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 ( T) to the singlet state ( S) and room-temperature phosphorescence (RTP) from the lowest triplet state ( T) due to low energy gap between T and S, and energetic proximity of T with T. 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 (∼10 sand 10 s) at 100 °C, would have great promise for high-efficiency LEDs.

Imidazole, a subunit of histidine, plays a crucial role in proton-relay processes that are important for various biological activities, such as metal efflux, viral replication and photosynthesis. We show here how an imidazolyl ring incorporated into a rotary switch based on a hydrazone enables a switching cascade that involves proton relay between two different switches. The switching process starts with a single input, zinc(II), that initiates an E/Z isomerization in the hydrazone system through a coordination-coupled proton transfer. The resulting imidazolium ring is unusually acidic and, through proton relay, activates the E/Z isomerization of a non-coordinating pyridine-containing hydrazone switch. We hypothesize that the reduction in the acid dissociation constant of the imidazolium ring results from a combination of electrostatic and conformational effects, the study of which might help elucidate the proton-coupled electron-transfer mechanism in photosynthetic bacteria.

Two different coumarin derivatives have been connected via an imine linkage to obtain a new fluorescence signaling system. This compound itself does not show any emission due to rapid isomerization around the C[double bond]N bond. However, in the presence of a Mg(II) ion, this isomerization is stopped because of bonding to the metal ion resulting in high-intensity (approximately 550-fold) emission. Other metal ions like Li(I), Ca(II), and Zn(II) show very little emission, while biologically relevant transition-metal ions do not show any emission. In this way, the Mg(II) ion can be detected in the presence of these ions.

No abstract