Optical characterization and analysis of the gas/surface adsorption phenomena on phthalocyanines thin films for gas sensing application

Zn(II) tetra-4-(2,4-di-t-amylphenoxy)-phthalocyanine (1a), Zn(II) tris-(2,4-di-t-amylphenoxy)-[4-(4-mercapto-phenylimino-methyl)-phenoxy] (1b) and Zn(II) tris-(2,4-di-t-amylphenoxy)-[4-(4-formyl)-phenoxy] (1c) phthalocyanine were synthesized. The molecular structures were confirmed by LC–MS, 1H NMR, FT-IR and UV–vis spectra. Spin coated layers of these phthalocyanines have been used as optochemically interactive materials for the detection of volatile organic compounds (VOCs) in the UV–vis spectral range. An optical characterization in controlled atmosphere have been carried out by acquiring the absorption spectra of the phthalocyanine complexes both in dry-air and in the presence of different volatile organic compounds in order to study the optical sensing properties of these thin organic layers towards specific volatile organic compounds. The optical absorption spectra have been analyzed by using a deconvolution analysis centered on the Q and Soret bands. The results of the optical VOCs sensing tests showed interesting differentiation in the optical responses depending on the peripheral substituents of the macromolecules. Morphologic analyses were performed by atomic force microscopy (AFM). The VOC/surface absorption processes were also analyzed in order to understand the VOC-detection mechanisms.