One-Pot Synthesis and Structure-Property Relationship of Aminomaleimides: Fluorescence Efficiencies in Monomers and Aggregates Easily Tuned by Switch of Aryl and Alkyl

Organic fluorophores have attracted great interest owing to their wide applications. They usually contain an electron-conjugated system with an aromatic moiety and show high emission in dilute solutions but weaker or even no emission upon aggregation. Here, a simple one-pot, three-component reaction (3CR) (method I) for the synthesis of various di- and monosubstituted aminomaleimides (DAMIs and MAMIs) has been developed, and the reported 3CR (method II) has been found to be efficient only for the synthesis of MAMIs with R-2 = alkyl. Twelve AMIs were designed and synthesized for investigation of the influence of structures on their optical properties in monomers and aggregates. It was found that alkyl MAMIs, alkyl DAMIs, and aryl AMIs/DAMIs show very different fluorescence efficiencies in different solvents, and only MAMIs with butyl and oleyl show high emissions in powders similar to those in nonpolar solutions. Single-crystal structures indicate that their fluorescence efficiencies in aggregates mainly correlate with molecular packing modes. The efficient synthesis method, the sensitive fluorescence on-off response to protic solvents or polar solvents, and the unusual high emissions of AMI without any aromatic moiety in both monomer and aggregates are expected to attract great interest in the fields of application and theory.