Silver chloride cyanines

The cyanine dye, 3,3 -diethyl-9-methylthiacarbocyanine chloride, had a much greater effect than gelatin in decreasing the reaction rate of the silver chloride. The rate of reduction of silver chloride varied linearly with the amount of silver chloride surface not covered by the dye, and the rate attained at complete coverage was of the order of one-thousandth that for the undyed precipitate. The dye exerted scarcely any effect upon the reduction of silver ions from silver sulfite complex solution. 

The effect of the cyanine dye and of gelatin on the reaction rate shows that reduction of silver ions from solution is not the rate-controlling process. These influences of adsorbed components on the reaction rate speak against the concept that solution of the silver halide is the rate controlling process. Hence, the silver catalyzed reduction of silver chloride by hydroxylamine takes place substantially at the solid silver/ silver halide interface. 

Early work showed that low light intensity excitation sources had to be used to avoid excited-state annihilation processes [193, 194]. Using a low-intensity mode-locked laser source and single photon counting, Muenter measured the rates of fluorescence decay, k, for some typical monomeric cyanine dyes on silver chloride and silver bromide cubic crystals [195] k was obtained from Eq. (108) for k, and assuming that kf + A nr) could be determined from measurements of dye lifetimes in... 

Tran [391,392] has reported ng detection of dyes on filter paper by SERS. Silver colloidal hydrosols stabilised by filter supports enhance the Raman scattering of adsorbed dyes. Typical detection limits are 500 pg (crystal violet), 7 ng (l,l,9-trimethyl-2,2 -cyanine perchlorate), 15 ng (3,3 -diethylthiacarbocyanine chloride) and 240 ng (methyl red) using a 3 mW He-Ne laser. 

Akins " reported an enhancement of about 2000 for cyanine chloride when adsorbed on a silver sol. However, the dye absorption is centered around 530 nm, while for the Raman studies a 564-nm excitation was used, i.e., a slightly off-resonance situation. An absorption feature, not present for the dye by itself or the sol alone, was seen at about 575 nm. Akins interprets it as due to a dye aggregate. However, as will be seen in Section II.5, similar bands are commonplace in SERS systems. In a separate study, Li et alP tried to evaluate the enhancement factor for cyanine chloride at 488 nm (in the absorption band) on a silver electrode and on a sol. Their estimate is a factor of about 50 for the colloid and 10" on the electrode. One should recall the difficulties inherent in such determinations (see Section II.I). 

C9H21CIN2O2, Bis(dimethyl)-pentamethine-cyanine chloride, 41B, 36 C9H22N2S2, Diethylammonium diethyldithiocarbamate, 44B, 28 C9H2 Ag,I13N2, N,N,N,N, N ,N -Hexamethylisopropylenediamine diiodide - silver iodide, 42B, 20... 

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