Optical sensing responses of tetraphenyl porphyrins toward alcohol vapours: A comparison between vacuum evaporated and spin-coated thin films

Thin porphyrin films for gas sensing applications are generally produced through chemical techniques. In this work thin solid films of three tetraphenyl porphyrins (H2TPP, Fe(TTP)Cl and CoTPP) have been deposited by means of vacuum evaporation technique. A preliminary characterization of the samples has been performed by means of Fourier Transform Infrared (FT-IR) and UV–vis absorption spectra. The behaviour of these samples exposed to methyl, ethyl and isopropyl alcohol vapours was investigated and compared to the behaviour of the samples deposited through spin coating technique. Elovich kinetics and Langmuir adsorption isotherms have been also studied. The comparison points out that the vacuum evaporated samples exhibit more pronounced and faster responses and higher sensitivity than spin-coated films.