Abstract: The spectrum characteristic and photostability of three near-infrared absorbing cyanine dyes with typical structure have been studied. The results show that the stability of three dyes with molecular structure of heterocyclic stem nuclei against photooxidation is in such order: benzoxazole $GRT benzothiazole $GRT benselenazole. It was found through quenching experiments that the photooxidation of cyanine dyes not only relates to the singlet oxygen but also to the superoxide anoin, however single oxygen plays a dominant role. We have succeeded in drastically improving the photostability of three cyanine dyes by using a dithiol nickel chelate as a singlet oxygen quencher.!13
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