Multiple stimulus modulated organic crystal polymorphs with tunable luminescence behavior.

Polymorphism is defined as the ability of a substance to exist in two or more crystalline forms, which provide a unique platform for revealing the relationship between its spatial structure and properties. However, organic crystal polymorphism can be commonly obtained by growing crystals in different solvents or at different temperatures. This study reports a compound named p-An-Br containing carbazole and anthracene chromophores with three multiple stimulus modulated crystal polymorphs with green, yellow and red fluorescence, respectively. Interestingly, switching of p-An-Br between crystal G, crystal Y and crystal R can be achieved through the uptake and release of methanol using different stimuli, which shows dynamically adjustable luminescent colors. Significantly, structure-property investigations via the in-depth analysis of molecular conformations and frameworks of the polymorphic crystals demonstrate that the diverse conformations and abundant noncovalent interactions have a predominant impact on emission behavior. Consequently, the crystals R can be used for the highly sensitive and specific sensing of methanol with a detection limit of 39.35 ppm. This study not only provides a new strategy for crystal polymorphism, but also develops an effective method for the detection of methanol.