Bis(1,3-dithiole) Polymethine Dyes for Third-Order Nonlinear Optics – Synthesis, Electronic Structure, Nonlinear Optical Properties, and Structure-Property Relations

Autor: Simonsen, Klaus Bæk, Geisler, Tommy, Petersen, Jan Conrad, Arentoft, Jesper, Sommer-Larsen, Peter, Greve, Daniel Rodriguez, Jakobsen, Christian, Becher, Jan, Malagoli, Massimo, Brédas, Jean Luc
Zdroj: European Journal of Organic Chemistry; December 1998, Vol. 1998 Issue: 12 p2747-2757, 11p
Abstrakt: The synthesis of a series of new sulfur-containing polymethine dyes is reported. The linear optical properties of these bis(1,3-dithiole) (mono-, tri-, penta-, and hepta-)methine dyes show intense and narrow optical absorptions typical of cyanine dyes. The absorption maximum is increasingly red-shifted from 489 nm for the monomethine dye to 911 nm for the heptamethine compound. Based on third-harmonic generation measurements at fundamental wavelength between 1064 nm and 1907 nm, γ values were evaluated to lie in the range between 1·10–33 e.s.u. and 14·10–33 e.s.u. showing that the nonlinear response of the bis(1,3-dithiole) polymethine dyes compare well with other organic π-electron systems of similar size. Comparisons of the experimental values of γ to calculated static values obtained by ab initio and semiempirical calculations (AM1, PM3) have been made as well as comparisons to dynamic values estimated from a free-electron model. The computed dynamic values can be described by a power law; γ ≈ L5 where L denotes the length of the molecules. Our studies confirm the stabilizing effect of a carbocyclic ring in the cyanine backbone making the heptamethine dye an unusually stable and highly nonlinear polymethine chromophore possessing a strong NIR optical transition and very good transparency in the visible region.
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