Abstract
The photobehaviour of four aza-analogues of EE-distyrylbenzene bearing the heteroatom in
the two side rings [1,4-di-(2-pyridylethenyl)benzene] or in the central ring [2,5-di-(phenylethenyl)pyridine,
2,6-di(phenylethenyl)pyridine and the corresponding diene, 2,6-di(phenylbutadienyl)pyridine] has been investigated
in aqueous solutions at pH 2 and 9, where the molecules are in mono-protonated and neutral
forms, respectively. The type of conjugation, linear for the first two compounds and crossed for the others,
is particularly important in determining the spectral and photochemical properties. The main effects of the
protic solvent are a reduction of the radiative deactivation, prevalent in the corresponding hydrocarbons, and
an increase of the reactive deactivation, very modest in the hydrocarbons. The increase in photoreactivity to
detriment of fluorescence, observed in protic medium with respect to non-polar solvents, is drastically emphasized
in acid medium where the fluorescence quantum yield decreases by an order of magnitude leading
to high values of the