Photoswitching of Dihydroazulene Derivatives in Liquid-Crystalline Host Systems

Anne Ugleholdt Petersen, Martyn Jevric, Richard J Mandle, Mark T Sims, John N Moore, Stephen J Cowling, John W Goodby, Mogens Brøndsted Nielsen

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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.

Original languageEnglish
Pages (from-to)5090-5103
Number of pages14
JournalChemistry : A European Journal
Issue number21
Early online date27 Mar 2017
Publication statusPublished - 11 Apr 2017


  • Journal Article

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