Peripheral vs Nonperipheral Sulfonyl-Modified Mn(III) Phthalocyanines: Comparative Characterization of Aggregation Behavior and Thermal Stability

Two Mn(III) phthalocyanine complexes bearing sulfonylphenoxy substituents in peripheral and nonperipheral positions were synthesized and comparatively analyzed. Their structural, optical, and thermal behaviors were examined using FT-IR, UV-Vis, MALDI-TOF-MS, TGA/DTA, and XRD techniques. The substitution position was found to significantly affect aggregation, solubility, crystallinity, and decomposition profile. The nonperipheral complex exhibited reduced aggregation, sharper absorption features, and superior thermal resistance, attributed to better electron delocalization and steric protection. MALDI-TOF-MS confirmed its more stable ionization with fewer fragment signals. In contrast, the peripheral analogue showed higher aggregation and earlier thermal degradation. XRD patterns also revealed that nonperipheral substitution led to more ordered packing and sharper diffraction peaks. UV-Vis spectra showed bathochromic shifts and monomeric behavior for the nonperipheral compound, while the peripheral one presented broader bands and signs of H-type aggregation. These results clearly demonstrate that minor changes in substitution geometry play a key role in modulating the physicochemical properties of Mn(III) phthalocyanines, offering design advantages for their use in optoelectronic, sensing, and high-temperature applications.