Highly Efficient Luminescence of Cu(I) Compounds: Thermally Activated Delayed Fluorescence Combined with Short-Lived Phosphorescence

Luminescent materials showing thermally
activated delayed fluorescence
(TADF) have gained high attractiveness as emitters in organic light
emitting diodes (OLEDs) and other photonic applications. Nevertheless,
even utilization of TADF can be further improved, introducing a novel
concept. This is demonstrated by a new class of brightly luminescent
low-cost Cu­(I) compounds, for which the emission stems from both the
lowest excited triplet T1 and singlet S1 state.
At T = 300 K, these materials exhibit quantum yields
of more than ΦPL = 90% at short emission decay times.
About 80% of the emission intensity stems from the singlet due to
TADF, but importantly, an additional 20% is contributed by the lower
lying triplet state according to effective spin–orbit coupling
(SOC). SOC induces also a relatively large zero-field splitting of
the triplet being unusual for Cu­(I) complexes. Thus, the overall emission
decay time is distinctly reduced. Combined use of both decay paths
opens novel photonic applications, in particular, for OLEDs.