An improved azo chromophore for optical NO2 sensing

Abstract

In previous studies, the response to NO₂ of a number of substituted azobenzenes was characterised for sensitivity and kinetics over a range of temperatures. These studies indicated that the optimal sensor of this sort must be based on a chromophore with a binding energy for the target gas of approximately 70 kJ mol⁻¹. Here, we present data for the best chromophore which has resulted, dispersed in an addition-cure polysiloxane matrix. We characterise the activation energy for the binding of NO₂ to the azobenzene sites and report measurements of the response time of thin films from which the diffusion constant of NO₂ in the matrix is deduced. We report on the behaviour of the films when operated in the cycled mode. We present quartz-crystal microbalance data allowing absolute calibration of the fractional site occupancy in a related system.