Red‐NIR Luminescent Hybrid Poly(methyl methacrylate) Containing Covalently Linked Octahedral Rhenium Metallic Clusters

Abstract

The embedding of functional inorganic entities into polymer matrices has become an intense field of investigation in which the main challenges are to keep the added value of the inorganic entities while preventing their self-aggregation within the organic matrix. We present a simple way to obtain a homogeneous highly red-NIR luminescent hybrid copolymer that contains covalently bonded nanometric-sized {Re(6)} octahedral clusters. The [Re(6)Se(i)(8)(OH)(a)(6)](4-) cluster complexes are primarily functionalized in two steps with tert-butylpyridine (TBP) and methacrylic acid (MAC) to give neutral [Re(6)Se(8)(TBP)(4)(MAC)(2)] building blocks that are copolymerized with methyl methacrylate (MMA) either in solution or in bulk in the presence of azobisisobutyronitrile as an initiator. Several samples containing 0, 0.025, 0.05, and 0.1 wt % of functionalized {Re(6)} clusters were prepared. As the {Re(6)} cluster/MMA ratio is very low, the obtained copolymers keep the entire processability of pure poly(methyl methacrylate) (PMMA), as demonstrated by differential scanning calorimetry and thermogravimetric analysis. Voltammetric and luminescence studies also indicate that the intrinsic properties of the clusters are preserved within the polymer matrix. All the samples show a bright (emission quantum yield=0.07), broad, and structureless emission band, which extends from lambda=600 nm to more than lambda=950 nm, with the maximum wavelength centered around lambda(em)=710 nm either in solution or in the solid state. Moreover, the high stability of the incorporated inorganic phosphors prevents the material from photobleaching, and thus the luminescence properties are kept entirely even after nine months of ageing.

Supramolecular Frameworks Built up from Red‐Phosphor­escent trans‐Re6 Cluster Building Blocks: One Pot Synthesis, Crystal Structures, and DFT Investigations

“…Similar to other [{Re 6 Q i 8 }L a 6 ] complexes based on a {Re 6 Q 8 } 2+ cluster core (Q = S or Se) [10,24,77,78] the powdered samples 1 and 2 emit bright red phosphorescence upon UV photoexcitation (λ ex = 355 nm). Emission spectra are shown in Figure 7.…”

Synthesis and structures of new octahedral heterometal rhenium-osmium cluster complexes

“…Like the majority of previously studied chalcogenide octahedral rhenium cluster complexes [12,13,[23][24][25][26][27][28][29][30][31][32][33][34][35], the [Re 5 OsSe 8 (OH) 6 ] 3-in the solution shows broad and structureless emission in the wave length region from ~550 to longer than 950 nm with the maximum wavelengths (λ em ) centered at around 717 nm (Fig. 3).…”

Synthesis, crystal structure, and photophysical properties of acid (H3O)2[{W6Br8}Br6] · 4H2O

“…Tens of works presenting the luminescence proper ties of various octahedral molybdenum and rhenium clusters have been published to date [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. However, the photophysical properties of the W 6 clusters are poorly studied.…”

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It is well known that upon UV irradiation many chalcogenide and halide hexanuclear clusters of tran sition metals, for example, [{Re 6 Q 8 }L 6 ] (Q = S, Se) and [{M 6 X 8 }L 6 ] (M = Mo, W; X = Cl, Br), where L are various inorganic and organic ligands, luminesce in the red spectral range with microsecond emission life times [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Phosphorescence in the red spectral range and, as a consequence, the ability to generate singlet oxygen, as well as specific features of the struc tures of similar octahedral clusters of heavy metals, suggest that these compounds are potentially promis ing for the use as photosensitizers in photodynamic therapy and as X ray contrast preparations in diagnos tics of oncological diseases.

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