Self-Assembled Monolayers and Multilayers Derived from Organosilicon Derivatives

1 Self-Assembled Monolayers and Multilayers Derived from Organosilicon Derivatives 

SAOTS was established to be a true monolayer (rather than a bi- or multilayer) by conductivity and Forster-type energy transfer measurements [183]. Energy transfer experiments were carried out on a composite system which consisted of a mixed OTS and donor cyanine dye (D) monolayer on a glass slide, on top of which a mixed cadmium arachidate acceptor cyanine dye (A) monolayer was deposited (by the LB technique) in such a manner that it covered only half of the glass slide. The other half was covered by a pure 

Preferential adsorption of a surfactant from a mixture depends on the structures of the amphiphiles and the substrate. Self assembly by physisorption is reversible, while that by chemisorption is irreversible. Thus, surfactants physisorbed in monolayers can be replaced by surfactants which are able to chemisorb. Such behavior was demonstrated by allowing a donor cyanine surfactant, D (capable of physisorption), and OTS (known to chemisorb) to 

Removal of reversibly adsorbed (physisorbed) cyanine-dye molecules, D, led to skeletonized, SA silane monolayers having pinholes in the shape of D (Fig. 18) [185]. Such pinholes can, in turn, serve as templates for similarly shaped guest molecules. This approach opens the door for molecular recognition and device construction based on molecular recognition [186-190]. The idea relies upon the construction of a well-packed, SA monolayer from a mixture of OTS molecules and a solvent removable guest species. Removal of the guest molecules leaves pinholes with precise dimensions which only accept molecules with 

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]. 

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