Cyanine dyes, resonance

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. 

Structural hybrid, in resonance theory. 69 Structures, of dyes, in relation with elecuo-chemical potential. 75 extreme of cyanine dyes, 69 Styryl compounds, nomenclature of, 29 Styryl dyes, in basicity scale, 71 with dialkylamino group, 77 as models in relation with pKa, 50 and role of anhvdrobases. 50 as sensitizers, in photography. 79 stereo aspect of condensation. 50 synthesis of, 49... 

Symmetrical cyanine dyes, because of the resonance shown in Figure 6.4 (in which the two contributing structures are exactly equivalent), are completely symmetrical molecules. X-ray crystal structure determinations and NMR spectroscopic analysis have demonstrated that the dyes are essentially planar and that the carbon-carbon bond lengths in the polymethine chain are uniform. The colour of cyanine dyes depends mainly on the nature of the terminal groups and on the length of the polymethine chain. The bathochromicity of the dyes is found to increase... 

Figure 6.4 Valence-bond (resonance) approach to cyanine dyes...

The valence-bond (resonance) description of the triphenylmethine dye Malachite Green (125) is illustrated in Figure 6.5. Comparison with Figure 6.4 reveals their structural similarity compared with cyanine dyes. Formally, the dye contains a carbonium ion centre, as a result of a contribution from resonance form II. The molecule is stabilised by resonance that involves delocalisation of the positive charge on to the p-amino... 

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-... 

Theoretical trend of dipole moment in donor- and acceptor-bisub-stituted oligoacetylene, with varying bond length alternation, (BLA) from the undissociated state (D=-—A) where, by convention, BLA > 0, through a resonant state with equal bond lengths (cyanine dye D.A BLA = 0), to the zwitter-... 

Ficken and Kendall " discuss the relative basicities of the pyridine and pyrrolenine nitrogen atoms in the azaindolenines (Scheme 7) based on Brooker deviation measurements from light-absorption data of their cyanine dyes. These indicate that N(7 in the 7-azaindolenine (31) is considerably more basic than N(d in the sense that the 7-quaternary salt (117) displays less tendency to be stabilized by a isomerization than does the 1-quaternary salt (120). They relate this to the formation of an unstable o-quinonoid resonance form. In the case of the 4-azaindolenine (32), it was suggested that the pyridine N(4) is expected to be more basic than N(X), although reaction 12 J. Clark and D. D. Perrin, Quart. Rev. London) 18, 295 (1964). 

Crystal violet, a trigonal conjugated cationic dye with electronic CT from peripheral dimethylamino donor groups to an electron deficient sp hybridized central carbon atom. A resonantly enhanced (3 value of 580 x 10 ° esu has been reported at 1.064 nm, in acetone solution = 590 nm) by Zyss et al. [16] The 1st hyperpolarizability, p, of crystal violet dye was measured at 1450 and 1500 nm by Rao et al. [91]. The resonance-free P value, p(°) for this octupole is comparable with that of the dipolar dye Disperse Red 1 but with the nonlinearity-transparency trade-off worse for the octupole. Symmetric cyanine dyes of the kind Me2N+ CH-(CH CH)n-NMe2 normally exhibit no first hyperpolarizabilities but have relatively long absorption... 

An exhaustive study of the relationship between resonance and colour was made by Booker et al. Rev. Mod. Phys., 1942, 275 et seq.).The basis from which they started was that a simple cyanine dye would be a resonance hybrid of (15) and (16)... 

Pyrvinium (Table 7-10) is an unsymmetrical red cyanine dye whose amidinium ion system exhibits unusual resonance (Eq. 7.12). Its mechanism of action is not fully understood, nor has it recently been investigated. It was shown to interfere irreversibly with glucose absorption and has been effectively used in the treatment of pinworms and threadworms, which both reside in the low-oxygen environment of the human intestine. Under more aerobic conditions of filarial worms similar dye compounds have been found to inhibit oxygen consumption. 

The kinetics of the photoisomerization of bilirubin has been studied because of the relevance to phototherapy. The fluorescence of bilirubin increases on binding to human serum albumin. This and other primary photoprocesses have been investigated by picosecond spectroscopy. Karvaly has put forward a new photochemical mechanism for energy conversion in bacteriorhodopsin. An extensive review of the photophysics of light transduction in rhodopsin and bacteriorhodopsin has been made by Birge. The dynamics of cis-trans isomerization in rhodopsin has been analysed by INDO-CISD molecular orbital theory. Similar calculations on polyenes and cyanine dyes have also been reported. A new picosecond resonance Raman technique shows that a distorted... 

FIGURE 93 Forster resonant energy transfer between an LLB bioconjugated to a biotinylated antibody and a cyanine dye coupled to another biotinylated antibody. 

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