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Fluorescence spectroscopy was used to study carcinogen-induced conformational heterogeneity in DNA duplexes. The fluorophore 2-aminopurine (AP) was incorporated adjacent (5′) to the lesion (G*) in eight different DNA duplexes [d(5′-CTTCTPG*NCCTC-3′):d(5′-GAGGNXTAGAAG-3′), G* = FAF adduct, P = AP, N = G, A, C, T, and X = C, A] modified by FAF [N-(2′-deoxyguanosin-8-yl)-7-fluoro-2-aminofluorene], a fluorine-tagged model DNA adduct derived from the potent carcinogen 2-aminofluorene. Steady-state measurements showed that fluorescence intensity and Stern−Volmer constants (Ksv) derived from acrylamide quenching experiments decreased for all carcinogen-modified duplexes relative to the controls, which suggests greater AP stacking in the duplex upon adduct formation. Conformation-specific stacking of AP with the neighboring adduct was evidenced by a sequence-dependent variation in fluorescence intensity, position of emission maximum, degree of emission quenching by acrylamide, and temperature-dependent spectral changes. The magnitude of stacking was in the order of FAF residue in base-displaced stacked (S) > minor groove wedged (W) > major groove B type (B). This work represents a novel utility of AP in probing adduct-induced conformational heterogeneities in DNA duplexes.