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Chiral Periodic Mesoporous Organosilica in a Smectic-A Liquid Crystal: Source of the Electrooptic Response
Chiral periodic mesoporous organosilica (PMO) materials have been shown to deracemize a configurationally achiral, but conformationally racemic liquid crystal in which the PMO is embedded. In particular, application of an electric field E in the liquid crystal’s smectic-A phase results in a rotation of the liquid crystal director by an angle proportional to E, which is detected optically — this is the so-called “electroclinic” effect. Here we present results from electroclinic measurements as a function of frequency and temperature, which allow us to distinguish the component of optical signal that arises from liquid crystal chirality induced within the PMO’s chiral pores from that induced just outside the silica colloids. Our central
result is that the overwhelming source of our electrooptic signal emanates from outside the PMO, and that the contribution from the liquid crystal embedded in the chiral pores is much smaller and below the noise level.
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- Award ID(s):
- 1505389
- NSF-PAR ID:
- 10012637
- Date Published:
- Journal Name:
- Liquid crystals
- ISSN:
- 1366-5855
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The molecule (
E )‐(5‐(3‐anthracen‐9‐yl‐allylidene)‐2,2‐dimethyl‐[1,3] dioxane‐4,6‐dione) (E ‐AYAD ) undergoesE →Z photoisomerization. In the solid state, this photoisomerization process can initiate a physical transformation of the crystal that is accompanied by a large volume expansion (ca. 10 times), loss of crystallinity, and growth of large pores. This physical change requires approximately 10 % conversion of theE isomer to theZ isomer and results in a gel‐like solid with decreased stiffness that still retains its mechanical integrity. The induced porosity allows the expanding gel to engulf superparamagnetic nanoparticles from the surrounding liquid. The trapped superparamagnetic nanoparticles impart a magnetic susceptibility to the gel, allowing it to be moved by a magnetic field. The photoinduced phase transition, starting with a compact crystalline solid instead of a dilute solution, provides a new route for in situ production of functional porous materials. -
Chiral surfaces are of growing interest for enantioselective adsorption and reactions. While metal surfaces can be prepared with a wide range of chiral surface orientations, chiral oxide surface preparation is much more challenging. Herein, we demonstrate that the chirality of a metal surface can be used to direct the homochiral growth of a thin film chiral oxide. Specifically, we study the chiral ‘29’ copper oxide, formed by oxidizing a Cu(111) single crystal at 650 K. Surface structure spread single crystals which expose a continuous distribution of surface orientations as a function of position on the crystal, enabled us to systematically investigate the mechanism of chirality transfer between metal and oxide with high-resolution scanning tunneling microscopy. We discovered that the local underlying metal facet directs the orientation and chirality of the oxide overlayer. Importantly, single homochiral domains of the ‘29’ oxide were found in areas where the Cu step edges that templated growth were ≤20 nm apart. We used this information to select a Cu(239 241 246) oriented single crystal and demonstrate that a ‘29’ oxide surface can be grown in homochiral domains by templating from the subtle chirality of the underlying metal crystal. This work demonstrates how a small degree of chirality induced by very slight misorientation of a metal surface (~1 sites/ 20 nm2) can be amplified by oxidation to yield a homochiral oxide with a regular array of chiral oxide pores (~75 sites/ 20 nm2). This offers a general approach for making chiral oxide surfaces via oxidation of an appropriately miscut metal surface.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1080/02678292.2015.1119321
