Fluorinated metal phthalocyanines: interplay between fluorination degree, films orientation and ammonia sensing properties

Abstract

In this work, the sensor response of MPcFx (M=Cu, Co, Zn; x=0, 4, 16) films toward gaseous NH3 (10-50 ppm) was studied by a chemiresistive method and compared to that of unsubstituted MPc films to reveal the effects of central metals and F-substituents on the sensing properties. A combination of atomic force microscopy and X-ray diffraction techniques has been used to elucidate the structural features of thin MPcFx films deposited by organic molecular beam deposition. It has been shown that the sensor response of MPcF4 films to ammonia is noticeably higher than that of MPc films, which is in good correlation with the values of binding energy between the metal phthalocyanine and NH3 molecule as calculated by DFT method. At the same time, in contrast to the DFT calculations MPcF16 demonstrated the less sensor response compared to MPcF4, which appeared to be connected with the different structure and morphology of their films. ZnPcF4 films were shown to exhibit the sensitivity to ammonia up to the concentrations as low as 0.1 ppm and can be used for the selective detection of ammonia in the presence of some reducing gases and volatile organic compounds. Moreover, ZnPcF4 films can be used for the detection of NH3 in the gas mixture simulating exhaled air (N2 – 76%, O2 – 16%, H2O – 5%, CO2 – 3%).