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

We described a new approach to sensing of carbon dioxide based on photoinduced electron transfer (PET) quenching. Fluorophores like naphthalene and anthracene are known to be quenched by unprotonated amines by the PET mechanism. We examined the fluorescence spectral properties of two amine-containing fluorophores, 1-naphthylmetylamine (NMA) and 9-ethanolaminomethylanthracene (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 partial pressures of CO(2). The intensity and lifetime changes of NMA are completely reversible when CO(2) is removed by purging with argon. Our results are consistent with decreased quenching by the covalently linked amino groups when CO(2) 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 carbamate formation. In either event, these results suggest that CO(2) can be detected directly using amine-containing fluorophores without the use of bicarbonate and a pH-sensitive fluorophore.