattered from the surface of [C12mim][BF4]. Angle-dependent time-of-flight distributions and OH yields, respectively, were recorded from high- and low-energy O atoms. There were no significant changes in the measurements using either approach, nor the properties derived from them, accompanying the transition from the SmA to the isotropic phase. This indicates that the surface structure of [C12mim][BF4] remains essentially unchanged across the phase boundary, implying that the bulk order and surface structure are not strongly correlated for this material. This effect is ascribed to the strong propensity for the outer surfaces of ionic liquids to be dominated by alkyl chains, over an underlying layer rich in anions and cation head groups, whether or not the bulk material is a liquid crystal. In a comparative study, the OH yield from the surface of the liquid crystal, 8CB, was found to be affected by the bulk order, showing a surprising step increase at the SmA-nematic transition temperature, whose origin is the subject of speculation.
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Affiliation(s)
- Simon M Purcell
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, United Kingdom
| | - Maria A Tesa-Serrate
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, United Kingdom
| | - Brooks C Marshall
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States
| | - Duncan W Bruce
- Department of Chemistry, University of York , Heslington, York YO10 5DD, United Kingdom
| | - Lucía D'Andrea
- Department of Chemistry, University of York , Heslington, York YO10 5DD, United Kingdom
| | - Matthew L Costen
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, United Kingdom
| | - John M Slattery
- Department of Chemistry, University of York , Heslington, York YO10 5DD, United Kingdom
| | - Eric J Smoll
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States
| | - Timothy K Minton
- Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States
| | - Kenneth G McKendrick
- Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, United Kingdom
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11
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Roscioni OM, Zannoni C. Molecular Dynamics Simulations and their Application to Thin-film Devices. UNCONVENTIONAL THIN FILM PHOTOVOLTAICS 2016. [DOI: 10.1039/9781782624066-00391] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The performance of devices based on organic semiconductors strongly depends on the molecular organisation in thin films. Due to the intrinsic complexity of these systems, a combination of theoretical modelling and experimental techniques is often the key to achieve a full understanding of their inner working. Here, we introduce the modelling of organic semiconductors by means of molecular dynamics simulations. We describe the basic theoretical framework of the technique and review the most popular class of force fields used to model organic materials, paying particular attention to the peculiarities of confined systems like nano-thick films. Representative studies of the organisation of organic functional materials in thin film phases are also reviewed.
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Affiliation(s)
- Otello Maria Roscioni
- Dipartimento di Chimica Industriale “Toso Montanari”, Università di Bologna viale Risorgimento 4 40136 Bologna Italy
| | - Claudio Zannoni
- Dipartimento di Chimica Industriale “Toso Montanari”, Università di Bologna viale Risorgimento 4 40136 Bologna Italy
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12
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Sims MT, Abbott LC, Cowling SJ, Goodby JW, Moore JN. Experimental and molecular dynamics studies of anthraquinone dyes in a nematic liquid-crystal host: a rationale for observed alignment trends. Phys Chem Chem Phys 2016; 18:20651-63. [DOI: 10.1039/c6cp03823a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The experimental alignment trend of a set of anthraquinone dyes in a nematic host is rationalised by calculated molecular order parameters and transition dipole moments.
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Affiliation(s)
- Mark T. Sims
- Department of Chemistry
- The University of York
- Heslington
- UK
| | | | | | - John W. Goodby
- Department of Chemistry
- The University of York
- Heslington
- UK
| | - John N. Moore
- Department of Chemistry
- The University of York
- Heslington
- UK
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