Peripheral anchoring groups strategy enables frontier molecular orbital delocalization and fast radiative decay of narrowband ultraviolet emitters for suppressing efficiency roll-off

Abstract

Ultraviolet organic light-emitting devices with neat film as emissive layer commonly suffer from low brightness, poor color purity, and severe efficiency roll-off owing to the intrinsic molecular properties. Herein we present a peripheral anchoring functional group approach to decorating “space-crowded donor−acceptor−donor” type carbazole-pyridine derivatives, for developing stable and bipolar ultraviolet fluorophores featuring narrowband emission. The introduction of anchoring group not only increases the delocalization of frontier molecular orbital distributions, enhancing the bipolar transport ability, but also confers the moderate rigidity and torsion of molecular conformation that shortens fluorescence lifetimes in aggregation state. Consequently, the non-doped devices with phenylcarbazole and naphthalene modified emit stable ultraviolet emission with the peaks of 395 and 388 nm and the full width at half maximums of 39 and 43 nm. Moreover, the maximum external quantum efficiencies (EQEs) of ∼4.0% and a mitigated efficiency roll-off at the high brightness of 3000 cd m−2 (EQE3000: ∼3.8%) are achieved, which provides an opportunity for ultraviolet OLEDs to realize the applications at high brightness levels.