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 (FOPCOT) 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 N,N'-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 FOPCOT^•+ and FOPCOT²⁺, which display strong optical absorptions at 1743 and 1198 nm, respectively. Magnetic circular dichroism study on spin-coated thin films of FOPCOT²⁺ yielded a maximum Verdet constant of -2.5 × 10⁵ deg T^-1 m^-1 at 1224 nm.