Stilbazolium cations

Figure 30. Schematic illustration of the packing of stilbazolium cations inside a magnesium-rich saponite clay. Stereoselective dimerization takes place to give the syn head-to-tail dimer. [Reproduced with permission from K. Takagi, H. Usami, H. Fukaya, and Y. Sawaki, J. Chem. Soc., Chem. Commun. 1174 (1989).]...

Duan et al. [67-69] investigated first hyperpolarizability of stilbazolium cation with different donors as shown in Figure 5 and their measured values are shown in Table 2. 

The experimental values for stilbazolium cations are obtained using two-state model and from the experimental (3 values obtained from the literature [67-69], which was measured at a fundamental wavelength of 1064 nm light from Nd YAG laser. The trends in static hyperpolarizabilities with the change of substituents follow tire Hammett Parameter Constant (cTp) as we have seen before for neutral molecules. 

Figure II. Extended conjugated, all trans, ruthenium complex of stilbazolium cations have used in our...

Aqueous acidic solutions of either stilbazolium cation exhibit only "monomer" absorption and fluorescence at concentrations of 0.005M or lower. Increasing the stilbazolium concentration in aqueous HCI (0.1-1.0M) to 0.01 M or higher results in a red-shifted, broadened and structureless "excimer" fluorescence and a slightly broadened absorption spectrum (Table 1). Irradiation of these concentrated stilbazolium solutions result in a decrease in the trans- cis isomerization and the formation of the a dimer as the principle photoproduct for both cations (Tables 2 and 3). Although both the cis isomer and the a dimer are formed from each cation in the concentrated homogeneous solution, only the 5 dimer forms from cation 1 while the p dimer and small amounts of the e dimer form from cation 2. 

Scheme 1. Possible Geometries of Stilbazolium Cations at Interface Leading to Formation of 5 Dimer from Cations 1 (31).

It is clear from these results that the AOT reversed micelles have more than a concentrating effect upon the stilbazolium cations. Changes In the size of the water pool have a profound effect upon the outcome of the dimerization reaction. The interface not only concentrates the monomers but aisp orients the cations in such a way as to force a nonpreferential association between the stilbazolium molecules. These results indicate that it is possible to exert topological control over the... 

We have recently been investigating the behavior of stilbazolium cations at other anionic interfaces such as Nafion 117 and montmorillonite ciay. Nafion< 117 readily adsorbs the stilbazolium cations with a maximum coverage level (ratio of stilbazolium to exchangeable cations) of 100% and 90% for cations 1 and 2, respectively. 

By analyzing the ELD spectra of 2- and 4-[4-(dimethylamino)styryl]-l-ethylpyridinium cations on saponite suspended in DMF (Fig. 20), the tilt and roll angles of the dye were found to be controlled by the amount of the intercalated dye as well as the molecular structure (the position of cationic site within the dye) (103). The adsorption models of 4-[4-(dimethylamino)styryl]-l-ethylpyridinium cations on solid saponite are shown in Figure 21. Depending on the coverage, the orientation of 4-[4-(dimethylamino)styryl]-l-ethylpyridinium varied, as shown in Figure 21. The important role of the orientation of the stilbazolium cations will be discussed in a subsequent section. 

FIGURE 39 Schematic representation of the sensitized isomerization of cis-stilbazolium cation in the interlayer space of saponite. 

FIGURE 30 Formation of syn head-to-tail dimmers of stilbazolium cations in the presence of clay. 

---