Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 134, Issue 38, Pages 16000-16007Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja307316s
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- DTRA/ARO [W911NF-07-1-0533]
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An oxidative cyclization reaction transforms nonemissive azoanilines into highly fluorescent benzotriazoles. We have found that introduction of multiple electron-donating amino groups onto a simple o-(phenylazo)aniline platform dramatically accelerates its conversion to the emissive polycyclic product. Notably, this chemistry can be effected by mu M-level concentrations of copper(II) ion in water (pH = 6-8) at room temperature to elicit >80-fold enhancement in the green emission at lambda(em) = 530 nm. Comparative kinetic and electrochemical studies on a series of structural analogues have established that the accelerated reaction rates correlate directly with a systematic cathodic shift in the oxidation onset potential of the azo precursors. In addition, single-crystal X-ray crystallographic analysis on the most reactive derivative revealed the presence of a five-membered ring intramolecular hydrogen-bonding network An enhanced contribution of the quinoid-type resonance in such conformation apparently facilitates the mechanistically required proton transfer step, which, in conjunction with electron transfer at lower oxidation potential, contributes to a rapid cyclization reaction triggered by copper(II) ion in water.
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