Studies on the Orientation and Polarized Photoluminescence of α-Naphthalene Acetate in the Layered Double Hydroxide Matrix

This paper reports a novel method to tune the fluorescence properties of α-naphthalene acetate (α-NAA) in a two-dimensional matrix of layered double hydroxide (LDH) by changing the orientation of the chromophore. The α-NAA and 1-heptanesulfonic acid sodium (HES) with different molar ratios were co-intercalated in the galleries of Zn 2 Al LDH by the anion exchange method. Thin films of α-NAA−HES/LDH ( x %, x stands for the molar percentage of α-NAA), which have a well c -orientation confirmed by the X-ray diffraction (XRD) and scanning electron microscopy (SEM), were obtained by the solvent evaporation method on Si substrates. On the basis of the results from XRD and fluorescence polarization, the orientation (Ψ angle) of the α-NAA molecule in the LDH matrix was calculated to be 59° ( x = 12.1%), 61° ( x = 15.1%), 64° ( x = 20.0%), 65° ( x = 23.3%), 68° ( x = 30.0%), and 71° ( x = 34.4%) with respect to the normal to the thin film, respectively. Furthermore, the fluorescence wavelength, emission intensity, and lifetime correlate with the orientation of α-NAA remarkably and can be finely controlled by varying the fluorophore content in a rigid and constrained environment of the host. The optimal luminous intensity and the longest fluorescence lifetime of α-NAA−HES/LDH ( x %) can be obtained with an x value ranging from 15 to 20%.