Manipulating the Excited States from Charge-Transfer to Hybridized Local and Charge-Transfer Towards High-Performance Blue Electroluminescence

Abstract

Manipulating the excited states of organic luminescent materials can efficiently improve the utilization of both singlet and triplet excitons for developing high-performance organic light-emitting diodes (OLEDs), but the issue remains difficult due to the lack of well-controlled ways. Here, we proposed a molecular design strategy of excited state manipulation from charge-transfer (CT) to hybridized local and charge-transfer (HLCT) via adjusting the cyano position on pyridine acceptor. The meta-substituted PyAn4CN is mainly composed of a CT component, while the para-substituted PyAn5CN is endowed with a HLCT component. On further extending the conjugation of PyAn5CN by inserting a benzene unit between the pyrene and anthracene core, the HLCT character is preserved in PyPhAn5CN, accompanied by a faster radiative decay. Consequently, the vacuum-evaporated OLEDs exhibit blue electroluminescence (EL) with the emission peaks in the range of 455-460 nm and high external quantum efficiency (EQE) up to 7.52%, together with well-suppressed efficiency roll-offs of 0.8% and 3.7% at the luminance of 100 and 1000 cd m-2, respectively. More importantly, the solution-processed device shows an excellent performance with EQE of 6.49%, which is one of the best results in the solution-processed HLCT OLEDs. Our results clearly indicate that the formation of HLCT state is an efficient way to realize high-efficiency blue electrofluorescence.

Keywords: organic light-emitting diode, hybridized local and charge-transfer, charge-transfer, excited state, Electroluminescence