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The adsorption of dyes and particularly of cyanines at silver halide, silver or mica substrates is generally accompanied by changes in the dye spectra. Depending on the system, these changes have been quantitatively evaluated either by reflectance measurements with application of the KubelkaMunk relation or by transmission spectroscopy. Surface concentrations and saturation coverages of the dyes as well as surface areas and average particle dimensions of the substrates were obtained. These values generally agreed well with independently determined measurements and yielded Langmuir adsorption coefficients, apparent standard free energies of adsorption, and probable orientations of the adsorbed dyes.Tt is the purpose of this paper to describe methods for determining and A interpreting dye spectra in aqueous dispersions of silver halides and other substrates. Such spectra can be utilized for the direct measurement of surface concentrations of dyes from which, in turn, the surface area of the substrate can be derived. The techniques involved are not limited to a specific dye class but will be illustrated in this paper by the behavior of cyanine dyes.The known factors which influence the solution spectra of cyanines have been recently reviewed (14,46,73). It will be sufficient to sum marize here some of the concentration-dependent spectral properties for the specific case of l,l'-diethyl-2,2'-cyanine; this cyanine was employed in many of the present experiments. In alcohol as in dilute water solutions this dye, which will be referred to as Pseudocyanine, although it has also been called Pseudoisocyanine, appears to exist only in an extended con figuration and has its maximum absorption near 523 n.m. This transition 173 Downloaded by UCSF LIB CKM RSCS MGMT on December 2, 2014 |