Highly efficient non-doped deep blue organic light-emitting diodes based on a pyreno[4,5-d]imidazole derivative with narrowband emission and small efficiency roll-off

Abstract

Based on the straightforward architecture, rapid response, and support for flexible screens, organic light-emitting diodes (OLEDs) have found extensive applications in modern lighting and display systems. With technological advancements, OLEDs have evolved from early fluorescent types to phosphorescent emitters, and eventually to third-generation systems such as MR-TADF and HLCT emitters. However, blue OLED materials continue to face challenges in stability and efficiency because of their inherently wide bandgap characteristics. In this study, we present a rational design for two deep blue materials, C–PyIN and N–PyIN, achieved by linking a pyreno[4,5-d]imidazole (PyI) unit with a naphthalene moiety via a benzene bridge. Photophysical studies and theoretical calculations reveal that C-PyIN possesses a unique hybridized local and charge-transfer (HLCT) state property, whereas N–PyIN displays pure local excitation (LE) state emission. Notably, non-doped OLEDs incorporating C–PyIN and N–PyIN as emissive materials exhibit electroluminescent (EL) peaks at 440 nm and 444 nm, with CIE coordinates of (0.15, 0.08) and (0.15, 0.11), narrow full width at half maximum (FWHM) of 56 and 57 nm, and impressive external quantum efficiencies (EQEs) of 8.3 % and 5.0 %, respectively. More significantly, non-doped OLEDs employing C–PyIN and N–PyIN demonstrate exceptionally low efficiency roll-offs of merely 1.5 % and 6 % at a luminance of 1000 cd m^–2, respectively. These findings demonstrate that C-PyIN and N-PyIN are promising deep blue light-emitting materials with excellent electroluminescence performance and stability, contributing to the advancement of efficient deep blue OLEDs.