Saponite aggregation

Dye aggregation has been a topic of interest because it is thought to be a key issue in natural and artificial photosynthetic systems as well as in photonic materials such as nonlinear optical materials. The adsorpion of a cationic cyanine dye, l,l -diethyl-2,2 -cyanine (pseudoisocyanine, abbreviated as PIC, whose molecular structure is shown in Fig. 11) on smectites (montmorillonite and saponite) was reported (172,173). It is well known that the spectral properties of cyanine dyes are strongly affected by aggregation (174,175). These aggregates (so-called... 

In contrast to the observations for aqueous suspensions, the cast films of PIC/clays give different results. J-aggregates are absent when the amount of PICBr is 2.5 mmol/100 g clay. On the other hand, when the amount of PIC is increased to 50 mmol of PIC/100 g clay, the band due to monomeric PIC disappears and the J-band appears at around 570 nm, irrespective of clay type. The basal spacings of the PIC/saponite films were ca. 1.3 and 1.7 nm for 2.5 and 50 mmol of PIC/100 g saponite, respectively. The PIC cations distribute molecularly on the surface of clays when the loading amount is low. Higher dye loadings result in their aggregation within the interlayer space. 

Changes in the aggregation state of y-stilbazolium [4-(2-phenylvinyl)pyri-dinium] ion on saponite by coadsorption of alkylanunonium ions (C N+) has been investigated (222). Figure 32 shows the effect of CgN+ on photoreactivity of preintercalated stilbazolium ions on clay. On coadsorbing longa- than the stilbazolium ion, the major photoreaction was changed from cyclodimerization to E-Z isomerization and the excimer emission of the intercalated stilbazolium ions was dramatically reduced. The formation of dimers or clusters of adsorbent were simulated by a Monte Carlo method for a two-dimensional lattice. 

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