Modulation of Photophysical Properties of N-Confused Hexaphyrins through Carbon–Metal Bonding and Structural Modifications─A Theoretical Insight

To understand the influence of N-confusion and C–M bonding on the absorption characteristics of expanded metalloporphyrins, the structural, electronic, and optical properties of N-confused hexaphyrin(1.1.1.1.1.1) bis-metal complexes (7-PdAu and 7-PtAu) were investigated by employing density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Our findings demonstrate that forming C–M bonds leads to a saddle-shaped hexaphyrin structure, enhancing the metal–ligand interaction compared to O–M bonds. This structural alteration results in reduced aromaticity and a narrowing of the HOMO–LUMO gap, along with a significant bathochromic shift in the electronic absorption spectrum. Notably, the 7-PdAu and 7-PtAu complexes exhibit pronounced absorption bands beyond 1100 nm, indicating their potential as candidates for near-infrared (NIR) phototherapeutic and optoelectronic applications. Overall, this work underscores the synergistic effects of N-confusion and carbon–metal bonding in tuning the photophysical properties of porphyrin-based systems, paving the way for advanced applications in photonics.