Metal phthalocyanines bearing electron-withdrawing fluorine substituents were synthesized a long time ago, but interest in the study of their films has emerged in recent decades. This is due to the fact that, unlike unsubstituted phthalocyanines, films of some fluorinated phthalocyanines exhibit the properties of n-type semiconductors, which makes them promising candidates for application in ambipolar transistors. Apart from this, it was shown that the introduction of fluorine substituents led to an increase in the sensitivity of phthalocyanine films to reducing gases. This review analyzes the state of research over the last fifteen years in the field of applications of fluoro-substituted metal phthalocyanines as active layers of gas sensors, with a primary focus on chemiresistive ones. The active layers on the basis of phthalocyanines with fluorine and fluorine-containing substituents of optical and quartz crystal microbalance sensors are also considered. Attention is paid to the analysis of the effect of molecular structure (central metal, number and type of fluorine substituent etc.) on sensor properties of fluorinated phthalocyanine films.

In this work, the effect of fluorine and chlorine substituents in tetrasubstituted zinc phthalocyanines, introduced into the non-peripheral (ZnPcR₄-np, R = F, Cl) and peripheral (ZnPcR₄-p, R = F, Cl) positions of macrocycle, on their structure and chemiresistive sensor response to low concentration of ammonia is studied. The structure and morphology of the zinc phthalocyanines films (ZnPcR₄) were investigated by X-ray diffraction and atomic force microscopy methods. To understand different effects of chlorine and fluorine substituents, the strength and nature of the bonding of ammonia and ZnPcHal₄ molecules were studied by quantum chemical simulation. It was shown on the basis of comparative analysis that the sensor response to ammonia was found to increase in the order ZnPcCl₄-np < ZnPcF₄-np < ZnPcF₄-p < ZnPcCl₄-p, which is in good agreement with the values of bonding energy between hydrogen atoms of NH₃ and halogen substituents in the phthalocyanine rings. ZnPcCl₄-p films demonstrate the maximal sensor response to ammonia with the calculated detection limit of 0.01 ppm; however, they are more sensitive to humidity than ZnPcF₄-p films. It was shown that both ZnPcF₄-p and ZnPcCl₄-p and can be used for the selective detection of NH₃ in the presence of carbon dioxide, dichloromethane, acetone, toluene, and ethanol.

A comparative analysis of the chemiresistive sensor response of thin films of a series of tetrasubstituted phthalocyanines of various metals with F-substituent in peripheral (MPcF₄-p, M = Cu, Co, Zn, Pb, VO) and non-peripheral (MPcF₄-np) positions in macroring to low concentrations of ammonia (1–50 ppm) was carried out. It was found that MPcF₄-p films exhibit a higher sensor response than MPcF₄-np ones. A CoPcF₄-p film demonstrated a calculated LOD of 0.01 ppm with a recovery time of 215 s, while a VOPcF₄-p film had LOD of 0.04 ppm and the recovery time of 270 s. The selectivity test showed that CO₂, ethanol, acetone, benzene, and formaldehyde did not interfere with the determination of ammonia, while H₂S at a concentration of more than 10 ppm could act as an interfering gas. It was shown that, as a result of quantum-chemical calculations, the observed regularities are best described by the interaction of NH₃ with phthalocyanines through the formation of hydrogen bonds between NH₃ and side atoms of the macroring. In the case of MPcF₄-p, the NH₃ molecule approaches the macrocycle more closely and binds more strongly than in the case of MPcF₄-np. The stronger binding leads to a stronger effect of the ammonia molecule on the electronic structure of phthalocyanine and, as a consequence, on the chemiresistive sensor response of the films to ammonia.

In this work, octafluoro-substituted phthalocyanines of zinc, vanadyl, and cobalt (MPcF₈, M = Zn(II), Co(II), VO) were synthesized and studied. The structures of single crystals of the obtained phthalocyanines were determined. To visualize and compare intermolecular contacts in MPcF₈, an analysis of Hirshfeld surfaces (HS) was performed. MPcF₈ nanoscale thickness films were deposited by organic molecular beam deposition technique and their structure and orientation were studied using X-ray diffraction. Comparison of X-ray diffraction patterns of thin films with the calculated diffractograms showed that all three films consisted of a single crystal phase, which corresponded to a phase of single crystals. Only one strong diffraction peak corresponding to the plane (001) was observed on the diffraction pattern of each film, which indicated a strong preferred orientation with the vast majority of crystallites oriented with a (001) crystallographic plane parallel to the substrate surface. The effect of the central metals on the electronic absorption and vibrational spectra of the studied phthalocyanines as well as on the electrical conductivity of their films is also discussed.

In this work, the tetra-, octa- and hexadecachloro-substituted copper phthalocyanines CuPcCl_x (where x can equal 4, 8 or 16) were investigated by the methods of vibrational (IR and Raman) spectroscopy and X-ray diffraction. The assignment of the most intense bands, both in IR and Raman spectra, was carried out on the basis of DFT calculations. The structure of a CuPcCl₄ single crystal grown by sublimation in vacuum was refined for the first time. The effect of chloro-substitution on the structure of CuPcCl_x thin films deposited in a vacuum onto a glass substrate at 50 and 200 °C was studied. It was shown that CuPcCl₄ formed polycrystalline films with the preferential orientation of the (100) crystallographic plane of crystallites parallel to the substrate surface when deposited on a substrate at 50 °C. Introduction of more Cl-substituents into the phthalocyanine macrocycle leads to the formation of amorphous films on the substrates at 50 °C. At the elevated substrate temperature, the growth of polycrystalline disordered films was observed for all three copper phthalocyanines.