A novel stilbene-based organic dye with trans-cis isomer, polymorphism and aggregation-induced emission behavior

• A novel stilbene-based organic dye was developed.
• The dye display trans-cis isomer.
• Each isomer has two conformation polymorphs.
• AIE behavior of the trans isomer is unusual.

Cis-trans isomer and polymorphism of 9-(4-(4-nitrostyryl)phenyl)-9H-carbzole (Dye 1) were obtained unexpectedly. Each isomer has two polymorphs, which was characterized by X-ray single crystal diffraction. Polymorphs T1 and T2 are trans-configuration and both crystallize in monoclinic space group P21/c. Polymorphs C1 and C2 are cis-configuration and crystallize in triclinic space group P-1 and monoclinic space group P21/c, respectively. Trans-isomer shows better stability and higher density than that of cis-isomer, but cis-isomer displays better solubility than that of trans-isomer. The molecular structures and packing arrangements of the four kinds of crystals show different features. The twisted conformation of cis-isomer effectively avoids π-π interactions and close packing. Both the trans and cis isomers show remarkable aggregation-induced emission effect in the acetonitrile/water mixture. In addition, fluorescence cell imaging experiment proves the potential application of the two isomers of dye 1.

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