Controlling the Fluorescence Behavior of 1-Pyrenesulfonate by Cointercalation with a Surfactant in a Layered Double Hydroxide

Abstract

Zn-Al layered double hydroxides (LDHs) containing solely 1-pyrenesulfonate (PS) or 1-heptanesulfonate (HS) anions, or a mixture of the two with HS/PS molar ratios ranging between ca. 7.5 and 82, were prepared by the direct synthesis method and characterized by powder X-ray diffraction, thermal and elemental analyses, scanning electron microscopy, and FT-IR, FT-Raman, and C-13{H-1} CP MAS NMR spectroscopies. Well-ordered intercalates were obtained with basal spacings of 18.8 angstrom for the LDH intercalated by PS and 19.2-19.4 angstrom for the other materials containing HS: The photophysics of the solids, as well as the PS probe dissolved in water and common organic solvents (aiming to compare the behavior of the \"isolated\" molecule with that in the solid); Were investigated by steady-state and time-resolved fluorescence techniques. The fluorescence spectra of the solid samples display two bands with maxima at 376 and 495 nm. Depending on. the HS/PS ratios, the band intensity ratio (obtained at 375 and 520 am) changes, reflecting different contributions from monomer and dimer species. The decays collected at 375 nm are biexponentials with a major component (similar to 97% of the total fluorescence) of 105 ns for the highest HS/PS ratio, which further loses importance with an increase in the PS content. When the decays are collected at 480 and 520 nm, the fits are triexponentials with a Major component varying from 108 to 124 is, attributed to an excimer. Steady-state, and time-resolyed measurements with PS in solution (ethanol, methanol, DMF, DMSO, and water) were also measured, and a comparison of the vibronic I-1/I-3 ratio and lifetimes in water (65 ns) with those in the LDHs indicates that the PS probe in the cointercalated LDHs is surrounded by the HS surfactant.