Synthesis of a series of heterocyclic compounds based on pyrazole units is reported. The possibility of using these compounds, as solid-state thin layers deposited on quartz substrates, for optical recognition of hazardous pollutant gases was investigated. The gases SO2, NO2, CO, CH4, and NH3 were studied. Two of the ligand layers had reversible sensitivity toward SO2, with good reaction time. The presence of CO, CH4 NO2, and NH3 had no effect on the optical properties. Morphological characterization by use of AFM microscopy was also investigated.