Condensation of 1,1-bis(4-dimethylaminophenyl) ethylene with substituted ke
tones in acetic anhydride in the presence of perchloric acid yielded NIR po
lymethine dyes. The VIS-NIR spectra of the dyes were measured and interpret
ed by the semiempirical AM1 method. The influence of molecular structure va
riations as well as of the electron density distribution, on the position o
f the peaks at longest wavelength has been studied. The results indicate th
at the additional (dimethylamino)phenyl bonded to C-5 atom might lead to la
mbda(max), increase. On the other hand, the use of substituents with higher
electron donor or acceptor character should not significantly affect the p
osition of lambda(max). (C) 1998 Elsevier Science Ltd. All rights reserved.