Quasi-Intrinsic Fluorescent Probes for Sensitive Detection of the Carcinogenic DNA Adduct ABPdG via Push–Pull Electronic Effect-Mediated Intermolecular Charge Transfer

N'-(2'-Deoxyguanosin-8-yl)-4-aminobiphenyl (ABPdG) is the major guanine adduct-linked aromatic amine from rubber manufacturing, dye production, and tobacco smoke. The selective detection of the 4-aminobiphenyl biomarker in DNA could provide mechanistic understanding on mutagenesis and the related cancer risk. In this work, a set of quasi-intrinsic fluorescent cytosine analogues are proposed to identify ABPdG via Watson-Crick H-bonds without disrupting the native DNA double helix. Compared with natural cytosine, these analogues possess red-shifted absorption that contributes to the selective photoexcitation. More importantly, the modifications could bring efficient fluorescence quantum yields and short fluorescence lifetimes due to the additional π-conjugation. Differing from the insensitive fluorescence of these optical probes responsible for the presence of the natural G-base, the photoluminescence tends to be quenched after pairing with targeted ABPdG under the excited-state intermolecular charge transfer (ESICT) mechanism. The effects of electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) on ESICT are further examined. It is revealed that the EDG substitution could strengthen the intermolecular hydrogen bonds between paired bases, thus driving the ESICT-induced fluorescence quenching. Moreover, the spectral characters with linking deoxyribose are investigated to evaluate the direct usefulness of the proposed C-analogues in a biological environment.