Tunable Photoluminescence Properties of Fluorescein in a Layered Double Hydroxide Matrix by Changing the Interlayer Microenvironment

This paper reports a novel method to tune the fluorescence properties of fluorescein (FLU) in a 2D matrix of layered double hydroxide (LDH) by changing the interlayer microenvironment. FLU and surfactants with different alkyl chain lengths were cointercalated in the galleries of a Zn₂Al LDH by the anion exchange method. Thin films of FLU-C_nH_2n+1SO₃/LDH (n = 5, 6, 7, 10, and 12, respectively; n stands for the number of carbon in the alkyl chain), which possess a well c-orientation revealed by XRD and SEM, were obtained by the solvent evaporation method on Si substrates. It was found that the orientation of FLU and its anisotropy, fluorescence wavelength, fluorescence quantum yield, and lifetime correlate with the microenvironment of the LDH gallery, which can be tuned by simply changing the alkyl chain length of the surfactant. The optimal fluorescence quantum yield, anisotropy, the longest fluorescence lifetime and the strongest photostability of the FLU-C_nH_2n+1SO₃/LDH film can be obtained with n = 7, due to the “size-matching” rule between the organic dye and surfactant.