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Azobenzene-based chiral dopants in cholesteric liquid crystals are of interest since the properties they induce in the liquid crystal could be tuned photochemically. Here, we use a substituted binaphthyl with a halogenated azobenzene as a chiral dopant to induce a photoswitchable cholesteric phase in the nematic 4-n-pentyl-4’-cyanobiphenyl. The azobenzene group chemically attached to the chiral dopant undergoes isomerization from trans to cis upon irradiation with green light (wavelength 535 nm), and from cis to trans upon irradiation with blue light (wavelength 450 nm). The transition between the two isomers causes helicity inversion of the cholesteric, with a left-handed trans isomer and a right-handed cis isomer. We report on the kinetics of photoisomerization of both processes (trans-to-cis and cis-to-trans) in the nematic host by following the pitch evolution over time. We show that the kinetic mechanism corresponds to a two-step process: a first-order isomerization followed by a second-order autocatalytic isomerization. This mechanism differs from the typical first-order kinetics for cis-to-trans or trans-to-cis isomerization in azobenzenes. The autocatalytic process is attributed to interactions between the chiral dopant and the nematic host.
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Chiral organosilica particles and their use as inducers of conformational deracemization of liquid crystal phases
Chiral organosilica particles of size ~200 nm were synthesized from an enantio-pure multi-armed chiral D-maltose organosilane precursor in the absence of co-condensation with an achiral monomer. Two distinct experiments were performed to demonstrate the particles’ ability to induce conformational deracemization of a host liquid crystal. The first involves an electric field-induced tilt of the liquid crystal director in the deracemized smectic-A phase. The other involves domain wall curvature separating left- and right-handed liquid crystal helical pitch domains imposed by the cells’ substrates. The results demonstrate unequivocally that enantio-pure organosilica nanoparticles can be synthesized and can induce chirality in a host.
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- Award ID(s):
- 1505389
- PAR ID:
- 10053252
- Date Published:
- Journal Name:
- Chemical physics letters
- ISSN:
- 0009-2614
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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