Effects of molecular organization on photophysical and photochemical behavior: Quenching by subphase iodide of fluorescence in pyrene-bearing probes at the nitrogen-water interface

Abstract

The quenching by subphase iodide of pyrene covalently bound to amphiphatic molecules in spread monolayers has been measured. The probes employed were 2-(6-pyreneylhexanoyl)-3-palmitoyl-sn-glycero-1-phosphorylcholine, 10-(6(8)-octadecylpyrenyl) decanoic acid and 1-pyrenedocosanoic acid; the host lipids utilized were dioleoylphosphatidylcholine (DOL) and dipalmitoylphosphatidylcholine (DPL). It has been observed in all cases that pyrene fluorescence is significantly quenched in the uncompressed layer and that this quenching diminishes markedly as the surface pressure is increased over the liquid expanded region. Beyond this range a plateau in the fluorescence decay is reached in DOL, while in DPL changes in quenching are related to phase transitions. These findings indicate significant probe-water interaction at low surface pressure. Residual iodide quenching in DOL above 10 dyn cm −1 indicates some continued water-probe contact which may be due to the liquid character of the host layer and the double-bond character of the lipid while the very small residual quenching in DPL suggests tight packing in the non-liquid phases.