Constructing highly efficient multiple resonance fluorescence materials by inserting benzothiophene within B/N-skeletons

Abstract

In this study, two novel multiple resonance (MR)-type blue emitters, namely SBN-1 and SBN-2, were synthesized and prepared for the development of highly efficient and stable blue fluorescent organic light-emitting diodes (OLEDs). The MR-type blue emitters are characterized by the presence of two benzothiophene groups within their MR-conjugated systems, with small dihedral angles, which distinguishes them from the well-known DABNA-1 derivatives and results in highly planar conjugated structures. Additionally, the MR effect still contributes to narrowband emissions of SBN-1 and SBN-2, showing small full width at half maximums (FWHMs) of 21 and 20 nm in toluene, respectively. Simultaneously, the MR-type materials embedding benzothiophene fragments could restrain the quenching effect between intermolecular interaction by introducing auxiliary aryl/heteroaryl amines containing the tert-butylbenzene or 9,9-dimethylxanthene group, giving long device lifetime. The fluorescent OLEDs based on SBN-1 and SBN-2 demonstrate pure blue emissions at 462 and 458 nm with CIE coordinates of (0.126, 0.194) and (0.133, 0.139), along with high external quantum efficiencies of 4.9% and 5.0%, respectively. Notably, SBN-2 exhibits an operational lifetime of up to approximately 220 hours until reaching a luminance level equivalent to 95% initial luminance (LT₉₅) at an intensity level of 1000 cd m⁻².