Electrochromic Materials Can Change Color Through Electricity

Smart glass can change color quickly using electricity. LMU chemists developed a new material which leads to the change. Imagine having automatic dimming rear view mirror lights. This is possible using electrochromic materials. When the voltage gets applied, it changes the color and the light absorption too. Being controlled by a light sensor, the rearview mirror could give out a strong dazzling type of light.

The experts have found out that in addition to the electrochromic materials, covalent organic frameworks (COFs) also play a major role. COFs mainly consist of an organic type of building blocks which in combinations bring out nanoporous and crystalline networks. The color change here is triggered by the voltage which results in reduction or oxidation of the material.

Electrochromic Materials Can Change Color Through Electricity

Construction principle

The team led by Thomas Bein developed COF structures with coloration efficiencies and switching type speeds higher than the inorganic compounds. COFs are found to be attractive since their material type properties could be adjusted by the modification of the molecular building blocks.

Derga Bessinger said that they used the modular construction principle of COFs and designed the building blocks for their purposes including a specific type of thienoisoindigo molecule. Being incorporated into the COF, the new type of component demonstrates how better and strongly it could improve the COF properties. With the new material, they could absorb the less wavelength UV light and achieve better photoactivity into the near-infrared spectral regions, said Bessinger.

COF structures are sensitive to the oxidation process. This means that a little voltage is only necessary to bring out a color change of the COFs and the also the complete process is reversible. The time taken for the color change is 0.38 sec while the time taken for the reverse process to reach the initial state is 0.2 seconds. Thus, being a faster process.

Why high speed?

The conductive type framework of the COFs helps in the quick transport of the electrons in the lattice. Also, the optimized type of pore size which is surrounding the electrolyte solution could quickly reach every corner. This is important as a positive type of charge developed in the COF structure which is oxidized must be charge compensated with the negative ions of the electrolyte.

Last but not least such smart glass could be used for applications like switchable solar protection and privacy shield-type windows.

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