Multistimuli-Responsive Luminescent Porous Organic Polymers with Chiroptical Properties and Acid-Induced Degradation

Porous organic polymers (POPs) have attracted great attention in past decades. Although diverse functional POPs have been developed, multistimuli-responsive POPs with excellent aggregate-state luminescence together with good chiroptical properties have rarely been reported. Herein, two pairs of Salen-type enantiomeric POPs with multistimuli-responsive luminescence and chiral features were designed and synthesized by facile polycondensation reactions between polyfunctional aggregation-induced emission luminogen (AIEgen)-containing salicylaldehyde derivatives and chiral diamines. With Salen units in polymer backbones as tetradentate ligands, a series of POP-metal complexes were further prepared. The obtained POPs and metal complexes show good porosity, high thermal stability, and obvious circular dichroism signals. Moreover, benefiting from the coexistence of AIEgen and Salen units in polymer structures, these POPs exhibit excellent luminescence performance in aggregate states and tunable fluorescence behaviors in response to external stimuli of Zn2+ ion, mechanical forces, organic solvent, and acids. Due to the dynamic feature of Schiff base C=N bonds, the present POPs can efficiently undergo hydrolysis reactions under strong acidic conditions to reproduce the AIEgen- containing monomers, and such an acid-induced degradation process can be directly visualized and dynamically monitored via fluorescence variation. These properties collectively make the POPs candidate materials for applications in heterogeneous asymmetric catalysis, fluorescence sensing, biomedicine, etc.