Langmuir-Blodgett films measured

Fig. 10 (a) Schematic representation of the I-V measurement of the Cgo derivative based molecular rectifier, (b) I-V characteristics of the Langmuir-Blodgett film of the fullerene penta-pod showing current rectification at bias voltage of 1.0 V measured at different junction positions, with high rectification ratios (RR) registered at each junction. (Reprinted with permission from [98])... 

The results illustrated above show that the CFT method is suitable for making chemical-sensor measurements using both bulk polymers and, in particular, thin film materials that are intrinsically weak conductors. Therefore, the CFT looks premising for such materials as poly(phenylacetylene) derivatives 24., for which carefully shielded electrometer measurements have been required in the past because of current levels at the threshold of detectability. Furthermore, the fact that the CFT always makes AC measurements reduces the problem of DC polarization of electrodes. In addition, the CFT approach should be suitable for other "chemiresistor" applications, such as the metal-substituted phthalocyanines proposed by Jarvis et. al. 2 and for Langmuir—Blodgett films 26. which, because they are so thin, may prove impossible to use in parallel-plate form, but which can be routinely used with the high-sensitivity interdigi-tated-electrode approach provided by the CFT. 

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]. 

Because of their electrical, optical, and redox properties as well as the thermal and chemical stability, the Pcs also have been tried in the detection of volatile organic compounds and poisonous gases, which is very important for environment and human health. In the past decades, the possible applications of Pc thin film as sensor for atmospheric gaseous pollutants have been extensively studied [73, 74], Langmuir-Blodgett films of some multinuclear and multidouble-decker lutetium Pcs have also been used for those measurements [75,76], More details about conductivity and sensing properties of Pcs can be found elsewhere [77,78]. 

Langmuir-Blodgett films are not very stable and are thus difficult to use for many contact angle studies. If the adsorbed film is altered by the sessile drop, successive advancing contact angles measured at the same location will differ. 

The use of an evanescent wave to excite fluorophores selectively near a solid-fluid interface is the basis of the technique total internal reflection fluorescence (TIRF). It can be used to study theadsorption kinetics of fluorophores onto a solid surface, and for the determination of orientational order and dynamics in adsorption layers and Langmuir-Blodgett films. TIRF microscopy (TIRFM) may be combined with FRAP ind FCS measurements to yield information about surface diffusion rates and the formation of surface aggregates. 

Unimolecular films provide a rich area for study in interfacial chemistry which has only been briefly introduced here. Other investigations include the kinetics of film formation, the viscosity of the monolayer, and measurements of surface potential changes [Gl]. Unimolecular films in condensed format may be removed from the surface of the liquid on which they are formed using a glass plate or other suitable solid substrate. The hydrophilic ends of the molecules in the film remain in contact with the solid surface, and the hydrophobic ends, with the air. This type of unimolecular film, which is called a Langmuir-Blodgett film, is also the subject of considerable research interest. 

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