A surface-bound molecule that undergoes optically biased Brownian rotation.
Developing molecular systems with functions analogous to those of macroscopic machine components, such as rotors, gyroscopes and valves, is a long-standing goal of nanotechnology. However, macroscopic analogies go only so far in predicting function in nanoscale environments, where friction dominates over inertia. In some instances, ratchet mechanisms have been used to bias the ever-present random, thermally driven (Brownian) motion and drive molecular diffusion in desired directions. Here, we visualize the motions of surface-bound molecular rotors using defocused fluorescence imaging, and observe the transition from hindered to free Brownian rotation by tuning medium viscosity. We show that the otherwise random rotations can be biased by the polarization of the excitation light field, even though the associated optical torque is insufficient to overcome thermal fluctuations. The biased rotation is attributed instead to a fluctuating-friction mechanism in which photoexcitation of the rotor strongly inhibits its diffusion rate.
1] Laboratory for Photochemistry and Spectroscopy, Katholieke Universiteit Leuven, Heverlee 3001 Belgium [2] ISIS & icFRC, Université de Strasbourg & CNRS UMR 7006, Strasbourg 67000, France.
James A
JA
Hutchison
Laboratory for Photochemistry and Spectroscopy, Katholieke Universiteit Leuven, Heverlee 3001 Belgium.
Hiroshi
H
Uji-i
Laboratory for Photochemistry and Spectroscopy, Katholieke Universiteit Leuven, Heverlee 3001 Belgium.
Ania
A
Deres
Nano-Science Center/Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark.
Tom
T
Vosch
Laboratory for Photochemistry and Spectroscopy, Katholieke Universiteit Leuven, Heverlee 3001 Belgium.
Susana
S
Rocha
Synthetic Chemistry Group, Max Plank Institute for Polymer Research, Mainz D-55128 Germany.
Sibylle
S
Müller
Department of Polymer Chemistry, Zernike Institute for Advanced Materials, Rijksuniversiteit Groningen, Nijenborgh 4, Groningen 9747 AG, The Netherlands.
Andreas A
AA
Bastian
Drittes Physikalisches Institut, Universität Göttingen, Göttingen D-37077 Germany.
Jörg
J
Enderlein
Synthetic Chemistry Group, Max Plank Institute for Polymer Research, Mainz D-55128 Germany.
Hassan
H
Nourouzi
Synthetic Chemistry Group, Max Plank Institute for Polymer Research, Mainz D-55128 Germany.
Chen
C
Li
Department of Polymer Chemistry, Zernike Institute for Advanced Materials, Rijksuniversiteit Groningen, Nijenborgh 4, Groningen 9747 AG, The Netherlands.
Andreas
A
Herrmann
Synthetic Chemistry Group, Max Plank Institute for Polymer Research, Mainz D-55128 Germany.
Klaus
K
Müllen
Laboratory for Photochemistry and Spectroscopy, Katholieke Universiteit Leuven, Heverlee 3001 Belgium.
Frans
F
De Schryver
1] Laboratory for Photochemistry and Spectroscopy, Katholieke Universiteit Leuven, Heverlee 3001 Belgium [2] Nano-Science Center/Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark.
Johan
J
Hofkens