Aggregation-induced emission organic metal halide complex for X-ray scintillation

The expanding applications of X-ray scintillation across various areas, from healthcare to security detection call for the development of new-generation scintillators that offer enhanced sensitivity, efficiency, and versatility. Here, we report for the first time the use of organic metal halide complexes with aggregation-induced emission (AIE) for X-ray scintillation, which can be facilely synthesized and processed in the solution phase. By reacting an AIE organic molecule, 4-(4-(diphenylamino) phenyl)-1-(propyl)-pyridinium (TPA-PD) with zinc chloride (ZnCl2) in solution at room temperature, an organic metal halide complex, (TPA-PD)2ZnCl2, is produced with a high synthetic yield of 87%. Optical and radioluminescence characterizations find that (TPA-PD)2ZnCl2 exhibits bluish-green photoluminescence and radioluminescence peaked at around 450 nm, with a photoluminescence quantum efficiency (PLQE) of 65%, and an absolute light yield of 13 423 Photon per MeV. Moreover, short photoluminescence and radioluminescence decay lifetimes are recorded at 1.81 ns and 5.24 ns, respectively. For X-ray scintillation, an excellent response dose-response linearity and a low limit of detection of 80.23 nGyair S-1 are obtained for (TPA-PD)2ZnCl2. By taking advantage of the high X-ray absorption of metal halides and fast radioluminescence of AIE molecules, our design of covalently bonded organic metal halide complexes opens up new opportunities for the development of high-performance solution-processable scintillators.

Novel Star-Shaped Viologens Containing Phenyl and Triphenylamine Moieties for Electrochromic Applications

The two star-shaped viologens containing 1,3,5-substituted phenyl (1) and triphenylamine (2) central cores and n-hexyl chains were synthesized and characterized. Both compounds exhibited promising optoelectronic properties and underwent multiple oxidation/reduction processes resulting in various colors. Four possible redox states of tripyridium salt containing a phenyl or triphenylamine core can occur depending on the applied potentials. The wide color range, from colorless through blue, azure to green-gray, was observed during the electrochemical reduction of compound 1. In the case of compound 2, the color change observed during spectroelectrochemical measurements was from yellow to colorless during the cathodic process and from yellow to green during the anodic process. The observed color change for both viologens was reversible. The triphenylamine-cored viologen (2) also exhibited emission in visible range and solvatochromism. It also exhibited luminescence in the solid state when excited with a UV lamp. These studies provide insights into the design of advanced materials for applications in displays.

Molecular engineering to enhance the reactive oxygen species generation of AIEgens and exploration of their versatile applications

Fluorescent dyes with aggregation-induced emission (AIE) characteristics have shown potential applications in the fields of biological imaging, photodynamic therapy and photothermal therapy, in which photosensitizers (PSs) play a crucial role. However, how to design high-quality PSs with high reactive oxygen species (ROS) generation efficiency remains unclear. In this contribution, an effective molecular design strategy to improve the ROS generation efficiency of AIE PSs was proposed. A series of tetraphenylethylene derivatives containing the pyridine ring or pyridinium with different substituents were designed and synthesized. All the molecules were weakly emissive when molecularly dissolved in solution but displayed intense emission upon aggregation, demonstrating a phenomenon of AIE characteristic. Pyridinium molecules could be used as visualization agents to specifically stain the mitochondria in living cells, while most of the molecules failed to generate ROS upon white light irradiation. In contrast, TPE-Pys-BP containing benzophenone produced ˙OH and 1O2 efficiently in the presence of light due to its large spin-orbit coupling constant to promote efficient intersystem crossing. Such a property allowed TPE-Pys-BP to serve as a PS to kill cancer cells using photodynamic therapy. TPE-Pys-BP also exhibited mechanochromic luminescence (ML), and its emission could be reversibly switched between two distinct colors through repeated grinding and fuming processes. A security paper was fabricated using the ML properties of TPE-Pys-BP.

Induced Near-Infrared Emission and Controlled Photooxidation based on Sulfonated Crown Ether in Water

Regulation of physio-chemical properties and reaction activities via noncovalent methodology has become one of increasingly significant topics in supramolecular chemistry and showed inventive applications in miscellaneous fields. Herein, we demonstrate that sulfonated crown ether can form very stable host-guest complexes with a series of push-pull-type photosensitizers, eventually leading to the dramatic fluorescence enhancement in visible and near-infrared regions. Meanwhile, severe suppression in singlet oxygen (¹ O₂ ) production is found, mainly due to the higher energy barriers between the excited single and triple states upon host-guest complexation. Moreover, such complexation-induced tuneable ¹ O₂ generation systems has been utilized in adjusting the photochemical oxidation reactions of polycyclic aromatic hydrocarbons (anthracene) and sulfides ((methylthio)benzene) in water. This supramolecularly controlled photooxidation based on the selective molecular binding of crown ether with photosensitizers may provide a feasible and applicable strategy for monitoring and modulating many photocatalysis processes in aqueous phase.

Counterion Migration Driven by Light-Induced Intramolecular Charge Transfer

A series of D-π-A ⁺ pyridinium compounds, in which D = -NPh₂ and A⁺ = -PyMe⁺ are linked by various amounts of linear phenyl spacers, were strategically designed and synthesized. Their characterization revealed the presence of excited-state intramolecular charge transfer (ESICT) that triggers a corresponding response from the counterion. In medium and strong polar solvents, the fast solvent relaxation occurring after ESICT overwhelms the counterion effect, showing typical emission solvatochromism. In weakly polar solvents, ESICT induces counteranion migration for electrostatic stabilization, the time scale of which is dependent on the radius of the counteranion, the length of the π-linker, and the viscosity of the solvent. In low-viscosity organic solvents such as toluene, counteranion migration occurs within several tens to hundreds of picoseconds, resulting in a time-dependent continuous emission that can be resolved from the spectral temporal evolution. Concrete evidence for this is provided by the chemical synthesis of a D-π-A ⁺ pyridinium-sulfur trioxide^- zwitterion, where anion migration is restricted due to its internally locked ion pair. As a result, only a single emission band can be observed. These comprehensive studies prove that the ion migration process may be significant for a wide range of ESICT-type ionic fluorophores. Such an ionic movement, triggered by optically pumped ESICT of the D-π-A ⁺ dyad, is similar to the molecular machine driven by the redox reaction, but with a facile access and fast response.