White Light Emission Achieved by Dual-TADF in a Single Emissive Layer of Multicomponent Emitters

White light emission (WLE) from multicomponent organic
systems
has attracted significant attention in recent years due to easy access
of bright blue and yellow/orange, or red emitters. However, realizing
WLE from a single emissive layer of multicomponent organic thermally
activated delayed fluorescence (TADF) systems is an exasperating task
due to uncontrolled Förster energy transfer and Dexter-type
triplet–triplet energy transfer (TTET). To address this issue,
we demonstrated WLE using blend films (WL1, WL2, and WL3) of blue
(CPPN, CQ, and DMOC-DPS) and orange (PTzQ) TADF emitters. WL1 comprises
CPPN and PTzQ, while DMOC-DPS and PTzQ were used to construct WL2.
Spectroscopic analysis revealed that WL1 and WL2 exhibited dual emission
features (quantum yields = 48–54%; Commission Internationale
de l’éclairage coordinates: 0.34, 0.31; 0.31, and 0.34) via simultaneous blue- and orange-TADF covering the visible
region. The WLE feature is observed due to (i) similar absorption
and different Stokes shifted emission color of both the emitters and
(ii) the absence of TTET caused by large triplet–triplet gaps
(>0.4 eV) between the emitters. In contrast, WLE via fluorescence and TADF was observed in WL3 due to TTET. This finding
is expected to provide new insights for designing high-energy-efficient
WLE for white organic light-emitting diodes.