Gas sensing and electrochemical properties of tetra and octa 2H-chromen-2-one substituted iron(ii) phthalocyanines

The synthesis of novel alpha tetra, beta tetra and beta octa 4-(4-methoxyphenyl)-8-methyl-coumarin-7-oxy, and beta octa 4-chloro-5-(4-(4-methoxyphenyl)-8-methylcoumarin-7-oxy) substituted iron(ii) phthalocyanines has been achieved by the reaction of the corresponding phthalonitriles with iron(ii)acetate. The compounds were characterized by elemental analysis, FT-IR, UV-vis, and MALDI-TOF mass spectrometry. The reduction and oxidation properties of the compounds were identified by voltammetric and in situ spectroelectrochemical measurements. The gas sensing behavior of the spin coated films of the differently substituted iron(ii) complexes towards CO₂, CO and SO₂ was investigated at various temperatures between 300 K and 500 K. While exposure to SO₂ had no considerable influence on the sensor current, the presence of CO and CO₂ gases led to a large increase in sensor currents. The effect of relative humidity on the CO and CO₂ sensing capability of the spin coated films was also studied. The results showed that the presence of water vapor, acting as an interference gas, causes a decrease in the CO₂ sensitivity, but an increase in the CO sensitivity of the sensors. The experimental adsorption data were analyzed using the Elovich kinetic model. Linear regression analysis results show that the Elovich equation provides the best correlation for the CO₂ and CO adsorption processes under humid conditions. However, the experimental data deviated considerably from the theoretical model under a dry atmosphere.