Biomarkers for phenolic carcinogen exposure, 8-(4' '-hydroxyphenyl)-2'-deoxypurines, have been found to possess pH-sensitive fluorescent properties. Phenolic ionization constants (pK(a)) establish substituent (sigma(-)) constants of 0.46 for N1-Me-dG and 0.55 for dA. Their fluorescent properties prompted the synthesis of 4 that possesses fluorescent pH sensing in the physiological pH region. Our results demonstrate the potential utility of these adducts for pH sensing within nucleic acids, as well as establishing a basis for phenol-mediated carcinogenesis.