Dimer formation, dyes

Cyanine dye-CD complexes were first reported by Kasatani et al. in 1984 using 3,3 -diethyloxadicarbocyanine iodide (DODC) [22]. It was found that this dye formed complexes with (3- and y-CDs but not with a-CD. Later, they demonstrated the same tendency with cyanines 1 and 2 [23]. It was shown that inclusion of cyanine dyes in [i-CD and Me-(3-CD helps to inhibit dimer formation as well as to enhance the photostability of these cyanines, thereby enhancing the dyes utility as a fluorescent probe [7, 24],... 

An interesting equilibrium study was performed by Kasatani and coworkers on the interaction of a series of cyanine dyes with beta and gamma cyclodextrin, using u.v.-visible spectrophotometric measurements. The results were consistent with the enhancement of dimer formation by inclusion of the dye molecules within the cyclodextrin. As expected from the work of others, such geometrical factors " as the size of the aromatic groups and the lengths of the central methine chains strongly influence the occurrence of dimer formation within the cyclodextrin cavity. 

Linear-dichroic spectra of SA monolayers prepared from mixtures of OTS and a cyanine-dye surfactant established the absence of dimerization and the orientation of the chromophore parallel to the substrate [183]. In contrast, the same cyanine dye underwent sandwich-type dimer formation in LB films and had its chromophore oriented perpendicular to the water surface [192]. These results highlight an important difference between LB and SA monolayers. Parameters which determine monolayer formation on an aqueous subphase are also responsible for the orientation and organization of the surfactants therein. Furthermore, the configuration of the surfactants is retained regardless of the structure of the substrate to which the floating monolayer was subsequently transferred to by the LB technique. Conversely, in SA monolayers, surfactant organization is primarily dependent upon the nature of the substrate [183]. 

On the basis of the above dimer formation model, a time course of the absorbance of Y-Dye (/4(f)) produced in an individual droplet has been analyzed [104]. The coupling reaction between QDI and Y-Cp is assumed to proceed at the oil-droplet/water interface (rate constant, kt) and the association equilibrium between the Y-Dye monomer and dimer is attained immediately upon the dye formation. In the actual experiments, QDI is oxidized partly by 02 dissolved in the water phase, so that Y-Dye is produced in a DBP droplet even before electrolysis of QDI. To correct this contribution, [Y-Dye] is defined as [Y-Cp]0 — [Y-Cp]j exp( — fc,[QDI]wf), where [Y-Cp]0 and [Y-Cp], are the Y-Cp concentrations at the emulsion preparation and t = 0 (before electrolysis), respectively. According to the... 

The reduction of organic dye methyl orange (MO) over CdS colloids with the particles size d = 2R - 5 nm has appeared to be a convenient reaction for detail studying the kinetics of photocatalytic processes. This dye is readily reducible with no dimers formation. The MO adsorption spectrum in the pH range of 10-12, practically does not change. This allows simplifying the interpretation of the experiments on redox transformations of MO and considering the reaction of photostimulated reduction of MO as a model one. 

Extrapolating each isotherm to infinite concentration, gives the susceptibility of the full monolayer (which is the value of 5 on an arbitrary scale). The ratio Lang/ Frum = 2 is very suggestive of a packing of the dye molecules that is twice as dense in the phase in equilibrium with the bulk above a concentration of 6 pM. This suggests that in keeping with previous observations of dimer formation at the interface, an alternative way to view such a pair of ordered layers may be as adsorbed dimers. 

The influence of the counter anion on the excited state relaxation time of cationic polymethine dyes has also been reported . The fluorescence lifetime is dependent on the anion in weakly polar media but independent in polar media. The fluorescence behaviour of highly concentrated rhodamine GG solutions in methanol and water can be separated into monomer and dimer contributions2. Absorption emission and excitation spectral data support the view that the dye rose bengal forms H-type aggregates in water and polar protic solvents 1. The spectroscopic behaviour of rhodamine 6G in polar and nonpolar solvents as well as in thin glass and PMMA films shows dimer formation occurs and their stabilities have been compared under different conditions. The equilibrium between the neutral... 

A number of colloidal systems containing dyes have been investigated. The fluorescence lifetime of acridine orange has been measured in the SOS premicellar region. A short lifetime of less than 3ns is found for the monomer but the emission lifetime increases with dimer formation and SDS concentration. Quenching of 7-ethoxycoumarins by inorganic ions in, dye solubilizates in... 

Chambers, R.W. Kajiwara, T. Keams, D.R. Effect of dimer formation on the electronic absorption and emission spectra of ionic dyes. Rhodamines and other common dyes. J. Phys. Chem. 1974, 78, 380-387. 

In context with the formation of peraminosubstituted 1,4,5,8-tetraazaful-valenes of type 85 it must be mentioned that the bis-vinylogous compounds 94 can be easily prepared by reaction of acetamidine with bisimidoylchlo-rides derived from oxalic acid (96S1302). In the course of a complex reaction a cyclic ketene aminal was produced it immediately underwent an oxidative dimerization to yield deeply colored TAFs. Tlieir high chemical stability can be compared with that of indigoid dyes and manifests itself, for example, by the fact that they are soluble in hot concentrated sulfuric acid without decomposition. Tire same type of fulvalene is also available by cy-... 

Problems related to the use of a guest dye can be reduced if the polymer contains a fluorescent chemical group. Gohil and Salem [70] took advantage of such intrinsic fluorescence to characterize the in-plane distribution of orientation in biaxially drawn PET films. In these experiments, the chain-intrinsic fluorescent label is due to the formation of dimers by two terephthalic moieties, exclusively within the noncrystalline regions. A comparison between sequential and simultaneous drawing along the MD and TD directions was undertaken for a fixed MD draw ratio of 3.5 and various TD draw ratios. The orientational order was characterized by two "orientation ratios" Rmd and RTD such that... 

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