Rational design of hybridized local and charge transfer emitters towards high-performance fluorescent blue OLEDs

Abstract

Hybridized local and charge-transfer (HLCT) emitters are promising for the realization of high-performance blue organic light-emitting diodes (OLEDs). However, the rational design of efficient HLCT emitters remains challenging. Here, we present two blue emitters (TAP1 and TAP2) with the HLCT state through the construction of D–π–A molecules. Theoretical calculations reveal the large overlap and partial separation of “hole” and “particle” orbitals for S₁ excited states, demonstrating the HLCT nature of the emitters. Together with the clear solvatochromic phenomenon, we propose that introducing the π-conjugated anthracene unit into an appropriate donor–acceptor segment is an effective strategy to finely regulate the locally excited and charge transfer components and construct versatile HLCT emitters. Employing TAP2 and TAP1 as emitters, the blue OLEDs exhibit good color purity, high efficiency, and extremely low efficiency roll-offs with Commission internationale de l’éclairage coordinates of, respectively, (0.14, 0.10) and (0.15, 0.11), narrow full width at half maximum values of 45 nm and 52 nm, maximum external quantum efficiency values of 5.53% and 5.16%, and efficiency roll-off values of 0.5% and 1% at the practical brightness of 1000 cd m⁻². By virtue of the transient photoluminescence decay curves, excited state energy levels and natural transition orbital analysis, we classify that the reverse intersystem crossing at high-lying excited states from T₂ to S₁ serves as an efficient approach to harvest triplet excitons and thus boost the exciton utilization efficiency. The superior properties of HLCT emitters in this work provide inspiration for the rational design of promising materials for high-performance blue OLEDs.