Light stability of a β-cyclodextrin inclusion complex of a cyanine dye

Abstract

The stability to light of 1,3,3,1′,3′,3′-hexamethyl-2,2′-indotricarbocyanine iodide (HITC) included in β-cyclodextrin (β-CyDx) has been examined. The quantum yield of the photodegradation of HITC was found to decrease with increasing formation of the inclusion complex, showing that the photostability of the dye can be improved by the formation of the complex. Emission from singlet oxygen (¹Δ_g→³Σ^–_g, 1268 nm and 1580 nm) for systems of HITC with or without β-CyDx in aqueous solution was also measured. It was found that the amount of singlet oxygen generated by flash irradiation is reduced by the inclusion complex formation, and that the lifetime of singlet oxygen increased with increasing concentration of β-CyDx, suggesting that the photodegradation of HITC for the system of HITC/β-CyDx is reduced by two factors; first, the inhibited formation of singlet oxygen, and secondly, the inhibited attack of singlet oxygen on the dye.