Sensing of carbon dioxide by a decrease in photoinduced electron transfer quenching

We described a new approach to sensing of carbon dioxide based on photoindu ced electron transfer (PET) quenching. Fluorophores like naphthalene and an thracene are known to be quenched by unprotonated amines by the PET mechani sm. We examined the fluorescence spectral properties of two amine-containin g fluorophores, 1-naphthylmetylamine (NMA) and 9-ethanolaminomethylanthrace ne (EAA). When dissolved in an organic solvent, both fluorophores displayed increased intensity when equilibrated with gaseous carbon dioxide. In the case of NMA, we found that the mean lifetime increased with increasing part ial pressures of CO2. The intensity and lifetime changes of NMA are complet ely reversible when CO2 is removed by purging with argon. Our results are c onsistent with decreased quenching by the covalently linked amino groups wh en CO2 is dissolved in the solution. At present, we are not certain whether the increased intensity is due to protonation of the amino groups or to ca rbamate formation. In either event, these results suggest that CO2 can be d etected directly using amine-containing fluorophores without the use of bic arbonate and a pH-sensitive fluorophore. (C) 1999 Academic Press.