Host-controlled switching between TADF and RTP in acridone-carboline donor-acceptor dyads.

Purely organic, metal-free emitters that combine thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) provide an attractive route to triplet harvesting without heavy-metal complexes. Here, we report two acridone-carboline donor-acceptor emitters, Acr-Me-Cb and Acr-Anisyl-Cb, that exhibit bluish-green emission centered at 422 nm and high photoluminescence quantum yields of up to 85% in toluene. A moderate singlet-triplet energy gap (ΔEST ≈ 0.3 eV) enables competing reverse intersystem crossing and triplet stabilization pathways, allowing delayed fluorescence and phosphorescence to be accessed within the same molecular framework. Host-dependent photophysical studies in CBP and PVA matrices reveal distinct relaxation channels: 10 wt% CBP-doped films show TADF at 300 K with delayed lifetimes of 67 and 136 μs for Acr-Me-Cb and Acr-Anisyl-Cb, respectively, whereas rigid PVA films promote RTP with an afterglow of ∼1 s under ambient conditions. These results establish acridone-carboline dyads as a host-responsive platform for switching between TADF and RTP in metal-free organic emitters.