An E.S.R. study of the reaction of cobalt phthalocyanines with ammonia and dioxygen

Comparative Gas Sensing in Cobalt, Nickel, Copper, Zinc, and Metal-Free Phthalocyanine Chemiresistors

“…Phthalocyanines (Pcs), both metalated (MPcs) and metal-free (H 2 Pc), are metal−organic semiconductors that have been applied as chemiresistive sensors. − MPc sensitivity to vapor-phase molecules may be tuned by manipulation of the metal center and by substitution of functional groups on the organic ring. − Conductivity in MPc films depends strongly on atmospheric chemical species, particularly oxidants and reductants. , P-type MPcs are insulating in dark, high-vacuum environments and become semiconducting on exposure to air. − This air-induced conductivity has been attributed to coordination of O 2 to surface MPc metal centers, forming superoxide adducts which extract electrons, generating charge carriers (holes) in the bulk film. − Superoxide adducts have been detected directly through EPR studies. − Oxygen adsorption on H 2 Pc has been reported as occurring on the four meso -nitrogens, leading to weaker conductivity gains . Other oxidizing gases (O 3 , NO X , Cl 2 , and others) induce similar conductivity gains in p-type MPc films through charge transfer or redox reactions which generate holes in the film. − Similar charge transfer interactions have been used to identify nitrated explosives in conjunction with pattern recognition algorithms …”

“…[10][11][12] Superoxide adducts have been detected directly through EPR studies. [13][14][15] Oxygen adsorption on H 2 Pc has been reported as occurring on the four meso-nitrogens, leading to weaker conductivity gains. 16 Other oxidizing gases (O 3 , NO X , Cl 2 , and others) induce similar conductivity gains in p-type MPc films through charge transfer or redox reactions which generate holes in the film.…”

Gas Sensing Mechanism in Chemiresistive Cobalt and Metal-Free Phthalocyanine Thin Films

“…This air-induced conductivity has been attributed to different mechanisms. For polycrystalline films, it is assumed that O 2 absorbs only at the air/MPc interface and at grain boundaries because the MPc crystal structure is very tight and unaffected by exposure to air. − It has been reported that the formation of charge-transfer complexes by coordination of O 2 to MPc metal centers at the air/phthalocyanine interface leads to the formation of oxidized MPc + and O 2 - species and injection of hole charge carriers into the bulk solid. ,, The presence of the superoxide adduct of CoPc has been detected in several electron paramagnetic resonance (EPR) studies. , There is also evidence that weaker O 2 adsorption may occur on the four meso -nitrogens of free base H 2 Pc, leading to conductivity increases that are not as large as those for the MPcs. − As a surface dopant, O 2 occupies only a fraction of the binding sites on the film; therefore, interactions with analyte vapors in air could result in two different mechanisms of analyte binding (Scheme ). Analytes could either bind to open surface metal coordination sites or compete with O 2 for occupied metal surface sites.…”

Aggregative Properties of Water-soluble Metal Phthalocyanines in a Borate Buffer Solution

“…The peculiarity of these macroheterocycles consists in that they can form different dimers in aqueous media, depending on conditions. Moreover, cobalt(II) phthalocyanines tend to form stable molecular complexes with O 2 [32,33]. When measuring the electronic absorption spectra of borate solutions of Co(4-SO 3 Na) 4 Pc before calorimetric experiments, we detected relaxation effects (see figure).…”