Conductometric gas sensing studies of tert-butyl silicon-[bis ethyloxy]-phthalocyanine LB films

Ultrathin Langmuir-Blodgett film properties of tert-butyl silicon-[bis ethyloxy]-phthalocyanine (tbPcSi(OC₂ H₅)₂) have been studied and characterised. Surface pressure–area isotherms reveal an area per molecule of around 0.85 nm², and that a compact ‘solid’ phase occurs in the region 10–30 m N m⁻¹. LB films of different thicknesses were deposited onto gold interdigitated electrodes on glass in order to facilitate I–V measurements and assess the conductometric sensing properties in response to 5 ppm NO₂. The I–V characteristic is Ohmic and yields conductivity in the range comparable to that obtained for other phthalocyanine monomers. The gas sensing behaviour of these films in response to NO₂ was investigated and modelled using a double exponential model. Preliminary UV–visible spectroscopic investigations indicate that the film also responds optically.