Self-assembled organic–inorganic composite superlattice thin films incorporating photo- and electro-chemically active phosphomolybdate anion

Abstract

A highly ordered multilayer film was formed by casting chloroform solutions of an ionic complex between a dimethyldioctadecylammonium (DODA) and a phosphomolybdate anion PMo 12 O 40 32 (PMo 12 ) on a glassy carbon electrode and solid substrates (CaF 2 , quartz, and borosilicate glass). A well-ordered lamellar superlattice structure was identified by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) experiments. IR spectra showed that the Keggin structure of the phosphomolybdate anion is preserved in the composite film. The superlattice film showed good photochromic and electrochemical properties. Irradiated with UV light, the transparent film changed from colorless to blue. Then, bleaching occurred when the film was in contact with ambient air or O 2 in the dark. A possible photochromic mechanism was proposed according to electron paramagnetic resonance (EPR), Fourier transform infrared spectra (FTIR), UV-vis spectra, and related literature. The electrochemical behavior of the composite film was also examined by cyclic voltammetry in detail.

Structure, photochromic, and electrochemical properties of dioctadecylamine/H3PMo12O40 Langmuir–Blodgett film

“…Especially, the fading would not take place under a nitrogen atmosphere or in a vacuum. Ambient air or oxygen atmosphere plays an important role in the change from blue back to colorless, which is in agreement with the results of casting and LbL multilayer films reported in literature [14,18]. However, this process was accelerated and completed in a short time when we heated the colored film in air to about 70 • C in the dark-the temperature just above the phase transition of the film.…”

“…We found that the unchanged surrounding structure of the DOA bilayer is favorable for further investigation of the functionality because the photochromic process of POMs is also a redox process. Second, we found that the reversibility of photochromism based on DOA is much better than the reversibility based on tetraalkyl ammonium salt, which was used in the reported casting film [14]. In addition, it is convenient to prepare hybrid LB films by directly transferring DOA onto PMo 12 subphases, while the alkylamine must be presoaked in acidic solution and needs longer pumping time for better quality in the LbL film.…”

“…Furthermore, some inherent properties of POMs are directly associated with their aggregated structures in various assemblies [11][12][13]. For example, Zhang and co-workers have fabricated ordered photochromic multilayer films by casting the chloroform solution of a SEC composite [14]. The second method is based on the layer-by-layer (LbL) adsorption method [15,16].…”

Fabrication of polyoxometalate-based nano/micrometer composite films by electrophoretic deposition method

“…The IR spectrum of the SEC films shows very strong bands below 1200 cm −1 , due to the POM. [33]. The shift of the different peaks may be related to the organization and especially to the presence of positively charged DODA in the films [33][34][35][36].…”

“…[33]. The shift of the different peaks may be related to the organization and especially to the presence of positively charged DODA in the films [33][34][35][36]. We select (DODA) 3 PMo 12 O 40 as the object for investigation, as the DODA + and PMo 12 O 3− 40 are the classical surfactant and POM, respectively.…”