Photodegradation in the infrared region of indocyanine green in aqueous solution

Indocyanine green (ICG) is a water soluble anionic tricarbocyanine dye which has been widely used for biological applications. The photodegradation and aggregation of ICG were studied in aqueous solution by absorbance spectrum measurements. Two excitation wavelengths were used: 780 and 808 nm. The photodegradation analysis was performed based on the number of absorbed photons and rate equations of the electronic excited states. The aggregation effect is influenced by the solvent medium. A third emission band at 640 nm, observed when in PBS solution, could be observed, associated with a trimeric band. The degradation of the aggregated forms does not follow the Beer-Lambert law. The photodegradation rates were distinct between the two excitation wavelengths, showing distinct photodegradation behaviors.