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

Abstract

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.

Preparation of an anion dye intercalated into layered double hydroxides and its controllable luminescence properties

“…The fluorescence polarization technology was used to determine the orientation of ANS, and was performed according to the method reported by our group previously with some modifications [22]. Thin films of ANS-LDHs were fabricated according to the same procedure as reported by our group [22].…”

“…Thin films of ANS-LDHs were fabricated according to the same procedure as reported by our group [22]. The spectra of the composites film were registered after excitation at 370 nm and scanned in the range 425-600 nm.…”

“…Recently, the immobilization of photoactive molecules and their optic-functionalization with LDHs have been reported [18][19][20][21]. Our previous work [22] shows that the immobilization of guest molecules with a preferential arrangement in LDHs results in a desired alignment of photo-functional molecules in a macro-scale domain. This inspires us to challenge the goal of incorporation of ANS into LDH host matrix, which may possess the following advantages: (1) the solid matrix offers a confined environment for the immobilization and homogeneous distribution of dye molecules based on host-guest interactions, which can reduce dye aggregation and fluorescence quenching effectively; (2) the solid matrix would enhance the optical and thermal stability of the dye, which is a prerequisite to meet Scheme 1.…”

Recent Advances in Stimuli‐Responsive Photofunctional Materials Based on Accommodation of Chromophore into Layered Double Hydroxide Nanogallery

“…(2) The orientation and arrangement of the chromophores can be tuned by changing the layer charge density and chemical composition, which can further adjust the optical properties of the nanocomposites [13,14]. (3) LDH host matrix provides chromophore molecules with a confined and stable environment, which reduces molecular thermal agitation (intermolecular collisions, vibrations, and rotations) by host-guest interactions, and the fluorescence quenching is therefore reduced [15,16].…”

Layered Double Hydroxide Materials: Assembly and Photofunctionality

“…According to the different stability and affinity of the interlayer guests, nitrate-LDH is always applied as a precursor in the ion-exchange process. For example, Shi et al [104] have fabricated α-naphthalene acetate (α-NAA) and β-naphthalene acetate (β-NAA) intercalated LDH materials through ion-exchange method. The XRD in Fig.…”