Phthalocyanine infrared absorption

Klug, H. P. and Alexander, L. E. (1974). X-ray diffraction procedures for polycrys-talline and amorphous materials. John Wiley Sons, New York. [117, 253, 254] Knudsen, B. 1. (1966). Copper phthalocyanine. Infrared absorption spectra of polymorphic modifications. Acta Chem. Scand., 20, 1344-50. 

Figure 10 Absorption spectra of a phthalocyanine green pigment and phthalocyanine infrared absorbers.

The palladium phthalocyanine (67), developed by Mitsui Toatsu and Ciba58,59 is one of the leading phthalocyanine infrared absorbers for CD-R (Compact Disk-Rewritable) (see Chapter 9.13). Bulky groups (R) reduce undesirable molecular aggregation, which lowers the extinction coefficient and hence the absorptivity and reflectivity. Partial bromination allows fine tuning of the film absorbance and improves reflectivity. The palladium atom influences the position of the absorption band, the photostability and the efficiency of the radiationless transition from the excited state.58 It is marketed by Ciba as Supergreen.60... 

Endo A, Matsumoto S, Mizuguchi J (1999) Interpretation of the near-infrared absorption of magnesium phthalocyanine complexes in terms of exdton coupling effects. J Phys Chem A 103(41) 8193—8199... 

Kaeida, O., et al. (Nippon Shokubai). Novel Phthalocyanine Compounds Production Method Thereof Near Infrared Ray Absorption Materials Containing the Same. European Patent 523,959, July 14, 1992. 

Phthalocyanines are analogues of the natural pigments chlorophyll and heme. However, unlike these natural pigments, which have extremely poor stability, phthalocyanines nre probably the most stable of all the colorants in use today. Substituents can extend the absorption to longer wavelengths, into the near infrared, but not to shorter wavelengths, and so their hues are restricted to blue and green. 

Besides phthalocyanine pigments developed for office copiers, new polymorph materials for laser printer utilization have been prepared. These materials, whose absorption characteristics were extended to the near-infrared region, were prepared by vacuum sublimation techniques. Recently, for safety reasons and to reduce the cost of production, solvent-pigment interactions have received great attention [41]. 

Of particular interest are phthalocyanines with strong absorption in the near infrared. A considerable effort has gone into the synthesis of new compounds and the development of methods for conversion of known phthalocyanines into morphologies that are infrared sensitive. This lias been difficult because the absorption spectra and photogeneration efficiencies depend on the chemical and crystal structure, particle size and morphology, as well as the presence of absorbed surface species (Sappok, 1978 Whitlock et al., 1992 Kubiak et al., 1995). As a consequence, specific methodologies must be developed for the synthesis, purification, and treatment of each compound. Methods of fabrication must also be designed to ensure that the desired characteristics are retained or induced (Mayo et al., 1994 Yao et al., 1995). 

Table 1 summarizes the analytical results obtained for the thermal reaction of I and of VI. With the exception of the experiment in which methanol was added to VI, the extent of phthalocyanine formation was very small. Moreover, the infrared spectra of these reacted samples exhibited absorptions characteristic of amide or imide carbonyl as well as those for tria-zine. Under these conditions, phthalocyanine formation is not favored. For example, the yield of phthalocyanine ring formation, based on the consumption of starting material, was less than 5% for the model phthalonitrile VI, and less than 10% for the bis-phthalonitrile I. In a separate experiment a thin film of I deposited on a salt plate was allowed to cure while exposed to the atmosphere. Periodic infrared examination of the curing film showed that as the cyano absorbance diminished the absorbance in the carbonyl region increased until the latter was the predominant infrared band. These results demonstrate that... 

Beryllium metal, previously etched with acid, reacts with phthalonitrile to yield beryllium phthalocyanine, the only square planar derivative of beryllium known (10). Both anhydrous beryllium and magnesium phthalocyanines react readily with moisture to form very stable dihydrates. Dehydration may be effected only by sublimation in vacuo. Sidorov has studied the interaction of sublimed layers of beryllium and magnesium phthalocyanines with water, by infrared spectroscopy (825). Some of the absorption bands arising from the phthalocyanine unit shift when water vapor is introduced. This behavior was not noted with other phthalocyanines (see Section VI,A). 

A quinoline-soluble thorium phthalocyanine is formed in the reaction of thorium tetrachloride with phthalonitrile at 260°C 378), but no analytical data were reported. An ill-characterized sulfonated derivative has also been recorded 119). Uianyl phthalocyanine (U02Pc) has been observed as the product of the reaction of bis(dimethylformamide)uranyl acetate with dilithium phthalocyanine 119, 120), and of the reaction of uranyl acetate with phthalic anhydride 187, 233). Recently, however, Bloor et al. 31) reported that uranyl phthalocyanine formed by the reaction of uranyl chloride and phthalonitrile in dimethylformamide at 180°C has different infrared and visible absorption spectra from those originally quoted 187, 233) and they conclude, on the basis of infrared data, that the uranyl phthalocyanine obtained by previous workers was essentially a mixture of a metal-free phthalocyanine and inorganic uranium salts. 

Uranyl phthalocyanine 31) has a linear 0—U—O bond system whose asymmetric stretching frequency occurs at 920 cm-1. A band observed at 278 cm-1 in the far infrared is assigned to the 0—U—O bending vibration. The electronic spectrum of uranyl phthalocyanine in 1-chloronaphthalene is unique in having no absorption in the 500-800 mju region. All other phthalocyanines exhibit bands in this region (see Section V,B). The complex may be purified by sublimation, but is demetallated in sulfuric acid. 

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