Very bright mechanoluminescence and remarkable mechanochromism using a tetraphenylethene derivative with aggregation-induced emission

Monotonous luminescence has always been a major factor limiting the application of organic room-temperature phosphorescence (RTP) materials. Enhancing and regulating the intermolecular interactions between the host and guest is an effective strategy to achieve excellent phosphorescence performance. In this study, intermolecular halogen bonding (CN…Br) was introduced into the host-guest RTP system. The interaction promoted intersystem crossing and stabilized the triplet excitons, thus helping to achieve strong phosphorescence emission. In addition, the weak intermolecular interaction of halogen bonding is sensitive to external stimuli such as heat, mechanical force, and X-rays. Therefore, the triplet excitons were easily quenched and colorimetric multi-stimuli responsive behaviors were realized, which greatly enriched the luminescence functionality of the RTP materials. This method provides a new platform for the future design of responsive RTP materials based on weak intermolecular interactions between the host and guest molecules.

Halogen Bonding: A New Platform for Achieving Multi-Stimuli-Responsive Persistent Phosphorescence.

The architectural design and fabrication of low-cost and reliable organic X-ray imaging scintillators with high light yield, ultralow detection limits and excellent imaging resolution is becoming one of the most attractive research directions for chemists, materials scientists, physicists and engineers due to the devices’ promising scientific and applied technological implications. However, the optimal balance among X-ray absorption capability, exciton utilization efficiency and photoluminescence quantum yield of organic scintillation materials is extremely difficult to achieve because of several competitive non-radiative processes, including intersystem crossing and internal conversion. Here we introduced heavy atoms (Cl, Br and I) into thermally activated delayed fluorescence (TADF) chromophores to significantly increase their X-ray absorption cross-section and maintaining their unique TADF properties and high photoluminescence quantum yield. The X-ray imaging screens fabricated using TADF-Br chromophores exhibited highly improved X-ray sensitivity and imaging resolution compared with the TADF-H counterpart. More importantly, the high X-ray imaging resolution of >18.0 line pairs per millimetre achieved from the TADF-Br screen exceeds most reported organic and conventional inorganic scintillators. This study could help revive research on organic X-ray imaging scintillators and pave the way towards exciting applications for radiology and security screening. Heavy atoms like Cl, Br and I introduced into thermally activated delayed fluorescence chromophores can increase the X-ray absorption cross-section. Light yield of ~20,000 photons MeV–1, detection limit of 45.5 nGy s−1 and imaging resolution of >18.0 line pairs per millimetre is demonstrated. 

https://repository.kaust.edu.sa/bitstream/10754/685327/1/Wang%20et%20al-NP-revised-Final.pdf

Heavy-atom engineering of thermally activated delayed fluorophores for high-performance X-ray imaging scintillators

X-ray-induced photodynamic therapy utilizes penetrating X-rays to activate reactive oxygen species in deep tissues for cancer treatment, which combines the advantages of photodynamic therapy and radiotherapy. Conventional therapy usually requires heavy-metal-containing inorganic scintillators and organic photosensitizers to generate singlet oxygen. Here, we report a more convenient strategy for X-ray-induced photodynamic therapy based on a class of organic phosphorescence nanoscintillators, that act in a dual capacity as scintillators and photosensitizers. The resulting low dose of 0.4 Gy and negligible adverse effects demonstrate the great potential for the treatment of deep tumours. These findings provide an optional route that leverages the optical properties of purely organic scintillators for deep-tissue photodynamic therapy. Furthermore, these organic nanoscintillators offer an opportunity to expand applications in the fields of biomaterials and nanobiotechnology. 

/pdf/organic-phosphorescent-nanoscintillator-for-low-dose-x-ray-1q0tmxfz.pdf

Organic phosphorescent nanoscintillator for low-dose X-ray-induced photodynamic therapy

Mechanoresponsive luminescent organic crystals have recently attracted increasing interest owing to their potential applications in advanced optoelectronic devices, mechanosensors, security technologies, etc. In the past few years, an increasing number...

Luminescent polymorphic crystals: mechanoresponsive and multicolor-emissive properties

Thermally activated delayed fluorescence (TADF) has been explored actively in luminescent organic materials. Yet, realizing such TADF-active, multifunctional emitters with high emission efficiency still remains hugely challenging. In this context, a series of twist-conjugated organic molecules bearing diphenylsulfone and 9,9-dimethylacridine moieties are designed and prepared, and are found to show, in one molecule, TADF, room-temperature phosphorescence, triboluminescence, and aggregation-induced emission enhancement. In addition, remarkably high photoluminescence quantum efficiency, up to ≈100%, is achieved for these novel molecules. Single-crystal analysis and theoretical calculations reveal that the through-space charge transfer (TSCT) effect in these molecules is responsible for both the multifunctional emission and high emission efficiency. A maximum external quantum efficiency of 20.1% is achieved, which is among the highest recorded in a solution-processable device containing TSCT-based TADF materials. These results illustrate a new approach to achieving highly efficient TADF-active, multifunctional emitters.

Intramolecular Through-Space Charge Transfer Based TADF-Active Multifunctional Emitters for High Efficiency Solution-Processed OLED

There are few reports about purely organic phosphorescence scintillators, and the relationship between molecular structures and radioluminescence in organic scintillators is still unclear. Here, we presented isomerism strategy to study the effect of molecular structures on radioluminescence. The isomers can achieve phosphorescence efficiency of up to 22.8 % by ultraviolet irradiation. Under X-ray irradiation, both m-BA and p-BA show excellent radioluminescence, while o-BA has almost no radioluminescence. Through experimental and theoretical investigation, we found that radioluminescence was not only affected by non-radiation in emissive process, but also highly depended on the material conductivity caused by the different molecular packing. This study not only allows us to clearly understand the relationship between the molecular structures and radioluminescence, but also provides a guidance to rationally design new organic scintillators.

Influence of Isomerism on Radioluminescence of Purely Organic Phosphorescence Scintillators

Room temperature phosphorescence (RTP) and mechanoluminescence (ML) materials are in high demand because of their promising applications in optoelectronic devices. However, most materials bear only one of these properties and molecules bearing both of them are rarely reported. Here, we report a carbazole derivative 1, which displays both RTP activity and near-ultraviolet ML properties. These properties are highly related to the packing modes and molecular configuration as revealed by the analysis of their crystal structures and theoretical calculations. The near-ultraviolet ML of 1 can further serve as the exciting light source to transfer its energy to luminescent dyes to realize colorful ML. The thermal-responsive RTP of 1 can be utilized to prepare anti-counterfeiting tags for simple security protection. This work has put forward a simple but efficient strategy to prepare multifunctional molecular systems bearing both RTP and ML properties.

Controllable room temperature phosphorescence, mechanoluminescence and polymorphism of a carbazole derivative.

Purely aromatic hydrocarbon materials with ultralong room-temperature phosphorescence (RTP) were reported recently, but which is universally recognized as unobservable. To reveal the inherent luminescent mechanism, two compounds, i.e., PT with a faint RTP and HD with strong RTP featured by nonplanar geometry, were chosen as a prototype to study their excited-state electronic structures by using quantum mechanics/molecular mechanics (QM/MM) model. It is demonstrated that the nonplanar ethylene brides can offer sigma-electron to strengthen spin-orbit coupling (SOC) between singlet and triplet excited states, which can not only promote intersystem crossing (ISC) of S1->Tn to increase the population of triplet excitons, but also accelerate the radiative decay rate of T1->S0, and thus improving RTP. Impressively, the nonradiative decay rate only has a small increase, owing to the synergistic effect between the increase of SOC and the reduction of reorganization energy of T1->S0 caused by the restricted torsional motions of aromatic rings. Therefore, a bright and long-lived RTP was obtained in aromatic hydrocarbon materials with twisted structure. This work provided a new insight into the ultralong RTP in pure organic materials.

/pdf/theoretical-insight-into-the-ultralong-room-temperature-wytllloqxm.pdf

Wenqi Gong

Papers

Intramolecular Through-Space Charge Transfer Based TADF-Active Multifunctional Emitters for High Efficiency Solution-Processed OLED

Influence of Isomerism on Radioluminescence of Purely Organic Phosphorescence Scintillators

Controllable room temperature phosphorescence, mechanoluminescence and polymorphism of a carbazole derivative.

Theoretical Insight Into the Ultralong Room-Temperature Phosphorescence of Nonplanar Aromatic Hydrocarbon.