Synthesis of new pentacarbon chain streptocyanines (pentamethinium salts)

Fluorescent Streptocyanine Dyes: Synthesis and Photophysical Properties – Synthesis of a New Hemicarboxonium Salt

“…In recent years we have developed the synthesis of streptocyanine dyes from the reaction of penta- [7] , hepta- [8] and nonacarbon chain (9-C) carboxonium salts [9] with various nitrogen nucleophiles. So, the absorption wavelengths of these dyes can be tuned across the visible and near-infrared spectrum by changing the length of the conjugated chain and/or the terminal substituents.…”

Synthesis and Reactivity of a New Heptacarbon Chain Carboxonium Salt − Access to a New Class of Streptocyanine Dyes

“…[7] 5-C carboxonium salts are obtained by condensation of arylethanones with triethoxymethane in a strongly acidic medium. [8] Unfortunately, the absorption and fluorescence properties of these streptocyanine dyes proved to be still inadequate for near-infrared applications (the maximum absorption wavelength obtained is 600 nm).…”

“…[2,12] Based on these observations, we attempted the synthesis of a new heptacarbon chain (7-C) carboxonium salt 1 (Figure 1) and we report here the development of this original result. The replacement of triethoxymethane, which is used for the synthesis of the 5-C carboxonium salts, [7,8] by its vinylog, 1,3,3-triethoxypropene, does not lead to significant amounts of the expected 7-C carboxonium salt. It appears, surprisingly, that the presence of triethoxymethane is crucial, as we obtained pure 7-C carboxonium salt only with the following stoichiometry: triethoxymethane:4-methylphenylethanone:tetrafluoroboric acid 1:2:1.…”

Synthesis and Reactivity of a New Nonacarbon Chain Carboxonium Salt − Access to a New Class of Streptocyanine Dyes

“…[6,7] We had previously developed the synthesis of the pentacarbon (named 5-C) [8] and heptacarbon (named 7-C) [9] chain carboxonium salts ( Figure 1). Figure 1.…”

“…5-C (n ϭ 1) and 7-C (n ϭ 2) carboxonium salts [a] These salts react with various nitrogen nucleophiles to give 5-C and 7-C streptocyanines, with the maximum absorbance falling in the range 435 to 720 nm. [8,9] …”