Establishing carrier transport channels based on Ti-S bonds and enhancing the photocatalytic performance of MXene quantum dots-ZnIn2S4 for ammonia

In the process of photocatalytic synthesis of ammonia,the kinetics of carrier separation and transport,adsorption of nitrogen,and activation of the N N triple bond are key factors that directly affect the efficiency of converting nitro-gen to ammonia.Here,we report a new strategy for anchoring MXene quan-tum dots(MXene QDs)onto the surface of ZnIn2S4 by forming Ti-S bonds,which provide a channel for the rapid separation and transport of charge car-riers and effectively extend the lifespan of photogenerated carriers.The unique charge distribution caused by the sulfurization of the MXene QDs further enhances the performance of the photocatalysts for the adsorption and activa-tion of nitrogen.The photocatalytic ammonia synthesis efficiency of MXene QDs-ZnIn2S4 can reach up to 360.5μmol g�1 h�1.Density functional theory calculations,various in situ techniques,and ultrafast spectroscopy are used to characterize the successful construction of Ti-S bonds and the dynamic nature of excited state charge carriers in MXene QDs-ZnIn2S4,as well as their impact on nitrogen adsorption activation and photocatalytic ammonia synthesis efficiency.This study provides a new example of how to improve nitrogen adsorp-tion and activation in photocatalytic material systems and enhance charge carrier dynamics to achieve efficient photocatalytic nitrogen conversion.

How temperature and hydrostatic pressure impact organic room temperature phosphorescence from H-aggregation of planar triarylboranes and the application in bioimaging

Highly efficient persistent organic room temperature phosphorescence(RTP) has attracted increasing attention because of promising applications in fields of chemical sensors, optoelectronic devices, information security, and bioimaging, etc. Wherein,the crystal engineering of H-aggregation offers stabilization for long-lived triplet exciton for RTP, but the related research is rare because of the scarcity of ideal phosphorescent H-aggregate. Herein, we designed planar tricoordinate organoboron derivatives with molecular arrangement in ideal H-aggregation. The integration of Br atom can largely enhance RTP efficiency through increasing SOC effect, while the antiparallel molecular arrangement causes annihilation of triplet exciton. Thanks to good selfassembly property, their RTP can even be observed in PMMA matrix with doping ratio of merely 1 wt%. We further found that the cryogenic temperature contributes to stabilizing triplet exciton in H-aggregation, leading to red-shifted phosphorescence. By applying high hydrostatic pressure, the phosphorescence was largely enhanced and redshifted, demonstrating the crucial role of H-aggregation on RTP property. In phosphorescent tissue imaging of live mouse, nanoparticles of BrBA exhibited high contrast image via eliminating the interference of autofluorescence.

Different molecular conformation and packing determining mechanochromism and room-temperature phosphorescence

The phenomenon that different molecular packing modes in aggregates result in different optical properties has attracted intense attention,since it can provide useful information to establish the relationship between the micro-and macro-world.In this paper,DBTDO-DMAC was designed with 9,10-dihydro-9,9-dimethylacridine(DMAC)as electron donor.DBTDO-DPA and DBTDO-Cz were designed for comparison,which adopted diphenylamine(DPA)with twisted structure and carbazole(Cz)with planar structure as donors,respectively.As expected,two polymorphs(Crystal G and Crystal Y)of DBTDO-DMAC were obtained and exhibited distinct properties.Crystal G originating from planar conformation exhibited mechanochromism(MC)phenomenon and the emission color changed from green to yellow with a redshift of 35 nm after grinding.Nevertheless,Crystal Y with folded conformation displayed obvious room-temperature phosphorescence(RTP)with yellow afterglow.Careful single crystal analyses,powder X-ray diffraction and theoretical calculation reveal that the different emissive behaviors are highly related to the molecular conformation and packing modes.The successful adjustment of molecular conformation provides some guidance in the design of other MC and/or RTP luminogens,broadens the molecule family with the tunable molecular conformation and opens up a new avenue for exploring possible adjustment of molecular packing in aggregates.