Y‐Shaped D‐A Type Thioxanthone Derivatives: Mechano‐Induced Thermally Activated Delayed Fluorescence and High‐Contrast Mechano‐Responsive Luminescence.

High‐contrast mechano‐responsive luminescence (MRL) materials with mechano‐induced emission enhancement properties are fascinating candidates but few, for applications in rewritable media and recording devices. Here, an interesting design strategy of "Y‐shape" donor‐acceptor (D−A) type molecules for high‐contrast MRL materials was presented, based on substituted diphenylamine donor and planar acceptor. Interestingly, their D−A torsion angles are small in crystals but increased after ground, resulted in planar and twist intramolecular charge transfer (PICT and TICT) states, respectively. Therefore, high‐contrast MRL switching between weak blue (450 nm) fluorescence and bright yellow (552 nm) thermally activated delayed fluorescence (TADF) can be achieved for compound TXDO (4,4′‐dimethoxydiphenylamine donor), which photoluminescence quantum yield increased from 2.8 % to 54.7 % after ground. Most importantly, the two independent D−A conjugation dihedral angles are actually independent in the "Y‐shape" molecules. Especially for compound TXDT (4,4′‐di‐tert‐butyldiphenylamine donor), its crystal exhibited both PICT and TICT processes inside, resulted from the different dihedral angles of 11.8° and 35.5°, respectively. The TXDT crystal thus showed dual‐peak emission, including both TICT fluorescence and PICT room‐temperature phosphorescence. Therefore, this strategy of "Y‐shape" D−A type molecules provide a new approach to design advanced luminescent materials with mechano‐induced TADF feature, for high‐contrast MRL and single‐component white luminescence. [ABSTRACT FROM AUTHOR]