Balancing the Chain Flexibility and Rigidity of Crosslinked Polyacrylic Acid Toward Optimized Fluorescence Quantum Yield

ABSTRACT The balance of chain flexibility and rigidity may improve the fluorescence quantum yields (QYs) of unconventional aggregation‐induced emission (AIE) polymers. Herein, we prepared four crosslinked polyacrylic acids (CPAAs) with AIE effect using N,N′ ‐methylene bisacrylamide (MBA) as the crosslinker. The chain flexibility of the CPAAs decreases with the increase of MBA contents. These CPAAs show bright blue fluorescence under the irradiation of UV light. The maximum excitation wavelengths of the CPAAs are not near their UV absorption peaks because their emission is originated from the clustering of the oxygen atoms of the carbonyl groups, but not the ( n , π *) transition of the oxygen atoms. The emission spectra and fluorescent lifetime data both validate that all the CPAAs have similar emission species. Density functional theory calculations suggest the emission of the CPAAs comes from the carboxyl groups. One of the CPAAs with balanced chain flexibility and rigidity has an optimized fluorescence QY of 17.7%, which is much higher than that of the reported linear PAA of 4.5%.