Multilayered thin films of functional materials play an important role in many applications in nanotechnology. The intense and tuneable colours of some molecular materials allow for the development of a unique spectral fingerprint of each layer in thin film heterostructures. Herein, we report on electrochromic switching of bilayer thin films composed of Prussian blue (Fe^IIIFe^II) and its orange-coloured (Fe^IICr^III) analogue. The films could be switched from green to orange by reducing the blue FeFe top layer. The distinct optical absorption spectra of the two layers allowed spectroelectrochemical measurements to probe the electrochemical activity of the individual layers during the switching of the Prussian blue layer. We found that for producing layers of equal optical density, the thickness of the layers had to be different due to a difference in oscillator strength for the metal-to-metal charge-transfer transition. The films used here had a thickness of 300 ± 70 nm and 30 ± 15 nm for the FeCr and FeFe sub-layers, respectively. The colouration efficiency was found to be 147.8 ± 0.8 cm² C⁻¹ for the multilayered film. These results show that it is possible to obtain bilayers of Prussian blues that, with a unique optical spectral fingerprint of each sub-layer, retain the electrochromic functionality and therefore enable layer-sensitive studies of charge-transfer processes in thin film heterostructures of multifunctional materials.

中文翻译：

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普鲁士蓝及其Cr类似物的电致变色双层†

功能材料的多层薄膜在纳米技术的许多应用中起着重要的作用。某些分子材料的强烈且可调节的颜色允许在薄膜异质结构中形成每一层的独特光谱指纹。在这里，我们报道了由普鲁士蓝（Fe ^III Fe ^II）和其橙色（Fe ^II Cr ^III）组成的双层薄膜的电致变色转换）模拟。可以通过减少蓝色FeFe顶层将薄膜从绿色切换为橙色。两层的独特的光吸收光谱允许进行光谱电化学测量，以探测普鲁士蓝层转换期间各个层的电化学活性。我们发现，为了产生具有相同光密度的层，由于金属间电荷转移跃迁的振荡器强度不同，因此各层的厚度必须有所不同。对于FeCr和FeFe子层，此处使用的膜的厚度分别为300±70 nm和30±15 nm。发现着色效率为147.8±0.8cm ² C ^-1用于多层膜。这些结果表明，可以获得普鲁士蓝的双层，该双层具有每个子层的独特光谱指纹，并保留了电致变色功能，因此可以对多功能材料的薄膜异质结构中的电荷转移过程进行层敏感的研究。 。