Near-Infrared-II Absorbing Doubly N-Confused Dioxo-Heptaphyrins as Robust Photothermal Conversion Agents

We present the synthesis of a novel meso-aryl-substituted [32]heptaphyrin 1 composed of two confused pyrrole units with a cisoid configuration. Under specific oxidative conditions, the α-carbons of the confused pyrrole units in the precursor were directly linked to yield a hybrid bicyclic compound 2, which integrates distorted corrorin and sapphyrin moieties. Compound 2 possesses a pseudo-annulenoannulene structure along with an emissive character in the near-infrared region. Further chemical oxidation of 1 produces the dioxygenated derivative 1-O₂, transforming into a 30π-conjugation system. The dioxo-heptaphyrin 1-O₂ displays site-selective metal coordination ability within the distorted N4 donor core. The resulting zinc(II) and copper(II) metal complexes, Zn1-O₂ and Cu1-O₂, exhibit distinct second near-infrared absorption, contributing to photothermal conversion with exceptionally high photostability. Alongside ¹H NMR spectroscopic studies, the weak aromatic characters of Zn1-O₂ and Cu1-O₂ are also supported by the ultrafast excited-state decay features observed through femtosecond transient absorption spectroscopies. The findings of this study will provide new insight into the molecular designs of photothermal agents based on the flexible expanded porphyrinoids for cancer phototherapy.