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

Abstract

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" donoracceptor (DÀ A) type molecules for high-contrast MRL materials was presented, based on substituted diphenylamine donor and planar acceptor. Interestingly, their DÀ 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'-dimeth-oxydiphenylamine donor), which photoluminescence quantum yield increased from 2.8 % to 54.7 % after ground. Most importantly, the two independent DÀ 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" DÀ 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.

Anthracene–naphthylacetonitrile fluorescent isomers and Cl/H substituent dependent molecular packing, solid-state fluorescence and mechanofluorochromism

“…21–25 The non-planar molecular structure and weak intermolecular interactions also provided an opportunity to achieve mechanoresponsive fluorescent materials. 26–30 Mechanical pressure can disrupt the supramolecular interactions, molecular conformation and packing that strongly affect the optical bandgap, resulting in the modulation of fluorescence. 31–35 Hence, several π-conjugated organic derivatives have been synthesized and reported for mechanical stimuli-induced reversible fluorescence switching between two fluorescence states (on–on) or change of fluorescence intensity (on–off).…”