A Highly Fluorescent Azobenzene

Significance

The authors report the synthesis of a highly fluorescent boron-substituted azobenzene, (E)-[2-(4-methoxyphenylazo)phenyl]bis(pentafluorophenyl)borane. The boron-substituted azobenzene was synthesized by reacting (E)-2-iodo­azobenzene with n-BuLi and fluoroborane in Et₂O at -112 °C in 27% yield. The tight B-N coordination caused by fixation of the boron atom and the nitrogen atom at a suitable position to interact can provide more rigidity for the structure around the azo group. The enhanced rigidity of the structure suppresses the conformational change around the azo group and locks the photoisomerization process around the N-N double bond, which is the mechanism responsible for the very efficient radiationless deactivation and helps provide the extremely high fluorescent quantum yield.