it is an object of the present invention to provide quenching or fluorescent nucleic acid base analogs and applications thereof . the quencher of the present invention has a 2 - nitropyrrole structure represented by formula i : ( in formula i , r 1 and r 2 are groups independently selected from the group consisting of : ribose and deoxyribose ; hydrogen , hydroxyl and sh groups , and halogens ; substituted or unsubstituted alkyl , alkenyl , and alkynyl groups each having 2 to 10 carbon atoms ; one or more five - membered heterocyclic rings , one or more six - membered heterocyclic rings , and one or more fused heterocyclic rings , these heterocylic rings containing nitrogen or sulfur , and one or more aromatic rings ; sugars , sugar chains , amino acids , and peptides ; and fluorescent molecules linked via linkers ).