The effect of positional deuterium substitution on the acceptor moiety for TADF†

Abstract

Despite the successful commercialization of organic light-emitting diodes (OLEDs), achieving high efficiency and long lifespan in blue OLEDs often requires device structures that incorporate multiple layers featuring two or more blue-emitting layers, highlighting the ongoing challenge of achieving deep-blue OLEDs with extended lifetime. Significant improvements in lifetime have been demonstrated in blue thermally activated delayed fluorescent (TADF) OLEDs by utilizing 5CzBN with positional deuteration. We synthesized three emitters and observed a gradual increase in T₆₀ based on the positioning of benzonitrile as the acceptor, generally reflecting the molecular design of TADF systems such as the donor–π–acceptor configuration. To investigate the effects of deuteration, we measured the decrease in photoluminescence (PL) efficiency following UV irradiation to induce photodegradation. Additionally, we fabricated devices to confirm stability during operation. The photoluminescence (PL) efficiency and lifetime depend on the positional deuteration of the acceptor core. The 5CzBN-D(o,p) emitter, which is deutero-substituted, exhibited greater efficiency and a longer lifespan than 5CzBN-D(m). After 60 minutes of UV exposure, the decrease in PL for 5CzBN-D(o,p) was 53.4%, whereas for 5CzBN-D(m) it was 68%. Furthermore, the lifetime (LT₆₀) of 5CzBN-D(o,p) was 4.61 times longer than that of 5CzBN-D(m). These results indicate that the efficiency and lifetime in donor–π–acceptor chemical structures depend significantly on the position of the core with a strongly electron-withdrawing group.