Synthesis of Halogenated Curcumin Derivatives and Its Photodynamic Inactivation Effect on Vibrio parahaemolyticus

In order to enhance the photodynamic inactivation (PDI) effect of curcumin, a novel class of halogenated curcumin derivatives X-cur (X = F, Cl or Br) was synthesized and screened for its potential for PDI by ultraviolet-visible (UV-Vis) absorption and fluorescence spectroscopy, singlet oxygen (¹O₂) generation capacity and theoretical calculations of excited states. The results demonstrated that as the relative molecular mass of the nonmetallic heavy atom halogen increased, the spin-spin coupling effect was gradually strengthened, so the smallest energy level difference (ΔE_st(S1-T3)) between singlet excited state (S₁) and triplet excited state (T₃) (0.140 eV) and the highest spin-orbit coupling value (0.642262 cm^-1) were observed in Br-cur. This finding suggested that Br-cur was most likely to undergo transition into triplet state through intersystem crossing. Furthermore, compared to curcumin and other halogenated curcumins, Br-cur exhibited the smallest energy level difference (3.260 eV) between its S₁ and ground state (S₀). Due to the aforementioned factors, Br-cur was highly prone to photooxidation and had the highest ¹O₂ generation capacity. Br-cur had a PDI effect on Vibrio parahaemolyticus, a prevalent foodborne pathogen in aquatic products, which depended on its concentration and light exposure duration and was significantly higher than that of curcumin. Thus, Br-cur has great potential for application as a novel PDI agent.