SYNTHESIS AND ELECTRONIC STRUCTURE OF POTENTIALLY VALENCE ISOMERIC 1,2-DITHIOLYLIUM-4-OLATES

Abstract

Methylthio substituted 1,2-dithiolylium-4-olates 1 are obtained by thiolation of 1,3-dichlorpro pane-2-one or pyruvic thiomorpholide with sulfur and triethylamine in dimethylformamide and subsequent alklyation. Aminolysis yields the amino substituted derivatives. IR and UV/VIS spectra of the bis(methylthio), methylthio dimethylaminophenyl and bis(dimethylaminophenyl) compounds provide evidence in favour of the cyclic structure 1 whereas the spectra of the bis(amino) and amino methylthio compounds are rather compatible with non-cyclic valence isomeric structures 2. Both 1 and 2 react with acids to form 4-hydroxy-1,2-dithiolylium salts. The colour-structure relationships of 1,2-dithiolylium-4-olates were examined by PPP-type calculations. The lowest excited states and the colour determining transitions are accounted for in terms of the dithiolylium and olate moieties. The negative solvatochromism of the colour bands of 1 is related to the marked amount of oxygen-to dithiolylium charge transfer of the lowest-excited π→π∗ transition. In larger molecules such as 1h the colour is governed by the lowest electronic transition of polymethine-type subchromophores rather than that of the intramolecular charge transfer chromophores and, therefore are pertinent to cyaninedyes.