Kreuzer M, Benkler E, Paparo D, Casillo G, Marrucci L
Institute of Applied Physics, Darmstadt University of Technology, Hochschulstrasse 6, 64289 Darmstadt, Germany.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Jul;68(1 Pt 1):011701. doi: 10.1103/PhysRevE.68.011701. Epub 2003 Jul 11.
To explain the large photoinduced molecular reorientation phenomena observed in dye-doped liquids and liquid crystals, the hypothesis was formed that the rotational mobility of dye molecules is strongly altered during their electronic excitation. Here, we report the direct measurement of a 30%-50% mobility decrease of photoexcited anthraquinone dye molecules dissolved in a cyanophenyl liquid host. This mobility reduction is ascribed to an excited-state reinforcement of intermolecular hydrogen bonding. These results provide fully independent evidence for the validity of current models of the photoinduced reorientation and a working demonstration of the design concepts of "fluctuating-friction" molecular motors. We propose that a light-induced modulation of molecular mobility associated with electronic photoexcitation is of general relevance to the behavior of photosensitive organic materials, currently investigated for applications in optical data storage, liquid-crystal displays, and organic optoelectronic devices.
