Phthalocyanine polymorphism

Unsubstituted phthalocyanines and also halogenated phthalocyanines show very poor solubility in organic solvents. In the solid state, unsubstituted phthalocyanines exhibit, in most cases, inclined one-dimensional stacking of the planar molecules. Besides other polymorphous modifications PcCu shows an x- and / -arrangement.74-75... 

In the case of PcCu and PcH2, the most stable modification, which is formed during synthesis, is the -modification. For a more detailed discussion on the polymorphism in phthalocyanines, see refs 36 and 76. 

The feasibility of synthesizing oxovanadium phthalocyanine (VOPc) from vanadium oxide, dicyanobenzene, and ethylene ycol using the microwave synthesis was investigated by comparing reaction temperatures under the microwave irradiations with the same factors of conventional synthesis. The efficiency of microwave synthesis over the conventional synthesis was illustrated by the yield of crude VOPc. Polymorph of VOPc was obtained ttough the acid-treatment and recrystallization step. The VOPos synthesized in various conditions were characterized hy the means of an X-ray dif actometry (XRD), a scanning electron microscopy (SEM), and a transmission electron Microscopy (TEM). 

However, there are metal complex pigments. Without doubt the most important metal complex pigment is copper phthalocyanine (4). The phthalocyanines were discovered by accident in 19286 and now represent the second most important class of colorants after the azo colorants. Copper phthalocyanine itself exists in several polymorphic forms and gives beautiful blue and cyan colors with outstanding fastness properties.5-7 Halogenated copper phthalocyanines provide green pigments (see Section 9.12.4.3). 

Almost without exception, all modern laser printers now use titanyloxy-phthalocyanine, type IV polymorph (47), as the CGM. Unlike copper phthalocyanine, which is planar (Figure 7) titanyloxy-phthalocyanine has a shallow shuttlecock shape (Figure 8). This has a subtle effect on the packing of the molecules, which contributes to its excellent performance as a CGM. Indeed, titanyloxy-phthalocyanine has the best combination of properties and is unlikely to be surpassed.37... 

The synthesis of linear turns-quinacridone (2.38) was reported in 1935 by Liebermann [26] and was cursorily looked at as a red vat colorant but not developed commercially. It was more than twenty years later that the DuPont company introduced these compounds as pigments under the trade name of Cinquasia. Their chemical structures are based on Cl Pigment Violet 19 (2.38). As with the phthalocyanines, this compound can exist in several polymorphic forms in this case there are three, termed a-, p- and y- forms only the last two being useful as pigments. The first three pigments were called Cinquasia Red B (y-form, size above 1000 nm), Cinquasia Red Y (y-form, size below 1000 nm) and Cinquasia Violet R (P-form). 

Unsubstituted Copper Phthalocyanine Blue is polymorphous. X-ray diffraction diagrams point to five different crystal modifications (a, (3, y, 8, e) (Fig. 91). The relative thermodynamic stability of the individual cystal phases decreases in the following order (3>e>8>a = y [13-16],... 

Recently, by crystal structure studies the number of different polymorphs of Copper Phthalocyanine Blue has been extended to nine, various of which are differing mainly in herringbone-type interaction [17]. 

Polyhalogenated green copper phthalocyanine pigments are not polymorphous and thus exempt from change of modification. 

The similarly blue and equally polymorphous metal-free phthalocyanine existing in five different crystal modifications (a, (3, y, k, t) is chemically somewhat less stable than its copper complex [26] it decomposes slowly in a sulfuric acid solution. On the other hand, it can be chlorinated to afford metal-free Phthalocyanine Green. 

Phthalocyanines exhibit high polymorphism, as well [7]. They are insoluble nano crystalline materials, which produce poor x-ray powder diagrams with high preferred orientation and have been intensely investigated by electron microscopy and diffraction [8]. From copper phthalocyanine (CuPc) (Fig.2) nine polymorphs (a, P, y, 5, s, n, p, (, a and R) are known, but only the most stable P phase could be solved by single crystal x-ray diffraction [9] (P2i/c a=14.628 A, b= 4.790 A, c= 19.07 A, b=120.93°). 

Quinacridone is the trivial name given to the five-ring heterocyclic system exemplified by the linear irani-quinacridone (2.69). The yellow-red to reddish-violet shade pigments based on this ring system show outstanding durability and are used in plastics, in industrial and automotive finishes and in exterior finishes. Like copper phthalocyanines the unsubstituted linear quinacridone exhibits polymorphism and two crystal forms, the reddish violet P-form and the red y-form, are commercially... 

As already stated most phthalocyanines exhibit polymorphism, and many of these morphological forms absorb in the near-IR, especially in the solid state. For instance, in the case of the metal-free, unsubstituted parent phthalocyanine, usually designated... 

Most phthalocyanines show inferior dark decay to azo pigments, an exception being the titanyl phthalocyanines, where in the best cases, e.g. the a- and Y- forms, they show comparable dark decay coupled with superior photosensitivity. A comparison of the sensitivity of azo pigments and selected polymorphs of phthalocyanines is shown graphically in Figure 4.12. 

Solid /8-CrPc reacts reversibly with gaseous NO at ambient temperature to give a 1 1 adduct, which reacts with both py and 02 (Scheme 117).596 No structural information is available on the oxidation product of the nitrosyl complex. In contrast to the /3 form, solid ar-CrPc is unreactive towards either 02 or NO, a difference ascribed to the solid-state structures of the two polymorphs.597 Although the distance between the phthalocyanine planes is similar (340 pm), in both cases the metal-metal distance increases from 340 to 480 pm on going from the a to the /3 form. These distances are sufficient to permit access of 02 or NO in the /8 form, while excluding them from the a form. The addition of py to CrPc(NO) causes the NO stretching band in the IR spectrum to intensify and to sharpen considerably. The diffuse nature of this band in CrPc(NO) indicates the presence of a perturbed NO ligand but the introduction of py causes lattice expansion and eliminates the perturbation. 

The macrocyclic phthalocyanine ligand will form a complex Pt(phthalocyanine).1106 The crystal structure shows two polymorphs present because of molecular packing.1107 The platinum is in a square planar coordination geometry with a mean Pt—N distance of 1.98 A. The complex can be partially oxidized with iodine to give conducting mixed valence solids.1108 Eighteen fundamental and overtone combination bands are observed in the resonance Raman spectrum of platinum phthalocyanine, and from this data the symmetry of the excited singlets are found to be Dy.. Qlv or D2.1109... 

Copper Phthalocyanine Blue. CPC blue exists in several polymorphic modifications, two of which, the red-shade blue alpha and greenshade blue beta form, are of great commercial significance. Beta is the thermodynamically more stable phase and is the product resulting from manufacture by the two basic processes using either phthalonitrilc or phthalic anhydride as starting materials. The alpha form is usually obtained by conversion from the beta form and has to be stabilized to prevent phase reconversion. 

Differences in the orientations and polymorphism have been identified on vapor deposited thick films of iron phthalocyanines supported on glassy carbon (129). These "bulk" differences correlated directly with the ability of the film to catalyze... 

History. Braun and Tschemak [23] obtained phthalocyanine for the first time in 1907 as a byproduct of the preparation of o-cyanobenzamide from phthalimide and acetic anhydride. However, this discovery was of no special interest at the time. In 1927, de Diesbach and von der Weid prepared CuPc in 23 % yield by treating o-dibromobenzene with copper cyanide in pyridine [24], Instead of the colorless dinitriles, they obtained deep blue CuPc and observed the exceptional stability of their product to sulfuric acid, alkalis, and heat. The third observation of a phthalocyanine was made at Scottish Dyes, in 1929 [25], During the preparation of phthalimide from phthalic anhydride and ammonia in an enamel vessel, a greenish blue impurity appeared. Dunsworth and Drescher carried out a preliminary examination of the compound, which was analyzed as an iron complex. It was formed in a chipped region of the enamel with iron from the vessel. Further experiments yielded FePc, CuPc, and NiPc. It was soon realized that these products could be used as pigments or textile colorants. Linstead et al. at the University of London discovered the structure of phthalocyanines and developed improved synthetic methods for several metal phthalocyanines from 1929 to 1934 [1-11]. The important CuPc could not be protected by a patent, because it had been described earlier in the literature [23], Based on Linstead s work the structure of phthalocyanines was confirmed by several physicochemical measurements [26-32], Methods such as X-ray diffraction or electron microscopy verified the planarity of this macrocyclic system. Properties such as polymorphism, absorption spectra, magnetic and catalytic characteristics, oxidation and reduc-... 

Most modem laser printers now use titanyloxy phthalocyanine, type IV polymorph, as the CGM. This pigment has the best combination of properties and is unlikely to be surpassed. 

Of the metallophthalocyanines that crystallize in forms other than the a-, j3-, and y-polymorphs, the most notable are Pb(pc)2031 and Ga(pc)F1301. The Pb(pc) molecules are stacked metal-over-metal, as shown in Fig. 28, and the Pb-Pb spacing is 3.73 A. The phthalocyanine ring deviates markedly from planarity, although the separate isoindole moieties retain their planarity. In Ga(pc)F the Ga atoms are symmetrically bridged by F, with a Ga-F distance of 3.92 A the pc rings are eclipsed, rather than staggered1301. 

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]. 

Hor and Popovic (1994) measured photogeneration efficiencies of dispersions of HOGaPc in poly (vinyl butyral) (PVB) by delayed-field collection and field-induced fluorescence quenching techniques. The HOGaPc polymorph was described as type V. The transport layers contained N,N -diphenyl-N,N -bis(3-methylphenyl)-(l,r-biphenyl)-4,4 -diamine. Like many phthalocyanines, HOGaPc exhibits a linear correlation of the photogeneration and field-induced... 

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