Tetrafluorosubstituted Metal Phthalocyanines: Study of the Effect of the Position of Fluorine Substituents on the Chemiresistive Sensor Response to Ammonia

Abstract

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.

Cobalt and Iron Phthalocyanine Derivatives: Effect of Substituents on the Structure of Thin Films and Their Sensor Response to Nitric Oxide

“…Figure 7 shows a typical sensor response of FePcCl 4 film as an example. Similarly to the case of the sensor response of MPcF 4 films to ammonia [ 28 ], when NO was introduced into the cell, a sharp increase in resistance was observed, and after purging with argon, the resistance returned to its original value. With an increase in NO concentration, the change in resistance increased.…”

“…Despite the fact that strong binding should be observed in the case of interaction with a central metal atom [ 22 ], when the binding energies reach 1.5 eV for CoPc and 1.9 eV for FePc, depending on the orientation of the nitric oxide molecule, we did not consider this method of coordination for two reasons [ 28 ]. First, due to the π - π interaction, the typical distance between two phthalocyanine molecules in a stack is too small for any gas molecule to penetrate between them.…”

“…Moreover, Chia et al [ 67 ] demonstrated by in-situ X-ray absorption spectroscopy (XAS) and EXAFS that NO 2 interacts with CuPc at the pyrrole moiety of the Pc macrocycle, rather than on the metal center. In this regard, the simulated interaction was carried out through the side atoms of the macrocycles ( Figure 13 and Figure 14 ), similar to previous studies [ 21 , 28 ].…”

“…Note that, in the case of tetrasubstituted complexes of metal phthalocyanines, substituents can be introduced into both peripheral and non-peripheral positions of the phthalocyanine ring. In this paper, only phthalocyanine derivatives with substituents in the peripheral positions of the phthalocyanine ring were considered, due to the fact that they have a significantly higher sensor response toward electron donor gases compared to non-peripherally substituted examples [ 21 , 28 ].…”

“…In this situation, the molecule has several nonequivalent adsorption centers for gas molecules that bind through the side atoms of the macrocycle. At the same time, considering separately the interaction of an NH 3 molecule with CoPcF 4 and VOPcF 4 through four bridge nitrogen atoms, we showed that the parameters of this interaction were very close in all four cases [ 28 ]. In this regard, in order to simplify calculations by reducing the number of possible nonequivalent adsorption centers for the NO molecule, MPcR 4 molecules with C 4h symmetry ( Figure 2 ) were considered in this work, although symmetry constraints were not used in the calculation process.…”