Chromenopyrazole-based TADF emitters for bluish-green and skyblue OLEDs

Abstract

Thermally activated delayed fluorescence (TADF) materials have emerged as an efficient, sustainable alternative to phosphorescent emitters in organic light-emitting diodes (OLEDs), as they do not require heavy metals which are expensive and damaging to the environment. Nevertheless, the development of bright and high-efficiency blue-green TADF emitters remains a significant challenge. Herein, we present a series of novel molecules based on chromenopyrazole (CP) acceptor with various donor moieties: phenoxazine, phenothiazine, and phenoselenazine, demonstrating TADF emission. TADF has been confirmed by luminescence spectroscopy methods and quantum chemical TD-DFT calculations.Among the investigated dyes, phenoxazine-containing dye (POZCP) demonstrated the most favorable photophysical characteristics for OLED application, including a delayed fluorescence lifetime of 1.8 μs in the doped PMMA film. An OLED device employing POZCP exhibited bluish-green emission with a maximum luminance of 13864 cd/m², a current efficiency of 11.6 cd/A, a peak EQE of 14.6 %, T90 of 20 h and a low turn-on voltage of 3.0 V. Structural modification of POZCP by incorporating an additional phenyl ring as a π-spacer resulted in broader electroluminescence spectrum with sky-blue emission; however, this significantly suppressed the TADF process. These findings establish CP-based molecules as promising candidates for efficient blue TADF emitters and highlight their potential in next-generation OLED technologies.