Abstract Pure organic room‐temperature phosphorescence (RTP) materials have been widely utilized in security signs, anti‐counterfeiting, data encrypting, and other fields, which have attracted great attention. In the past few years, smart materials with color‐tunable organic RTP materials are reported by many researchers, while the work focused on the color‐tunable polymeric RTP materials is still rare, especially for molecular weight‐dependent polymeric RTP systems. Here, we designed and prepared three molecular weight polymers P1, P2, and P3 by different polymerization reaction times, and found that the fluorescence emissions of these polymer powders are various. Unexpectedly, the molecular weight‐dependent polymeric RTP materials are achieved through doping these polymers into polyacrylonitrile (PAN) matrix, and the International de l'Eclairage was redshift from (0.205,0.257) to (0.503,0.435). This phenomenon is ascribed to the different aggregation states formed by assembly of different molecular weight polymeric chains. Meanwhile, the electrostatic interaction between phosphor and PAN is hardly affected by water. Therefore, advanced information encryption can be achieved by using these polymeric phosphors as anti‐counterfeiting ink.
Abstract Room temperature phosphorescence (RTP) has drawn extensive attention in recent years. Efficient stimulus-responsive phosphorescent organic materials are attractive, but are extremely rare because of unclear design principles and intrinsically spin-forbidden intersystem crossing. Herein, we present a feasible and facile strategy to achieve ultraviolet irradiation-responsive ultralong RTP (IRRTP) of some simple organic phosphors by doping into amorphous poly(vinyl alcohol) matrix. In addition to the observed green and yellow afterglow emission with distinct irradiation-enhanced phosphorescence, the phosphorescence lifetime can be tuned by varying the irradiation period of 254 nm light. Significantly, the dynamic phosphorescence lifetime could be increased 14.3 folds from 58.03 ms to 828.81 ms in one of the obtained hybrid films after irradiation for 45 min under ambient conditions. As such, the application in polychromatic screen printing and multilevel information encryption is demonstrated. The extraordinary IRRTP in the amorphous state endows these systems with a highly promising potential for smart flexible luminescent materials and sensors with dynamically controlled phosphorescence.
The combination of circularly polarized luminescence (CPL) and pure-organic room temperature phosphorescence (RTP) potentially facilitates the construction of organic chiroptical optoelectronics and display materials, which however are challenging to use in realizing smart control of luminescent colors and switchable chiroptical properties. Here, we show a host-guest strategy to fabricate color-tunable RTP-based circularly polarized phosphorescence. Napthalimides were conjugated directly to chiral segments, of which supramolecular chirality and CPL activities in solid-states could be triggered by substituting bromine atoms on amines. Introducing tetracyanobenzene as an achiral host matrix via simple grinding would allow for the intersystem crossing to trigger red RTP and corresponding CPL by excitation lower than 320 nm, with a large Stokes shift more than 300 nm. The critical excitation wavelength of the RTP switch is determined by the absorbance of tetracyanobenzene. When the excitation wavelength was larger than 320 nm, blue fluorescence dominated with turned off RTP and CPL. The excitation wavelength-dependent RTP and CPL switch allows for detecting ultraviolet (UV) light, showing distinguishable red-blue luminescent color transition, accompanied by on/off RTP. Changing the host matrix from tetracyanobenzene to tricyanobenzene or dicyanobenzene could adjust the critical detecting wavelength limit from 320 to 300 nm. This work establishes a strategy to realize color-tunable, UV light detectable RTP and CPL under smart control.
The discrimination and quantification of the ingredients from natural medicines are a challenging issue due to their complicated and various structures. Metal–organic frameworks (MOFs) have shown great promise in sensing applications. Here, we report a fluorescent sensor array for rapid identification of some natural compounds using a sensor array composed of four kinds of lanthanide (Eu3+ and Tb3+) fluorescent MOFs (Ln-MOFs), which have diversified fluorescent responses to 26 active/toxic compounds including 12 saponins, 7 flavonoids, 3 stilbenes, and 4 anthraquinones. The fluorescence of the Ln-MOFs after reaction with the compounds was summarized as datasets and processed by principle component analysis (PCA) and hierarchical cluster analysis (HCA) methods. The corresponding responses of the 4 types of compounds are well separated on 2D/3D PCA score plots and HCA dendrograms. We have also tested typical blind samples by concentration-dependent PCA, and an accuracy of 100% was obtained. In addition, the response mechanisms of the Ln-MOFs to the compounds were also studied. Compared with traditional methods using liquid chromatography-mass spectrometry, the developed fluorescent sensor array provides a more efficient and economic strategy to discriminate various active/toxic ingredients in natural medicine.
Abstract Materials exhibiting ultralong luminescent lifetime show promising applications in the fields of information encryption, sensing, and bioimaging. Herein, we present a low‐cost and general strategy to achieve stimulus‐responsive ultralong organic phosphorescence (UOP) based on pyrene chromophores doped into polymer matrices. The UOP of the resulted systems presents radiation‐, concentration‐, time‐, and excitation‐dependent characteristics. The UOP color can be turned from blue to red by changing the excitation wavelength or the concentration of chromophores. Experimental results prove that these characteristics are attributed to the consumption of triplet oxygen and the different aggregation states of chromophores in the polymer matrices. Finally, we demonstrate that these systems could be applied for multilevel information encryption. This work would promote further development of multi‐responsive long‐lived luminescent materials.
Long-lived room temperature phosphorescence (RTP) materials are promising for applications in various fields including security information, medical diagnostics, and molecular imaging because of their unique optical properties. Previous RTP materials are mainly excited by ultraviolet light, while synthesizing long-lived RTP materials with visible-light-excitation remains a challenge. In particular, long-lived RTP materials that can be excited by green light are rare. Herein, a feasible and concise chemical strategy for constructing hydrogen-bonded frameworks in an aqueous environment is developed to fabricate large-size, green-light-excited, and excitation-dependent long-lived RTP carbon dot crystals (m,p/CDs-ME). The RTP performance of the crystals exhibits strong excitation wavelength dependence, leading to a full range of visible-light tuning from blue to red. Importantly, the maximum excitation wavelength of the RTP crystals is around 500 nm, thus successfully realizing green light excitation. m,p/CDs-ME presents long-lived phosphorescence (130 ms) under 500 nm excitation in aqueous solution, making it highly suitable for dopamine detection. This work not only provides a general guideline for the development of large size long-lived RTP crystals but also extends the operation scope of long-lived RTP materials in the detection of biomarkers by visible light excitation.
Room-temperature phosphorescence (RTP) materials have attracted much attention due to their unique luminescence properties. However, it is very challenging to tune the afterglow color of pure amorphous polymers by using only one kind of phosphor unit so far. Here, we proposed a strategy to induce pyrene derivatives (VPY) into the main chain of the polymer by free radical copolymerization, followed by alcoholysis to form poly(vinyl alcohol) derivative materials (PVA–PVPY) with strong hydrogen bond network structures. It was surprising that the obtained intrinsic polymers containing only one kind of phosphor unit achieved multicolor long-lived RTP. The RTP performance of the obtained polymers exhibited concentration, excitation, and time dependence. The experimental and theoretical results demonstrated that these characteristics were attributed to the different aggregated states of phosphor units in polymer chains, which revealed the luminescence mechanism of the aggregated and isolated states of phosphor units to produce multicolor RTP. In addition, we explored the application of these polymers based on color-tunable RTP properties in information encryption and flexible wearables. This strategy contributes to the development of multicolored smart luminescent materials as well as flexible wearable materials.
Polymer-based room-temperature phosphorescence (RTP) materials with high flexibility and large-area producibility are highly promising for applications in organic electronics. However, achieving such photophysical materials is challenging because of difficulties in populating and stabilizing susceptible triplet excited states at room temperature. Herein large-area, flexible, transparent, and long-lived RTP systems prepared by doping rationally selected organic chromophores in a poly(vinyl alcohol) (PVA) matrix were realized through a hydrogen-bonding and coassembly strategy. In particular, the 3,6-diphenyl-9H-carbazole (DPCz)-doped PVA film shows long-lived phosphorescence emission (up to 2044.86 ms) and a remarkable duration of afterglow (over 20 s) under ambient conditions. Meanwhile, the 7H-dibenzo[c,g]carbazole (DBCz)-doped PVA film exhibits high absolute luminance of 158.4 mcd m2 after the ultraviolet excitation source is removed. The RTP results not only from suppressing the nonradiative decay by abundant hydrogen-bonding interactions in the PVA matrix but also from minimizing the energy gap (ΔEST) between the singlet state and the triplet state through the coassembly effect. On account of the outstanding mechanical properties and the afterglow performance of these RTP materials, they were applied in the fabrication of flexible 3D objects with repeatable folding and curling properties. Importantly, the multichannel afterglow light-emitting diode arrays were established under ambient conditions. The present long-lived phosphorescent systems demonstrate a bright opportunity for the production of large-area, flexible, and transparent emitting materials.
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