The influence of the host molecules on the photoluminescent (PL) and electroluminescent (EL) properties of organic light-emitting diode (OLED) emitters showing efficient thermally-activated delayed fluorescence (TADF) has yet to be investigated in detail. Here we demonstrate that the choice of host can cause large variations in the PL quantum yield (ΦPL ∼15-70%) and delayed PL transient decay (τdel ∼2-70 ms) of a spiro-acridine-based TADF guest. We show that the effect of exciplex formation on ΦPL must be considered even at low concentrations of the TADF guest. Using the same TADF guest but changing the host layer, we are able to greatly vary the PL transient decay time from ∼4 to ∼70 ms while maintaining a high ΦPL ∼70%, which can lead to new applications. Detailed spectral characterization during PL decay reveals a gradually increasing singlet-triplet energy gap (ΔEST) as the origin of these observations. The time-varying ΔEST is explained based on dipole interactions between the host and guest molecules. Finally, PL and electrical considerations for host selection are discussed based on the performance of OLED devices.
ASJC Scopus subject areas
- 化学 (全般)