L. Strekowski et al., The addition reaction of hydroxide or ethoxide ion with benzindolium heptamethine cyanine dyes, DYE PIGMENT, 46(3), 2000, pp. 163-168
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.