Polymorphism and Multicolor Mechanofluorochromism of a D-π-A Asymmetric 4H-Pyran Derivative with Aggregation-Induced Emission Property

Abstract

A D-π-A 4H-pyran derivative (AMP) containing dicyanomethylene, benzene, and 4-hydroxybenzene units was designed and synthesized, which exhibited an aggregationinduced emission property. This asymmetric compound had three polymorphs, namely, yellow-emitting AMP-y, orangeemitting AMP-o, and red-emitting APM-r. AMP-y and APM-r showed very similar twisted conformations, and their different solid-state emissions depended not only on the molecular conformations but also on the zig-zag packing arrangements containing the coexistence of J-aggregation and H-aggregation with a subtle difference, whereas the solid-state emission of AMP-o mainly depended on the complete planar conformation. The polymorphs exhibited different stimulus-responsive fluorescence color changes upon grinding. AMP-y and APM-r displayed bathochromic and hypsochromic mechanofluorochromic (MFC) characteristics, respectively, and were both converted into orange-emitting solids, which were ascribed to the destruction of π•••π interactions in the packing arrangements and the resultant planarization of molecular conformations and the change of packing arrangements. However, although a crystal-toamorphous transformation occurred upon grinding, crystal AMP-o was MFC inactive because the grinding treatment could not result in the enhanced π•••π stacking interactions owing to the dislocation arrangements in the molecules with planar conformations. Our results indicate that the combination of the polymorphic and MFC properties is beneficial to enrich the fluorescence color changes of MFC-active materials. Furthermore, the different MFC properties of the polymorphs are helpful for understanding the mechanism of the mechanofluorochromism.

ICT and AIE Characteristics Two Cyano-Functionalized Probes and Their Photophysical Properties, DFT Calculations, Cytotoxicity, and Cell Imaging Applications

“…Overall, the weakly emissive AIE-2 probe became highly emissive on aggregation with high water fractions, showing AIEE. Similar types of AIEE behaviors were reported earlier in a THF-water solvent mixture of cyano-functionalized probes [41]. Not only the cyano-functionalized probes, but other functional groups containing probes have also been reported to have good AIEE active properties in different solvent mixtures, such as carbazole [42], diphenylamine [43], tetraphenylethene [44], hexaphenylsilole [45], and naphthalimide [46].…”

Design of High-Contrast Mechanochromic Materials Based on Aggregation-Induced Emissive Pyran Derivatives Guided by Polymorph Predictions

“…23,24 In some cases, both the conformation and molecular packing might be changed under stimuli. [25][26][27] Therefore, questions arise regarding which kind of molecule has the potential to aggregate in both monomer (namely without intermolecular π-π interaction) and π-dimer (with strong π-π interaction between neighboring molecules) and what kind of molecule can comprise conformations with a significant difference? If we can calculate the potential polymorphs of the designed molecules, we might be able to predict their MC behavior.…”

Multi‐Directional Mechanofluorochromism of Acetyl Pyrenes and Pyrenyl Ynones

“…Organic compounds that exhibit aggregation‐induced emission (AIE), charge transfer (CT) or polymorphism are promising candidates to host MFC due to the multiple accessible structures with orientation‐dependent emission properties in aggregated states [10–12] . For example, an AIE‐active 4H‐pyran derivative was reported to form three polymorphs with distinct MFC properties that share the same molecular arrangement in ground form [13] . A small difference in chemical structures and packing motifs can also induce significant difference in mechanical responses, represented by p ‐ and m ‐substituted tetraphenylethylene isomers with and without MFC [14] .…”