Polymethine Styryl Dyes

Transition from spacers with flexible polymethine chains to V-substitucnts in which the sulfo group is rigidly arranged in space (CESD le,f), makes it possible to influence the efficiency of these photochemical reactions and also to change the route of transformation of CESD [15,24], Thus, upon irradiation with UV light reversible [2+2]-photocycloaddition reaction takes place only in case of styryl dye le with ortho-sulfobenzyl substituent. 

Dyes, polymethine used for dyes having at least one electron donor and one electron acceptor group linked by methine groups or aza analogues aUopolar cyanine, dye bases, complex cyanine, hemicyanine, merocyanine, oxonol, streptocyanine, and styryl. Supersensitization has been reported for these types—18 cites for cyanines, 3 for merocyanine, and 6 for all other polymethine types. 

In order to determine the structural factors maximizing 2PA cross section values, we analyze (8) from Sect. 1.2.1. For all cyanine-like molecules, symmetrical and asymmetrical, several distinct 2PA bands can be measured. First, the less intensive 2PA band is always connected with two-photon excitation into the main absorption band. The character of this 2PA band involves at least two dipole moments, /

symmetry forbidden for centro-symmetrical molecules, such as squaraines with C, symmetry due to A/t = 0, and only slightly allowed for polymethine dyes with C2V symmetry (A/t is small and oriented nearly perpendicular to /t01). It is important to note that a change in the permanent dipole moment under two-photon excitation into the linear absorption peak, even for asymmetrical D-a-A molecules, typically does not lead to the appearance of a 2PA band. 2PA bands under the main absorption peak are typically observed only for strongly asymmetrical molecules, for example, Styryl 1 [83], whose S0 —> Si transitions are considerably different from the corresponding transitions in symmetrical dyes and represent much broader, less intense, and blue-shifted bands. Thus, for typical cyanine-like molecules, both symmetrical and asymmetrical, with strong and relatively narrow, S (I > S) transitions, we observe... 

Uncharged styryl (methine) disperse dyes were originally introduced to provide greenish yellow colours on cellulose acetate fibres. One such dye still in use is Cl Disperse Yellow 31 (6.226), which is made by condensing 4-(N-butyl-N-chloroethylamino)benzaldehyde with ethyl cyanoacetate. Suitable compounds for polyester usually contain the electron-accepting dicyanovinyl group, introduced with the aid of malononitrile. An increased molecular size leads to improved fastness to sublimation, as in the case of Cl Disperse Yellow 99 (6.227). A novel polymethine-type structure of great interest is present in Cl Disperse Blue 354 (6.228), which is claimed to be the most brilliant blue disperse dye currently available [85]. 

Rettig W, Rurack K, Sczepan M (2001) From cyanines to styryl bases - photophysical properties, photochemical mechanisms, and cation sensing abilities of charged and neutral polymethinic dyes. In Valeur B, Brochon JC (eds) New trends in fluorescence spectroscopy applications to chemical and life sciences. Springer, Berlin, pp 125-155... 

From Cyanines to Styryl Bases -Photophysical Properties, Photochemical Mechanisms, and Cation Sensing Abilities of Charged and Neutral Polymethinic Dyes, in Valeur B. and Brochon J. C. (Eds),... 

For convenience, unsymmctrical PMDs should be considered as the derivatives of the corresponding symmetrical polymethines, commonly called parent dyes. In contrast to symmetrical compounds, unsymmclrical PMDs can contain an even number of methine groups in the polymethine chains, for example, styryls (7), where X = S. O, NCHx, C(CHy)2, or CH=CH and (8), where Y = O, S, Sc or NCHj. 



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