Host polarity invariant TADF rISC mediated through vibronic coupling of two CT triplet states in Novel Hybrid Sulfone-Triarylboron Acceptor donor TADF molecules with ultra-long fluorescent lifetimes

Insert abstract text here. 10H-Dibenzo[b,e][1,4]thiaborinine 5,5-dioxide (SO2B) - a new high triplet (T1 = 3.05 eV) strongly electron-accepting boracycle - was successfully utilised in TADF emitters PXZ-Dipp-SO2B and CZ-Dipp-SO2B. We demonstrate the near complete separation of HOMO and LUMO leading to a low oscillator strength of the S1→S0 CT transition, resulting in very long ca. 83 ns and 400 ns prompt fluorescence lifetime for CZ-Dipp-SO2B and PXZ-Dipp-SO2B respectively, but retaining near unity photoluminescence quantum yield. Devices based on CZ-Dipp-SO2B have high EQE = 23.3% and maximum luminance of 18600 cd m-2 with low efficiency roll off at high brightness. For CZ-Dipp-SO2B rISC is mediated through the vibronic coupling of two CT states, without involving the 3LE, resulting in remarkable rISC rate invariance to environmental polarity and polarizability whilst giving near 100% IQE. This new form of rISC allows stable OLED performance to be achieved in different host environments.