| Summary: | In this work, the effect of fluorine and chlorine substituents in tetrasubstituted zinc phthalocyanines, introduced into the non-peripheral (ZnPcR<sub>4</sub>-np, R = F, Cl) and peripheral (ZnPcR<sub>4</sub>-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 (ZnPcR<sub>4</sub>) 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 ZnPcHal<sub>4</sub> 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 ZnPcCl<sub>4</sub>-np < ZnPcF<sub>4</sub>-np < ZnPcF<sub>4</sub>-p < ZnPcCl<sub>4</sub>-p, which is in good agreement with the values of bonding energy between hydrogen atoms of NH<sub>3</sub> and halogen substituents in the phthalocyanine rings. ZnPcCl<sub>4</sub>-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 ZnPcF<sub>4</sub>-p films. It was shown that both ZnPcF<sub>4</sub>-p and ZnPcCl<sub>4</sub>-p and can be used for the selective detection of NH<sub>3</sub> in the presence of carbon dioxide, dichloromethane, acetone, toluene, and ethanol.
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