Liquid crystalline dihydroazulene photoswitches

Abstract

A large selection of photochromic dihydroazulene (DHA) molecules incorporating various substituents at position 2 of the DHA core was prepared and investigated for their ability to form liquid crystalline phases. Incorporation of an octyloxy-substituted biphenyl substituent resulted in nematic phase behavior and it was possible to convert one such compound partly into its vinylheptafulvene (VHF) isomer upon irradiation with light when in the liquid crystalline phase. This conversion resulted in an increase in the molecular alignment of the phase. In time, the meta-stable VHF returns to the DHA where the alignment is maintained. The systematic structural variation has revealed that a biaryl spacer between the DHA and the alkyl chain is needed for liquid crystallinity and that the one aromatic ring in the spacer cannot be substituted by a triazole. This work presents an important step towards employing the dihydroazulenevinylheptafulvene photo/thermoswitch in photoactive liquid crystalline materials.

Molecular photoswitches in aqueous environments

“…108 The thermal lifetime of the metastable vinylheptafulvene (VHF) depends on substituents and medium it is embedded in and is usually in the minute to hours range. [515][516][517] The compound was not yet used in aqueous systems, but in liquid crystals, 518 polymer films, 519 in macrocycles, 520 rotaxanes, 521 for solar energy storage, 522,523 or to photocontrol emission properties. 515 Moreover, the DHA/VHF couple can be combined with further photochromic units to assemble multi-stage switches 404,[524][525][526][527] or with electrochemically active unit to achieve photoswitchable redox properties.…”

Photoswitching of Dihydroazulene Derivatives in Liquid‐Crystalline Host Systems

“…Previously, we have reported that DHAs 3 and 4 , which are both substituted with biaryl units (Figure ), exhibit mesophases not far above room temperature . The core DHA structure is rod‐shaped, which is a desirable quality for forming the nematic phase.…”

“…The core DHA structure is rod‐shaped, which is a desirable quality for forming the nematic phase. In the nematic phase, full conversion to the VHF was not possible, but photolysis of 4 did result in annihilation of the defects and established a higher degree of order in the resulting mesophase when the VHF underwent ring closure back to 4 . Synthetic developments in DHA chemistry have allowed for the introduction of aromatic substituents at the 7‐position .…”

“…Previously,w eh ave reportedt hat DHAs 3 and 4,w hich are both substituted with biaryl units (Figure 1), exhibit mesophases not far above room temperature. [17] The core DHA structure is rod-shaped, which is ad esirable qualityf or forming the nematicp hase. In the nematic phase, full conversion to the VHF was not possible, but photolysis of 4 did result in annihilation of the defects and establishedahigher degree of order in the resulting mesophase when the VHF underwent ring closure back to 4.…”

“…In the nematic phase, full conversion to the VHF was not possible, but photolysis of 4 did result in annihilation of the defects and establishedahigher degree of order in the resulting mesophase when the VHF underwent ring closure back to 4. [17] Synthetic developments in DHA chemistry have allowed for the introduction of aromatic substituents at the 7-position. [18,19] However,p lacing as ubstituent at this position on the seven-membered ring becomes complicated because, when performing switching experiments in solution, isomeric scrambling giving DHAs with the substituents in either the 6-or 7-positions can occur after one ring-opening/closure cycle.…”