Optical Monitoring of Gases with Cholesteric Liquid Crystals

A new approach to optical monitors for gases is introduced using cholesteric liquid crystals doped with reactive chiral compounds. The approach is based on cholesteric pitch length changes caused by a change in helical twisting power (HTP) of the chiral dopants upon reaction with the analyte. The co...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2010-03, Vol.132 (9), p.2961-2967
Main Authors: Han, Yang, Pacheco, Katherine, Bastiaansen, Cees W. M, Broer, Dirk J, Sijbesma, Rint P
Format: Article
Language:English
Subjects:
Carbon Dioxide - analysis
Cholesterol - chemistry
Disulfides - chemistry
Liquid Crystals - chemistry
Magnetic Resonance Spectroscopy
Molecular Structure
Oxidation-Reduction
Oxygen - analysis
Spectrophotometry, Infrared
Toluene - analogs & derivatives
Toluene - chemistry
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Summary:A new approach to optical monitors for gases is introduced using cholesteric liquid crystals doped with reactive chiral compounds. The approach is based on cholesteric pitch length changes caused by a change in helical twisting power (HTP) of the chiral dopants upon reaction with the analyte. The concept is demonstrated for monitoring carbon dioxide via reversible carbamate formation and for oxygen using the irreversible oxidation of a chiral dithiol to a disulfide. Monitoring of CO2 was achieved by doping a commercial cholesteric liquid crystalline mixture (E7) with 1.6% mol of the 1:1 complex of an optically pure diamine with a TADDOL derivative. Upon exposure to carbon dioxide, the reflection band of a thin film of the mixture shifted from 637 to 495 nm as a consequence of dissociation of the complex after carbamate formation of the diamine. An O2 monitor was obtained by doping E7 with a chiral binaphthyl dithiol derivative and a nonresponsive codopant. The reflection band of the oxygen monitor film changed from 542 to 600 nm, due to the conformational change accompanying oxidation of the dithiol to disulfide. These monitoring mechanisms hold promise for application in smart packaging, where carbon dioxide and oxygen are of special interest because of their roles in food preservation.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja907826z