Sandwich dimmer

From the results of SHG spectroscopy, the rhodamine dyes adsorb and form the in-plane associates at the heptane/water interface, pointing the xanthane moiety towards the heptane phase with a tilt angle as shown schematically in Figure 11.7. The structure of the associates at the interface differs from that in a bulk aqueous phase. In an aqueous solution, RB makes a sandwich dimmer when the concentration is above 1.0 x 10 M [66], and the molar fraction of the dimmer is 0.56 at 1.0 x 10 M. The absorption spectra of the sandwich dimmer show blue-shifted peak around 525 nm. In contrast, red-shifted peaks found in SHG spectra indicate that the in-plane associates are predominantly formed at the interface despite the presence of the sandwich dimmer in the water phase. The hydrophobic property arising from heptane molecules at the h tane/water interface would be crucial for the predominant formation of in-plane associates. 

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