Triply N-Confused Hexaphyrins(1.1.1.1.1.0) Synthesized From N-Confused Hexaphyrin(2.1.1.1.1.1): Aromaticity Modulation, Metal Coordination, and Photothermal Conversion

Antiaromatic compounds exhibit intriguing structures, reactivity, and physicochemical properties. To address the challenge in developing stable antiaromatic porphyrinoids, a vinylene bridge and an α,β′-linked pyrrole unit were used to synthesize a 28π Möbius aromatic N-confused oxohexaphyrin(2.1.1.1.1.1) (1). Subsequent oxidative C_β–C_β fusion afforded a stable Hückel antiaromatic formally triply N-confused oxohexaphyrin(1.1.1.1.1.0) (2) as a hybrid of 24 and 28π systems with two peripheral NH moieties, enabling further C–N fusion with the adjacent C₆F₅ moiety under basic conditions to yield the corresponding N-confused dioxohexaphyrin(1.1.1.1.1.0) (3), which shows Hückel antiaromaticity with a modulated circuit. Coordination of various metals within the distinct coordination cavities afforded two mono-rhenium complexes 3-Re-1 (NNη²-coordinated) and 3-Re-2 (NNO-coordinated) along with a mono-Pd complex 3-Pd-1 (CNNO-coordinated) with modulated antiaromaticity. On this basis, the heterobimetallic complex 3-O-Pd-Re was synthesized with the conjugation and antiaromaticity disrupted by further oxygenation. Notably, these compounds display distinctive near-infrared (NIR) absorption, enabling pronounced photothermal conversion under 1064 nm laser irradiation with efficiencies up to 61.4%. This work composes an effective post-fusion approach for developing multiply N-confused porphyrinoids with tunable antiaromaticity and distinctive coordination properties to achieve efficient NIR photothermal conversion behavior.