Dabcyl deoxythymidine (Dabcyl-dT) is classified as a dark quencher (a non-fluorescent chromophore) nucleotide base, and is typically used to internally label a Fluorescence Resonance Energy Transfer (FRET) DNA oligonucleotide probe with a quencher moiety. Such a labeling strategy is pertinent in cases where the distance between the quencher and fluorophore needs optimization for efficient quenching. Other basic technical information about Dabcyl is found in the Dabcyl-3’ technical sheet.