Synthesis, characterization, conduction and gas sensing properties of novel multinuclear metallo phthalocyanines (Zn, Co) with alkylthio substituents

Compound 1 has been prepared by the reaction of 4-nitrophthalonitrile and 2-nitro-2-methyl-1,3-propanediol by the common method of nucleophilic substitution of an activated nitro group in an aromatic ring. Interesting binuclear metallophthalocyanines (M = Zn and Co), compounds 2 and 3, respectively, of a new type have been synthesized from compound 1, 4,5-bis(hexylthio)phthalonitrile, and the corresponding metal salts [Zn(OAc)2 and CoCl2] by the method of statistically mixed condensation. Compound 2 was converted to the tetranuclear zinc (II) phthalocyanine 4 by the reaction with NaOH solution and activated zinc powder in a mixture of MeOH and THF as the solvent. Impedance spectroscopy (IS) and d.c conductivity (σd.c) measurements were performed on spin coated films of these compounds as a function of temperature (290–400 K) and frequency (40–105 Hz.) The sensing properties for volatile organic compounds (VOCs) were also investigated. Although the d.c conductivity shows typical Arrehenius behaviour for compound 2, a discontinous point was observed in the slope of ln σd.c versus 1/T plot for compound 4. Unlike the films of 2 and 4, the d.c behaviour of compound 3 obeys the variable range hopping (VRH) model. At room temperature, a curved line was observed from the complex plane plots of impedance for all compounds. These curved lines transformed into a full semicircle with increasing temperature. The a.c conductivity of the films is represented by the form ωs. The dependency of the frequency exponent s on temperature suggests a correlated barrier hopping. A sensor using compound 4 as the sensing layer had the highest sensitivity for all volatile organic compounds investigated and showed complete reversibility even at room temperature. The results indicated that the film of compound 4 has potential as a sensitive coating for the monitoring of VOC vapours.

Novel multinuclear metallo phthalocyanines (Zn, Co) with alkylthio substituents have been synthesized and their electrical conductance (a.c and d.c) and sensitivity to several volatile organic compounds are investigated by conductivity measurements.Figure optionsDownload as PowerPoint slide