Weijun Zhao

White light emission from a single organic molecule with dual phosphorescence at room temperature

The development of single molecule white light emitters is extremely challenging for pure phosphorescent metal-free system at room temperature. Here we report a single pure organic phosphor, namely 4-chlorobenzoyldibenzothiophene, emitting white room temperature phosphorescence with Commission Internationale de l’Éclair-age coordinates of (0.33, 0.35). Experimental and theoretical investigations reveal that the white light emission is emerged from dual phosphorescence, which emit from the first and second excited triplet states. We also demonstrate the validity of the strategy to achieve metal-free pure phosphorescent single molecule white light emitters by intrasystem mixing dual room temperature phosphorescence arising from the low- and high-lying triplet states.The development of single molecule white light-emitters is extremely challenging for pure phosphorescent metal-free systems at room temperature. Here the authors show a single pure organic room temperature phosphor, 4-chlorobenzoyldibenzothiophene, utilizing the emission from both T1 and T2 states.

Switching the emission of tetrakis(4-methoxyphenyl)ethylene among three colors in the solid state

Emission of a luminogen could be switched among three colors in the solid state by transformation among three different aggregation states. The partly amorphous solid of the luminogen exhibits excitation dependent emission due to the contribution of both amorphous and crystalline parts to the photoluminescence intensity.

Ultrafast Delivery of Aggregation-Induced Emission Nanoparticles and Pure Organic Phosphorescent Nanocrystals by Saponin Encapsulation

Saponins are a class of naturally occurring bioactive and biocompatible amphiphilic glycosides produced by plants. Some saponins, such as α-hederin, exhibit unique cell membrane interactions. At concentrations above their critical micelle concentration, they will interact and aggregate with membrane cholesterol to form transient pores in the cell membrane. In this project, we utilized the unique permeabilization and amphiphilic properties of saponins for the intracellular delivery of deep-red-emitting aggregation-induced emission nanoparticles (AIE NPs) and pure organic room-temperature phosphorescent nanocrystals (NCs). We found this method to be biocompatible, inexpensive, ultrafast, and applicable to deliver a wide variety of AIE NPs and NCs into cancer cells.

STIMULUS RESPONSIVE LUMINESCENT MATERIALS: CRYSTALLIZATION-INDUCED EMISSION ENHANCEMENT

Crystallization of a luminogen normally red-shifts and weakens its emission. During investigation of some luminogens exhibiting aggregation-induced emission (AIE), we first noticed that some AIE active luminogens display higher photoluminescence (PL) intensity and bluer emission in the crystalline state than in their amorphous phase, which is termed as crystallization induced emission enhancement (CIEE). The twisted conformations of CIEE active molecules afford loose packing patterns and rule out any detrimental strong interaction. Molecular conformations are locked more tightly in crystals than those in amorphous solid due to the regular weak interactions in crystals, which affords the CIEE effect. The loose packing patterns facilitate emission switching through morphology modulation. Many AIE active molecules have been developed based on restriction of intramolecular rotation (RIR) mechanism, and we obtained many CIEE compounds from those AIE active luminogens and investigated their utilities as stimuli responsive functional materials, especially as chemosensors, thermosensor, mechanosensors and solid-state emitters. Thus, we provide a possible design strategy for the stimuli responsive solid luminescent materials.

Dynamic Visualization of Stress/Strain Distribution and Fatigue Crack Propagation by an Organic Mechanoresponsive AIE Luminogen

Stress exists ubiquitously and is critically important for the manufacturing industry. Due to the ultrasensitive mechanoresponse of the emission of 1,1,2,2,-tetrakis(4-nitrophenyl)ethane (TPE-4N), a luminogen with aggregation-induced emission characteristics, the visualization of stress/strain distributions on metal specimens with a pure organic fluorescent material is achieved. Such a fluorescence mapping method enjoys the merits of simple setup, real-time, full-field, on-site, and direct visualization. Surface analysis shows that TPE-4N can form a nonfluorescent, crystalline uniform film on the metal surface, which cracks into fluorescent amorphous fragments upon mechanical force. Therefore, the invisible information of the stress/strain distribution of the metal specimens are transformed to visible fluorescent signals, which generally matches well but provides more details than software simulation. Remarkably, fatigue crack propagation in stainless steel and aluminum alloy can be observed and predicted clearly, further demonstrating the ultrasensitivity and practicability of TPE-4N.