Synthesis and characterization of differently substituted polynuclear phthalocyanine derivatives and investigation of their oxidative catalytic properties

Phthalocyanines are a class of synthetic macrocyclic compounds that mimic the function of natural porphyrins with which they show structural similarity. They form a large, planar ring system by the linkage of four isoindole units via nitrogen atoms. These blue-green N4-porphyrin derivative macrocyclic compounds exhibit high stability, structural flexibility, and rich redox chemistry, and are resistant to light, acids, and high temperatures. These properties make them suitable for various industrial applications. When used as fluorophores or photosensors, phthalocyanines can play a significant role in photodegradation. Phthalocyanines may be effective in photodegradation processes because of their broad light absorption capabilities and photochemical activity. They can be utilized in processes such as the degradation of organic pollutants under sunlight or in photocatalytic water-splitting for hydrogen production. Additionally, some phthalocyanines act as light-sensitive photocatalysts, producing reactive oxygen species (ROS), contributing to pollutant degradation. In this study, different types of phthalocyanines, including water-soluble silicon phthalocyanine (SiPc's) containing functional groups at axial positions, and Schiff base metal complex-fused zinc (II) phthalocyanine complexes (SchLM(II)@Zn-Pc), were synthesized and characterized. Water-soluble phthalocyanines were synthesized to enhance both solubility and catalytic effect, while other phthalocyanines were synthesized focusing on the ability of Schiff bases to form metal complexes and the catalytic activity of these complexes. The catalytic, photocatalytic, and catalytic/photocatalytic properties of the synthesized phthalocyanine complexes were investigated. In the first part of the study, starting materials were synthesized. 1,3-DII (1) was formed by condensing the starting material carrying a 4-carboxyphenoxy group with N,N-dimethyl-1,3-propanediamine. 3,5-di-tert-butyl-2-hydroxybenzaldehyde (2), the starting material for Schiff base metal complexes, was obtained by reacting 2,4-di-tert-butylphenol and urotropine in glacial acetic acid. 2-hydroxyethyl-N-((3-dimethylamino)propyl)carbamate (3), containing a carbamate-derived propyl amine group, was obtained according to a literature procedure. In the second part of the study, Schiff base metal complexes [SchLM(II)] were synthesized. 3,5-di-tert-butyl-2-hydroxybenzaldehyde (2) was dissolved with metal ions in methanol, and a solution of 2,3-diaminomaleonitrile in methanol was added to the mixture, resulting in the formation of Schiff base metal complexes [SchLNi(II) (4), SchLCo(II) (5), SchLZn(II) (6)]. These complexes were bound to zinc phthalocyanines at peripheral points, forming new asymmetrically substituted derivatives (SchLM(II)@Zn-Pc). Phthalocyanines centered with zinc but bound to different Schiff base metal complexes, SchLNi(II)@Zn-Pc (7) and SchLCo(II)@Zn-Pc (8), were obtained by the reaction of the prepared Schiff base metal complexes with phthalonitrile and Zn(CH3COO)2 salt in dimethylethanolamine. Finally, using the same synthesis method, the compound SchLZn(II)@Zn-Pc (9) was obtained, which contains the same metal center in both the phthalocyanine and the Schiff base metal complex. In the third part of the study, silicon phthalocyanine complexes were synthesized. The synthesis of the SiPcCl2 (10) complex was carried out with improvements on the processes in the literature. The SiPc(OR)2 (11) complex was obtained by the reaction of 10 and 3 in toluene in the presence of NaH. For the synthesis of one of the main target molecules, a water-soluble phthalocyanine, amidamine groups capable of forming inner salts were chosen as substituents, and the tertiary amines of these groups were reacted with sodium monochloroacetate. Thus, the betaine-derived water-soluble inner salt-structured silicon phthalocyanine [SiPc-BET] (12) was obtained. The structures and characterizations of the phthalocyanine complexes were elucidated by spectral data recorded through FL, FT-IR, 1H-NMR, 13C-NMR, UV-Vis., MALDI-TOF, ICP-OES, and melting point measurements. In the last part of the study, solubility studies were conducted to analyze the complexes, and 10-5 M concentration solutions were prepared in DMF solvent for comparison of bleaching properties. After determining their fluorescence properties, their performances as catalysts were examined under catalytic, photocatalytic, and catalytic/photocatalytic conditions in our system. Morin dye, which is visibly affected by bleaching, and hydrogen peroxide (H2O2) as the bleaching agent were preferred to determine the effectiveness of the complexes as oxidative bleaching catalysts. Catalytic measurements were carried out in a 1 M H2O2 solution and a sodium (NaHCO3/Na2CO3) buffer at pH 11.5 in the presence of the catalyst. Photocatalytic measurements were conducted in a sodium (NaHCO3/Na2CO3) buffer solution at pH 11.5, where the catalyst was activated by red light at a wavelength of 610 nm. The combined catalytic/photocatalytic measurements were performed in a 1 M H2O2 solution and a sodium (NaHCO3/Na2CO3) buffer at pH 11.5, with the catalyst activated by 610 nm red light. The oxidative bleaching rate and absorbance changes over time were recorded and plotted as graphs. The measurements of SchLNi(II)@Zn-Pc (7), SchLCo(II)@Zn-Pc (8), and SchLZn(II)@Zn-Pc (9) complexes revealed that the cobalt (II)-containing catalysts were significantly more effective. The catalytic activity observed upon catalyzing SiPcCl2 (10) and the betaine derivative silicon phthalocyanine [SiPc-BET] (12) with H2O2 was reduced. Furthermore, the singlet oxygen yield of these complexes (10, 12) was insufficient for their use as photocatalytic catalysts. The results of the catalytic/photocatalytic measurements supported these findings. Although Si-phthalocyanines are used as photosensitizers in cancer treatment, they were found to be unsuitable as oxidative bleaching catalysts. The kinetic measurements of SiPc(OR)2 (11) in MeOH solution showed an increase in oxidative catalytic activity due to the increased hydrophilic structure and solubility. The results of the catalytic/photocatalytic measurements supported the catalytic values. It was observed that with the increased solubility of complex 11 in MeOH, aggregation decreased, and high photocatalytic activity was exhibited. Although not at the desired level, it was concluded that photocatalytic and catalytic activity could be enhanced in silicon phthalocyanines by modifying the axial groups. However, the effects of silicon phthalocyanines were still below expectations. In the next phase, it is planned to investigate the anticancer properties of axially substituted phthalocyanines with high water solubility for use in photodynamic therapy.