Mechanochromic, thermoresponsive and triboluminescence behaviors of one divinyl thioxanthene based AIE luminogen with variable conformations

Strategic structure designs to develop organic multi-stimuli-responsive fluorescent materials are highly desired, but hard to achieve. We report here a novel multi-stimuli responsive luminescent material TXENE (1,2-di(9H-thioxanthen-9-ylidene)ethane) composed of double thioxanthene chromophores and a diene liker that integrate polymorphism, aggregation-induced emission (AIE), mechanoluminescence (MCL), thermoresponsive luminescence (TCL), and triboluminescent (TL) properties into one single molecule. Three crystalline polymorphs including TXENE-G and TXENE-Y with a terminal up-down conformer and TXENE-R with an up-up form are obtained. The X-ray structure analysis revealed that not only the intermolecular interactions but also the terminal chromophore-thioxanthene conformation (up-down vs. up-up) dominate polymorphism, thus leading to distinct luminescent properties. It is shown that MCL, TCL and TL properties can be systematically tuned via its aggregation state regulation; typically, the metastable TXENE-G and TXENE-R are MCL and TCL active, while TXENE-Y is TL active. Lastly, we illustrate the possible application of color-changeable indicators for information anti-counterfeiting and thermal sensing by using TXENE. This study demonstrates that multiple unique functions can be integrated into one single compound by fine controlling its aggregation states, which render a new strategy for the investigation of multifunctional organic materials.