Hybrid photochromic multilayer films based on chitosan and europium phosphomolybdate
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Multilayer films based on chitosan and K11[EuIII(PMo11O39)2] were prepared on different substrates using the layer-by-layer method. UV–Vis spectra of the films showed regular stepwise growth. X-ray photoelectron spectroscopy data confirmed the presence of chitosan and phosphomolybdate within the films and scanning electron microscopy images revealed a completely covered surface with a roughened texture. The film electrochemical responses and permeability were studied by cyclic voltammetry. Films revealed four surface-confined Mo-based reduction processes (MoVI → MoV). Studies with [Fe(CN)6]3−/4− and [Ru(NH3)6]3+/2+ showed that film permeability depended on the film thickness and on the charge of the outer layer. Irradiation of films with UV light confirmed their photochromic properties through the colour change from transparent to blue. Colouration–discolouration cycles could be repeated up to 36 cycles without the loss of optical contrast, indicating high film photochromic stability. These results provided valuable insights for exploring the potential application of polyoxometalate-based films for the construction of photochromic devices.
KeywordsLayer-by-layer films Phosphomolybdates Electrochemistry Photochromism Chitosan
The authors thank Fundação para a Ciência e a Tecnologia (FCT) and COMPETE for financial support through grant no. PEst-C/EQB/LA0006/2011, PTDC/CTM-POL/0813/2012, NORTE-07-0124-FEDER-000067–Nanochemistry and to COST Action CM-1203 PoCheMoN. DMF also thanks FCT for her PD grant SFRH/BPD/74872/2010.
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