Newly substituted pentamethine merocyanines. Part 1: Synthesis, physical properties, and synthetic applications

New 1,5-substituted pentamethine merocyanine dyes were synthesised in high yields. Their reaction towards acid chlorides or anhydrides leads to new hemicarboxonium salts with enhanced reactivity due to their better leaving groups. They are able to combine with soft nucleophiles to obtain a new cyanine dyes series. Thus, these merocyanines may be used as stable intermediate reagents in cyanine synthesis. Moreover, from a theoretical point of view, the synthesis of substituted derivatives of the well-known polyenic donor acceptor models for non-linear optics, opens the route to physicochemical determinations of their effects on the polarisation of the chain and the bond length alternation (Part 2 of study in progress).