PET photoinduced electron transfer pH indicators

Most fluorescent PET molecular sensors, including pH indicators of this type, consist of a fluorophore linked to an amine moiety via a methylene spacer. Photo-induced electron transfer (see Chapter 4, Section 4.3), which takes place from amino groups to aromatic hydrocarbons, causes fluorescence quenching of the latter. When the amino group is protonated (or strongly interacts with a cation), electron transfer is hindered and a very large enhancement of fluorescence is observed. 

Examples of PET pH indicators are given in Eigure 10.2 (dass C). The pfCa values of compounds P-9, P-10 and P-11 are 4.4, 7.2 and 5.9, respectively, in water-methanol (4 1, v/v), and the value is 9.6 for compound P-12 in water-ethanol (1 1, v/v). The latter offers the advantage of long wavelength excitation ( 500 nm). 

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