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.