Intrinsic bright green emission from hyperbranched polyphosphate esters: preparation, film fabrication and Fe³⁺ sensing

Unconventional fluorescent polymers have attracted intense attention due to their unique emission properties, excellent biocompatibility and facile preparation. Herein, a series of hyperbranched polyphosphate esters (HPPEs) without any large conjugated π bonds were synthesized. HPPEs showed aggregation-induced emission and concentration-enhanced emission characteristics, and emitted bright green light under different excitation wavelengths. Results demonstrated that the HPPE molecules aggregated together due to the strong inter/intramolecular hydrogen bonds and formed different aggregates in solutions of various concentrations. Then, the hydroxyl and O = P(O)₃ groups clustered and acted as the emission center. Moreover, the balance of the rigidity and flexibility of the polymers also enhanced the emission. Interestingly, HPPE doped PVA films could generate blue room temperature phosphorescence due to the enhanced rigidity, and HPPEs show excellent selectivity in Fe³⁺ sensing. Therefore, this work provides an excellent design strategy for green emissive polymers, and information on the emission origin of unconventional fluorescent polymers.