Various Self Assemblies of 10-(1-Pyrenyl) decanoic Acid

Abstract

Self assemblies of 10-(1-pyrenyl)decanoic acid (PDA) have been studied by fluorescence spectroscopy. In a pH 5.0 buffer solution, PDA showed both monomer and aggregate fluorescence emissions (Fig.1). A fluorescence excitation band due to the PDA aggregate was observed at 354 nm even when the spectrum was recorded at a monomer emission wavelength, indicating the occurrence of energy transfer from the aggregate(s) to the monomer. At higher pH, PDA was dissolved in water giving the monomer emission (Fig.1), and formed micelles at concentrations above 2×10^-5mol.dm^-3 (Figs.5 and 6). Fluorescence excitation spectra (Fig.5) as well as the fluorescence decay curves (Fig.7)suggest the occurrence of energy transfer from the aggregate(s) to the monomer and from the monomer to the nonfluorescent energy trap(s) in the PDA micelles. Below the cmc, PDA molecules also aggregated spontaneously upon addition of NaCl resulting in fluorescence quenching of PDA by NaCl (Fig.2). The fluorescence decay curves were composed of fast and slow components (Fig.4). This result as well as those of thefluorescence spectral measurements indicates that energies transferred from the PDA monomer to the nonfluorescent PDA aggregates. An excimer-like fluorescence of PDA was observed for a Langmuir-Blodgett membrane composed of PDA and stearic acid (1:12 molar ratio)at around 470 nm (Fig.8). Both monomer and excimer-like emissions decayed multiexponentially (Fig.9), indicating the occurrence of energy transfer from the monomer and excimer-like states to the nonfluorescent energy trap(s). An intermolecular π-π interaction between the pyrenyl moieties of PDA seems to be too weak to organize the PDA molecules regularly in water and the position of the pyrenyl moiety in the PDA molecule is not adequate for forming well-organized LB membranes,