Halogenated cyanine dyes for synergistic photodynamic and photothermal therapy

Cyanine dyes are widely used in the field of tumor phototherapy due to their excellent photophysical properties. To explore the heavy atoms effects on the photothermal and photodynamic performance of phototherapeutic agents, chlorine, bromine, and iodine were introduced to synthesize a series of cyanine dyes (IR6, IR7, and IR8). We have found that all halogenated cyanine dyes exhibited high excitation wavelength (around 800 nm) and low dark toxicity. Among them, IR8 behaved the best singlet oxygen production ability in the three dyes. For photothermal performance, IR8 exhibited the best photothermal conversion rate (46.6%), photothermal stability, and excellent therapy efficiency (half-maximal inhibitory concentration, IC50 = 16.2 μg/mL). IR7 behaved a greater enhancement of the photothermal conversion rate (43.4%) than IR6 (42.3%). In conclusion, the heavy atoms effects on the photothermal and photodynamic properties of cyanine dyes are positively correlated with the increase of the atomic number of the halogen atom, and the iodine atom may be the most worthy of consideration in the all halogen atoms.