Novel methoxyphenylthio-substituted phthalocyanines: synthesis, characterization, proton-transfer, and acid-sensing properties

This study involves the synthesis of novel methoxyphenylthio-substituted phthalocyanines and their starting phthalonitriles as well as the characterization and investigation of their physical and spectral properties. Herein, although phthalocyanines were categorized as alpha and beta-substituted, the numbers of external substituent methoxy groups selected to obtain soluble phthalocyanines were also different. After their molecular structure was characterized using elemental analysis, FT-IR, NMR, and MALDI-TOF-MS techniques, the exhaustive electronic spectra of novel phthalocyanines were studied. During extensive UV-Vis spectroscopy studies, proton transfer complexes in basic coordinating solvents and protonated species in solvents containing acids as impurities occurred incidentally in some phthalocyanines. Then, it was investigated whether this incidentally encountered situation was related to the number of methoxy groups as external substituents. Consequently, it was revealed that the acidity of H atoms in the center of phenylthio-substituted phthalocyanines could be altered by outer groups in the substituents, and the wavelengths of the Q bands of the novel Pcs changed under the influence of these outer groups. Computational TD-DFT study at the ωB97XD/6-311G(d,p) level confirmed the redshift observed in electronic spectra upon inserting two additional OCH3 at outer groups, originating from small decreases in the HOMO–LUMO energy gap. The NBO charge distribution justified the electron donation from sulfur atoms to the phthalocyanine ring.