Monolayer and Fluorescence Properties of a Chiral Amphiphilic Ruthenium(II) Complex at an Air−Water Interface

Monolayer properties of a chiral amphiphilic ruthenium(II) complex, [Ru(phen)2L]2+ (phen, 1,10-phenanthroline; L, 4,4‘-dicarboxyl-2,2‘-bipyridyl didodecyl ester), have been investigated by measuring surface pressure−molecular area (π−A) isotherms. The lift-off areas in the π−A curves show that the racemic mixture formed a more condensed monolayer than the enantiomer. The monolayers were observed with a fluorescence microscopy at the scale of 150 μm × 100 μm. For the racemic mixture, fluorescent wedge-shaped domains (10−50 μm in length) existed already at zero surface pressure. The subsequent appearance of small bright spots (>2 μm in diameter) on compressing a surface up to 20 mN/m was interpreted as the transformation of a nonfluorescent liquidlike monolayer to a fluorescent solidlike monolayer. Strongly bright spots with a diameter of less than 2 μm appeared when surface pressure exceeded 30 mN/m, indicating the collapse of a monolayer film. In contrast, no distinct fluorescent domain was observed for both enantiomers at any stage of compression. Instead, fluorescence intensity increased uniformly on compressing the surface. The results were interpreted in terms of the role of solvating water molecules in quenching a metal complex at the air−water interface.