Near-infrared-red-orange thermally activated delayed fluorescence emitters using a strong tetracoordinated difluoroboronated acceptor

We design two organoboron-based thermally activated delayed fluorescence (TADF) molecules, DMAC-PAPB and m-DMAC-PAPB, containing a strong tetracoordinated difluoroboronated acceptor, a phenyl-linking difluoro[amidopyrazinato-O,N]boron (APB) moiety, named PAPB. Theoretical calculations predict that PAPB has a deep lowest unoccupied molecular orbital (LUMO) energy level. DMAC-PAPB and m-DMAC-PAPB show a low-lying lowest excited singlet state (S-1) with small S-1 energy (2.04 eV and 1.85 eV, respectively), and small energy gaps (similar to 0.01 eV) between S-1 and the lowest triplet state, which satisfy the critical requisite for constructing red TADF emitters. Experimentally, DMAC-PAPB and m-DMAC-PAPB show red and near-infrared (NIR) luminescence with the peak photoluminescence wavelength at 650 nm and 701 nm in toluene, respectively. The solution-processed doped films both exhibit orange-to-red luminescence and obvious delayed fluorescence. These investigations exemplify the strong electron-accepting ability of PAPB and its potential in developing yellow, orange, red, and NIR organoboron-based TADF emitters.