Sulfur-locked multiple resonance emitters for high performance orange-red/deep-red OLEDs

Herein, an innovative concept for a paradigm shift in orange-red/deep-red multiple resonance (MR) emitters is proposed by linking the outer phenyl groups in a classical MR framework through intramolecular sulfur (S) locks. Endowed with the planar architectural feature of the MR mother core, the proof-of-concept S-embedded emitters S-BN and 2S-BN also exhibit considerable flatness, which proves critical in avoiding the direct establishment of potent charge transfer states and inhibiting the non-radiative decay process. The emission maxima of S-BN and 2S-BN are 594 nm and 671 nm, respectively, and both have a high photoluminescence quantum yield of approximately 100%, a rapid radiative decay rate of around 107 s-1, and a remarkably high reverse intersystem crossing rates of about 105 s−1. In addition, 2S-BN is the first example of a single boron deep red MR emitter. Notably, unprecedented maximum external quantum efficiencies of 39.9% (S-BN, orange-red) and 29.3% (2S-BN, deep-red) were also achieved in typical planar organic light-emitting diode structures with ameliorated efficiency roll-offs.