Polymethine Dyes

Abstract

Polymethine dyes (PMDs) encompass a large class of linear, conjugated, colored systems in the general form of \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}${{(}{\rm{G^{\pm }_{1}}}{\relbar \kern-5pt{\relbar}\kern-7pt{\relbar}}{\hskip-7pt}{(}{\hskip0.167em}{\rm{CH}}{\raise1pt\hbox{$\Relbar \kern-4pt{\Relbar}$}}{\rm{CH}}{\relbar \kern-5pt{\relbar}\kern-7pt{\relbar}}{\hskip-9pt}{)}_{n}{\rm{CH}}{\raise1pt\hbox{$\Relbar \kern-4pt{\Relbar}$}}{\rm{G_{2}}}{)}{\rm{X^{\mp }}}}$\end{document} , where G 1 and G 2 are end groups. In the ground and first excited states, the carbon–carbon bonds within the polymethine chain are practically equalized and alternating positive and negative charges appear at the carbon atoms. The main topological factors affecting PMD color are chain length, nature of end groups, electron shell occupation, asymmetry, chain branching, and chromophore interaction. Polymethines are highly reactive compounds. Their photochemistry, protonation, and reactions with electrophiles, nucleophiles, reactants, and radicals are surveyed. The most important reason for the extremely wide technical uses of PMD is their low electron‐transition energies. Attention is paid to the application of polymethines as spectral sensitizers, laser dyes, and polymerization initiators. Synthetic methods for obtaining PMDs with various chain lengths, end groups, and chromophore modification are summarized, along with molecular designs and economic aspects.

Amidino Pentadienylium Salts − A New Cyanine Dye Type

“…The conjugation path and extends the charge delocalization. Absorption maxima are consequently shifted to longer most noteworthy features of the structure are, as expected, associated with the considerable electron density delocaliwavelengths (570Ϫ583 nm), while molar extinction coefficients decrease sharply [7] . zation due to the symmetry of the compound.…”

“…As reported in the MHz) literature [7] , on extending the conjugation path, the UV spectra of cyanine dyes exhibit a bathochromic shift and a The cation in 1b is distinctly non-planar. As in the case approximately planar geometry [the deviations from the best least-squares plane are within 0.259(4) Å ].…”