Expanding the Toolbox of Octahedral Molybdenum Clusters and Nanocomposites Made Thereof: Evidence of Two-Photon Absorption Induced NIR Emission and Singlet Oxygen Production

Abstract

Octahedral Molybdenum clusters bright NIR phosphorescence is known since the 80's. However, their behavior toward NIR excitation has never been investigated. Here we report their abilities to emit NIR light and produce singlet oxygen upon two-photon absorption. This behavior is observed in solution, in the solid-state as well as when clusters are embedded homogeneously in a poly(dimethylsiloxane) matrix. Such discoveries open new perspectives in several fields like optoelectronic, photodynamic therapy or bioimaging.

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

“…Impressively, guided by this design strategy, octahedral Mo 6 nanoclusters were homogeneously distributed with a wide concentration (1−10 wt %) in a poly(dimethylsiloxane) matrix, and NIR-I room-temperature phosphorescence was determined via two-photon absorption (Figure 17b). 330 Very impressively, even after 48 months of aging, Mo 6 -doped silicone maintained intense NIR-I phosphorescence similar to the newly doped samples. This ultrahigh luminescence stability of octahedral Mo 6 nanoclusters originated from their strong and homogeneous interactions with the host matrix, which can greatly inhibit any unwanted phase segregation or leaching of integrated Mo 6 nanoclusters.…”

“…(b) Pictures under ambient light (upper panel) and two-photon emission spectra (bottom panel) of the Mo 6 clusters in a poly­(dimethylsiloxane) matrix. Reprinted with permission from ref . Copyright 2021 American Chemical Society.…”

Flexible and Transparent Luminescent Cellulose-Transition Metal Cluster Composites

“…In particular, MC containing molybdenum, an abundant, non-toxic, and cheap element compared to noble or rare earth metals, are highly emissive in the red NIR region when excited in the UV-Vis range [ 26 , 27 ]. Recently, we showed that such emission is also observed when MC are excited in the NIR via a two-photon absorption process [ 28 ]. They are obtained by high temperature synthesis as crystalline powders exhibiting a strong ceramic-like behavior.…”

Phosphorescent Metal Halide Nanoclusters for Tunable Photodynamic Therapy

“…The hexanuclear molybdenum (Mo)-based transition metal halide nanocluster (NC) salts have recently emerged as alternative PS candidates for PDT due to their desirable photophysical and photo-chemical properties, lack of toxic elements (such as Pb or Cd), and high degree of chemical stability. [17][18][19][20][21][22][23][24][25][26][27][28] Molybdenum dichloride was first synthesized in 1859 when Blomstrand prepared low-valence molybdenum halides by passing hydrogen over pentachloride in a hot tube. [29] Early on, it was considered to be a trimer; however, the first definite structural characterization was established in 1950 by Vaughan and Pauling in a crystal structure composed of the Mo 6 C1 14 2À ion with MoÀ Mo octahedron surrounded by eight face-bridging and six axial halides.…”

“…Here, we expand on this work to control the cytotoxicity and phototoxicity of highly emissive phosphorescent octahedral cluster complexes that generate singlet oxygen, opening the possibility for PDT in various cancer types. The hexanuclear molybdenum (Mo)‐based transition metal halide nanocluster (NC) salts have recently emerged as alternative PS candidates for PDT due to their desirable photo‐physical and photo‐chemical properties, lack of toxic elements (such as Pb or Cd), and high degree of chemical stability [17–28] . Molybdenum dichloride was first synthesized in 1859 when Blomstrand prepared low‐valence molybdenum halides by passing hydrogen over pentachloride in a hot tube [29] .…”