Dyes as guests in ordered systems: current understanding and future directions

Sims, Mark

doi:10.1080/02678292.2016.1189613

Cited by 30 publications

(24 citation statements)

References 103 publications

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“…The alignment of dyes in guest-host systems is generally quantified by a dichroic order parameter in which the orientation of the TDM is considered to be fixed within the molecular frame of the dye, as discussed in the Introduction and as given by eqn (2). This assumption may be valid for many dyes, and particularly for those with rigid chromophores, but its validity may need to be assessed for more flexible systems.…”

Section: Influence Of Flexibility On Tdm Orientationsmentioning

confidence: 99%

“…Dyes are often used as the guest molecules in such systems to provide optically anisotropic mixtures, for which a wide variety of applications have been proposed. 1,2 Most prominently, guest-host systems have been investigated for applications in display devices that can provide higher optical and energy efficiency than conventional LCD devices, along with the ability to operate in light-scattering modes in sheltered environments or outdoors. 3 In addition, guest-host systems have been suggested for a diverse range of other applications that include precursors for high performance thin-film polarizers, 4 optical storage devices utilising photochemical dye isomerisation, 5 optically controlled diffraction gratings, 6 security devices, 7 switchable windows using fluorescent guest molecules to collect solar energy, 8 and 3D imaging of micellar systems also using fluorescent dyes.…”

Section: Introductionmentioning

confidence: 99%

“…The dichroic order parameter relates directly to the optical anisotropy of a guest-host system, and it can be determined experimentally by measuring the polarized visible absorption spectra of a sample aligned within a cell. 2,13 In a more general context, small, highly symmetric guest molecules have been used as probes to study the alignment of liquid crystals themselves because these guest molecules can yield simpler data than that obtained from studying a host directly, and which can be analysed without the need to make assumptions about the symmetry of the host molecules. 14 Arising from this work, the calculation of the molecular alignment of guests within liquid crystal hosts has been the subject of a significant number of studies.…”

Section: Introductionmentioning

confidence: 99%

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Principal molecular axis and transition dipole moment orientations in liquid crystal systems: an assessment based on studies of guest anthraquinone dyes in a nematic host

Sims

Abbott

Cowling

et al. 2017

Phys. Chem. Chem. Phys.

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An assessment of five different definitions of the principal molecular axis along which molecules align in a nematic liquid crystal system has been made by analysing fully atomistic molecular dynamics (MD) simulations of a set of anthraquinone dyes in the cyanobiphenyl-based nematic host mixture E7. Principal molecular axes of the dyes defined by minimum moment of inertia, minimum circumference, minimum area, maximum aspect ratio, and surface tensor models were tested, and the surface tensor model was found to give the best description. Analyses of MD simulations of E7 alone showed that the surface tensor model also gave a good description of the principal molecular axes of the host molecules, suggesting that this model may be applicable more generally. Calculated dichroic order parameters of the guest-host systems were obtained by combining the surface tensor analysis with fixed transition dipole moment (TDM) orientations from time-dependent density functional theory (TD-DFT) calculations on optimised structures of the dyes, and the trend between the dyes generally matched the trend in the experimental values. Additional analyses of the guest-host simulations identified the range of conformers explored by the flexible chromophores within the dyes, and TD-DFT calculations on corresponding model structures showed that this flexibility has a significant effect on the TDM orientations within the molecular frames. Calculated dichroic order parameters that included the effects of this flexibility gave a significantly improved match with the experimental values for the more flexible dyes. Overall, the surface tensor model has been shown to provide a rationale for the experimental alignment trends that is based on molecular shape, and molecular flexibility within the chromophores has been shown to be significant for the guest-host systems: the computational approaches reported here may be used as a general aid in the predictive design of dyes with appropriate molecular shapes and flexibilities for guest-host applications.

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Section: Influence Of Flexibility On Tdm Orientationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Principal molecular axis and transition dipole moment orientations in liquid crystal systems: an assessment based on studies of guest anthraquinone dyes in a nematic host

Sims

Abbott

Cowling

et al. 2017

Phys. Chem. Chem. Phys.

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“…Several studies on LC devices with guest–host systems have showed enhanced optical and switching properties. [ 23,24 ] Adaptive windows that can adjust the light transmission according to the climatic conditions (allow more solar heat to enter in winter and less in summer) are in high demand. [ 25 ] Studies have proven that the guest–host LC devices are the most eligible candidates for such adaptive windows.…”

Section: Introductionmentioning

confidence: 99%

Cochleate‐Doped Liquid Crystal as Switchable Metamaterial Window Mediated by Molecular Orientation Modified Aggregation

Madhuri

Shuddhodana

Judeh

et al. 2020

Part & Part Syst Charact

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A diversity of fascinating hollow and porous micro and nanoparticles are being developed for drug delivery purposes; however, their applications in other systems are barely touched. When filled by an active material, they form a tunable photonic metamaterial. Here, a small concentration of organic hollow cylinders called cochleates embedded into liquid crystals (LCs) is demonstrated to form a new switchable composite to control light scattering with voltage and temperature. The biocompatible cochleates, which are hollow, tube‐like, and hydrophilic in nature, can trap the liquid crystal molecules thus altering the system behavior. A switching device as thin as 6 µm with 12 wt% cochleates concentration is shown to be adequate to reveal a switchable privacy window. Possible molecular arrangement of the liquid crystal within the cochleate particles is suggested, and unexpected increase of the scattering with temperature depending on the applied voltage is observed as a result of change in the cochleate aggregation depending on the LC molecule orientation.

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“…The dichroic order parameter is related directly to the absorbances, A || and A ⊥ , according to Equations (2) and (3), respectively [16], where ε is the absorption coefficient of the visible absorption band of the dye, c is the concentration of the dye and l is the path length of the cell.…”

Section: Introductionmentioning

confidence: 99%

Guest–host systems containing anthraquinone dyes with multiple visible transitions giving positive and negative dichroic order parameters: an assessment of principal molecular axes and computational methods

et al. 2017

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(2017) Guest-host systems containing anthraquinone dyes with multiple visible transitions giving positive and negative dichroic order parameters: an assessment of principal molecular axes and computational methods. Liquid Crystals, Northumbria University has developed Northumbria Research Link (NRL) to enable users to access the University's research output. Copyright © and moral rights for items on NRL are retained by the individual author(s) and/or other copyright owners. Single copies of full items can be reproduced, displayed or performed, and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided the authors, title and full bibliographic details are given, as well as a hyperlink and/or URL to the original metadata page. The content must not be changed in any way. Full items must not be sold commercially in any format or medium without formal permission of the copyright holder. The full policy is available online: http://nrl.northumbria.ac.uk/policies.html This document may differ from the final, published version of the research and has been made available online in accordance with publisher policies. To read and/or cite from the published version of the research, please visit the publisher's website (a subscription may be required.)Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tlct20 Three 1,4-disubstituted anthraquinone dyes with bis(4-n-butylphenyl) substituents connected via amine or amide linking groups have been studied as guest molecules dissolved in the nematic host E7. UV-visible absorption spectroscopy has shown each of the dyes to exhibit multiple absorption bands in the visible region, and dichroic order parameters obtained from polarised spectra of aligned guest-host samples were shown to differ significantly between the bands for each dye, and between the dyes. Time-dependent density functional theory calculations indicated that each dye exhibits several transitions, giving transition dipole moment vectors with a range of orientations, and fully atomistic molecular dynamics simulations of the guest-host mixtures showed differences in the calculated molecular alignments of the dyes. Combining the results from these two sets of calculations enabled a comparison of molecular alignment models based on the moments of inertia and the surface tensors of the dyes. The match between calculated and experimental values was improved significantly when using the surface tensor rather than the moment of inertia model, indicating that the shapes of the molecular surfaces of these dyes are crucial to their alignment. A novel method of calculating polarised UV-visible absorption spectra of dyes in liquid crystal hosts is also presented.

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Dyes as guests in ordered systems: current understanding and future directions

Cited by 30 publications

References 103 publications

Principal molecular axis and transition dipole moment orientations in liquid crystal systems: an assessment based on studies of guest anthraquinone dyes in a nematic host

Principal molecular axis and transition dipole moment orientations in liquid crystal systems: an assessment based on studies of guest anthraquinone dyes in a nematic host

Cochleate‐Doped Liquid Crystal as Switchable Metamaterial Window Mediated by Molecular Orientation Modified Aggregation

Guest–host systems containing anthraquinone dyes with multiple visible transitions giving positive and negative dichroic order parameters: an assessment of principal molecular axes and computational methods

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