Synthesis and characterization of ester substituted new phthalocyanines

Phthalocyanine term has been derived from words naphtha (mineral oil) and cyanine (dark blue) in Greek. Phthalocyanine was first synthesized in 1907 by chance. The term phthalocyanine was used for the first time by Reginald P. Linstead working at Imperial College of Science and Technology in order to describe new class of organic compounds. The most common use of phthalocyanines is as dyes and pigments. Additionally phthalocyanines are used as photoconductive materials in copying devices, as chemical sensors, electrocatalysis, electrochromic agent and as photosensitizers in photodynamic therapy. Phthalocyanines show up to 100 times more intense absorption around 680 nm when compared with the porphyrins. These features, along with the production of singlet oxygen makes them promising in number of applications. Many metal phthalocyanines can be synthesized as a result of displacement of two hydrogen atoms with almost all metal ions. Today, close to 70 different elements take part as the central atom phthalocyanines. Metal-free phthalocyanines and metal phthalocyanines without peripheral substituents are not soluble in organic solvents. This restricts the application areas. As intermolecular distance is increased by adding substituents to peripheral positions solubility increases. The conventional methods used in the characterization of organic compounds such as elemental analysis, IR and UV-vis are also used in the characterization of phthalocyanines. Especially in the visible range, position of the Q-band is affected by substituents and the central metal atom. Thus, this technique plays an especially important role in the characterization of phthalocyanines. NMR is a technique useful for soluble phthalocyanine derivatives. However, due to strong liability of the phthalocyanine compounds to aggregation in solution, broader peaks are appeared in NMR spectrum. Recent advances in mass spectrometry facilitates characterization of phthalocyanines. In particular, the Fast Atom Bombardment (FAB) and Matrix-Assisted Laser Desorption Ionization (MALDI) have started to create a significant place for characterization of high molecular mass phthalocyanines. In order to add various functional groups to phthalocyanines, nucleophilic substitution is applied especially phthalonitrile precursors. To this end, for synthesis of peripheral-tetrasubstituted phthalocyanine 4-nitrophthalonitrile, for synthesis peripheral-oktasubstituted phthalocyanine 4,5-dichlorophthalonitrile and for the synthesis of non-peripheral tetrasubstituted phthalocyanine 3,6-dihydroxyphthalonitrile are preferred as starting substances. Here, in the presence of a base such as sodium carbonate, potassium carbonate or cesium carbonate, the reaction occurs in a strong polar solvent such as DMF or DMSO. As reactive groups, alcohol, thiol or compounds containing active methylene groups are preferred. For purification of phthalocyanines, column chromatography techniques where alumina or silicagel is used as stationary phase can be applied. Due to the insolubity of non-substituted phthalocyanines, overall crystallization and chromatography purification methods is not possible. Sublimation method is not practical in the case of substituted phthalocyanines due to less thermal stability of substituents. In this study, 4-(carboxyphenylsulfanyl)-phthalonitrile (1) was synthesized in 87% yield by the reaction between 4-nitrophthalonitrile and 4–mercaptobenzoic acid in the presence of anhydrous K2CO3 in dry DMF. 2,9,16,23-Tetrakis(carboxyphenylsulfanyl)-phthalocyanine (2) was obtained by the cyclotetramerization of compound (1) in n-dodecanol which contain metallic lithium. The esterification reaction between compound (2) and n-dodecanol in the presence of dicyclohexylcarbodiimide in dichloromethane gives 2,9,16,23-tetrakis(dodecylcarboxyphenylsulfanyl)-phthalocyanine (3). The compound (3) was metallized by treatment with zinc and cobalt salts under reflux in DMF for 1 hour and tetrakis(dodecylcarboxyphenylsulfanyl)-phthalocyaninato zinc (II) (4) and tetrakis(dodecylcarboxyphenylsulfanyl)-phthalocyaninato cobalt (II) (5) were synthesized, respectively. The structures of synthesized compounds are verified by FT-IR, UV-Vis, 1H NMR, 13C NMR and mass spectroscopy techniques.