title: Ultrafast bidirectional dihydroazulene/vinylheptafulvene (DHA/VHF) molecular switches: photochemical ring closure of vinylheptafulvene proven by a two-pulse experiment.
abstract: The photochromic couple dihydroazulene/vinylheptafulvene (DHA/VHF) is an established system for molecular switching. The photoinduced ring opening of the thermally stable dihydroazulene proceeds in the picosecond time regime with subsequent rapid relaxation to the electronic ground state. So far it was not possible to reverse the reaction photochemically. It was always found that the back reaction proceeds thermally on a longer time scale. In the case of the cyanophenyl-DHA derivative utilized in the present study, this is accounted to s-cis/s-trans isomerization of the primarily formed s-cis VHF. Since this particular isomerization takes much longer than nanoseconds, we now successfully applied a second visible femtosecond pulse subsequent to the initial UV pulse (25 ps delay) achieving ring closure of the primarily formed s-cis VHF. The now bidirectional photoswitching was monitored by the changes in the cw spectrum. As a result, the DHA/VHF system is found to be a multifold switchable system by itself: it is both a very fast photoreversible switch and a photochemical/thermal switch with a thermal lock mode.
authors.affiliation: Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität, München, Germany.
authors.forename: Vincent
authors.initials: V
authors.lastname: De Waele
authors.forename: Uli
authors.initials: U
authors.lastname: Schmidhammer
authors.forename: Thomas
authors.initials: T
authors.lastname: Mrozek
authors.forename: Jörg
authors.initials: J
authors.lastname: Daub
authors.forename: Eberhard
authors.initials: E
authors.lastname: Riedle
mesh_terms: D052176:Azulenes; D003508:Cycloheptanes / Q000737:chemistry*; D003517:Cyclopentanes / Q000737:chemistry*; D010777:Photochemistry; D013056:Spectrophotometry, Ultraviolet; D014753:Vinyl Compounds / Q000737:chemistry*
chemical_list: D052176:Azulenes; D003508:Cycloheptanes; D003517:Cyclopentanes; D014753:Vinyl Compounds; C017332:fulvene; C005525:azulene