Monolayer and spectroscopic studies of an amphiphilic (phenylethynyl)anthracene probe in pure and mixed films with charged and neutral lipids

The amphiphilic and morphological properties of a novel, amino-subsituted bis(phenylethynyl)anthracene derivative (APA) are investigated at the air/water interface using a Langmuir film balance and fluorescence microscopy. The interfacial miscibility of APA and positively charged, negatively charged, and zwitterionic lipids in two-dimensional monolayer phases is characterized on the basis of surface pressure/area isotherms of binary monolayers recorded at different molar ratios of the lipid and dye components. "Excess" Gibbs free energies of mixing are calculated for the APA/lipid monolayers at different surface pressures. Organized supramolecular film structures of the (phenylethynyl)anthracene amphiphile and its mixtures with octadecylamine are deposited onto solid supports by using the Langmuir-Blodgett (LB) technique. Mono- and LB multilayers are characterized by means of W-visible spectroscopy. Evidence is obtained for a J-type aggregation of APA in LB monolayers. The aggregation is likely favored by stereochemical packing factors and pi-pi and dipole-dipole intermolecular interactions of the extended, conjugated pi-electron systems of the APA chromophore moieties. The novel probe is found to be highly fluorescent. The determined fluorescence quantum yield is 0.58. The strong fluorescence of the amphiphile and its thermal stability at elevated temperatures are factors favoring its potential application as an activator of chemiluminescence in ordered supramolecular systems.