The emission properties of ortho-phenylazo-phenols and naphthols

The fluorescence spectra of a series of orthohydroxy-arylazo compounds were investigated. Fluorescence was detected only in those derivatives known to exist either in tautomeric equilibrium with the corresponding phenylhydrazones, or only in that form. The emission is therefore ascribed to the hydrazone tautomer. There seems to be no evidence for emission from true arylazo compounds. Pronounced changes in absorption and emission spectra of 10⁻³ M solutions were observed at reduced temperatures, and are ascribed to aggregation phenomena.