Langmuir-Blodgett films charge-transfer complexes

The monolayer also provides an environment of variable dielectric so that intermolecular association between photoactive molecules can readily occur. For example, molecular association of pyrene within a Langmuir-Blodgett film is clearly seen through time-resolved fluorescence measurements on the picosecond timescale [92], Attenuated total reflectance studies of dyes in cast films can similarly reveal their positions and photophysical interactions [93], Photochromism in a monolayer assembly has been attributed to excitation of ion-pair charge transfer complexes formed within the array [94]. 

Association of molecules changes their As as has been proven for metal complexes, charge transfer complexes, Lewis acids, etc. In any case, complex formation can be followed by the variation of the CD. Molecular association is the first step to an aggregation and, furthermore, is the presupposition for supramolecular structures. Compounds with inter-molecular exciton interaction, e.g., carotenoids or cyanine dyes, have been successfully analyzed. The spontaneous association to chiral associates from achiral compounds, e.g., cyanines, have been proven and analyzed with the help of ECD spectroscopy. In this context, the successful CD analyses with Langmuir-Blodgett films as well as the analyses of membranes have to be mentioned where suprastruc-tural chirality can also emerge from achiral monomers. 

Recently, the Langmuir-Blodgett (LB) technique has been recognized as a useful way of tailoring thin films of molecular thickness. Interest in the LB technique has led to a number of investigations of different types of materials. For example, the classic long-chain fatty acids and alcohols as well as polymerizable molecules, e.g. diacetylenic acids [211-213], aromatic hydrocarbons, e.g. substituted anthracenes [214, 215], TCNQ radical anion salts [216, 217] and charge transfer complexes [218-220] and dye substances can now all be produced as monomolecular layers. 

Richard, J., Vandevyver, M., Barraud, A., Morand, J. R, Lapouyade, R., Delhaes, R., Jacquinot, J. R, and Rouillay, M., Preparation of new conducting Langmuir-Blodgett films based on ethylenedithiodecyltetrathiafulvalene charge transfer complex, J. Chem. Soc. Chem. Commun., 754, 1988. 

A number of other systems have been shown to be suitable for multilayer build-up by the ESA, like charged latex nanospheres [50,199,285-287] or metallo-supramolecular complexes [288-290]. ESA has also been combined with Langmuir-Blodgett transfer [291-294], and even superlattice films have been produced. 

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