Polybrominated diphenyl ethers (PBDEs)
have aroused global environmental
concerns because of their toxicity and ubiquitousness in the biological
and environmental systems. It is important to find an efficient method
for their decontamination and to understand their chemical transformation
in the environment. Here, we report that decabromodiphenyl ether (BDE209)
undergoes efficient reductive debromination reactions under visible-light
irradiation (≥420 nm) in the presence of various carboxylate
anions that are common in the environmental media. The debromination
reactions occur in a stepwise manner, producing a series of lower
brominated PBDE congeners. Solvent-derived radials are observed by
spin-trapping electron spin resonance (ESR) experiments during the
photoreaction. Further experiments by the UV–vis absorption
and isothermal titration calorimetry (ITC), combined with theoretical
calculations, reveal a new photochemical debromination pathway based
on the halogen binding interaction. According to this pathway, the
formation of halogen-binding-based complex between PBDE and carboxylate
enables the visible-light absorption and debromination of PBDEs, although
neither PBDEs nor carboxylates have visible-light absorption. The
halogen-bond-based photochemical debromination could find its application
for our better understanding of the transformation process of PBDEs
in the environment.