Abstract: Ethyl orange (EO^-) and 4-aminoazobenzene-4-sulfonic anion(4A^-) were intercalated into the layered double hydroxide (LDH), [Mg _0.66 Al _0.34 (OH) ₂] (CO₃) _0.17·0.67H₂O or exchanged on the external surface of the host by the method of ion-exchange procedures. The obtained compounds were characterized by X-ray diffraction, infrared and thermogravimetry techniques. The photophysical properties of the obtained compounds were studied by UV-Vis absorption and fluorescence spectroscope. The guest molecular sizes and structures were investigated utilizing an ab initio (HF/6-31G) method by G03w. These anions were arranged in the interlayer space as a monolayer of species with the main axis perpendicular to the layer plane. These results indicated that the fluorescence of intercalated sample of Mg-Al-EO-LDH increased greatly due to a more rigid and constrained environment of the host. However, the fluorescence of intercalated sample of Mg-Al-4A-LDH decreased due to the concentration quenching. Compared with those observed in the pure microcrystalline EO and 4A, the fluorescence intensity of the samples containing only surface-exchanged EO or 4A reduced because the charge transfer between EO or 4A molecules was enhanced. It suggests that the photophysical properties of guests can be changed by the guest-host interaction or guest-guest interaction.

Key words: hydrotalcites, intercalation, EO^-, 4A^-, photophysical property