Synthesis and characterization of new type of phenoxy derivative beta-substituted phthalocyanines

The word "phthalocyanine" comes from the Greek words "cyanine," which means dark blue, and "naphtha," which means mineral oil. The synthesis of phthalocyanine happened by accident in 1907; Reginald P. Linstead was working at the Imperial College London when he coined the term to introduced a novel group of organic compounds. Phthalocyanine complexes have garnered significant attention in recent years owing to their demonstrated technological capabilities. Moreover, the versatility of phthalocyanine complexes allows for tailored modifications to enhance their performance in specific applications. Recent research has also focused on elucidating the fundamental mechanisms underlying the unique properties of these compounds. The dye and polymer technology, the pharmaceutical industry, medicine, the description of the biological processes, agriculture and many other areas are greatly benefited from these compounds' properties. Therefore, the number of studies on the phthalocyanine complexes are increasing every day. However, the solubility of the compouds are one of the main problems, which can be used for high-tech applications. Therefore, preparing soluble phthalocyanine complexes are important as purpose-engineered to synthesize these substances with high technological features and pureness. Almost any metal ion can be used in place of two hydrogen atoms to create a variety of metal phthalocyanines. At the moment, approximately seventy different elements are used as the center atom in phthalocyanins. When substituents are added to peripheral positions, intermolecular distance rises and resolution improves. Phthalocyanines lacking metal and those with no peripheral substituents exhibit limited solubility in organic solvents, thus constraining their potential. Due to the strong intermolecular π - π interactions between phthalocyanine molecules, It causes the aggregation of phthalocyanine molecules, reducing their solubility. Phthalocyanine characterization also makes use of standard organic compound characterization techniques like elemental analysis, IR, NMR, and UV-Vis. Since substituents and the central metal atom affect the Q-band's position in the visible zone, this technique is crucial for understanding phthalocyanine. In this investigation, we have been successfully synthesized new zinc (II) (2), copper(II) (3) and cobalt (II) (4) phthalocyanines incorporating 3-chloro-4-fluorophenoxy groups, which exhibit extended absorption wavelengths compared to the unsubstituted phthalocyanine compound in the UV-visible spectra. Beginning with the synthesis of a novel an innovative precursor, 4-(3-chloro-4-fluorophenoxy) phthalonitrile (1), this compound's molecular structure was validated through a single crystal X-ray diffraction (XRD) analysis. To conclude, the synthesis of 4-(3-chloro-4-fluorophenoxy) phthalonitrile (1), as the initial compoun was achieved through a meticulously controlled process. It involved a reaction of about 3 days between 3-chloro-4-fluorophenol and 4-nitrophthalonitrile in dry DMF solvent at ambient temperature under nitrogen atmosphere, catalyzed by anhydrous K2CO3. Progress of the reaction was monitored periodically using TLC (thin layer chromatography) to ascertain completion, ensuring the integrity of the desired product's formation. Subsequently, the reaction mixture was terminated by pouring into about 300 mL of ice water. The resulting precipitate from the reaction mixture was carefully isolated through filtration, followed by thorough rinsing with water until the filtrate reached a neutral pH, ensuring the removal of any residual impurities. Subsequently, the obtained product underwent further purification to enhance its quality. This involved subjecting it to column chromatography using a CHCl3-MeOH eluent, with a ratio of 10 parts chloroform to 2 parts methanol by volume, allowing for effective separation based on polarity. Following purification, the compound was subjected to crystallization using a CHCl3-acetone solvent system (in a 5:1 volume ratio), resulting in the formation of the desired product (1) in the form of white transparent crystals. In order to synthesize phthalocyanines (2, 3, 4), we combined the starting material, "4-(3-chloro-4-fluorophenoxy) phthalonitrile (1)," with anhydrous metal salts (zinc (II) chloride, copper (II) chloride, or cobalt (II) chloride) in dry DMAE (N,N-dimethylaminoethanol) solvent (2 mL) supplemented with a catalyst concentration of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The reaction was conducted under reflux conditions with stirring for ten hours. UV-Vis spectroscopy serves as in the comprehensive characterization of phthalocyanine compounds, providing valuable insights into their molecular structure and electronic properties. The distinct peaks observed in UV-Vis spectra offer key information about the nature of chemical bonds and the arrangement of atoms within these compounds. The Q band, situated between 600-800 nm, is particularly significant as it corresponds to transitions involving electrons in the molecular orbitals of the phthalocyanine system. Similarly, the Soret band (B), appearing between 300-400 nm, signifies electronic transitions within the central metal ion and the surrounding ligands, further elucidating the complex behavior of these compounds. When synthesized phthalocyanines (2, 3, 4) were analyzed in THF solvent, the Q band absorptions were found at 675 nm 673 nm and 669 nm respectively, which is similar to typical metallophthalocyanines. Moreover, the Soret (B) band absorptions, which are indicative of phthalocyanine formation, were found at 351 nm , 345 nm and 330 nm for compounds (2), (3) and (4) respectively. The FT-IR spectra revealed prominent peaks corresponding to the characteristic aromatic C-H and sharp C≡N vibrations of 4-(3-chloro-4-fluorophenoxy) phthalonitrile (1) at 3090 and 2237 cm-1, respectively. The IR spectra exhibited asymmetric and symmetric stretching vibrations characteristic of Ar-O-Ar at approximately 1246 and 1051 cm-1, respectively. Additionally, strong C-F stretching vibrations were prominently observed in the range of 1000-1300 cm-1. Conversely, in benzene derivatives incorporating chlorine groups, the stretching vibrations of C–Cl typically manifest within the range of 600-800 cm-1. Specifically, the FT-IR spectrum of 4-(3-chloro-4-fluorophenoxy) phthalonitrile (1) displayed strong stretching vibrations of C-F at 1308 cm-1 and C-Cl at 823 cm-1. Upon analyzing the FT-IR spectra of (2), (3), and (4), it was noted that the results closely resembled those of the ligand compound (1), with only minor shifts observed. Notably, as a consequence of the cyclotetramerization reaction, the vibration corresponding to the sharp –CN groups of 4-(3-chloro-4-fluorophenoxy) phthalonitrile (1) at 2237 cm-1 vanished, a significant indication supporting the formation of (2), (3), and (4). In the 1H-NMR and 13C-NMR spectra of 4-(3-chloro-4-fluorophenoxy) phthalonitrile (1), recorded in [d6]-DMSO solvent, the aromatic proton signals were detected within the range of 8.10-7.28 ppm. These signals appeared as follows: 1H doublet for protons ortho to –CN and meta to -OAr, 1H doublet for protons ortho to –CN and ortho to –OAr, 3H multiplet for protons ortho to –F, ortho to –Cl, and meta to –CN, and 1H multiplet for protons meta to -F. The corresponding carbon signals (ppm) for 4-(3-chloro-4-fluorophenoxy) phthalonitrile (1) were observed at 161.520, 150.864, 136.993, 129.262, 123.680, 123.336, 123.096, 122.042, 121.939, 119.186, 117.445, 116.548, 113.978, and 109.356. The MALDI-TOF MS analysis using Dithranol as the matrix and m/z scale produced data that aligns with the intended structures, thereby validating the structures of all compounds examined in this study. Specifically, in the MALDI-TOF MS analysis utilizing Dithranol as the matrix, the protonated ion peak of 4-(3-chloro-4-fluorophenoxy) phthalonitrile (1) was observed at a high intensity, appearing at m/z 273.298 [M+H]+, which is consistent with the molecular weight of the target compound (1). The synthesized phthalocyanines (2,3 and 4) had protonated ion peaks of 1156.301 [M]+ , 1154.235 [M]+ and 1150.196 [M+H]+ respectively.