Bis-diazo, triaryl and aryldiazo-N-arylphenazonium quencher moieties, substituted with electron-withdrawing and electron-donating substituents which induce polarity in the delocalized aryl/diazo ring systems, are useful as labels when attached to biomolecules such as polynucleotides, nucleosides, nucleotides and polypeptides. The quencher moieties are non-fluorescent and accept energy transfer from fluorescent reporter labels by any energy-transfer mechanism, such as FRET.Fluorescence quencher compositions are useful in preparing quencher labeled biomolecules for various molecular biology assays based on fluorescence detection.