Aggregation-induced emission and the working mechanism of 1-benzoyl and 1-benzyl pyrene derivatives.

Over the past decade, research studies on solid-state luminescent materials featuring aggregation-induced emission (AIE) have achieved great success. It has been proved that lots of planar ACQ (aggregation-caused quenching) chromophores can be converted to AIE luminogens (AIEgens) by combining with an AIE-active unit such as tetraphenylethene (TPE). In this work, we present a new method to create AIE luminogens just by introducing benzoyl or benzyl to a planar chromophore, pyrene. The generated 1-benzoyl and 1-benzyl pyrene derivatives exhibit weak emission when molecularly dissolved in good solvents but strong emission from pyrene dimers when aggregated in poor solvent or the solid state. Their crystal structure analysis and theoretical calculations are performed to depict the working mechanism of these new AIEgens. The results show that the structural rigidification of these 1-benzoyl pyrene derivatives is the major cause for their AIE effect. This new AIE system along with a clear working mechanism will contribute to the development of AIE-related functional materials and theories.

Tetraphenylpyrimidine-Based AIEgens: Facile Preparation, Theoretical Investigation and Practical Application.

Aggregation-induced emission (AIE) has become a hot research area and tremendous amounts of AIE-active luminogens (AIEgens) have been generated. To further promote the development of AIE, new AIEgens are highly desirable. Herein, new AIEgens based on tetraphenylpyrimidine (TPPM) are rationally designed according to the AIE mechanism of restriction of intramolecular motion, and facilely prepared under mild reaction conditions. The photophysical property of the generated TPPM, TPPM-4M and TPPM-4P are systematically investigated and the results show that they feature the aggregation-enhanced emission (AEE) characteristics. Theoretical study shows the high-frequency bending vibrations in the central pyrimidine ring of TPPM derivatives dominate the nonradiative decay channels. Thanks to the AEE feature, their aggregates can be used to detect explosives with super-amplification quenching effects, and the sensing ability is higher than typical AIE-active tetraphenylethene. It is anticipated that TPPM derivatives could serve as a new type of widely used AIEgen based on their facile preparation and good thermo-, photo- and chemostabilities.

Green perovskite light-emitting diodes with simultaneous high luminance and quantum efficiency through charge injection engineering.

Metal halide perovskite light emitting diodes (PeLEDs) have recently experienced rapid development due to the tunable emission wavelengths, narrow emission linewidth and low material cost. To achieve state-of-the-art performance, the high photoluminescence quantum yield (PLQY) of the active emission layer, the balanced charge injection, and the optimized optical extraction should be considered simultaneously. Multiple chemical passivation strategies have been provided as controllable and efficient methods to improve the PLQY of the perovskite layer. However, high luminance under large injection current and high external quantum efficiency (EQE) can hardly be achieved due to Auger recombination at high carrier density. Here, we decreased the electron injection barrier by tuning the Fermi-level of the perovskite, leading to a reduced turn on voltage. Through molecular doping of the hole injection material, a more balanced hole injection was achieved. At last, a device with modified charge injection realizes high luminance and quantum efficiency simultaneously. The best device exhibits luminance of 55,000 cd m-2, EQE of 8.02% at the working voltage of 2.65 V, current density of 115 mA cm-2, and shows EQE T50 stability around 160 min at 100 mA cm-2 injection current density.

Unveiling the Different Emission Behavior of Polytriazoles Constructed from Pyrazine-Based AIE Monomers by Click Polymerization.

Polymers with aggregation-induced emission (AIE) characteristics have aroused tremendous interest because of their potential applications in large-area flexible display and luminescent self-assembling, and as stimuli-responsive and porous materials. However, the design of AIE-active polymers is always not as easy as that of small molecules because their properties are hard to predict. In some cases, the polymers prepared from the AIE-active monomers show the aggregation-caused quenching (ACQ) instead of AIE effect. To understand the structure-property relationship of the polymers constructed from the AIE monomers, in this paper, two pyrazine-containing AIE monomers were utilized to construct luminescent polymers by click polymerization. The photophysical property investigation indicates that the polytriazole containing tetraphenylpyrazine units is AIE-active, whereas that bearing 2,3-dicyano-5,6-diphenylpyrazine units suffers from the ACQ effect. Through systematical investigation, the cause for such difference was unveiled. Thus, this work provides a useful guidance for further design of AIE-active polymers.