Phthalocyanin sensor

This problem was solved by means of phthalocyanin sensors. Phthalocyanin, an organic semiconductor, was deposited as a thin film on a microstructured silicon substrate. This could detect nitrogen oxides, ozone, and sulfur dioxide it took less than 1 s to detect concentrations below 1 ppm. 

The extreme sensitivity of phthalocyanine sensors to oxidants has raised the possibility that common urban pollutants ozone and NOx are responsible for much of the conductivity of phthalocyanine devices in ambient conditions [133]. Indeed, phthalocyanine OTFTs on prolonged exposure to ambient air often exhibit an increase in device current however, their FET characteristics are also degraded so that they no longer can be switched off [34]. High humidity can reverse the process and restore FET characteristics. The high sensitivity of phthalocyanine OTFTs to pollutants may limit sensing applications and improved stability in... 

With liquid crystal metal phthalocyanine compounds as mass sensors, the LSER approach has proven useful. Analyte uptake has been measured using QCM methods, and adsorption of volatile organic compounds (VOCs) into the liquid crystalline coating appears to follow similar trends as for organic polymer film sensors. It should be noted that the analytes examined (toluene, chloroform, carbon tetrachloride, benzene, hexane, and methanol) are volatile compounds that are very weak ligands toward metals [167], Thus, the composite sensor response for metal phthalocyanine sensors based on conductivity is a complex property that depends on analyte redox properties, basicity, and sensor crystallinity. 

Reverse saturable absorption is an increase in the absorption coefficient of a material that is proportional to pump intensity. This phenomenon typically involves the population of a strongly absorbing excited state and is the basis of optical limiters or sensor protection elements. A variety of electronic and molecular reorientation processes can give rise to reverse saturable absorption many materials exhibit this phenomenon, including fuUerenes, phthalocyanine compounds (qv), and organometaUic complexes. 

Chemical and biological sensors (qv) are important appHcations of LB films. In field-effect devices, the tunneling current is a function of the dielectric constant of the organic film (85—90). For example, NO2, an electron acceptor, has been detected by a phthalocyanine (or a porphyrin) LB film. The mechanism of the reaction is a partial oxidation that introduces charge carriers into the film, thus changing its band gap and as a result, its dc-conductivity. Field-effect devices are very sensitive, but not selective. 

Other sensors are mostly grouped towards the triethylamine. In the case of porphyrins 6-8, 13 the coordinated metal is no longer able to drive the selectivity pattern and the presence of the peripheral alkyl chains completely shadows the coordination interactions. This result can explain the failure to observe the coordination interaction in the sensing mechanism of the metal complexes of the closely related alkyl chains functionalized phthalocyanines reported in the past by Gopel and coworkers [22]. 

Metal oxide sensors (MOS), smart, 22 717 Metal oxide supported catalysts, 5 336-337 coke formation on, 5 267—270 Metal passivation, in industrial water treatment, 26 137 Metal peroxides, 18 410 Metal phosphates, tertiary, 18 840 Metal-phosphorus alloys, 19 59 Metal phthalocyanines, electrochromic materials, 6 572t, 576-577 Metal prefinishing, detersive systems for, 8 413t... 

A semiconductor sensor-based instrument was described for determination of the composition and concentrations of vapors of organic nitro compounds and nitrogen dioxide in the atmosphere. Four organic semiconductor sensors [e.g. aluminum phthalocyanine fluoride (222a)] were tested in conjunction with platinized platinum preconcentrators sensitivity is to ppm levels of nitrobenzene450. 

Nonlinear optical organic materials such as porphyrins, dyes, and phthalocyanines provide optical limiting properties for photonic devices to control light frequency and intensity in a predictable manner. The optical limit of CNTs composites is saturated at CNTs exceeding 3.8wt% relative to the polymer mass (Chen et al., 2002). Polymer/ CNT composites could also be used to protect human eyes, for example, optical elements, optical sensors, and optical switching (Cao et al., 2002). 

Sensing of chlorine is possible with a phthalocyanine-based optode that is elec-trochemically reset [101]. Also a direct electrochemical Clark-type sensor employing carbon electrodes has been investigated [102]. For this type of sensor, the various types of carbon gave different responses and the edge-plane sites of graphitic electrodes were identified as electrochemically active. Both chlorine reduction and chlorine evolution were studied and the effects of the trichloride anion, Ch", were highlighted. 

For example, porphyrins have been proposed as active elements in gas-sensor devices. This field has become one of the fastest growing areas in both research and commercial respects. Several authors have proposed the use of some organic materials, e.g., phthalocyanine and porphyrin derivatives (15-18) to improve the device s performance characteristics, such as low operating temperature, selectivity, and so on. 

The combination of a phthalocyanine ring with crown ether moieties and redox-active tetrathiafulvalenes gave compound 117 (Scheme 64) and was described by Zou as a good candidate for a redox-active Na+ sensor [133]. 

Crown ether-phthalocyanines 118 (n = 0, 1,2) (Scheme 65) were used as gas sensors for N02. They were found to be superior to the previously used materials... 

In summary, phthalocyanines modified with crown ethers are interesting synthetic targets as they are prone to form columnar phases. Their electron conductivity and complexation properties make them interesting candidates for the design of sensor materials or supramolecular switches. 

Scheme 65 Crown ether phthalocyanines 118 as sensor materials for NQ2...

The preparation of L-B films from metal-free phthalocyanine and from tetra tert-butyl phthalocyanine was reported by Baker et al. in 1983 (17). Since then the preparation of a series of tetracumylphen-oxy derivatives suitable for preparing L-B coating films has been reported by Snow and Jarvis (18), and the results of tests of gas sensors made with these coatings have been reported by Barger et al. (19). ... 

A detailed examination of the mechanisms of reaction of these vapors with the various types of phthalocyanines is beyond the scope of this work. The reader is directed to the papers by van Ewyk, Chadwick and Wright (14) or Langton and Day (11) for further information in this area. Experiments described here were conducted primarily to survey a series of materials under identical conditions in order to get a relative ranking of candidate materials for practical gas sensors, and to aid decisions about which monolayerforming derivatives to synthesize. 

Monolayer Films of Phthalocyanine Derivatives. A series of organic derivatives of phthalocyanines were prepared that have two important characteristics of materials to be deposited by the Langmuir-Blodgett technique (1) they are soluble in volatile organic solvents, and (2) they form monomolecular films on the surface of water. Further study of deposited films of these phthalocyanine derivatives will be necessary in order to determine the exact orientations on the surface, but regardless of their orientations, they offer interesting possibilities for construction of thin films of ordered arrays of molecules on the surface of gas sensors. 

Figure 6. Characteristic patterns of response of an array of six sensors coated with different phthalocyanines to various vapor exposures. The maximum concentration was 100 ppm for ammonia, sulfur dioxide, and DMMP and 1000 ppm for water, ethanol, air and benzene. The central metal of each phthalocyanine is shown at the top.

The results illustrated above show that the CFT method is suitable for making chemical-sensor measurements using both bulk polymers and, in particular, thin film materials that are intrinsically weak conductors. Therefore, the CFT looks premising for such materials as poly(phenylacetylene) derivatives 24., for which carefully shielded electrometer measurements have been required in the past because of current levels at the threshold of detectability. Furthermore, the fact that the CFT always makes AC measurements reduces the problem of DC polarization of electrodes. In addition, the CFT approach should be suitable for other "chemiresistor" applications, such as the metal-substituted phthalocyanines proposed by Jarvis et. al. 2 and for Langmuir—Blodgett films 26. which, because they are so thin, may prove impossible to use in parallel-plate form, but which can be routinely used with the high-sensitivity interdigi-tated-electrode approach provided by the CFT. 

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