Dipping direction

Phthalocyanines (Pc) are attractive materials for their potential functions including the semiconductive behaviours in addition to the thermal and chemical stabilities. In particular, control of orientation of the Pc macrocycles in thin films is expected to provide novel molecular electronic devices. Previously, we have found that copper tetrakis(butoxycarbonyl) Pc is oriented nearly perpendicular to the surface and also the dipping direction in the LB films [46], while octa-alkyl Pc derivatives [H2Pc(R)8, CuPc(R)a R = CnH2n+i. n=7,9,11] take the orientation with Pc macrocycles nearly parallel to the plane of films deposited by the horizontal lifting method to form a non-alternating X-type film [47], as illustrated schematically in... 

Figure 5 The incident (5 and polarization angle a dependence of polarized absorption. The y and z axes indicate the dipping direction and the surface normal. The transition dipole M and its xy projection makes and 0 from the z and y axes, respectively.

Figure 21 shows three possible routes to obtain oriented PAV films by the LB technique. In these route, it is anticipated that orientational orderliness of precursor polymers is introduced in the precursor LB films through the formation of two-dimensionally oriented monolayer of a polyelectrolyte precursor-anionic amphiphile polyion complex at the air/subphase interface and orientation of the precursor monolayers along the dipping direction dining the deposition process. As a result, it is expected to obtain oriented PAV LB films with well-developed jt-coryugation system. In this study, we successfully prepared oriented PAV films using two routes of them, b-1 and b-2 route [35-37]. The chemical structures of PAVs, their polyelectrolyte precursors and an anionic amphiphile used in this study are shown in Fig.22. 

The absorbance of the PPV LB film at peak wavelength measured with polarized light parallel to the dipping direction is about twice large that measured with polarized light perpendicular to the dipping direction. The anisotropy of absorbance... 

Fig.24. Absorption spectra of a PPV LB films (1,2) and a PPV cast film (3). Spectra of 1 and 2 were measured with polarized light parallel and perpendicular to the dipping direction.

Fig.27. )P and absorption spectra of an MOPPV LB film. Open and solid circles show value of x(3) of the MOPPV LB film in the direction parallel and perpendicular to the dipping direction. Open triangles show x of an MOPPV cast film. Solid and broken lines show the absorption spectra measured by the polarized light parallel and perpendicular to the dipping direction, respectively. Dotted line shows an absorption spectrum of the MOPPV cast film.

In Cl, the analyte is introduced into the ion source the same way as described for El, i.e., via direct insertion probe (DIP), direct exposure probe (DEP), gas chromatograph (GC), or reservoir inlet (Chap. 5.3). 

The DNA-aligned thin film could also be obtained with the LB method, in which anionic DNA strands were transferred with cationic monolayers at the interface using vertical dipping method. DNA was aligned along the dipping directions. 

Aqueous reference electrodes, such as SCE and Ag/AgCl electrodes, are often used in noil-aqueous systems by dipping their tips into lion-aqueous solutions of the salt bridge. The tip should not be dipped directly into the solution under study, because the solution is contaminated with water and the electrolyte (usually KC1). When we use such aqueous reference electrodes, we must take the liquid junction potential (LJP) between aqueous and non-aqueous solutions (Table 6.2) into account. If we carefully reproduce the composition of the solutions at the junction, the LJP is usually reproducible within 10 mV. This is the reason why aqueous reference electrodes are often used in non-aqueous systems. However, the LJP sometimes exceeds 200 mV and it is easily influenced by the electrolytes and the solvents at the junction (Section 6.4). The use of aqueous reference electrodes should be avoided, if possible. 

Helical polymers, formed as they usually are from chiral monomers, are themselves chiral. If an attempt is made to stack them in a regular parallel array, there will be a tendency for successive layers to be gradually twisted round with respect to the original layer. It is possible that the chiral effect is responsible for the fact that the polyglutamates tend to deposit at an angle of 35° to the dipping direction. A study of a racemic mixture of one of these materials would clarify this point. 

Fig. 22(b) shows polarized visible absorption spectra of mixed LB films of MS-C2o binary and MS-C20-AL18 ternary systems prepared by using an aqueous subphase containing Cd2+ ions, where the ratio in the mixed system is [MS] [C20] [AL18] = l 2 x (x — 0 and 1) [77-84]. The thick and thin lines in Fig. 22(b) refer to the spectra, Atl and A , measured by linearly polarized light with the electric vector parallel and perpendicular to the dipping direction of the substrate, respectively. For x = 0, a sharp absorption peak is observed at 590 nm, which is red-shifted from the MS monomer peak at around 540 nm. The dichroic ratio R of the 590 nm band is R> 1, where R is defined as A /A . For x= 1.0, on the other hand, a sharp blue-shifted band with R< 1 appears at 505 nm. Fig. 22(c) refers to the cases of the corresponding binary and ternary systems fabricated under the subphase without the Cd2+ ions [84], Unlike the results in Fig. 22(b), remarkably red- and blue-shifted bands are not observed... 

Fig. 22. (a) Chemical structure of MS and a schematic representation of the intramolecular charge transfer in MS. Polarized visible absorption spectra of the mixed LB films of the MS-C20 binary and MS C2o AL X ternary systems with the molar mixing ratios of [MS] [C20] [ALi8] = 2 x (x = 0 and 1) fabricated under a subphase (b) with and (c) without Cd2+ ions. The thick and thin lines represent An and A measured by linearly polarized light with the electric vector parallel and perpendicular to the dipping direction of substrates, respectively. (Reproduced with permission from Ref. [84]. Copyright (2006) Elsevier.)... 

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