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Photocontrolled nanophase segregation in a liquid-crystal solvent

Nature volume 398, pages 54–57 (1999)Cite this article

Abstract

Materials whose structure or electrical or optical properties can be controlled with light are said to be photoactive. Liquid crystals are of interest as photoactive media, because their fluidity maintains the possibility of molecular motion in response to photon absorption, while their orientational and/or positional ordering offers the possibility of cooperative behaviour that can amplify relatively weak photochemical effects. Moreover, liquid crystals impose their own ordering on solutes. For example, smectic A liquid crystals, comprised of one-dimensional stacks of fluid layers with the molecular axes aligned normal to the layers1, produce a modulation in solute concentration with a period equal to the layer spacing2,3. Here we present computer simulations which show that the positional ordering of a photoactive solute (an azobenzene derivative, denoted 7AB) in a smectic host (denoted 8CB) depends sensitively on its photochemical state. The photoactive molecules are driven from within the smectic layers to locations between the layers by trans-to-cis photoisomerization. This would explain the recent observation4,5,6,7 of a reversible increase in the smectic A layer spacing of a solution of 7AB in 8CB accompanying the photoisomerization process. The effect might be exploited for low-power, high-resolution optical data storage, and more generally for the manipulation of organic materials at the nanometre scale.

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Figure 1: Time evolution of smectic layer spacing d for the trans-7AB and cis-7AB simulations.
Figure 2: Instantaneous configurations from large-scale atomistic simulations of 7AB-8CB mixtures.
Figure 3: Mass density profiles along the layer normal for 8CB (open circles) and 7AB (filled circles), averaged over the final 2 ns of the trans-7AB (a) and cis-7AB (b) simulations.
Figure 4: Orientational distributions for selected portions of the 7AB molecule.

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Acknowledgements

We thank T. Darden for use of his particle-mesh Ewald code, D. Coleman for help in producing the molecular graphics, and D. Finotello and B. Zalar for discussions. This work was supported by the NSF, the US Air Force Office of Sponsored Research, and the Kent State Liquid Crystal Institute (a grant of computer time).

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Author notes

  1. Yves Lansac

    Present address: Dipartimento di Chimica Fisica e Inorganica, Universitá di Bologna, Viale Risorgimento 4, 41036, Bologna, Italy

Authors and Affiliations

  1. Department of Physics, Condensed Matter Laboratory, and Ferroelectric Liquid Crystal Materials Research Center, University of Colorado, Boulder, 80309, Colorado, USA

    Yves Lansac, Matthew A. Glaser & Noel A. Clark

  2. Liquid Crystal Institute and Chemical Physics Program, Kent State University, Kent, 44242, Ohio, USA

    Oleg D. Lavrentovich

Authors
  1. Yves Lansac
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  2. Matthew A. Glaser
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  4. Oleg D. Lavrentovich
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Correspondence to Matthew A. Glaser.

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Lansac, Y., Glaser, M., Clark, N. et al. Photocontrolled nanophase segregation in a liquid-crystal solvent. Nature 398, 54–57 (1999). https://doi.org/10.1038/17995

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