CruzQuench™ 4 azide is designed to be a superior quencher to ROX, TF4 and Texas Red®. TQ4 has (a). much stronger absorption; (b). much higher quenching efficiency; and (c). versatile reactive forms with desired solubility for labeling oligonucleotides and peptides. This TQ4 product is reactive to alkynes, and useful for click chemistry.