Cyanine efficiency

Excited-state properties of the cyanine and related dyes are complex. Most cyanine dyes exhibit small Stokes shifts for duorescence maxima. Typical carbocyanines (1) with n = 1 show 14- to 16-nm shifts in methanol solution with low quantum efficiencies for duorescence (Op ) of less than 0.05. The diearbocyanine analogues also show small Stokes shifts but higher quantum yields (Lpj = 0.3-0.5). 

O Regan B, Schwartz DT (1995) Efficient photo-hole injection from adsorbed cyanine dyes into electrodeposited copper(I) thiocyanate thin films p-type semiconductors. Chem Mater 7 1349-1354... 

To detect adulteration of wine. Bums et al. (2002) found that the ratios of acetylated to p-coumaroylated conjugates of nine characteristic anthocyanins served as useful parameters to determine grape cultivars for a type of wine. Our laboratory utilized mid-infrared spectroscopy combined with multivariate analysis to provide spectral signature profiles that allowed the chemically based classification of antho-cyanin-containing fruits juices and produced distinctive and reproducible chemical fingerprints, making it possible to discriminate different juices. " This new application of ATR-FTIR to detect adulteration in anthocyanin-containing juices and foods may be an effective and efficient method for manufacturers to assure product quality and authenticity. 

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... 

Although direct reaction of lanthanide mono-porphyrins with free phthalo-cyanine or its lithium derivatives is generally more efficient than the template synthesis, and gives rise to mixed-ligand complexes, the template strategy can also be applied for synthesis of phthalocyanine-porphyrin complexes, as in the case of unsymmetric bisphthalocyanine complexes (Scheme 8.2, B(b)) [106, 136, 145, 146]. Thus, metallation of free porphyrins with lanthanide salts in TCB or n-octanol leads to single-decker complexes, which then react with phthalonitriles under the action of DBU in alcoholic media to give the desired compounds. 

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.

Table I lists a variety of organic nonlinear materials which have appeared in the literature their relative powder efficiencies, absorption cutoffs and /3 values (if available) are also provided. These materials are "typical" only in that they represent results from the few classes of organic compounds investigated to date, yet they are instructive in that one learns which molecular properties may be important. A few caveats are in order to avoid misinterpretation of the data in Table I. Except for compound 10 (19) all the powder efficiency and cutoff data are from our own measurements. Powder measurements were performed on ungraded samples using the Nd YAG output at 1.06/t as fundamental since powder efficiency is a function of particle size distribution and a variety of other factors (3) these values are only semiquantitative. The cutoff values are the wavelengths for which 10-4M solutions in ethanol (unless otherwise indicated) have no absorbance. The cutoff values will be similar to those found in crystal state except where intermolecular charge transfer is important in the crystal or the molecule is solvatochromic, this latter effect being quite common for cyanine dyes such as...

Figure 16 Fluorophores with efficient chemical excitation in the PO-CL reaction. TMP, 2,4,6,8-tetrathiomorpholinopyrimido 5,4-rf pyrimidine DTDCI, 3,3 -diethylthiadicarbo-cyanine iodide.

Buston JEH, Young JR, Anderson HL (2000) Rotaxane-encapsulated cyanine dyes enhanced fluorescence efficiency and photostability. Chem Commun 11 905-906... 

This sequence of reactions is not possible in the absence of a micelle as the DI excited state is too short-lived to efficiently transfer to Cu++. The micelle positions Cu++ and (DI) in close proximity for efficient reaction, and, subsequently, separates the products and prevents back reaction. The crown ether type surfactants can be used to solubilize a cyanine dye in the... 

The styryl series of laser dyes are structurally similar to the cyanines, except that one of the heterocyclic bases has been replaced by a styryl moiety. They are more efficient laser dyes than the corresponding cyanines because they exhibit larger Stokes shifts, but otherwise share most of the characteristics of the cyanines. There seems to be little development of styryl dyes in the infrared underway as biophysical probes. 

Penmans P, Eorrest SR (2001) Very-high-efficiency double-heterostructure copper phthalo-cyanine/Cgo photovoltaic cells. Appl Phys Lett 79 126... 

This scheme of frequency tripling was successfully tested with fuchsin in hexafluorisopropanol (a solvent selected for its low index of refraction and relatively flat dispersion curve) to frequency-triple the output of a neodymium laser 67,68) With an input power of 10 MW/cm2 a third-harmonic output of 0.2 mW/cm2 was measured. This low value was mainly due to the relatively high absorption of fuchsin at 355 nm. An improvement of the efficiency by a factor of 80 was found with hexamethylindocarbocyanine iodide in hexafluorisopropanol because of the much lower absorption of this dye at 355 nm. Since the absorption minimum of this dye is at 383 nm, one could expect an additional efficiency increase by a factor of 70 for a fundamental laser wavelength of 1.15 / 69>. Other cyanine dyes have been used for frequency tripling a fundamental wavelength of 1.89 /mi 70>. 

It is unlikely in such cases where different species exist on the surface that the photocurrent spectrum coincides with the absorption spectrum, since the efficiency of charge transfer will be different for different species. Memming 52> has concluded that for a cyanine dye adsorbed on a SnO 2-electrode the monomer seems to be more effective for charge injection than the dimer or higher aggregates. Hauffe and co-worker S3> have found that chelating dyes are especially efficient for sensitized electron injection into ZnO-electrodes which is seen in the variation of the photocurrent spectrum. 

Cyanine and merocyanine dyes have also been tested as dye photosensitizers [132-137]. A nanocrystalline 2 solar cell sensitized by the special merocyanine dye as shown in Fig. 15 revealed a good efficiency of 4.2-4.5% (7 =... 

Muenter and Cooper (30) measured the room-temperature fluorescence of two J-aggregated dyes, l,l -diethyl-2,2 -quino-cyanine and 1,1, 3,3 -tetraethyl-5,5, 6,6 -tetrachlorobenzimid-azolocarbocyanine, adsorbed on cubic AgBr grains. The quantum efficiency of spectral sensitization was inversely related to the relative fluorescence. The fluorescence by the dyes in the molecular state was low compared to that for the aggregated dyes. Addition of a styryl or thiohydantoin dye as a supersensitizer for the quinocyanine quenched its fluorescence and increased the relative efficiency from 0.06 to nearly 1.0. 

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