Thermally Activated Delayed Fluorescence of Aggregates Induced by Strong π-π Interactions and Reversible Dual-Responsive Luminescence Switching

A reversible dual-responsive luminescent material was introduced by our group to show the simultaneous color and lifetime switching in response to external stimuli. Pristine crystalline powder of (E)-2-(benzo[d]thiazol-2-yl)-3-(pyren-1-yl)acrylonitrile (Py-BZTCN) shows the ordered pi-pi stacking with only near-monomer-normal orange-yellow fluorescence, but it exhibits red emission with thermally activated delayed fluorescence (TADF) after grinding, which can be reversibly recovered by heating or fuming treatment. Grinding disturbs the ordered pi-pi stacking of pristine powder, leading to the formation of small aggregates with compressed distance and increased overlap of pi-pi stacking between adjacent molecules. The cause of switching was verified by single-crystal X-ray diffraction experiments of two corresponding crystals. This strong ir ir interaction effectively promotes the excited-state energy splitting and substantially decreases the singlet-triplet energy gap (Delta E-ST) of aggregates, resulting in the red TADF emission of aggregates through reverse intersystem crossing. This finding proposes a new route to realizing the TADF emission of aggregates through strong intermolecular interactions based on non-TADF monomer, thereby enabling a novel high-contrast dual-responsive luminescence switching. [GRAPHICS] .

Automated summary

A reversible dual-responsive luminescent material was developed, with the ability to switch between colors and lifetimes in response to external stimuli. This was achieved by manipulating the intermolecular interactions of individual molecules, resulting in red emission through thermally activated delayed fluorescence (TADF) of aggregates.