title: Molecular reorientation by photoinduced modulation of rotational mobility.
abstract: 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.
authors.affiliation: Institute of Applied Physics, Darmstadt University of Technology, Hochschulstrasse 6, 64289 Darmstadt, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Kreuzer
authors.forename: E
authors.initials: E
authors.lastname: Benkler
authors.forename: D
authors.initials: D
authors.lastname: Paparo
authors.forename: G
authors.initials: G
authors.lastname: Casillo
authors.forename: L
authors.initials: L
authors.lastname: Marrucci
mesh_terms: D000880:Anthraquinones / Q000494:pharmacology; D055592:Biophysical Phenomena; D001703:Biophysics; D004583:Electrons; D008027:Light; D008956:Models, Chemical; D015233:Models, Statistical; D020409:Molecular Motor Proteins; D013053:Spectrophotometry; D013997:Time Factors
chemical_list: D000880:Anthraquinones; D020409:Molecular Motor Proteins