Regular assembly of 9-fluorenone-2,7-dicarboxylate within layered double hydroxide and its solid-state photoluminescence: a combined experiment and computational study

The assembly of an organic dye molecule incorporated into inorganic host matrices has received considerable attention for developing new types of organic–inorganic hybrid photofunctional materials. In this work, we report 9-fluorenone-2,7-dicarboxylate (FDC) assembled into Mg-Al- and Zn-Al-layered double hydroxide (LDH) systems and their solid-state photophysical properties. The detailed structure and chemical compositions of the obtained composites were characterized by X-ray diffraction, elemental analysis, thermogravimetry and differential thermal analysis (TG-DTA), infrared spectra (IR) and 13C nuclear magnetic resonance (NMR), which show that the positively-charged LDH layer can delocalize the electronic density of the anionic FDC to some extent. Moreover, FDC/LDH systems exhibit a blue-shift photoemission and enhanced fluorescence lifetime compared with those of the pristine FDC sample, and the FDC/LDH thin films exhibit well-defined polarized luminescence with the fluorescence anisotropy of 0.15–0.25. In addition, a periodic density functional theoretical (DFT) calculation was employed to calculate the geometric and electronic structures of the FDC/LDH systems. It was found that the FDC/LDH can be regarded as energy transfer systems from the interlayer organic chromophore to the inorganic host layer due to close energy levels between two components. Therefore, based on the combination of experimental and theoretical studies on the chromophore assembled LDH systems, this work not only gives a detailed investigation on the relationship between the layered host–guest structures and photoluminescence properties, but also provides a new insight into the energy-transfer performance of guest dye molecules confined between the 2D inorganic host matrix.