title: Multimode-photochromism based on strongly coupled dihydroazulene and diarylethene.
abstract: Synthesis and photophysical/photochemical investigations of 1,8a-dihydro-2,3-bis(2,5-dimethy-3-thienyl)-azulene-1,1-dicarbonitrile (1A) and 1,8a-dihydro-2,3-diphenylazulene-1,1-dicarbonitrile (2A) are reported. The photoprocesses and thermal reactions of systems 1 and 2 were studied by time-resolved and steady-state techniques under various conditions. The dihydroazulene (DHA)-dithienylethene (DTE) conjugate 1A is photochemically converted into the dihydrothienobenzothiophene (DHB) isomer 1C and the vinylheptafulvene (VHF) isomer 1B. System 2 exhibits exclusively DHA/VHF photochromism. For both systems the VHF form thermally reverts back into the DHA form. Their rate constant (kB-->A) increases with the solvent polarity and the relaxation kinetics proceed by means of an activation barrier of 65-80 kJ mol(-1); kB-->A and the activation parameters of the isomerisation reactions are rather similar. The photostationary state of the 1A-->1B and 1A-->1C photoisomerisation is sensitive to the irradiation wavelength. The concept of cycloswitching is discussed.
authors: Institut für Organische Chemie der Universität Regensburg, Germany.
authors: T
authors: T
authors: Mrozek
authors: H
authors: H
authors: Görner
authors: J
authors: J
authors: Daub