title: Photoswitching of Dihydroazulene Derivatives in Liquid-Crystalline Host Systems.
abstract: Photoswitches and dyes in the liquid-crystalline nematic phase have the potential for use in a wide range of applications. A large order parameter is desirable to maximize the change in properties induced by an external stimulus. A set of photochromic and nonphotochromic dyes were investigated for these applications. It was found that a bent-shaped 7-substituted dihydroazulene (DHA) photoswitch exhibited liquid-crystalline properties. Further investigation demonstrated that this material actually followed two distinct reaction pathways on heating, to a deactivated form by a 1,5-sigmatropic shift and to a linear 6-substituted DHA. In addition, elimination of hydrogen cyanide from the photoactive DHA gave both bent and linear azulene dyes. In a nematic host that has no absorbance around 350 nm, it was found that only the linear DHA derivative has nematic properties; however, both 6- and 7-substituted DHAs were found to have large order parameters. In the nematic host, ring opening of either DHA to the corresponding vinylheptafulvene resulted in a decrease in dichroic order parameter and an unusually fast back-reaction to a mixture of both DHAs. Likewise, only the linear azulene derivative showed mesomorphic properties. In the same nematic host, large order parameters were also observed for these dyes.
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark.
authors.forename: Anne Ugleholdt
authors.initials: AU
authors.lastname: Petersen
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark.
authors.forename: Martyn
authors.initials: M
authors.lastname: Jevric
authors.affiliation: Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.
authors.forename: Richard J
authors.identifier: http://orcid.org/0000-0001-9816-9661
authors.initials: RJ
authors.lastname: Mandle
authors.affiliation: Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.
authors.forename: Mark T
authors.identifier: http://orcid.org/0000-0001-9438-5527
authors.initials: MT
authors.lastname: Sims
authors.affiliation: Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.
authors.forename: John N
authors.identifier: http://orcid.org/0000-0002-8783-5195
authors.initials: JN
authors.lastname: Moore
authors.affiliation: Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Cowling
authors.affiliation: Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.
authors.forename: John W
authors.initials: JW
authors.lastname: Goodby
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark.
authors.forename: Mogens Brøndsted
authors.identifier: http://orcid.org/0000-0001-8377-0788
authors.initials: MB
authors.lastname: Nielsen
keywords: dyes/pigments; electrocyclic reactions; fused-ring systems; host-guest systems; liquid crystals