CO2-Responsive fluorescent hyperbranched poly(ether amine)s

A series of anthracene-capped, hyperbranched poly(ether amine)s (hPEA-AN) with varying hydrophilicity were designed and synthesized. Their fluorescence emission intensity in aqueous solution increases after carbon dioxide (CO2) bubbling as a result of the protonation of the tertiary amino groups in the polymer. On the one hand, the increase is more prominent when the polymer is more hydrophobic, and the increase upon CO2 bubbling is faster at a lower polymer concentration. On the other hand, the amino groups in the polymer can be partially deprotonated after N2 bubbling, which is accompanied by a weakening of the fluorescence intensity. However, this process is very slow, which may be ascribed to the diffusion restriction of N2 molecules inside the core of the micellar aggregates of hPEA-AN. The peculiar fluorescence switching behavior upon alternating CO2/N2 bubbling seems to be related to the particular architecture of hyperbranched polymers.