Optical NO2 sensing based on sol-gel entrapped azobenzene dyes

A novel thin film based on an azobenzene chromophore incorporated into a so l-gel network is demonstrated to be sensitive to NO, gas and shows comparab le sensing performance to a Langmuir-Blodgett (LB) film of the same chromop hore attached to a polysiloxane backbone. Sensing was carried out by UV-Vis ible absorption spectroscopy monitoring increase in the n-pi* transition at 475 nm with simultaneous decrease in the pi-pi* transitions at 240 nm and 360 nm on exposure to 100 ppm NO2 gas. Preliminary stability studies show o nly a limited loss of response (<5%) on repeated gas exposure. Increasing t he temperature from 293 K to 313 K caused a decrease in the response of the sol-gel system similar to that observed in the Langmuir-Blodgett film of t he polysiloxane derivative, suggesting this to be a fundamental temperature property of the chromophore-gas interaction. The sol-gel immobilization ap proach provides a convenient route to sensors based on this principle. (C) 1999 Elsevier Science S.A. All rights reserved.