Emission-Tunable B←N Lewis Pair-Functionalized Naphthalenes

Herein, we simultaneously synthesized three different double B←N Lewis pair-functionalized naphthalenes including the asymmetric BNNY and BNNO and the mirror-symmetric BNNR, via a one-pot method. The annulation modes of the B←N Lewis pairs and the substituents on the boron atoms efficiently tune the molecular frontier orbitals and emission colors. α-Position fusion leads to a significant enhancement of the HOMO energy level and a decrease in the HOMO-LUMO gap, while the electron-withdrawing groups attached to the boron atom make the LUMO energy level more stable. In particular, the LUMO energy level of BNNO is as low as -3.12 eV. BNNY, BNNO, and BNNR emit cyan, green, and red fluorescence at 509, 534, and 620 nm, respectively, with fluorescence quantum yields of 24 %, 49 %, and 30 %, respectively.