Phthalocyanine Chromophore

The term phthalocyanine was first used by R. P. Linstead in 1933 [1] to describe a class of organic dyes, whose colors range from reddish blue to yellowish green. The name phthalocyanine originates from the Greek terms naphtha for mineral oil and cyanine for dark blue. In 1930-1940, Linstead et al. elucidated the structure of phthalocyanine (H2Pc) and its metal complexes [1-11]. The basic structure is represented by phthalocyanine (1) itself  

Phthalocyanine forms complexes with numerous metals of the Periodic Table. A large number of complexes with various elements are known [12-18], Metal phthalocyanines MPc (2) and compounds with metalloids such as B, Si, Ge, and As or nonmetals such as P display a wide variety in their coordination chemistry. 

The coordination number of the square-planar complexes of Cu, Ni, or Pt is 4. Higher coordination numbers of 5 or 6 with one or two additional ligands such as water or ammonia result in square-based pyramidal, tetrahedral, or octahedral structures (3) [19-22], 

The phthalocyanines are structurally related to the macrocyclic ring system porphyrin (4). Formally, phthalocyanine can be regarded as tetrabenzotetraaza-porphyrin and as the condensation product of four isoindole units. 

The phthalocyanines are structurally similar to naturally occurring porphyrins such as hemoglobin (5), chlorophyll a, and vitamin B12. Phthalocyanines themselves do not occur in nature. 

---

As far as dyes are concerned, chelates of type Cb are termed 1 2 or symmetrical 1 2 metal complexes if the two tridentate ligands are equal, and mixed or unsymmetrical 1 2 metal complexes in the other case. Chelates of type Bb represent 1 1 metal complexes. The types Cb and Bb include, in general, azo and azo-methine metal complex dyes, whereas chelates of the quadridentate types Ac and Be are derived predominantly from formazan and phthalocyanine chromophores. 

Reaction of VI with Various Additives (Table II). Compound VI (0.5 mmol) and 0.125 mmol of the additive were placed in sealed tubes and heated at 165°. The tubes were initially monitored in terms of change from a fluid to solid and those which solidified were opened and the i r spectra taken to determine the extent of reaction. Those samples which had not undergone sufficient reaction were resealed and reheated. When the i r showed that sufficient reaction had occurred, the contents were analyzed for phthalocyanine chromophore content. 

Phthalocyanine content was determined by electronic absorb-tion at 697 nm (dioxane). Analytically pure samples of VII were used to generate a calibration curve which was then used to deter--mine the amount of phthalocyanine chromophore generated from reactions of VI and also of I. 

Martinez-Diaz, M., S. Esperanza, A. de la Escosura, M. Catellani, S. Yunus, S. Luzzati, and T. Torres. 2003. New polythiophenes bearing electron-acceptor phthalocyanine chromophores. Tetrahedron Lett 44 8475-8478. 

Clearly improved electrode characteristics were obtained when the ZnO was prepared in a separate reaction step in the presence of a more favorable structuredirecting agent before the phthalocyanine chromophores were adsorbed in a subsequent step . Films of ZnO with a high porosity at preserved crystallinity were obtained in the presence of Eosin Since Eosin Y could be desorbed... 

Phthalocyanine Dyes. The phthalocyanine molecule is much too big to be used on hydrophobic fibers and therefore is only used in its sulfonated form as the basis for direct and reactive dyes (see Phthalocyanine compounds). Its forces of attraction are different from a small linear yeUow a2o dye with which it is used to form bright greens. CompatibiHty between the two is likely to be a problem in practice and to overcome this, green dyestuffs containing a phthalocyanine dye linked via a saturated chromophore blocker (—x—) have been made, eg,... 

Theoretically, the dye or chromogen can be any colored species. Of course, requirements for fastness, solubiUty, tinctorial value, ecology, and economy must be met. Most commonly used chromophores parallel those of other dye classes. Azo dyes (qv) represent the largest number with anthraquiaone and phthalocyanine making up most of the difference. Metallized azo and formazan dyes are important and have gained ia importance as a chromophore for blue dyes duriag receat years (6) (see Dyes and dye intermediates). 

In view of the immense commercial importance of phthalocyanines as pigments, it is perhaps surprising that only a few are of importance as textile dyes. This is primarily due to the size of the molecules they are too large to allow penetration into many fibres, especially the synthetic fibres polyester and polyacrylonitrile. An example of a phthalocyanine dye which may be used to dye cellulosic substrates such as cotton and paper is C. I. Direct Blue 86 (96), a disulfonated copper phthalocyanine. In addition, a few blue reactive dyes for cotton incorporate the copper phthalocyanine system as the chromophoric unit (Chapter 8). 

Phthalocyanine-based dyes are especially useful for CD-R, as the chromophore absorption band falls in the desirable spectral range, and they are noted for excellent photostability. Unlike cyanine dyes, phthalocyanines tend to have very poor solubility, particularly in solvents such as alcohols and aliphatic hydrocarbons (which do not attack polycarbonate and are therefore used for spin coating). Therefore, the main barrier to the wider use of these dyes is the relatively high cost of synthesizing soluble derivatives. Suitable modifications to the Pc core which have been developed, notably by Mitsui Toatsu, are shown in Scheme 7. The bulky R groups reduce undesirable molecular association (which in turn lower the extinction coefficient and hence reflectivity), whereas partial bromination allows fine-tuning of the film absorbance and reflectivity. The metal atom influences the position of the absorption band, the photostability, and the efficiency of the radiationless transition from the excited state.199 This material is marketed by Ciba as Supergreen.204... 

There are no clear advantages in terms of functional performance between the two classes of dyes, except that phthalocyanines are generally more light stable but tend to be more expensive to synthesize and modify. Phthalocyanine dyes are not suitable for DVD-R media, since the main chromophore cannot readily be modified to produce a sufficiently large hypsochromic shift. Other dyes potentially suitable for DVD-R include metal azo complexes, quinophthalones, and diphenyl-methanes. The cyanine dyes are particularly useful as they can be readily modified to tailor the optical absorbance requirements for all current optical disk recording applications.199... 

Metal phthalocyanines functionalized with four helicenes (62) have also been reported to form chiral columnar aggregates.76 In chloroform solutions of these metal phthalocyanines aggregation into columns occurred upon addition of ethanol, as was observed by UV-Vis spectroscopy. CD spectroscopy revealed that the chromophores within the columnar aggregates are in a chiral environment, implying that the chirality of the peripheral helicenes has been transferred to the supramolecular aggregates. These phthalocyanines stack with a typical intermolecular distance of 3.4 A, and calculations have indicated that to allow this distance the two phthalocyanine moieties have to be rotated because of the bulkiness of the helicenes. It can easily be imagined that a phthalocyanine provided with both R and S helicenes cannot stack in such a defined manner because of the steric interactions between the nonconform helicenes. 

Aerobic biodegradation processes often show unsatisfying results because a number of azo dyes are resistant to aerobic microbiological attack. The main process for removal of dyes in the aerobic part of a CWWT is based on an adsorption of the dyes on the biomass. Further problems in the destruction of chromophores result during the treatment of phthalocyanine dyes, anthraquinoid dyes, and vat and sulfur dyes, which contain rather persistent chromophores. 

---