SWITCHING OF EXCIMER MONOMER RATIO IN CHIRAL BILAYER-MEMBRANES CONTAINING PYRENYL GROUPS

A chiral amphiphilic derivative of D-l-pyrenylalanine carrying one quaternary ammonium group and two octadecyl groups (1P18) was synthesized. A lamellar structure was observed for the aqueous dispersion of the pyrenyl amphiphile. The molecular assembly showed a gel to liquid crystal (LC) phase transition at 35.2°C. Circular dichroic spectra indicated that the pyrenyl groups were regularly arranged in the gel phase but randomly oriented in the LC phase. The change of the chromophore orientation induced a marked change in fluorescence spectrum. The monomer fluorescence was intense in the gel phase, but it almost disappeared in the LC phase. Instead, the excimer fluorescence increased its intensity in the LC phase. The phase-dependent change was not observed in a racemic mixture of the pyrenyl amphiphile. Circularly polarized fluorescence spectrum indicated the presence of two types of excimers: one emits left-handed circularly polarized fluorescence at ca. 450 nm; the other emits righthanded circularly polarized fluorescence at wavelengths longer than 500 nm. © 1990, American Chemical Society. All rights reserved.