Dibenzo[b,d]furan/thiophene-fused double boron-based multiresonance emitters with narrowband ultrapure green electroluminescence

Abstract

Herein, double boron (DB)-based narrowband pure-green multiresonance (MR) emitters DBF-DBN and DBT-DBN have been designed and synthesized. Dibenzo[b,d]furan and dibenzo[b,d]thiophene as linkages between two B–N skeletons endow target DB-MR-emitters with a rigid and symmetric molecular structure, which efficiently extends the π-conjugation length and suppresses vibrational relaxation, resulting in a narrowband pure-green emission. DBT-DBN exhibits a remarkably higher reverse intersystem crossing (RISC) rate (k_RISC = 7.4 × 10⁵ s⁻¹) than DBF-DBN (k_RISC = 1.1 × 10⁵ s⁻¹) due to the heavy-atom effect of sulfur. The organic light-emitting diode (OLEDs) based on DBT-DBN shows an ultrapure green emission with maximum external quantum efficiencies (EQEs) up to 31.3%, an emission peak at 520 nm, and a narrow full-width at half-maximum (FWHM) of 24 nm, meeting the BT.2020 green standard.