Construction, Characterization, and Properties of Poly(iminofuran-spiro-oxindole)s through Catalyst-Free Multicomponent Spiropolymerization of Diisocyanides, Activated Alkynes, and Bis-isatins

Spiropolymers built from monomers without spirocyclic structures have garnered significant academic interest and hold substantial technological value. However, their construction still remains a challenging project, primarily due to limited polymerization methods. Herein, we introduce a novel multicomponent spiropolymerization for synthesizing poly(iminofuran-spiro-oxindole)s from diisocyanides, activated alkynes, and bis-isatins without the use of catalyst, even under mild conditions. The common natural product isatin, a vital feedstock in the dye industry and pharmaceutical fields, has been elegantly and rationally employed to construct spiropolymers. The resultant spiropolymers demonstrate favorable solubility, excellent thermal stability, satisfactory isolated yields (up to 92.6%), and high molecular weights (up to 56800 g/mol). The experimental data and theoretical calculations reveal that only the carbonyl group located at position 3 of isatin is involved in the formation of spiropolymers. Notably, despite lacking conventional fluorophores, the prepared poly(iminofuran-spiro-oxindole) displays both clusterization-triggered emission and aggregation-enhanced emission properties. Intriguingly, the photoluminescence can be quenched by both ferrous and ferric ions efficiently in an organic solution and only ferric ions exclusively in an organic/water mixture. It is highly anticipated that this instructive work will open a new avenue of spiropolymer construction and contribute to expanding diverse applications.