Fused Octapyrrolyl Cyclooctatetraene with Large NIR-II Faraday Rotation

The increased mechanical flexibility, solution processability, ease of fabrication, and high Verdet constants have made organic Faraday rotators a promising alternative to conventional inorganic magneto-optical (MO) materials. Despite this, organic Faraday rotators have not been developed to address near-infrared (NIR) MO applications, limiting their device applications. Here, we describe a three-step synthesis and MO characterization of a fused octapyrrolyl cyclooctatetraene (<b>FOPCOT</b>) which exhibits a record high Verdet constant of a small molecule in the NIR-II region. Notably, the cyclooctatetraene core is constructed in a three-step one-pot reaction whereby a <i>N</i>,<i>N</i>'-dipyrrolyl acetylene is generated and immediately reacted with Rosenthal's complex to produce the corresponding zirconacycle intermediate in situ. The cascade is completed with a copper-mediated transmetalation that reductively eliminates to yield the octapyrrolyl cyclooctatetraene. This transformation offers a distinct alternative to conventional methods for pyrrole incorporation into polycyclic aromatic hydrocarbons. Stoichiometric oxidation with AgPF₆ affords the oxidized analogues <b>FOPCOT</b>^<b>•</b><b>⁺</b> and <b>FOPCOT</b>^<b>2+</b>, which display strong optical absorptions at 1743 and 1198 nm, respectively. Magnetic circular dichroism study on spin-coated thin films of <b>FOPCOT</b>^<b>2+</b> yielded a maximum Verdet constant of -2.5 × 10⁵ deg T^-1 m^-1 at 1224 nm.