pH:

Relatively little changes in pH could sometimes cause substantial changes within the fluorescence intensity and spectral features of fluorescence. For example, serotonin displays a shift in fluorescence emission maximum from 330 nm at neutral pH to 550 nm within strong acid without any change within the absorption spectrum. In the molecules containing acidic or primary functional groups, the changes within pH of the medium change the degree of ionisation of the functional groups. This in turn might affect the extent of conjugation or the aromaticity of the molecule that affects its fluorescence. For instance, aniline shows fluorescence although in acid solution it does not show fluorescence because of the formation of anilinium ion. Thus, pH control is necessary while working with such molecules and suitable buffers should be employed for the reasons.