Molecular orientation and gas-sensing properties of Langmuir–Blodgett films of copper phthalocyanine derivatives

Thin films of 2, 9, 16, 23-tetra-octyloxy copper phthalocyanine (CuPcA₈) and 2, 9, 16, 23-tetra-hexadecylocy copper phthalocyanine (CuPcA₁₆) were prepared by Langmuir–Blodgett technique and were characterized by UV–vis spectra. The macro-ring orientation of the two copper phthalocyanine molecules in the films was explored by polarized UV–vis spectra. The linear relationship between the absorption intensity and the number of deposited layers confirmed the highly ordered layered-structure of the films. Moreover, it was found the phthalocyanine molecules were arranged with an angle of 49.8° and 63.6° to the substrates for CuPcA₈ and CuPcA₁₆, respectively. The gas-sensing properties of the LB films to methanol, ethanol, and propanol were detected at room temperature. By introducing appropriate substituent onto the macro-ring of the phthalocyanine, the molecular orientation in the films could be controlled, and their gas response might be improved.