Molecular Orientation and Fluorescence Studies on Naphthalene Acetate Intercalated Zn2Al Layered Double Hydroxide

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• 作者：Wenying Shi ; Min Wei ; Jun Lu ; Feng Li ; Jing He ; David G. Evans ; Xue Duan
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：December 18, 2008
• 年：2008
• 卷：112
• 期：50
• 页码：19886-19895
• 全文大小：366K
• 年卷期：v.112,no.50(December 18, 2008)
• ISSN：1932-7455

文摘

This paper describes a systematic study on molecular orientation and fluorescence properties for the Zn₂Al layered double hydroxide (LDH) intercalated with α-naphthalene acetate (α-NAA) and β-naphthalene acetate (β-NAA), respectively. α-NAA and β-NAA intercalated Zn₂Al LDH (denoted as α-NAA LDH and β-NAA LDH) were prepared by the ion-exchange method and their thin films on Si substrates were obtained by the solvent evaporation method. The powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) of α-NAA LDH and β-NAA LDH confirm the intercalation of guests between sheets of LDH. The XRD and scanning electron microscope (SEM) images of α-NAA LDH and β-NAA LDH thin films show that they are well c-oriented assembly with platelet-like morphology. UV−vis absorption and fluorescence spectra (emission, lifetime, and time resolution) indicate that the intercalated NAA is accommodated in its monomer form and depolarization factors exhibit no influence on its fluorescence emission process, which makes the evaluation for its interlayer molecular orientation reasonable and feasible by polarized fluorescence method. Fluorescence polarization method was applied to investigate the preferential orientation of the interlayer α-NAA and β-NAA molecules, and the results show that α-NAA and β-NAA are intercalated between sheets of Zn₂Al LDH as monomeric units with a tilt angle Ψ (defined as the angle between the transition moment of NAA molecule with respect to the normal to the LDH layer) of 60° and 65°, respectively. Compared with the physical mixture samples of NAA and LDH, the intercalation of NAA leads to an increase in the fluorescence lifetime. This indicates a more dilute and constrained interlayer environment for the guest, which reduces the internal mobility and the flexibility of NAA and thus improves its fluorescence lifetime.