Triplet-Induced Singlet Oxygen Photobleaches Near-Infrared Dye-Sensitized Upconversion Nanosystems

Therapid photobleaching of near-infrared (NIR) dye-sensitizedupconversion nanosystems is one of the crucial problems that has blockedtheir technological applications. Uncovering the photophysical andphotochemical pathways of NIR dyes would help to elucidate the photobleachingmechanism and thereby improve the photostability of the system. Herewe investigate the triplet dynamics of NIR dyes and their interactionwith triplet oxygen in the typically investigated IR806-sensitizedupconversion nanoparticle (UCNP) nanosystem. Low-temperature fluorescenceat 77 K provides direct proof of the generation of singlet oxygen(O-1(2)) under 808 nm laser irradiation. Mass spectrometryindicates that all three double bonds in the structure of IR806 canbe broken in the photochemical process. Coupling IR806 to the surfaceof UCNPs can accelerate its triplet dynamics, thus producing more O-1(2) to photocleave IR806. Importantly, we find thatthe addition of & beta;-carotene can scavenge the generated O-1(2), thereby providing a simple method to effectively inhibitphotobleaching.