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 (T2) to the singlet state (S1) and room-temperature phosphorescence (RTP) from the lowest triplet
state (T1) due to low energy gap between T2 and S1, and energetic
proximity of T1 with T2. We found in thermal effect that the intensity of the
dual features is enhanced with increasing temperatures up to 100 °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 (∼107 s–1and 101 s–1) at 100 °C, would have great promise for high-efficiency LEDs.