A hyperbranched polysiloxane with imine bonds: red fluorescence emission with a long fluorescence lifetime at room temperature

In recent years, due to their excellent biocompatibility and environmental friendliness, non-conjugated AIE polymers have attracted extensive attention. However, problems such as short emission wavelengths and low fluorescence lifetimes have severely limited the applications of these materials. In this paper, a siloxane monomer A1 containing an imine bond was designed and synthesized, and it was used as a raw material to synthesize a hyperbranched polysiloxane P1 with imine bonds and hydroxyl groups at the end of the polymer chain. Surprisingly, P1 exhibited bright red fluorescence, and its fluorescence lifetime reached an uncommon microsecond level (11.40 μs). The luminescence mechanisms of A1 and P1 were explored through experimental and theoretical calculations. It was proposed that the introduction of local rigid planar structures could promote charge delocalization and enhance through-space interactions. Thus, the emission wavelength has a red-shift and the fluorescence lifetime has been improved. In addition, the solvent effects and pH responsiveness of P1, as well as the application of P1 for Mn²⁺ detection, were also studied.