Spectral Luminescent Properties and Nature of Electronically Excited States of Sulfaguanidine in Water

The absorption and fluorescence spectra of sulfaguanidine, its complexes with hydrogen bonds, and doubly charged cationic forms have been studied experimentally and theoretically. The orbital nature of electronically excited states is established and a theoretical interpretation of the absorption and fluorescence spectra is given. It was shown that the main reason for the anomalously large Stokes shift of fluorescence is the rearrangement of the benzoid structure of the phenyl fragment of sulfaguanidine into a quasi-quinoid one. The influence of the formation of hydrogen bonds and the addition of a proton on the amount of charge transfer between weakly bound fragments of the molecule has been established.