Luminescent Hydrogel Particles Prepared by Self-Assembly of β-Cyclodextrin Polymer and Octahedral Molybdenum Cluster Complexes

Abstract

A series of luminescent octahedral molybdenum cluster complexes were obtained by treating Na2[Mo6I8(OMe)6] with icosahedral closo-dicarbaborane C-carboxylic acids in refluxing tetrahydrofuran. The study of the photophysical properties of Na2[Mo6I8(1-OOC-1,2-closo-C2B10H11)6] (1), Na2[Mo6I8(1-OOC-1,7-closo-C2B10H11)6] (2), and Na2[Mo6I8(1-OOC-1,12-closo-C2B10H11)6] (3) in acetonitrile revealed a red luminescence with high quantum yields up to 0.93 for 2, an efficient quenching of the luminescence by oxygen, and high quantum yields of singlet oxygen formation of approximately 0.7. Self-assembly between compound 2 and β-cyclodextrin polymer led to monodisperse hydrogel particles with a diameter of approximately 200 nm and unchanged luminescence spectra and kinetics features over 14 days. In contrast, bare cluster complex 2 in water formed aggregates and hydrolyzed over the time as indicated by a progressive red shift of the luminescence maxima. The invariance of key photophysical parameters of the hydrogel particles coupled with a high oxygen sensitivity of the luminescence are attractive features for long-term biological experiments involving optical oxygen probing. In addition, this hydrogel is a singlet oxygen sensitizer in water with promising properties for photodynamic therapy.

Carboranes in the chemist's toolbox

“…Electrochemical data together with transmission, atomic force, and electron force microscopies, along with scanning electron microscopy, suggest that carborane-functionalized graphene oxide is a good candidate for developing conductive self-assembled monolayers. 115 The carborane cages in the hydrogel are protected from hydrolysis, and the clusters function as efficient singlet oxygen sensitizers. In the last case, luminescent hydrogel particles that exhibit high quantum yield were obtained via self-assembly of a β-cyclodextrin polymer with hexacarboranyl-hexamolybdenum cluster complexes of the composition Na 2 [Mo 6 I 8 [OC(O)-C 2 B 10 H 11 ] 6 whose carborane units are o-, m-, or p-carborane, and function as efficient singlet oxygen sensitizers that may be useful as dual agents for photodynamic therapy/BNCT agents.…”

Cellular internalisation, bioimaging and dark and photodynamic cytotoxicity of silica nanoparticles doped by {Mo6I8}4+ metal clusters

“…Firstly, similarly to their structural analogues, hexarhenium clusters [{Re 6 Q 8 }L 6 ] m (Q = S or Se), these complexes demonstrate high chemical and photostability of the cluster cores {Mo 6 X 8 } 4+ that are primarily responsible for their triplet excited state photoluminescence (i.e. 4,5,11,15 Additionally, the metal cluster complexes can also act as powerful photosensitisers in the singlet oxygen ( 1 O 2 ) generation, [5][6][7][8][16][17][18] which makes them especially interesting for applications associated with the generation of singlet oxygen in vivo, such as, for example, photodynamic therapy (PDT). Secondly, their broad emission spectra extend in the red/near infra-red region (from ∼550 to more than 950 nm) 4-13 overlapping the so called "optical tissue window" (650 − 900 nm), where the boundaries of the region are defined by the minimal light absorption of hemoglobin (< 650 nm) and water (> 900 nm).…”

MoII Cluster Complex‐Based Coordination Polymer as an Efficient Heterogeneous Catalyst in the Suzuki–Miyaura Coupling Reaction

“…To the best of our knowledge, the only example reported to date is a coordination polymer composed of the {Mo 6 Cl 8 } 4+ cores bonded with 4,4′‐bipyridine linear linkers with interesting luminescent properties . With regard to the apical ligands, carboxylated ligands are advantageous because of the chemical stability of the resulting complexes and the wide range of functionalities provided by these ligands …”