title: Upconverting-nanoparticle-assisted photochemistry induced by low-intensity near-infrared light: how low can we go?
abstract: Upconverting nanoparticles (UCNPs) convert near-infrared (NIR) light into UV or visible light that can trigger photoreactions of photosensitive compounds. In this paper, we demonstrate how to reduce the intensity of NIR light for UCNP-assisted photochemistry. We synthesized two types of UCNPs with different emission bands and five photosensitive compounds with different absorption bands. A λ=974 nm laser was used to induce photoreactions in all of the investigated photosensitive compounds in the presence of the UCNPs. The excitation thresholds of the photoreactions induced by λ=974 nm light were measured. The lowest threshold was 0.5 W cm(-2) , which is lower than the maximum permissible exposure of skin (0.726 W cm(-2) ). We demonstrate that low-intensity NIR light can induce photoreactions after passing through a piece of tissue without damaging the tissue. Our results indicate that the threshold for UCNP- assisted photochemistry can be reduced by using highly photosensitive compounds that absorb upconverted visible light. Low excitation intensity in UCNP-assisted photochemistry is important for biomedical applications because it minimizes the overheating problems of NIR light and causes less photodamage to biomaterials.
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz (Germany).
authors.forename: Zhijun
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz (Germany).
authors.forename: Wen
authors.initials: W
authors.lastname: Sun
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz (Germany).
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Butt
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz (Germany). wusi@mpip-mainz.mpg.de.
authors.forename: Si
authors.initials: S
authors.lastname: Wu
keywords: nanoparticles; near infrared; photocages; photochemistry; upconversion