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26 August 2005 Photo-induced rotation of single molecules
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We present the investigation of optically-induced rotation of single DCM (4-(dicyano methylene)-2-methyl-6-(p-dimethyl aminostyril)-4H-pyran) molecules in a low-Tg polymer matrix. The rotation process is based on the photo-isomerization of the molecule occurring upon a resonant linearly polarized optical excitation. This pumping process creates a photo-selection angular cone, resulting in a motion of the molecular dipole perpendicularly to the linear excitation, stabilized by the polymer re-organization. Ensemble measurements are seen to be biased by the difficulty to discriminate between the re-orientation process and angular selective photo-bleaching. Such photo-bleaching effect can however be observed independently in single molecules data. The thermal rotational motion of single molecules in the polymer were first investigated, showing heterogeneous behaviors with orientational fluctuations of a about ten seconds time scale, due to the local viscosity and elasticity of the polymer environment. Under a linearly polarized pump at several hundreds of W/cm2 intensity, a photo-induced orientation motion towards the perpendicular direction to the pump was observed for 50% of the molecules, within a typical time of a few tens of seconds. The remaining molecules showed orientational fluctuations dominating over the pump effect.
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Gabriel Dutier, Vincent de Beaucoudrey, Joseph Zyss, and Sophie Brasselet "Photo-induced rotation of single molecules", Proc. SPIE 5929, Physical Chemistry of Interfaces and Nanomaterials IV, 59290J (26 August 2005);


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