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 λem = 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 facilitate...

Reactivity-Based Detection of Copper(II) Ion in Water: Oxidative Cyclization of Azoaromatics as Fluorescence Turn-On Signaling Mechanism

The resonance Raman spectra of Orange II and Para Red: molecular structure and vibrational assignment

An efficient triple azo coupling reaction between anilines and phloroglucinol furnished a series of C3-symmetric molecules 7−9 supporting multiple conjugation pathways that converge at the molecular core. A combination of 1H/13C NMR spectroscopy, X-ray crystallography, and density functional theory computational studies provided a coherent picture of the [n,π]-conjugated molecular core, which is best described as the tris(hydrazone) [rather than tris(azo)] tautomer stabilized by resonance-assisted hydrogen bonding. For a homologous series of compounds, an increase in the torsional angles between the planar molecular core and the peripheral aryl groups results in a systematic blue shift in the low-energy electronic transitions (7, 523 nm; 8, 505 nm; 9, 445 nm in CHCl3) that qualitatively correlates with the shrinkage of effective conjugation through structural distortion. Similar spectral shifts could also be induced by amine substrates that interact with the intramolecular hydrogen-bonding network to trig...

J. Kelemen

Papers

Azo—hydrazone tautomerism in azo dyes. III. The tautomeric structure of 1-(4′-nitrophenylazo)-2-naphthylamine from crystal structure determination