First observation of fluorescence self-quenching in Langmuir films

Abstract

Systematic investigations of dipalmitoyl-phosphatidylethanolamine head labelled with nitrobenzoxadiazole (DPPE-NBD) are performed both on monolayers at the air—water interface and deposited on solid substrates as Langmuir—Blodgett films. This dye compound is frequently used as a fluorescent additive in fluorescence microscopy investigations. It is also a suitable model compound. We present experimental evidence for the self-quenching of the fluorescence when higher-order domains of the dye are formed at the air—water interface. A coexistence of two completely different types of domains at the phase coexistence region for a single-component system is observed. From small-angle X-ray diffraction, pressure—area isotherms and molecular space filling models, an average tail tilt angle of 31° towards the normal to the substrate surface is estimated when deposition is carried out at 50 mN/m. These data, together with information from polarized FTIR spectra, support a conclusion of a decrease of tail tilt and increase of the order of the deposited films on increase of the deposition pressure.