Metalla‐Carbaporphyrinoids Consisting of an Acyclic N‐Confused Tetrapyrrole Analogue Served as Stable Near‐Infrared‐II Dyes

Abstract

AbstractWe present herein the synthesis of novel pseudo‐metalla‐carbaporphyrinoid species (1M: M=Pd and Pt) achieved through the inner coordination of palladium(II) and platinum(II) with an acyclic N‐confused tetrapyrrin analogue. Despite their tetrapyrrole frameworks being small, akin to well‐known porphyrins, these species exhibit an unusually narrow HOMO–LUMO gap, resulting in an unprecedentedly low‐energy absorption in the second near‐infrared (NIR‐II) region. Density functional theory (DFT) calculations revealed unique dπ‐pπ‐conjugated electronic structures involving the metal dπ‐ligand pπ hybridized molecular orbitals of 1M. Magnetic circular dichroism (MCD) spectroscopy confirmed distinct electronic structures. Remarkably, the complexes feature an open‐metal coordination site in the peripheral NN dipyrrin site, forming hetero‐metal complexes (1Pd‐BF2 and 1Pt‐BF2) through boron difluoride complexation. The resulting hetero metalla‐carbaporphyrinoid species displayed further redshifted NIR‐II absorption, highly efficient photothermal conversion efficiencies (η; 62–65 %), and exceptional photostability. Despite the challenges associated with the theoretical and experimental assessment of dπ‐pπ‐conjugated metalla‐aromaticity in relatively larger (more than 18π electrons) polycyclic ring systems, these organometallic planar tetrapyrrole systems could serve as potential molecular platforms for aromaticity‐relevant NIR‐II dyes.