Mihoko Yamada

The study introduces a novel C 3 ‐symmetric β‐diketone compound, BTA‐D3 , and its monomeric counterpart, D , with a focus on their synthetic procedure, photophysical properties and aggregation behavior. Both compounds exhibit characteristic absorption and weak fluorescence in solution, with BTA‐D3 displaying higher absorption coefficients due to its larger number of diketone units. Density Functional Theory (DFT) calculations suggest increased co‐planarity of diketone groups in BTA‐D3 . A significant finding is the Aggregation‐Induced Emission (AIE) property of BTA‐D3 , as its fluorescence intensity increases dramatically when exposed to specific solvent ratios. The AIE behavior is attributed to intermolecular excitonic interaction between BTA‐D3 molecules in self‐organized aggregates. We also studied fluorescence anisotropy of BTA‐D3 and D . Despite its larger size, BTA‐D3 showed reduced anisotropy values because of efficient intramolecular energy migration among three diketone units. Furthermore, BTA‐D3 demonstrates unique polymorphism, yielding different emission colors and structures depending on the solvent used. A unique approach is presented for promoting the growth of self‐organized aggregate structures via solvent evaporation, leading to distinct fluorescence properties. This research contributes to the understanding of C 3 ‐symmetric structural molecules and provides insights into strategies for controlling molecular alignment to achieve diverse fluorescence coloration in molecular materials.