Printable Optical Sensors Based on H-Bonded Supramolecular Cholesteric Liquid Crystal Networks

Nicole Herzer†, Hilal Guneysu†, Dylan J. D. Davies†, Derya Yildirim†, Antonio R. Vaccaro†, Dirk J. Broer†, Cees W. M. Bastiaansen†‡, and Albertus P. H. J. Schenning*†

^† Functional Organic Materials & Devices, Eindhoven University of Technology, PO Box 513, Eindhoven, The Netherlands

^‡ Department of Materials, Queen Mary University of London, Mile End Road, London E1 4NS, U.K.

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja301845n

Publication Date (Web): April 23, 2012

Copyright © 2012 American Chemical Society

A printable H-bonded cholesteric liquid crystal (CLC) polymer film has been fabricated that, after conversion to a hygroscopic polymer salt film, responds to temperature and humidity by changing its reflection color. Fast-responding humidity sensors have been made in which the reflection color changes between green and yellow depending on the relative humidity. The change in reflection band is a result of a change in helix pitch in the film due to absorption and desorption of water, resulting in swelling/deswelling of the film material. When the polymer salt was saturated with water, a red-reflecting film was obtained that can potentially act as a time/temperature integrator. Finally, the films were printed on a foil, showing the potential application of supramolecular CLC materials as low-cost, printable, battery-free optical sensors.