Cyanine dyes association

SPECTROPHOTOMETRIC DETERMINATION OF PHOSPHATE AND ARSENATE IONS BY MEANS OF IONIC ASSOCIATES OF CYANINE DYES WITH POLYOXOMETALATES... 

Phthalocyanine-based dyes are especially useful for CD-R, as the chromophore absorption band falls in the desirable spectral range, and they are noted for excellent photostability. Unlike cyanine dyes, phthalocyanines tend to have very poor solubility, particularly in solvents such as alcohols and aliphatic hydrocarbons (which do not attack polycarbonate and are therefore used for spin coating). Therefore, the main barrier to the wider use of these dyes is the relatively high cost of synthesizing soluble derivatives. Suitable modifications to the Pc core which have been developed, notably by Mitsui Toatsu, are shown in Scheme 7. The bulky R groups reduce undesirable molecular association (which in turn lower the extinction coefficient and hence reflectivity), whereas partial bromination allows fine-tuning of the film absorbance and reflectivity. The metal atom influences the position of the absorption band, the photostability, and the efficiency of the radiationless transition from the excited state.199 This material is marketed by Ciba as Supergreen.204... 

With the example of stained E. coli cells, the squaraine rotaxane 15b containing a zinc(II)-dipicolylamine (Zn-DPA) ligand, which is known to selectively associate with the anionic surfaces of bacterial cells, was found to be almost 100 times more photostable as compared to Cy5-Zn-DPA [55]. This can be attributed to stronger cell-surface affinity of 15b, leading to a slower off rate for the probe. The remarkable stability of 15b permits fluorescence imaging experiments that are impossible with probes based on conventional NIR cyanine dyes such as Cy5. Squaraine rotaxanes are likely to be superior substitutes for conventional cyanine dyes for biomedical imaging applications that require NIR fluorescent probes. 

As discussed in Chapter 3.1.1, reactive cyanine dye derivatives are ideal fluorescent labels for tumour-specific carriers or vehicles, such as antibodies, proteins and peptides. In the literature, a variety of approaches can be found, where such dyes were employed in the design of fluorescent bioconjugates with enhanced selectivity for tumour-associated antigens. 

One of the limitations associated with the use of fluorogenic dyes as labels for nucleic acids is the relatively high background fluorescence intensity in solution. This problem can be ameliorated by the use of asymmetric cyanine dyes. Another approach that can achieve low fluorescence background is based on the use of FRET pairs. If the acceptor and donor are in close proximity to... 

However, as far as interplay of conductivity and second-order NLO in hybrid molecular materials is concerned, very few studies are available (534, 535). As previously mentioned, both conducting and second-order NLO properties are formally connected to the same concept of charge transfer, though intermole-cular in conductors but intramolecular in compounds exhibiting second-order optical nonlinearity. Attempts to associate the [Ni(dmit)2] anion with cationic cyanine dyes known to exhibit second-order optical non-linearity such as DAMS+ (4-dimethylamino-l-methylstibazolium), DAMP+ (4-dimethylamino-1-methylpyridinium) and NOMS+ (4 -nitro-l-methylstibazolium) (Scheme 28)... 

Cyanine borates exist as tight ion pairs certain of the salts have even been shown to form ion pairs in which the center-to-center distance between the ions is less than the sum of the individual radii [27-29]. Since the lifetime of the excited singlet state of cyanine dye is quite short, too short to allow an efficient encounter at an achievable concentration of borate in a situation in which diffusion is necessary, the self-association of the cyanine cation and borate anion is a prerequisite for efficient photoinduced reaction. 

Sensitive methods for lead include a number based on ion-associates formed by the anionic iodide-lead complex and the basic dyes, such as Malachite Green (benzene, e = 8.0-10 ) (58,59], Brilliant Green (59], Ethyl Violet [59], fuchsin (formula 27.1) (extraction with benzene-cyclohexane from 0.2 M H2SO4, e = 2.0-10 at 560 nm [60], and cyanine dyes [61]. In the method involving the antipyiine dye Chrompyrazole I (formula 23.1), the pseudo-solution formed is stabilized with the non-ionic surfactant OP-10 [62]. 

Basic dyes were applied for the determination of Te in thin films [48,49] and steel [52]. Tellurium was determined in synthetic rubber by measurement of absorbance of the hydride [55]. The cyanine dye, N,N -di(acetoxyethyl)indocarbocyanine, associated with the chloride complex of Te(IV), has been used for the determination of Te in semiconductor thin films [62]. 

Association of molecules changes their As as has been proven for metal complexes, charge transfer complexes, Lewis acids, etc. In any case, complex formation can be followed by the variation of the CD. Molecular association is the first step to an aggregation and, furthermore, is the presupposition for supramolecular structures. Compounds with inter-molecular exciton interaction, e.g., carotenoids or cyanine dyes, have been successfully analyzed. The spontaneous association to chiral associates from achiral compounds, e.g., cyanines, have been proven and analyzed with the help of ECD spectroscopy. In this context, the successful CD analyses with Langmuir-Blodgett films as well as the analyses of membranes have to be mentioned where suprastruc-tural chirality can also emerge from achiral monomers. 

Over the years, spectrophotometry (UV-VIS) has been used to study such physicochemical phenomena as heats of formation of molecular addition compounds and complexes in solution, determination of empirical formulas, formation constants of complexes in solution, hydration equilibria of carbonyl compounds, association constants of weak acids and bases in organic solvents, tautomeric equilibria involving acid base systems, protein-dye interactions, chlorophyll-protein complexes, vitamin A aldehyde-protein complex, association of cyanine-dyes, determination of reaction rates, determination of labile intermediates, and dissociation constants of acids and bases. 

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