Highly Efficient Blue Electroluminescence Based on a Pyreno[4,5-D]Imidazole Derivative Containing Pyrene and Fluorine

Abstract

Organic light emitting diodes (OLEDs), a new type of display device, are regarded as an important development direction for display technology. Molecules with hybridized local and charge transfer (HLCT) properties can optimize exciton utilization by reverse intersystem crossing and transitioning from high-energy triplet to singlet states, and donor–acceptor type molecules can be constructed to realize the HLCT states. Thus, in this study, pyrene (acceptor), pyreno[4,5-d]imidazole (donor), and fluorine atoms are employed to promote the formation of the HLCT state and enhance the utilization of excitons. The resulting molecules, 2FPyIPy and 2FPyIPPy, exhibit distinct HLCT characteristics and generate numerous singlet excitons. The non-doped devices of both molecules exhibit stable blue‐light emission with peaks located at 465 and 473 nm, respectively, and the external quantum efficiencies (EQEs) are 6.0% and 7.4%, respectively, with negligible roll-off at 10,000 cd m−2. Additionally, the doped devices exhibit improved color purity. Notably, the doped device based on 9-(3,5-difluorophenyl)-10-(4-(pyren-1-yl)phenyl)-9H-pyreno[4,5-d]imidazole exhibits a maximum EQE of 10.7%, which is among the highest values for state-of-the-art blue OLEDs and is the highest value for PyI-based doped devices. The exceptional performance of these materials can be attributed to the appropriate donor–acceptor design strategy and the incorporation of fluorine atoms.

Keywords: Pyreno[4, 5-d]imidazole, Blue luminophore, Fluorine substituents, HLCT state, OLEDs