A highly selective multi-responsive fluorescence sensor for Zn2+ based on a diarylethene with a 4,6-dimethylpyrimidine unit

A novel turn-on mode fluorescent diarylethene containing a 4,6-dimethylpyrimidine unit was developed to fluorescently sense Zn2+. Its multiple-responsive properties induced by Zn2+/EDTA and ultraviolet/visible light have been systematically studied. The fluorescence sensor could efficiently detect Zn2+ with a 10 times enhancement of emission intensity and fluorescence color change (dark-green). In addition, the sensor showed clear discrimination from Cd2+. The limit of detection of the sensor was measured to be 8.48 × 10-8 mol L-1 for Zn2+. Finally, a molecular logic circuit was fabricated with the emission at 528 nm as the output signal and light and chemical stimuli as input signals.

Visualization and Manipulation of Molecular Motion in the Solid State through Photoinduced Clusteroluminescence

The development of molecular machines has long been a dream of scientists and is expected to revolutionize many aspects of technology and medicine. As the prerequisite of a practicable molecular machine, studies on the solid-state molecular motion (SSMM) are not only of scientific importance but also practically useful. Herein, two nonconjugated molecules, 1,2-diphenylethane (s-DPE) and 1,2-bis(2,4,5-trimethylphenyl)ethane (s-DPE-TM), are synthesized, and their SSMM is investigated. Experimental and calculation results reveal that s-DPE and s-DPE-TM are capable of performing light-driven SSMM to form excited-state through-space complexes (ESTSC). The radiative decay of ESTSC generates an unexpected visible emission termed clusteroluminescence, which serves as a tool to visualize the process of SSMM. Meanwhile, the original packing structure can be recovered from ESTSC after the removal of light irradiation. This work provides a new strategy to manipulate and "see" the SSMM and gains new insights into clusteroluminescence.

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

Background: Diarylethenes are well-known photochromic compounds, which undergo cyclization and cycloreversion reactions between open- and closed-ring isomers. Recently, diarylethene derivatives with photoswitchable fluorescent properties were prepared. They are applicable for fluorescence imaging including bio-imaging. On the other hand, a new system called “excited state intramolecular proton transfer (ESIPT)” is reported. In the system, absorption and emission bands are largely separated due to the proton transfer, hence it showed strong fluorescence even in the crystalline state. We aimed to construct the photochromic system incorporating the ESIPT mechanism.

Results: A diarylethene incorporating a fluorescent moiety that exhibit ESIPT behavior was prepared. The ESIPT is one of the examples which express the mechanisms of aggregation-induced emission (AIE). This compound emits orange fluorescence with a large Stokes shift derived from ESIPT in aprotic solvents such as THF or hexane, while it exhibits only a photochromic reaction in protic solvents such as methanol. In addition, it shows turn-off type fluorescence switching in an aprotic solvent and in crystals. The fluorescence is quenched as the content of closed-ring isomers increases upon UV light irradiation.

Conclusions: A diarylethene containing an ESIPT functional group was prepared. It showed fluorescent turn-off behavior during photochromism in aprotic solvents as well as in crystalline state upon UV light irradiation. Furthermore, it showed AIE in THF/water mixtures with blue-shift of the emission.

Efficient “turn-off” fluorescence photoswitching in a highly fluorescent diarylethene single crystal

Efficient “turn-off” fluorescence photoswitching with full reversibility was successfully demonstrated in a fluorescent diarylethene single crystal.

Photoswitchable Fluorescent Diarylethene Derivatives with Thiophene 1,1-Dioxide Groups: Effect of Alkyl Substituents at the Reactive Carbons

Photoswitching and fluorescent properties of sulfone derivatives of 1,2-bis(2-alkyl-4-methyl-5-phenyl-3-thienyl)perfluorocyclopentene, 1–5, having methyl, ethyl, n-propyl, i-propyl, and i-butyl substituents at the reactive carbons (2- and 2′-positions) of the thiophene 1,1-dioxide rings were studied. Diarylethenes 1–5 underwent isomerization reactions between open-ring and closed-ring forms upon alternate irradiation with ultraviolet (UV) and visible light and showed fluorescence in the closed-ring forms. The alkyl substitution at the reactive carbons affects the fluorescent property of the closed-ring isomers. The closed-ring isomers 2b–5b with ethyl, n-propyl, i-propyl, and i-butyl substituents show higher fluorescence quantum yields than 1b with methyl substituents. In polar solvents, the fluorescence quantum yield of 1b markedly decreases, while 2b–5b maintain the relatively high fluorescence quantum yields. Although the cycloreversion quantum yields of the derivatives with methyl, ethyl, n-propyl, and i-propyl substituents are quite low and in the order of 10⁻⁵, introduction of i-butyl substituents was found to increase the yield up to the order of 10⁻³. These results indicate that appropriate alkyl substitution at the reactive carbons is indispensable for properly controlling the photoswitching and fluorescent properties of the photoswitchable fluorescent diarylethenes, which are potentially applicable to super-resolution fluorescence microscopies.