Dyes in Liquid Crystals: Experimental and Computational Studies of a Guest-Host System Based on a Combined DFT and MD Approach.

John N. Moore,Mark T. Sims,John W. Goodby,Laurence C. Abbott,Stephen J. Cowling

doi:10.1002/chem.201406372

John N. Moore, Mark T. Sims + Show 3 more

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https://doi.org/10.1002/chem.201406372

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Abstract

Practical applications of guest–host liquid crystal systems are critically dependent on the alignment of the guest species within the liquid crystal host. UV/Vis absorption spectroscopy shows that the 1,5-dihydroxy-2,6-bis-(4-propylphenyl)-9,10-anthraquinone dye aligns within the E7 nematic host, giving an experimental dichroic ratio of 9.40 and dye order parameter of 0.74. This alignment was modelled by using a combination of density functional theory (DFT) and molecular dynamics (MD) computational approaches that do not require the input of experimental data. Time-dependent DFT calculations show that the electronic transition dipole moment is highly aligned with the long molecular axis of the dye. Fully atomistic MD simulations show that the long axis of the dye is less highly aligned within the E7 host, indicating that this contribution limits the overall dye alignment and, thereby, the potential practical applications of this particular system. Importantly, this study demonstrates an experimental and combined DFT and MD computational approach that may be applied generally to guest–host systems, providing a potential route to their rational design.

Highlights

The potential for using dyes in liquid crystal devices arose from the first reported observation of dye alignment in a nematic host,[1] and numerous modes of guest–host device operation have been suggested subsequently.[2,3] These devices are based on the principle that the guest chromophore aligns with the liquid crystal host, enabling the application of an electric field to switch the orientation of the liquid crystal matrix between that of an absorbing state and a transmitting state, as shown schematically in Figure 1, because the absorption transition is aligned along a specific axis within the dye
A guest anthraquinone dye has been shown experimentally to align within a nematic liquid crystal host
density functional theory (DFT) calculations have given the alignment of the transition dipole moment within the dye, and fully atomistic molecular dynamics (MD) simulations have modelled the alignment of the dye within the host

Summary

Introduction

The potential for using dyes in liquid crystal devices arose from the first reported observation of dye alignment in a nematic host,[1] and numerous modes of guest–host device operation have been suggested subsequently.[2,3] These devices are based on the principle that the guest chromophore aligns with the liquid crystal host, enabling the application of an electric field to switch the orientation of the liquid crystal matrix between that of an absorbing (coloured) state and a transmitting (colourless) state, as shown schematically in Figure 1, because the absorption transition is aligned along a specific axis within the dye. The potential for using dyes in liquid crystal devices arose from the first reported observation of dye alignment in a nematic host,[1] and numerous modes of guest–host device operation have been suggested subsequently.[2,3] These devices are based on the principle that the guest chromophore aligns with the liquid crystal host, enabling the application of an electric field to switch the orientation of the liquid crystal matrix between that of an absorbing (coloured) state and a transmitting (colourless) state, as shown schematically, because the absorption transition is aligned along a specific axis within the dye Such guest–host devices do not necessarily require polarizers or colour filters because the absorption properties are defined by the guest dye molecules and their alignment; they may provide more robust devices with higher optical efficiencies and lower power consumption than some more conventional liquid crystal displays (LCDs), including the poten-.

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