An Optically Active Polymer for Broad‐Spectrum Enantiomeric Recognition of Chiral Acids

Abstract

Recognition of enantiomers of chiral acids by anion-π or lone pair-π interactions has not yet been investigated but is a significant and attractive challenge. This study reports an optically active polymer-based supramolecular system with capabilities of discriminating enantiomers of various chiral acids. The polymer featuring alternate π-acidic naphthalenediimides (NDIs) and methyl l-phenylalaninates in the backbone exhibits an unprecedented slow self-assembly process that is susceptible to perturbation by various chiral acids. Thus, the combination of anion-π or lone pair-π interactions and sensitivity of the polymeric self-assembly process to external chiral species endows the system with recognition capabilities. This is the first time that anion-π or lone pair-π interactions have been applied in the recognition of enantiomers of various chiral acids with a single system. The results shed light on new strategies for material design by integrating π-acidic aromatic systems and chiral building blocks to afford relevant advanced functions.

Weakly Basic Anion Recognition by Naphthalenediimide‐Based Polymer

“…The time‐dependent CD spectra showed that AcO − had a significant influence on the self‐assembly and the chiral supramolecular architectures of PNDI (Figure b). The negative CD signal at 382 nm becomes significantly weaker with time, which is contrary to the behavior in the absence of anions (Scheme a). The positive CD signal for PNDI at 334 nm disappears in the presence of AcO − .…”

“…Polymer anion receptors, which usually supply multivalent and cooperative supramolecular interactions with anions, have attracted considerable attention owing to their unique features of signal amplification and enhanced sensitivity versus non‐polymeric systems . Recently, we found a supramolecular system based on the chiral polymer PNDI whose feature of slow self‐assembly was prone to disturbance by external chiral acids (Scheme ) . The disturbance of self‐assembly gives the polymer the capacity for enantiomeric recognition of chiral acids and salts.…”

“…Fluorescence spectra of PNDI provide evidence for the influence of the anions on the self‐assembly of the polymer. The aggregation‐induced emission at 455 nm ( λ ex 360 nm) with a hyperchromic effect over time was observed for PNDI ; however, this effect was completely quenched in the presence of AcO − or Cl − (Figure ). The affinity of anions with NDIs broke the self‐assembly process and disturbed the aggregation of the polymer, which is the fundamental and intrinsic reason for the broad‐spectrum anion recognition by the polymer .…”

“…In conclusion, we studied the application of the π‐acidic NDI‐based polymer PNDI for the recognition of weak basic oxyanions (AcO − , PhCO 2 − , ClO 4 − , and IO 4 − ) and halides (Cl − , Br − , and I − ). The recognition is achieved through anion‐NDI interactions and the sensitivity of the polymer self‐assembly to external anions . The anions trigger the formation of characteristic NDI .…”

Anion-π and lone pair-π interactions with s-tetrazine-based ligands

“…The lone pair-π [1][2][3][4][5][6][7] and anion-π [1,[8][9][10][11][12][13][14][15][16][17][18][19] interactions are emergent noncovalent forces whose occurrence has recently been recognized in both synthetic architectures [8,20,21] and biomolecular structures [4,[22][23][24][25][26] and are now taken into account for the construction of new functional materials [27][28][29][30][31][32][33][34], receptors [35][36][37][38][39][40][41][42][43] carriers [44][45][46]…”