Metalla‐Carbaporphyrinoids Consisting of an Acyclic N‐Confused Tetrapyrrole Analogue Served as Stable Near‐Infrared‐II Dyes
Biju Basumatary, Hidetoshi Tsuruda, Dariusz W. Szczepanik, Jiyeon Lee, Jaehyeok Ryu, Shigeki Mori, Kyo Yamagata, Takayuki Tanaka, Atsuya Muranaka, Masanobu Uchiyama, Jiwon Kim, Masatoshi Ishida, Hiroyuki Furuta
Abstract
Abstract We 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 d π ‐p π ‐conjugated electronic structures involving the metal d π ‐ligand p π 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‐BF 2 and 1Pt‐BF 2 ) 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 d π ‐p π ‐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.