Bis(dicyanoinethylene) and Bis(cyanoimino) Derivatives of Indigo and Thioindigo

摘要

Indigo and related compounds are of great technical importance owing to their properties as dyes. The indigo chromophore giving this class of relatively small and simple molecules their characteristic intense color has been the subject of numerous investigations. Surprisingly, no indigo derivatives are known in which the O atoms of the carbonyl groups have been replaced by other electron-withdrawing groups. We report here on our successful synthesis of compounds of this type. In our studies we focused on dicyanomethylene and cyanoimi-no groups, in particular, as acceptor groups. (The analogy between dicyunovinyl and carbonyl functions was discussed in detail previously.) Since these groups extend the it-electron system, it was expected that the resulting chromogens would absorb at longer wavelengths, possibly even in the near-IR (> 700 nm). An additional bathochromic shift due to the twist of the compounds about the central double bond as a result of steric repulsion may also contribute (cf. ref. ).