No abstract

Aggregation-induced emission (AIE)-active maleimide dyes, namely, 2-p-toluidino-N-p-tolylmaleimide, 3-phenyl-2-toluidino-N-p-tolylmaleimide, 2-p-thiocresyl-3-p-toluidino-N-p-tolylmaleimide, and 2,3-dithiocresyl-N-arylmaleimides, were synthesized by facile synthetic procedures. The dyes show intense emission in the solid state, and emission colors were controlled from green (λmax =527 nm) to orange (λmax =609 nm) by varying the substituents at the 2- and 3-positions of the maleimide and the packing structures in the solid state. 2,3-Disubstituted maleimide dyes effectively underwent redshifts of their emission wavelength. Furthermore, some of the dyes exhibited mechanochromism and polymorphism, and their emission properties were dramatically dependent on the morphology of the solid samples. The mechanisms of the emission behaviors were investigated by X-ray diffraction. The substituent of the nitrogen atom of the maleimide ring affected the intermolecular interactions and short contacts, which were observed by single crystal X-ray crystallography, to result in completely different emission properties.

Aggregation induced emission (AIE) active N-alkyl aminomaleimide dyes with various kinds of N-alkyl groups were synthesized in a one pot process.

A mechanochromic luminescent dye based on a simple aminomaleimide skeleton was readily synthesized in a one-pot process. It exhibited an on/off mechanochromic luminescent switching property dependent on external stimuli, unlike a traditional mechanochromic color change. The green emission was turned on by grinding in a mortar and turned off by heating or treatment with dichloromethane. In the crystalline state, two molecules were stacked by cofacial π-π interactions, which caused concentration self-quenching. The crystalline-to-amorphous transition induced by grinding removed cofacial π-π stacking, which led to intensive emission. Crystallizing processes recovered the cofacial π-π stacking, resulting in elimination of the emission. Theoretical calculations and X-ray diffraction analyses revealed that the dye molecule was distorted in the crystalline state; thus even a mechanical stimulus caused the crystalline-to-amorphous transition.