Aromatic Groups Help Light Up Micelles

Sensor developers may have a new tool. An intriguing class of molecular capsules featuring tunable fluorescence properties has been created from a hybrid of two typically incompatible chemical entities: micelles and aromatic compounds (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201208643). In addition to being photoactive themselves, the aromatic micelles can encapsulate dye molecules, presenting scientists with opportunities to design new sensors and other materials. Michito Yoshizawa and colleagues at Tokyo Institute of Technology designed the flexible surfactant molecules by attaching two hydrophobic anthracene groups to a central phenyl ring, which acts like a hinge. Aromatic compounds are rigid and planar, making it difficult for them to form micelles. Two ammonium or sulfo­betaine groups attached to the central phenyl ring provide the hydrophilic portion of the surfactant molecules. When added to water, the hydrophobic aromatic portions congregate to form a spherical cavity with a diameter of about 1 nm. The aromatic micelles fluoresce blue-green light, which can be changed when they encapsulate a hydrophobic organic dye. The fluorescence could be tuned with different combinations of dyes and aromatics.