Effects of protonation on the photophysical properties of pyridyl- and dimethylamino-diphenylhexatriene derivatives

The ultraviolet spectroscopic properties of pyridyl and dimethylamino derivatives of 1,6-diphenylhexa-1,3,5-triene and the changes in them following protonation are described. Heteroatom position dependent absorption and fluorescence shifts observed for protonated pyridyl derivatives are discussed with reference to corresponding stilbene analogues which have similar properties. Pyridylhexatrienes with additional nitro substituents have substantially modified absorption and fluorescence spectra, resembling those of nitrodiphenylhexatrienes. Dimethylamino derivatives show protonation modulated substituent effects of the photophysical properties of the parent molecule. These implicate an intramolecular charge-transfer excited state of the neutral form in which the substituent is the electron donor.