Dual Emission through Thermally Activated Delayed Fluorescence and Room-Temperature Phosphorescence, and Their Thermal Enhancement via Solid-State Structural Change in a Carbazole-Quinoline Conjugate

The emergence of single-component organic dual light emitters holds great promise for white light-emitting diodes (WLEDs) and biological detection due to the involvement of broad emission covering visible spectrum. Here we show experimental studies on dual emission of carbazole-quinoline conjugate (CQ) that exhibits both thermally activated delayed fluorescence (TADF) via reverse intersystem crossing (rISC) from the higher-lying triplet state (T-2) to the singlet state (S-1) and room-temperature phosphorescence (RTP) from the lowest triplet state (T-1) due to low energy gap between T-2 and Si, and energetic proximity of T-1 with T-2. We found in thermal effect that the intensity of the dual features is enhanced with increasing temperatures up to 100 degrees C, which can be explained by a thermal-induced structural change (TISC) mechanism that compensates the emission losses due to nonradiative transitions at elevated temperatures. This property, in addition to its enhanced TADF and phosphorescence decay rates (similar to 10(7) s(-1) and 10(1) s(-1)) at 100 degrees C, would have great promise for high-efficiency LEDs.