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Title
Japanese: 
English:Tetraaryldiborane(4) Can Emit Dual Fluorescence Responding to the Structural Change around the B–B Bond 
Author
Japanese: 庄子 良晃, 田中 直樹, Yasuhiro Ikabata, Hayato Sakai, Taku Hasobe, Norbert Koch, Hiromi Nakai, 福島 孝典.  
English: Yoshiaki Shoji, Naoki Tanaka, Yasuhiro Ikabata, Hayato Sakai, Taku Hasobe, Norbert Koch, Hiromi Nakai, Takanori Fukushima.  
Language English 
Journal/Book name
Japanese: 
English:Angewandte Chemie International Edition 
Volume, Number, Page Volume 61    Issue 1    e202113549
Published date Oct. 22, 2021 
Publisher
Japanese: 
English: 
Conference name
Japanese: 
English: 
Conference site
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Official URL https://onlinelibrary.wiley.com/doi/full/10.1002/anie.202113549
 
DOI https://doi.org/10.1002/anie.202113549
Abstract Newly synthesized tetramesityldiborane(4) shows exceptional chemical stability and blue/orange dual fluorescence capability associated with the B−B bond rotation in the excited state. The relative intensity of the dual fluorescence is sensitive to the viscosity of the medium, highlighting the potential of this diborane(4) as a ratiometric viscosity sensor. We report the successful synthesis of tetramesityldiborane(4) (Mes4B2) through the reductive coupling of a dimesitylborinium ion. Owing to the steric protection conferred by the mesityl groups, Mes4B2 shows exceptional chemical stability and remains intact in water. Single-crystal X-ray analysis revealed that Mes4B2 has an orthogonal geometry, where the B–B center is completely hidden by the mesityl groups. Remarkably, Mes4B2 emits dual fluorescence at 460 and 620 nm, both in solution and in the solid state. Theoretical calculations showed that Mes4B2 in the excited S1 state adopts a twisted or planar geometry, which is responsible for the shorter- or longer-wavelength fluorescence, respectively. The intensity ratio of the dual fluorescence is sensitive to the viscosity of the medium, which suggests that Mes4B2 has potential as a ratiometric viscosity sensor.

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