Cyanine dye system

FIGURE 14.16 Model to explain exciton quenching dynamics in PPE-S03 /cyanine dye systems, (a) Single (una egated) chains (b) aggregated polymer. (Reprinted from Tan, C, E. Atas, J.G. Muller, M.R. Pinto, V.D. Kleiman, and K.S. Schanze. /. Am. Chem. Soc., 126, 13685-13694, 2004. With permission.)... 

Figure 3.28 A model cyanine dye system (a) A 6 electron in 5 orbital model cyanine system showing two formal VB structures, (b) the formal cis-trans isomerization coordinate (see next figure) (c) the branching-space vectors, which correspond to symmetric and antisymmetric skeletal deformation of the sigma frame (the symmetric motion connects the two VB structures shown in part (a).)...

The color and constitution of cyanine dyes may be understood through detailed consideration of their component parts, ie, chromophoric systems, terminal groups, and solvent sensitivity of the dyes. Resonance theories have been developed to accommodate significant trends very successfully. For an experienced dye chemist, these are useful in the design of dyes with a specified color, band shape, or solvent sensitivity. More recendy, quantitative values for reversible oxidation—reduction potentials have allowed more complete correlation of these dye properties with organic substituent constants. 

More recent research provides reversible oxidation-reduction potential data (17). These allow the derivation of better stmcture-activity relationships in both photographic sensitization and other systems where electron-transfer sensitizers are important (see Dyes, sensitizing). Data for an extensive series of cyanine dyes are pubflshed, as obtained by second harmonic a-c voltammetry (17). A recent "quantitative stmcture-activity relationship" (QSAR) (34) shows that Brooker deviations for the heterocycHc nuclei (discussed above) can provide estimates of the oxidation potentials within 0.05 V. An oxidation potential plus a dye s absorption energy provide reduction potential estimates. Different regression equations were used for dyes with one-, three-, five-methine carbons in the chromophore. Also noted in Ref. 34 are previous correlations relating Brooker deviations for many heterocycHc nuclei to the piC (for protonation/decolorization) for carbocyanine dyes the piC is thus inversely related to oxidation potential values. 

A useful classification of sensitizing dyes is the one adopted to describe patents in image technology. In Table 1, the Image Technology Patent Information System (ITPAIS), dye classes and representative patent citations from the ITPAIS file are Hsted as a function of significant dye class. From these citations it is clear that preferred sensitizers for silver haUdes are polymethine dyes (cyanine, merocyanine, etc), whereas other semiconductors have more evenly distributed citations. Zinc oxide, for example, is frequendy sensitized by xanthene dyes (qv) or triarylmethane dyes (see Triphenylmethane and related dyes) as well as cyanines and merocyanines (see Cyanine dyes). 

Ethyl iodide and 5-amino-2-methyl-l,3,4-thiadiazole react at 110° to give the N-3 salt (78 R = Me, R = NH2, R" = Et), as shown by the presence of the very reactive methyl group this salt is also used to prepare cyanine dyes. The slow quatemization at the ring-nitrogen atom furthest from the amino group is consistent with the reactions observed in other ring systems. As would be e pected, 5-alkylthio-2-methyl-l,3,4-thiadiazoles form salts at the N-3 (78 R = Me, R - S-alkyl).i ... 

Humphry-Baker R, Gratzel M, Steiger R (1980) Drastic fluorescence enhancement and photochemical stabilization of cyanine dyes through micellar systems. J Am Chem Soc 102(2) 847-848... 

Cyanine dyes have the common molecular formula R2N [CH=CH]nCH=N+R2 where the mono- or poly-methine chain is flanked by two nitrogen atoms that form part of a heterocyclic system (see Fig. 6.6). The most common cyanine derivatives used for labeling molecules are Cy3 and Cy5. These are symmetrical... 

Figure 9.51 Time-resolved FRET assay systems involve energy transfer between the lanthanide chelate and an organic dye that are brought together as two labeled molecules bind to an analyte. In this illustration, an antibody labeled with a lanthanide chelate is used along with a Cy5-labeled antibody to detect a protein target in solution. Excitation of the lanthanide label results in energy transfer and excitation of the cyanine dye only if they are held within close enough proximity to allow efficient FRET to occur. Under these conditions, excitation of the lanthanide chelate results in cyanine dye emission, which will not occur if the labeled antibodies have not bound to a target.

Organic fluorescent dyes with the appropriate spectral properties also can be paired with lanthanide chelates in FRET systems. For instance, many rhodamine dyes and the cyanine dye Cy5 have ideal excitation wavelengths for receiving energy from a nearby europium chelate. The LeadSeeker assay system from GE Healthcare incorporates various Cy5-labeled antibodies for developing specific analyte assays. In addition, if using a terbium chelate as the donor, then a Cy3 fluorescent dye can be used in assays as the acceptor. 

Biver, T., De Biasi, A., Secco, E, Venturing M., and Yarmoluk, S. (2005) Cyanine dyes as intercalating agents Kinetic and thermodynamic studies on the DNA/Cyan40 and DNA/CCyan2 systems. Biophys. J. 89, 374-383. 

The spectra of linear polyenes are modelled well as one-dimensional free-electron systems. The cyanine dyes are a classical example. They constitute a class of long chain conjugated systems with an even number n of 7r-electrons distributed over an odd number N = n — 1 of chain atoms. The cyanine absorption of longest wavelength corresponds to promotion of an electron from the highest occupied energy level, En/2 to the lowest unoccupied level, such that in terms of a free-electron model... 

The first cyanine dye was made in 1856 by Greville Williams. Thus the blue charge-resonance system 6.216 was produced when oxidative coupling took place between N-... 

Stabilization of the redox cycle is relatively important in construction of potentially useful electrochromic materials, because the molecules needed for application require high redox-stability. Recently, S. Hiinig et al. proposed the concept of violene-cyanine hybrid to produce stabilized organic electrochromic materials (3). The hybrid is constructed by a violene-type redox system containing delocalized closed-shell polymethine dyes as end groups. The hybrid is expected to exhibit the color of a cyanine dye, by an overall two-electron... 

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