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内容記述 |
Although azobenzenes have the potential to possess both aggregation-induced emission (AIE) and photoresponsivity, examples are still limited due to their low emission efficiency. Herein, we report a new supramolecular strategy utilizing a large molecular dipole moment to enhance emission efficiency in the aggregate state and to induce controllable crystal polymorphism, thereby demonstrating the first observation of azobenzene-based whispering gallery mode (WGM) emission with multiple sharp peaks. While dipolar azobenzene monomers in toluene are non-emissive, the drop-cast film exhibits red emission under photoexcitation due to the AIE effect. Microscopic photoluminescence (PL) measurements revealed that the film comprises a mixture of crystals, with major red and minor near-infrared (NIR) emissions. By tuning the recrystallization temperature in toluene, we successfully controlled the crystal polymorphism and revealed the PL properties of each form using time-resolved PL spectroscopy and theoretical approaches. A direct transition from the NIR-emissive crystal to the red-emissive one was observed upon thermal annealing. Remarkably, the micro-sized particles exhibited multiple sharp PL peaks due to the microresonator effect, attributed to WGM emission, and the WGM peak positions shifted upon photoirradiation. This work provides a fundamental principle for the creation of new photoresponsive WGM-based materials. |
