Luminous Ultrathin Films by the Ordered Micellar Assembly of Neutral Bis(8-hydroxyquinolate)zinc with Layered Double Hydroxides

This article describes a novel method to effectively assemble a neutral complex molecule, bis­(8-hydroxyquinolate)zinc (Znq₂) with the exfoliated Mg–Al-layered double hydroxide (LDH) nanosheets, to obtain the ordered ultrathin films (UTFs) by employing a layer-by-layer assembly technique. Anionic block copolymer micelles, poly­(tert-butyl acrylate-co-ethyl acrylate-co-methacrylic acid) (PTBEM), were chosen as a molecular carrier for the incorporation of Znq₂ molecules and then alternatively electrostatic assembly with the cationic LDH nanosheets. (Znq₂@PTBEM/LDH)_n UTFs present a stepwise growth upon the increasing deposited cycles monitored by the UV–vis absorption and fluorescence spectroscopy. The UTFs exhibit the blue-shifted luminescence (λ_em = 488 nm) of 57 nm by comparison to the Znq₂ solution and enhanced cyan polarized photoemission character with the luminescence anisotropy (r) of ca. 0.14 in comparison with Znq₂@PTBEM micelle film (r = 0.07) and the Znq₂ solution (r = 0.02), due to the orientation arrangements induced by the LDH layers. The orderly periodical layered structure with a thickness of ca. 13 nm per UTF bilayer can be predicted from the small-angle X-ray diffraction pattern, being in approximate accordance with the height of a single layer of Znq₂@PTBEM micelle in the interlayer region. Scanning electron microscopy and atomic force microscopy indicate that the film surface is continuous and relatively smooth. This work gives a feasible method for immobilizing functional neutral molecules into the gallery of LDHs for designing and achieving novel organic–inorganic ultrathin films.