Tunable fluorescence efficiency of hyperbranched polysiloxanes via changing side chain groups

Nontraditional fluorescent polymers lack of large π-systems possess very potential applications in various fields. Herein, we report a class of hyperbranched polysiloxanes exhibiting multicolor fluorescence from blue to green when excited by different wavelengths. The quantum yield (QY) of pure P1 achieves a higher of 21.1% in comparison with P2 containing cyclic piperazine groups. The ethylenediamino groups on the side chain of P1 possess local flexibility, which facilitates the formation of larger aggregates. As-prepared polymers demonstrate excellent applications in selectively fluorescence detection for Fe3+ and Co2+, and information encryption. Moreover, the fluorescence of P1 and P2 exhibit a pronounced pH-dependent emission. Density functional theory (DFT) calculations reveal that the through-space n-n interactions formed among electron-rich N and O facilitate spatial electronic delocalization and rigidify the molecular conformation, resulting in the fluorescence. Incorporating polymers into matrix enables fluorescent films and hydrogels to be fabricated. This work provides a novel strategy for the rational design nontraditional fluorescent polymers with high QY.