Thermally responsive AIE-active polyurethanes based on a tetraaniline derivative

Polyurethanes with different soft-hard segment ratios were successfully synthesized, with an aggregation-induced-emission (AIE)-active tetraaniline derivative (NH₂-B₃-Ani₄-NH₂) as the hard segment. The resulting polyurethanes exhibited typical AIE features. The fluorescence intensities of polyurethane films changed with heat treatments. The fluorescence intensities of the polyurethane films decreased sharply after quenching treatment, yet their fluorescence intensities exceeded the original intensities of the films after thermal annealing at 80 °C for 24 h. Differential Scanning Calorimetry (DSC) results implied that the melting peaks in polyurethane films disappeared after quenching treatment, but the melting peaks appeared again after thermal annealing. These results proved that the arrangement of the structure had an important effect on the AIE properties of the polyurethane films. Meanwhile, the fluorescence intensities of these polyurethanes decreased with the increase of temperature, indicating that all three polyurethanes exhibited temperature-dependent fluorescent characteristics. Based on the above investigations, the AIE-active polyurethanes may provide a platform for the development of stimuli-responsive fluorescent materials.