Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 16, Issue 17, Pages 5026-5035Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201000258
Keywords
azo compounds; boranes; fluorescence; fluorescent probes; substituent effects
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Funding
- Ministry of Education, Culture, Sports, Science and Technology, Japan
- Japan Society for the Promotion of Science
- JGC-S Scholarship Foundation
- Japan Society for the Promotion of Science for Young Scientists
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2-[Bis(pentafluorophenyl)-boryl]azobenzenes bearing hydrogen, methoxy, dimethylamino, trifluoromethyl, fluoro, n-butyl, and tert-butyldimethylsiloxy groups at the 4'-position or methoxy and bromo groups at the 4-position have been synthesized. The 4-bromo group of the 2-bory1-4-bromoazobenzene derivative was converted to phenyl and diphenylamino groups by palladium-catalyzed reactions. The absorption and fluorescence properties have been investigated using UV/Vis and fluorescence spectroscopy. The 2- borylazobenzenes emitted an intense green, yellow, and orange fluorescence, in marked contrast to the usual azobenzene fluorescence. The 4'-siloxy derivative showed the highest fluorescence quantum yield (0.90) among those reported for azobenzenes to date. The correlation between the substituent and the fluorescence properties was elucidated by studying the effect of the substituent on the relaxation process and from DFT and TD-DFT calculations. An electron-donating group at the 4'-position was found to be important for an intense emission. Application of fluorescent azobenzenes as a fluorescent vital stain for the visualization of living tissues was also investigated by microinjection into Xenopus embryos, suggesting these compounds are nontoxic towards embryos.
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