Visualizing\nthe Initial Step of Self-Assembly and\nthe Phase Transition by Stereogenic Amphiphiles with Aggregation-Induced\nEmission

Many highly ordered\nstructures with smart functions are generated\nby self-assembly with stimuli responsiveness. Despite that electron\nmicroscopes enable us to directly observe the end products, it is\nhard to visualize the initial step and the kinetic stimuli-responsive\nbehavior of self-assembly. Here, we report the design and synthesis\nof stereogenic amphiphiles, namely, (Z)-TPE-OEG and\n(E)-TPE-OEG, with aggregation-induced emission (AIE)\ncharacteristics from the hydrophobic tetraphenylethene core and thermoresponsive\nbehavior from the hydrophilic oligoethylene glycol monomethyl ether\nchain. The two isomers can be easily isolated by high-performance\nliquid chromatography and characterized by 2D NMR spectroscopy. While\n(Z)-TPE-OEG self-assembles into vesicles, its (E)-cousin forms micelles in water. The initial step of their\nself-assembly processes can be visualized based on AIE characteristics,\nwith a sensitivity much higher than the method based on transmittance\nmeasurement. The entrapment and release capabilities of the (Z)-stereogenic amphiphile are demonstrated by employing\npyrene as a guest. The thermoresponsive behavior of the (Z)-amphiphile results in its continuous phase transition from microscopic\nself-assembly to macroscopic aggregation, which is successfully visualized in situ by confocal laser scanning microscopy accompanied\nby the AIE technique. Such a kinetic process shows different stages\naccording to the microscopic visualization, and these stages have\nnever been monitored through roughly observing the appearance of precipitates.\nIt is anticipated that this study can deepen the understanding of\nthe self-assembly processes for better monitoring and controlling\nthem in different systems.