Frontier molecular orbital engineering in spiro-based molecules: achieving aggregation-induced delayed fluorescence for non-doped OLEDs

Abstract

Frontier molecular orbital engineering has been demonstrated to achieve aggregation-induced delayed fluorescence (AIDF) for non-doped OLEDs. As a proof of concept, a new model compound, AT-spiro-DMACF, is reported on the basis of the TXADO-spiro-DMACF reference by changing the spiro-linked moiety from thioxanthene dioxide to anthracen-9(10H)-one. Such a minor alteration makes the lowest unoccupied molecular orbital (LUMO) shift from the inner fluorene to the outer anthracen-9(10H)-one, while retaining the almost same highest occupied molecular orbital (HOMO) distribution. In this case, the intermolecular charge transfer between the HOMO and LUMO becomes favorable, leading to aggregation-induced emission and thermally activated delayed fluorescence. As a result of this AIDF nature, AT-spiro-DMACF achieves a good non-doped device performance with a peak external quantum efficiency of 9.8% (31.1 cd A⁻¹, 33.7 lm W⁻¹) and Commission Internationale de l’Eclairage coordinates of (0.35, 0.54). The result clearly indicates that frontier molecular orbital engineering is an effective strategy for the development of AIDF emitters that are suitable for non-doped OLEDs.