pH-Dependent fluorescence and singlet energy transfer in water-soluble polymers containing eosin and phenol red chromophores.

The pH-dependent fluorescence and energy transfer properties of water-soluble polyacrylamide labeled with a donor (eosin) and acceptor (phenol red) were studied. Eosin emission intensity decreases with pH increases. This observation corresponds to the expectation that the fluorescence intensity of eosin should diminish with pH increases resulting from increased spectral overlap between dyes. The lower energy transfer efficiency compared to a pH sensor made with the same polymer, but with a cross-linker, can be explained by the larger distances between the two chromophores resulting from conformational flexibility and electrostatic repulsion of the chromophore ions.