Accelerating Intersystem Crossing in Multiresonance Thermally Activated Delayed Fluorescence Emitters via Long-Range Charge Transfer.

Multiresonance thermally activated delayed fluorescence (MR-TADF) emitters are excellent candidates for high-performance organic light-emitting diodes (OLEDs) due to their narrowband emission properties. However, the inherent mechanism of regulating the rate of intersystem crossing (ISC) is ambiguous in certain MR-TADF skeletons. Herein, we propose a mechanism of accelerating ISC in B/S-based MR-TADF emitters by peripheral modifications of electron-donating groups (EDGs) without affecting the narrowband emission property. The long-range charge transfer (LRCT) stems from the introduced EDG leading to high-lying singlet and triplet excited states. The ISC process is accelerated by the enhanced spin-orbital coupling (SOC) between the singlet short-range charge transfer (SRCT) and triplet LRCT manifolds. Meanwhile, the narrowband emission derived from the MR-type SRCT state is well retained as expected in the peripherally modified MR-TADF emitters. This work reveals the regulation mechanism of photophysical properties by high-lying LRCT excited states and provides a significant theoretical basis for modulating the rate of ISC in the further design of MR-TADF materials.

Boosting the Release of Leaving Group from Blebbistatin Derivative Photocages via Enhancing Intramolecular Charge Transfer and Stabilizing Cationic Intermediate.

Blebbistatin (Bleb) derivatives are a visible light photocage platform. During the photocleavage process, intramolecular charge transfer (ICT) and cationic intermediates play a decisive role. However, slow photolysis rate and low photolysis quantum yield are the main problems for Bleb's derivatives. Herein, by introducing a substituted OCH3 group at the para-position of the D ring, Bleb and Bleb derivatives with various leaving groups were synthesized and studied, and the photolysis performance was unveiled by steady-state spectra, photolysis rate experiments, photolysis quantum yield, and density functional theory calculations. Substituted OCH3 derivatives of Bleb may enhance the photolysis rate and increase the photolysis quantum yield because the electron-donating group can promote the ICT process and stabilize the cationic intermediate during the photolytic reaction. More generally, the insights gained from this structure-reactivity relationship may provide theoretical guidance and aid in the development of new highly efficient photoreactions.

Near-Infrared Light Triggered a High Temperature Utilizing Donor-Acceptor Cocrystals.

Developing a suitable initiation for the energetic materials that respond to a low-power near-infrared laser can aid in replacing the current expensive and bulky laser-initiation systems. Here, we report on a system of molecularly tailored 1:1 donor-acceptor (D-A) charge-transfer (CT) cocrystals that manifest ultrabroad absorption (200-2500 nm) characteristics as well as noteworthy very fast self-assembly behaviors. The very narrow highest occupied molecular orbital-lowest unoccupied molecular orbital gap enables N,N,N',N'-tetramethyl-p-phenylenediamine and tetrahalo-1,4-benzoquinones (TMPD-TXBQ) cocrystals to have a great light-harvesting ability in the near-infrared range. When irradiated with a low-power hand-held 808 nm laser with an input energy of only 40 mJ or a power density of 260 mW·cm-2, these TMPD-TXBQ cocrystals immediately undergo an efficient photothermal conversion followed by a dramatic exothermic thermal polymerization reaction due to the face-to-face D-A-D-A stacking in these cocystals to achieve a temperature as high as 318.9 °C. This temperature is high enough for a thermal initiation of most common energetic materials, and thus this TMPD-TXBQ cocrystal can potentially act as a near-infrared laser initiator that is compact, lightweight, and cost-effective.

Blue or Near-Infrared Light-Triggered Release of Halogens via Blebbistatin Photocage.

Photocages can provide spatial and temporal control to accurately release the various chemicals and bioactive groups when excited by light. Although the absorption spectra of most photocages are in the ultraviolet absorption region, only a few absorb in the visible or near-infrared region. Blebbistatin (Bleb) would release a hydroxyl radical under blue one-photon or two-photon near-infrared light (800 nm) irradiation. In this work, typical chlorine and bromine as leaving groups substituted hydroxyl compounds (Bleb-Cl, Bleb-Br) are synthesized to evaluate the photocage's capability of Bleb's platform. Driven by the excited-state charge transfer, Bleb-Cl and Bleb-Br show good photolysis quantum yield to uncage the halogen anion and the uncaging process would be accelerated in water solution. The photochemical reaction, final product's analysis, and femtosecond transient absorption studies on Bleb-Cl/Bleb-Br demonstrate that Bleb can act as a photocage platform to release the halogen ion via heterolytic reaction when irradiated by blue or near-infrared light. Therefore, Bleb can be a new generation of visible or near-infrared light-triggered photocage.