TY - JOUR

T1 - Photoswitching of Dihydroazulene Derivatives in Liquid-Crystalline Host Systems

AU - Petersen, Anne Ugleholdt

AU - Jevric, Martyn

AU - Mandle, Richard J.

AU - Sims, Mark T.

AU - Moore, John N.

AU - Cowling, Stephen J.

AU - Goodby, John W.

AU - Nielsen, Mogens Brøndsted

PY - 2017

Y1 - 2017

N2 - 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 350nm, 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.

AB - 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 350nm, 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.

KW - Dyes/pigments

KW - Electrocyclic reactions

KW - Fused-ring systems

KW - Host-guest systems

KW - Liquid crystals

U2 - 10.1002/chem.201700055

DO - 10.1002/chem.201700055

M3 - Journal article

C2 - 28195368

AN - SCOPUS:85016396875

VL - 23

SP - 5090

EP - 5103

JO - Chemistry: A European Journal

JF - Chemistry: A European Journal

SN - 0947-6539

IS - 21

ER -