This paper describes conjugated polymers with 2,5-diarylfuran moieties as nonconjugated pendants that respond to singlet oxygen (O-1(2)) by fluorescence quenching. By oxidizing the diarylfurans to more electron-poor moieties such as enol esters, singlet oxygen causes poly(fluorene-co-phenylene) conjugated backbones to donate excited electrons to the oxidized pendants, resulting in quenching of up to 93% of the initial fluorescence of the polymer, while an analogous furan-substituted poly(phenylene-ethynylene) showed no quenching upon furan-O-1(2) reaction. All furan derivatives reacted rapidly with O-1(2) (k = 10(7)-10(8) M-1 s(-1)), with more electron-poor furans reacting more slowly, but yielding more efficient fluorescence quenching, than less electron-poor furans.