Abstract:
In order to study the effect of amino acids on the chirality and aggregation induced emission (AIE) feature of polymers, polymethacrylate containing both biphenyl and Boc-
D-alanine was synthesized using free radical polymerization. Biphenyl, a simplest AIE moiety, was introduced into the side chains as a spacer connecting the main chains and the side chains themselves. The molecular weight of the obtained polymer were determined to be 8.7×10
4 by gel permeation chromatography. The circular dichroism (CD) spectrum of the prepared polymer displayed a significantly positive peak around 270 nm, implying that a torsion conformation was formed in the polymer. FT-IR spectra proved that hydrogen bonds were formed between the side chains, which played important roles in the stabilizing of the chirality of the polymer. Importantly, the fluorescence intensity of such polymer in 90% tetraphydrofuran (THF)/water mixture is 5.7 times higher than that in pure THF, indicating an obvious AIE phenomenon. Transmission electron microscopy (TEM) images further revealed that such polymer could self-assemble into aggregates of nanoparticles in THF/water mixtures. These results suggest that the AIE property can be mainly attributed to the restriction of the intramolecular rotation of biphenyl in aggregates. More importantly, such polymer could respond to the variation of pH adjusted by HCl and NaOH: the fluorescence intensity increased with the addition of NaOH, but decreased with the addition of HCl. It is likely that such a pH-responsive behavior results from the change of solubility of the polymer in acid base solutions. Such polymer nanoparticles with the AIE-property and the chirality have a promising potential for various practical applications, such as bio-imaging, chemical sensor, and so on.