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

Abstract

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.