CruzQuench™ 2 succinimidyl ester is designed to be a superior quencher to FAM, HEX, TET, JOE, CFLsm2 and rhodamine 6G. CQ2 has (a). much stronger absorption; (b). much higher quenching efficiency; and (c). versatile reactive forms with desired solubility for labeling oligonucleotides and peptides. This CQ2 product is primarily used for labeling peptides. It is also used for post-labeling of amino-modified oligonucleotides.