title: Reactivity-based detection of copper(II) ion in water: oxidative cyclization of azoaromatics as fluorescence turn-on signaling mechanism.
abstract: 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 μM-level concentrations of copper(II) ion in water (pH = 6-8) at room temperature to elicit >80-fold enhancement in the green emission at λ(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.
authors.affiliation: Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States.
authors.forename: Junyong
authors.initials: J
authors.lastname: Jo
authors.forename: Ho Yong
authors.initials: HY
authors.lastname: Lee
authors.forename: Wenjun
authors.initials: W
authors.lastname: Liu
authors.forename: András
authors.initials: A
authors.lastname: Olasz
authors.forename: Chun-Hsing
authors.initials: CH
authors.lastname: Chen
authors.forename: Dongwhan
authors.initials: D
authors.lastname: Lee
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D003300:Copper / Q000032:analysis*; D018360:Crystallography, X-Ray; D003500:Cyclization; D005453:Fluorescence; D010084:Oxidation-Reduction; D014867:Water / Q000737:chemistry*
chemical_list: D001391:Azo Compounds; D014867:Water; D003300:Copper