Singlet Oxygen Generation from Polyaminoglycerol by Spin-Flip-Based Electron Transfer

Reactive oxygen species have drawn attention owing to their strong oxidation ability. In particular, the singlet oxygen (¹O₂) produced by energy transfer is the predominant species for controlling oxidation reactions efficiently. However, conventional ¹O₂ generators, which rely on enhanced energy transfer, frequently suffer from poor solubility, low stability, and low biocompatibility. Herein, we introduce a hyperbranched aliphatic polyaminoglycerol (hPAG) as a ¹O₂ generator, which relies on spin-flip-based electron transfer. The coexistence of a lone pair electron on the nitrogen atom and a hydrogen-bonding donor (the protonated form of nitrogen and hydroxyl group) affords proximity between hPAG and O₂. Subsequent direct electron transfer after photo-irradiation induces hPAG^•+-O₂ ^•- formation, and the following spin-flip process generates ¹O₂. The spin-flip-based electron transfer pathway is analyzed by a series of photophysical, electrochemical, and computational studies. The ¹O₂ generator, hPAG, is successfully employed in photodynamic therapy and as an antimicrobial reagent.