Unsymmetrically Substituted Phthalocyanines

Although many attempts have been made to separate or exclusively synthesize one isomer of an unsymmetrically substituted phthalocyanine,72-89-296,297 the product mixture has been separated in only two cases.96 103,104 Besides the chromatographic separation of the statistical product mixture it is also possible to prepare exclusively the D4h isomer by use of steric hindrance of bulky substituents, e.g. 7-ferr-butylnaphthalene-l,2-dicarbonitrile only forms the respective An isomer of the tetra(to -butyl)-substituted 1,2-NcFe by heating in hexan-l-ol.73 Recently, some 1,8,1 5,22-substituted pure isomers have also been synthesized by the use of bulky substituents in 3-substituted phthalonitriles298,299 at low temperature (see Section 2.1.4.).94... 

Unsymmetrically substituted phthalocyanines can be prepared from two differently substituted phthalonitriles in a statistical condensation. It is obvious that a mixture of six different phthalocyanines (see p 738) can be obtained AAAB, ABAB (opposite type), AABB (adjacent type), ABBB and the products of the self-condensation of the respective phthalonitriles. If one of the phthalonitriles is substituted with bulky substituents, the yield of isomers with these groups in close vicinity can be reduced. In the following example no product of the self-condensation of tetraphenylphthalonitrile (BBBB type) can be detected. 

Unsymmetrically substituted phthalocyanines 11 can be prepared out of two differently substituted phthalonitriles A and B, respectively. In the following example, one of the phthalonitriles is used in excess. 

Figure 13 Ring expansion of a haloboron(III) subphthalocyanine (49) to give an unsymmetrically substituted phthalocyanine, here the zinc(II) benzonaphthoporphyrazine (51).252,253 As usual, the product is...

While the subphthalocyanines are interesting in their own right, much of the recent impetus for preparing these macrocycles derives from their use as precursors in the synthesis of unsymmetrically substituted phthalocyanines, which are otherwise... 

The first documented example of a ring-expansion reaction involving a sub-phthalocyanine came in 1990. Here, Kobayashi and Osa and coworkers reported that by treating the t-butyl-substituted subphthalocyanine 2.286 with succinimide (2.296), one could obtain the unsymmetrically substituted phthalocyanine 2.297 in 13% yield (Scheme 2.3.5). Similarly, treating subphthalocyanine 2.286 with the dii-minoisoindoline analogs 2.298-2.300, afforded the unsymmetrically substituted... 

In the case of molecules having inversion symmetry, as non-substituted phthalocyanines, all the components of the first hypeipolarizability p are zero. For this reason, appropriately substituted phthalocyanines have to be designed if one wishes to obtain efficient second-order NLO responses. Thus, theoretical calculations developed at the end of the 80 s by T. J. Marks and coworkers [29] suggested that push-pull unsymmetrically substituted phthalocyanines with suitable electron-donor and acceptor groups and efficient intramolecular charge transfer should yield interesting compounds for second-order applications. 

In the phthalocyanine field, the octupolar route provides additional degrees of freedom to help in the design of efficient nonlinear molecules. One of the possible methodologies to reach Pc-based octupolar architectures is the arrangement of the Pc cores into D or structures by means of attaching the macrocycles to benzene [58] or to a tetravalent atom such as phosphorus. Thus, for example, aryl trisphthalocyanine phosphonium salt (Figure 5) has been prepared and the second-order NLO response at the molecular level has been measured by HRS [59]. The jShrs values at X = 1.06/a,m(189 x 10 esu) is superior to those available for other related unsymmetrically substituted phthalocyanines with dipolar characteristics. 

Synthesis and structure modification of unsymmetrically substituted phthalocyanines 07UK732. 

Up to now, mostly statistical methods have been used for the synthesis of unsymmetrically substituted phthalocyanines. For more details see chapter 5.1. For instance, 1,2,4,5-tetracyanobenzene is reacted with ammonia to the cyano-substituted isoindoline which is then added to the alkoxymethyl substituted isoindoline [148b] (Scheme 15). 

A number of unsymmetrically substituted phthalocyanines have been synthesized and... 

Scheme 59. Routes to unsymmetrically substituted phthalocyanines. Reagents (a) RO (b) Ai,iV-dimeth-ylaminoethanol, reflux.

Table 53. Transition temperatures for unsymmetrically substituted phthalocyanines 49.

Phthalocyanines can also be prepared by ring insertion reactions from subphthalocyanines (56]. This reaction is suitable for obtaining unsymmetrically substituted phthalocyanines and is discussed later. 

Figure 15.10 shows another route that in principle can lead to the formation of an unsymmetrically substituted phthalocyanine, in this case a monosubstituted one. In this route a subphthalocyanine is reacted with a monosubstituted isoindolenine with formation of the monosubstituted phthalocyanine [102,106]. This route has been applied for the preparation of a variety of unsymmetrically substituted phthalocyanines [102] however, the yields of the monosubstituted phthalocyanines are low and other side products are formed as well. Sub-phthalocyanines, shown in Fig. 15.10, are a class of compounds that have found much interest recently, mostly due to the possibility of preparing unsymmetrically substituted phthalocyanines [107,108]. 

Octasubstituted phthalocyanines are symmetrical when both the substituents are the same and are prepared from homogeneously disubstituted phthalonitriles containing the same substituents. Unsymmetrically octasubstituted phthalocyanines are obtained from heterogeneous disubstituted phthalonitriles having different substituents. The same principle can be extended to deca- and hexadeca-substituted phthalocyanines. Unsymmetrical phthalocyanines with different substituents in one or two benzene ring can be synthesized starting from two differently substituted phthalocyanines. This will afford a mixture of unsymmetrically substituted phthalocyanines, which have to be separated by chromatography (see below). 

Figure 13.14 Synthesis of an unsymmetrical substituted phthalocyanine via a subphthalocyanine.

Unsymmetrical azo pigments, 517, 535 Unsymmetrical perylene pigments, 520 Unsymmetrical squaraines, 507 Unsymmetrically substituted phthalocyanines, 696... 

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