Tunable Aggregation-Induced Emission as an Indicator of Intermolecular Distance in Supramolecular Assembly

Measuring the intermolecular distance in supramolecular structures in solution is important as well as challenging, especially for distance below 1.0 nm. The fluorescence emission is helpful in indicating intermolecular distances due to its sensitivity to the microenvironment, and the aggregation-induced emission (AIE) luminophores are especially useful against fluorescence quench in assembly and aggregation states. Herein, polyhedral oligomeric silsesquioxane (POSS) macroionic hybrids were synthesized with AIE luminophores chemically incorporated. The charged macromolecules self-assemble into hollow spherical blackberry-type stable supramolecular structures through the regulation of the electrostatic interactions. Macromolecules in the single-layered shell are closer to each other when assembled into spheres of larger size. Due to the rotational restriction of phenyl rings, the fluorescence emission was enhanced when more hybrids were involved in the assembly. In addition, some hybrids exhibit emission wavelength shift when neighboring macromolecules are closer to each other in the assembly structures. The study of macroionic-AIE hybrids in mixed solvent enabled us to gain a more direct visualization of intermolecular distances from the fluorescence emission changes.