Pure blue emitters based on benzo[4,5]thieno-S,S-dioxide-[3,2-b]benzofuran with high thermal stability

Abstract

Molecules with hybrid local charge transfer (HLCT) state can theoretically realize 100% exciton utilization by using high energy level triplet excitons to generate singlet excitons through reverse intersystem crossing, and thus has attracted attention. Because it is difficult to obtain HLCT molecules with both short-wavelength emission and high exciton utilization, it is challenging to develop high-performance pure blue organic light-emitting diodes (OLEDs). In this study, a series of novel D-π-A blue emitters (CZ-Ph-BTOBF, DCZ-Ph-BTOBF and SAF-Ph-BTOBF) with carbazolyl or acridinyl group as a donor, benzo [4,5]thieno-S,S-dioxide-[3,2-b]benzofuran (BTOBF) as an acceptor, and phenyl group as a π bridge are designed and synthesized. These emitters exhibit good thermal, morphological stability and HLCT excited-state characteristics. OLEDs using CZ-Ph-BTOBF efficiently emits pure blue light (472 nm, CIEx,y = 0.15, 0.17) with full width at half maximum (FWHM) of 65 nm and maximum external quantum efficiency (EQE) of 6.85%. The visible bright blue emission is corroborated by the remarkably high photoluminescent quantum yield up to 92% in doped thin films. OLEDs of DCZ-Ph-BTOBF also exhibit pure blue emission with enhanced color purity (CIEx,y = 0.15, 0.11) and narrow emission peaks (FWHM = 64 nm). In conclusion, by adding a phenyl π bridge between the donor and acceptor groups, triplet excitons can be utilized through HLCT excited states and thus the electroluminescence efficiency can be improved. These results suggest that the rationally designed BTOBF based emitters have great potential for achieving solution-processible, high-performance and stable blue OLEDs.