Intercalation of a manganese(ii)-thiacalixarene luminescent complex in layered double hydroxides: synthesis and photophysical characterization

Abstract

Utilizing the osmotic swelling of Layered Double Hydroxides (LDHs, [Mg_1−xAl_x(OH)₂]^x+(NO₃⁻)_x) in formamide, the anionic luminescent complex [(ThiaSO₂)₂(Mn^II)₄F]⁻ (ThiaSO₂ = p-tert-butylsulfonylcalixarene) is introduced between the positive layers, leading to doping of LDH. In the recovered LDH layers, the hexagonal prism morphology of the precursor is well retained. The formula of the resulting compound (Mg_0.71Al_0.29(OH)₂(NO₃)_0.288((ThiaSO₂)₂(Mn)₄F)_0.002(H₂O)_0.5) (1) was determined by elemental and thermogravimetric analysis. The low doping rate is attributed to the low negative charge density (e Å⁻²) of the complex. The basal spacing of 12.02 Å indicates that [(ThiaSO₂)₂(Mn^II)₄F]⁻ is sandwiched across the width by positive LDH layers. The photophysical properties of compound 1 were studied in the solid state. 1 presents luminescence properties upon UV excitation, with the emission maximum centered at 630 nm and 650 nm in the presence and the absence of atmospheric O₂, respectively. Photophysical studies have been carried out under different atmospheres and using various excitation wavelengths. The relationship of the extinction of emission with the presence of molecular oxygen is reported, and demonstrates the very high sensitivity of this compound to oxygen. Finally, incorporation of the luminescent complex within the LDH host allows the O₂-sensitivity to remain similar to that observed in solution whilst avoiding photo-degradation, thereby opening perspectives for use in oxygen sensing or singlet oxygen generation.