An Electron Acceptor With bis(Borondifluoride)-8-imidazodipyrromethene as the Core for Short-Wavelength Infrared...

Small-molecule electron acceptors with donor-acceptor (D-A) structures have emerged as attractive materials for organic optoelectronics, yet achieving strong absorption in the short-wavelength infrared (SWIR, 1000-3000 nm) region remains a fundamental challenge. Here, a resonant N-B←N unit, bis(borondifluoride)-8-imidazodipyrromethene (BIP), is introduced as a new electron-deficient core for constructing D-A type SWIR acceptors. Incorporation of the BIP unit induces a pronounced bathochromic shift of 255 nm and affords an ultranarrow optical bandgap of 0.86 eV, with thin-film absorption extending to 1450 nm. The resulting acceptor, BIP-M1, exhibits a high molar extinction coefficient of 3.8 × 10⁵ M^{- 1} cm^{- 1} and an exceptionally small Stokes shift of 0.054 eV, indicative of its strong SWIR absorption capability and suppressed nonradiative losses. Photodiode-type organic photodetectors based on BIP-M1 enable sensitive photoresponse over a broad spectral range from 300 to 1400 nm, delivering a responsivity of 0.18 A W^{- 1} and a specific detectivity of 3.93 × 10¹¹ Jones at 1200 nm, together with an ultralow Urbach energy of 19.19 meV. This study identifies resonant N-B←N units as powerful structural motifs for small bandgap molecular design and establishes BIP-based small molecular acceptors as a promising platform for next-generation SWIR optoelectronics.