Characterization of interactions between organic molecules and Co-Al-LDH using photo-physical techniques

Abstract

In this paper, 4-benzoylbenzoic acid (4-BBA) and 2-naphthalenesulfonic acid (2-NSA) were intercalated or co-intercalated into the layered double hydroxide (LDH) [Co_0.66Al_0.34(OH)₂](CO₃)_0.17·0.49H₂O by the method of ion-exchange. Powder X-ray diffraction, Fourier transform infrared spectroscopy, TG-DTA, X-ray photoelectron spectroscopy and photoluminescence spectra were used to characterize the structural and photophysical properties of the obtained compounds. It was found that Co²⁺ ions in the layers were coordinated with the guest molecules 2-NSA in the interlayer region, resulting in the intercalation compound Co-Al-2-NSA-LDH enhancing the blue emission of 2-NSA at 460 nm. The geometries and electronic structures of the guest molecules and their singlet vertical excitation energies and oscillator strengths were investigated at the B3LYP/6-31G level by density functional theory (DFT) and time dependent DFT calculations using G03w. The fluorescence polarization method was applied to test the preferential orientation of the interlayer 4-BBA and 2-NSA molecules. It indicated that spatial distribution of the guest molecules in the layer was a rather ordered arrangement and indicated that 4-BBA and 2-NSA were intercalated or co-intercalated between sheets of Co-Al-LDH as a bilayer interdigitated form. There was a coordinate possibility between Co-Al-LDH and the organic chromophores containing a sulfonic group, and intermolecular energy transfer from 2-NSA to 4-BBA in the layers might happen for the co-intercalation compound. So, this work provides new opportunities to design functional material by the combination of Co-Al-LDH with various types of organic chromophores, which will be very valuable.