The addition reaction of hydroxide or ethoxide ion with benzindolium heptamethine cyanine dyes

This paper pertains to a nucleophilic addition reaction at the C2 atom of a benz[c]indolium or 3,3-dimethyl-1H-benz[e]indolium subunit of the correspo nding near-infrared heptamethine cyanine that contains a chlorine atom at t he central meso position of the chromophore. An important finding is that t he efficient S(RN)1 replacement of the chloro substituent in such dyes is c ompletely suppressed in the reactions (i) of hydroxide and ethoxide ions, b oth of which are poor single electron donors and (ii) conducted in aqueous alcohol, a medium that does not promote single electron transfer. The adduc ts produced were isolated and characterized by elemental analysis, H-1 NMR, and C-13 NMR. The NIR-absorbing parent dye is regenerated quantitatively u pon treatment of the corresponding adduct with a weak acid, including silic a gel. (C) 2000 Elsevier Science Ltd. All rights reserved.