Molecular-Level Understanding of Dual-RTP via Host-Sensitized Multiple Triplet-to-Triplet Energy Transfers and Data Security Application.

Dual-room-temperature phosphorescence (DRTP) from organic molecules is of utmost importance in chemical physics. The Dexter-type triplet-to-triplet energy transfer mechanism can therefore be used to achieve DRTP at ambient conditions. Here, we report two donor-acceptor (D-A)-based guests (CQN1, CQN2) in which the donor (D) and acceptor (A) parts are held in angular orientation around the C-N single bond. Spectroscopic analysis along with computational calculations revealed that both guests are incapable of emitting either thermally activated delayed fluorescence (TADF) or RTP at ambient conditions due to large singlet-triplet gaps, which are presented to show host (benzophenone, BP)-sensitized DRTP via multiple intermolecular triplet-to-triplet energy transfer (TTET) channels that originate from the triplet state (T1 BP) of BP to the triplet states (T1 D, T1 A) of the D and A parts (TTET-I:T1 BP → T1 D; TTET-II:T1 BP → T1 A). In addition, an intramolecular TTET channel that occurs from the T1 D to T1 A states of the D and A parts of CQN2 is also activated due to the low triplet (T1 D)-triplet (T1 A) gap at ambient conditions. The efficiency of TTET processes was found to be 100%. The phosphorescence quantum yields (ϕP) and lifetimes (τP) were shown to be 13-20% and 0.48-0.55 s, respectively. Given the high lifetime of the DRTP feature of both host-guest systems (1000:1 molar ratio), a data security application is achieved. This design principle provides the first solid proof that DRTP via radiative decay of the dark triplet states of the D and A parts of D-A-based non-TADF systems is possible, revealing a method to increase the efficiency and lifetime of DRTP.

Thermally activated delayed fluorescence and room-temperature phosphorescence in naphthyl appended carbazole-quinoline conjugates, and their mechanical regulation.

The influences of naphthyl and/or phenyl rings at the 2,4-positions of the quinolinyl fragments in carbazole-quinoline conjugates are studied. The centric phase of one of the conjugates (ß-CQNN) revealed both thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP), while prompt fluorescence and RTP were observed in the non-centric phase (α-CQNN) that can regenerate the emission features of ß-CQNNvia mechanical grinding. This unique observation is explained by the modulation of the higher-lying triplet (T2) energy level caused by conformational change.

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 (r ISC) 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.