Photoinduced phenomena in water solution of melamine explaining the photostability of the compound.

Two tautomers of melamine (triamino and imino-diamino) were studied at the BLYP/aug-cc-pVDZ theoretical level. It was found that the two tautomers are bridged with the 1πσ* excited-state reaction path. The high photostability of melamine in water solution was explained with the mechanism of ring deformation which occurs along the 1ππ* excited-state reaction path. The two mechanisms are investigated at the TD BLYP level of theory using the linear interpolation in internal coordinates approach.