heynderickx arnault CINaM

The photoinduced proton transfer (PIPT) reaction occurring in 2-(2’,4’-dinitrobenzyl)pyridine (a-DNBP) and in some of its derivatives has drawn much attention due to the potential applications of these compounds as optically bistable systems for optical data storage, in holography, and as optical switching devices[].
For these applications, a lot of effort has been focused on the optimization of the efficiency of the photoreaction, the increase of the lifetime of the metastable form and a best understanding of the PIPT mechanism.
The pathways leading to the phototautomers of a-DNBP and the structure of the different tautomers [1c] are presented in figure 1.

New benzylpyridines, substituted either by sulfoxide or sulfone group in ortho position to the benzyl hydrogen, have been synthesized starting from 2-lithiopyridine.
It has been observed that 2-(2’,4’-diphenylsulfonyl) pyridine 17 underwent a reversible photoinduced proton transfer reaction in the crystalline phase as well as in ethanolic solution at ambient temperature.
The metastable coloured form was attribued to a “NH” quinoid tautomer.
It was concluded that contrarily to what was generally assumed, the presence of a nitro group on the ortho position of the benzyl group is not a necessary condition to provide proton transfer upon UV irradiation.