Study on the Photophysical Properties and Molecular Weight‐Dependent Clusteroluminescence of Polymethacrylic Acid

ABSTRACT There are few literatures that report the relationship between the molecular weights and the photophysical properties of unconventional aggregation‐induced emission (AIE) organic polymers. Herein, we prepared a group of polymethacrylic acids (PMAs) with increasing molecular weights through free‐radical polymerization in water. These PMAs show AIE effect and exhibit photoluminescence (PL) both in the solid state and in the aqueous solutions. The data of the ultraviolet–visible absorption spectra, fluorescent excitation and emission spectra, and fluorescent lifetimes all indicate that the PMAs have similar fluorescent emitting species, which are originated from the clusters of their carbonyl oxygen atoms. Due to the wide molecular‐weight distributions, the PMAs have multiple fluorescence emission centers, resulting in significant excitation wavelength‐dependent emission. As the molecular weights increase, the quantum yields (QYs) of the PMAs first increase and then decrease, suggesting that the QYs of the PMAs are directly related to the molecular weights. Meanwhile, the PL intensities of the PMA aqueous solutions gradually increase with the molecular weights, showing obvious molecular weight‐dependent clusteroluminescence.