Reversible Photomechanical Switching of Individual Engineered Molecules at a Surface

ORAL

Abstract

We have spatially resolved reversible light-induced mechanical switching in a single organic molecule bound to a metal surface. Scanning tunneling microscopy (STM) was used to image the features of an individual azobenzene molecule on a gold surface before and after reversibly cycling its mechanical structure between \textit{trans} and \textit{cis} states via photo-actuation (i.e., photoisomerization). Azobenzene molecules were engineered to increase their surface photomechanical activity by attaching varying numbers of \textit{tert}-butyl (TB) ligands (``legs'') to the azobenzene phenyl rings. We find that azobenzene molecules lacking TB legs or having only two legs do not switch on a gold substrate under UV irradiation, while molecules synthesized with four TB legs can be photoswitched on gold. STM images of the functionalized molecules show that increasing the number of TB legs ``lifts'' the azobenzene molecules from the substrate, thereby increasing their photomechanical activity. The reversibility of the photoreaction, along with comparison of experimental data to \textit{ab initio} simulation of isomerized azobenzene, confirms the photo-induced \textit{trans-cis} conversion of single molecules.

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Authors

  • Matthew Comstock

    • University of California at Berkeley

  • Niv Levy

    • Dept. of Physics, UC Berkeley ; Mat. Sci. Div, Lawrence Berkeley Natl. Lab
    • University of California at Berkeley

  • Armen Kirakosian

    • University of California at Berkeley

  • Jongweon Cho

    • Dept. of Physics, UC Berkeley ; Mat. Sci. Div, Lawrence Berkeley Natl. Lab
    • Department of Physics, University of California, Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory
    • University of California at Berkeley

  • Frank Lauterwasser

    • Dept. of Chemistry, UC Berkeley ; Mat. Sci. Div, Lawrence Berkeley Natl. Lab
    • University of California at Berkeley

  • Jessica Harvey

    • University of California at Berkeley

  • David Strubbe

    • Dept. of Physics, UC Berkeley ; Mat. Sci. Div, Lawrence Berkeley Natl. Lab
    • Department of Physics, University of California, Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory
    • University of California at Berkeley

  • Jean Fr\'echet

    • University of California at Berkeley

  • Dirk Trauner

    • University of California at Berkeley

  • Steven Louie

    • Molecular Foundry, Lawrence Berkeley National Laboratory and Department of Physics, University of California at Berkeley
    • Dept of Physics UC Berkeley, The Molecular Foundry LBNL, Mat Sci Div LBNL
    • Department of Physics, University of California at Berkeley and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
    • UC Berkeley, Lawrence Berkeley National Laboratory
    • University of California at Berkeley and Lawrence Berkeley National Laboratory
    • University of California at Berkeley
    • University of California, Berkeley \& Lawrence Berkeley National Laboratory
    • University of California at Berkeley and Lawrence Berkeley National Lab
    • Department of Physics, University of California, Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory

  • Mike Crommie

    • Dept. of Physics, University of California, Berkeley
    • Department of Physics, University of California at Berkeley
    • University of California at Berkeley
    • Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300