Abstract Condensation of 1,1-bis(4-dimethylaminophenyl)ethylene with substituted ketones in acetic anhydride in the presence of perchloric acid yielded NIR polymethine dyes. The VIS-NIR spectra of the dyes were measured and interpreted by the semiempirical AM1 method. The influence of molecular structure variations as well as of the electron density distribution, on the position of the peaks at longest wavelength has been studied. The results indicate that the additional (dimethylamino)phenyl bonded to C5 atom might lead to λmax increase. On the other hand, the use of substituents with higher electron donor or acceptor character should not significantly affect the position of λmax.