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 R2 = 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.