From (Sub)Porphyrins to (Sub)Phthalocyanines: Aromaticity\nSignatures in the UV–Vis Absorption Spectra

The\ndevelopment of novel synthetic methods has greatly expanded\nthe toolbox available to chemists for engineering porphyrin and phthalocyanine\nderivatives with precise electronic and optical properties. In this\nstudy, we focus on the UV–vis absorption characteristics of\nsubstituted phthalocyanines and their contracted analogs, subphthalocyanines,\nwhich feature nonplanar, bowl-shaped geometries. These macrocycles,\nwhich are central to numerous applications in materials science and\ncatalysis, possess extensive π-conjugated systems that drive\ntheir unique electronic properties. We explore how the change from\na metalloid (B) to a metal (Zn) and the resulting coordination environments\ninfluence the aromaticity and, consequently, the spectroscopic features\nof these systems. A combined computational and experimental approach\nreveals a direct correlation between the aromaticity of the external\nconjugated pathways and the Q bands in the UV–vis spectra.\nOur findings highlight key structural modifications that can be leveraged\nto fine-tune the optical properties of porphyrinoid systems, offering\nnew pathways for the design of advanced materials and catalysts with\ntailored functionalities.