Chemical Gas Sensor using Chiral Nematic Liquid Crystals

Abstract

With recent increased interest in health and environmental issues, many researchers started to develop biosensors for detection of illnesses as well as toxic substances. To develop these sensors, we utilized the unique properties of selective reflection in chiral nematic liquid crystals (CNLCs). Thus far, we have demonstrated that CNLCs, upon contact with volatile organic compounds (VOCs), develop a change in color in red or blue direction (red or blue shift). This color change is attributable to the change in the chiral pitch of CNLCs. The latter is suggested to be influenced by molecular interactions between CNLCs and VOCs, such as hydrogen bonding, π-π stacking, and LC ordering parameters. Among the CNLCs evaluated, we found that phenylpyrimidine (PPy) derivatives showed the largest blue shift in selective reflection spectrum upon contact with VOCs. We discovered that the large color shift is caused by low LC ordering as PPy derivatives has a low nematic-isotropic transition temperature.