Investigations of halogenated derivatives of diphenylsulphone thermally activated delayed fluorescent emitters

Abstract

Thermally activated delayed fluorescent (TADF) emitters are promising organic materials for application in OLED. The most demanded OLED emitters are the blue ones due to low stability of devices of this color. The main problem is the rate of spin flip transition from the lowest excited triplet to singlet state called reverse intersystem crossing (rISC). The rISC efficiency has the direct influence on the external quantum efficiency (EQE) of OLED. In organic blue emitters the spin-orbit coupling (SOC) is low which causes low rISC and low EQE. In our work, we are looking for the way to increase SOC and rISC in blue TDAF emitters. Previously we found that interactions of triplet and singlet states of charge transfer (CT) nature are playing the key role in rISC [1,2]. The influence of different substituents and their position on 3CT-1CT transition in blue TADF emitter DMAC-DPS was studied. We introduced different substituents at donor, acceptor and linker fragment of DMAC-DPS molecule. The substituent effects on the geometry (torsion angle over the σ-bound between donor and acceptor fragments), energy of states, SOC and 3CT-1CT gaps were analyzed. The impact of triplet states localized on donor and acceptor fragments was also analyzed. Our conclusions are helpful in further understanding of different rISC transitions.