Electrochromic Materials And Devices Based On Viologen Compounds Modified By Terpyridine Units

Organic electrochromic materials have attracted wide attention because of their low cost,easy structure modification,good optical properties,rich colors,rapid color conversion,and excellent cycle reversibility.Among them,organic small-molecule viologen compounds have excellent electron accepting ability,good redox reversibility and rich redox states,and have been widely used in smart windows of energy-saving buildings,anti-glare rearview mirrors of automobiles,electro-color-changing smart glasses and other fields.The application of viologen compounds in display mainly depends on the reversibility of its color change under electrical stimulation.However,the application in luminescent display is limited by the controllability of its emission characteristics.Previous studies have shown that the introduction of electron withdrawing groups into 4,4’-bipyridine enhances the electron deficiency of viologen compounds,and even the introduction of anode species such as ferrocene and Prussian blue does not improve the electrochromic/electroluminochromic properties of the device.In addition,the device structure and the volume size of the counterion also affect the bleaching speed of the device.Therefore,we use the electron-rich group terpyridine as the N-substituent to tune the electrochromic and electroluminochromic properties of viologen-based devices by changing the types of counter anions.Based on this,this thesis designed and synthesized terpyridine viologen compounds containing different counter anions,and successfully prepared electrochromic/electroluminochromic devices by adjusting their optoelectronic properties.The detailed work consists of the following two parts:1.Asymmetric terpyridine viologen compounds for large-area electrochromic/electroluminochromic devicesThe electron-rich group terpyridine was introduced into 4,4’-bipyridine,and asymmetric terpyridine viologen compounds Tpy-Vio-1 and Tpy-Vio-2 were designed and synthesized.Both Tpy-Vio-1 and Tpy-Vio-2 have abundant redox centers and good redox reversibility.Based on this,electrochromic/electroluminochromic devices(with an area of 1 cm~2)were fabricated using Tpy-Vio-1 and Tpy-Vio-2 as electroactive materials,respectively.Under electrical stimulation at-1.2 V and-1.8 V,the color of Tpy-Vio-1 device changed from orange to yellow-green and then to gray-green,and its luminescence color changed from orange to yellow and then to green;while under the electrical stimulation of-2.2 V and 3.2 V,the the color of Tpy-Vio-2 device changed from yellow to green and then to blue-green,and the emission color changed from yellow to dark yellow and then to green.Applying the corresponding reverse voltage,the color and emission color of both devices can return back to the original state.Moreover,the Tpy-Vio-1 device has 4 s and 10 s tinting time,8 s and10 s fading time,31%and 60%maximum transmittance difference and cycling stability at 7200 s and14400 s.Based on the excellent performance of the Tpy-Vio-1 device,a large-area electrochromic/electroluminochromic device(64 cm~2)was successfully fabricated.This large-area device can also achieve uniform and rich color and emission color changes without changing its operating voltage.This work has guiding significance for the application of smart windows.2.Symmetrical terpyridine viologen compounds for electrochromic devicesThe spatial asymmetry and symmetry of viologen also usually have a great influence on the electrochromic behavior of the device.On the basis of the above work,the symmetrical terpyridine viologen compounds Tpy-Vio-3 and Tpy-Vio-4 were further designed and synthesized.Both Tpy-Vio-3 and Tpy-Vio-4 have abundant redox centers.Based on this,electrochromic devices were fabricated using Tpy-Vio-3 and Tpy-Vio-4 as electroactive materials,respectively.At-1.6 V,the Tpy-Vio-3 device changed from orange to green;at-1.9 V,the Tpy-Vio-4 device changed from yellow to green.Among them,the Tpy-Vio-3 device can quickly recover to the initial state under the application of reverse voltage.Moreover,the Tpy-Vio-3 device has a maximum transmittance difference of 72%and a cycle stability of around 800 s,which enriches electrochromic materials system and provides a reference for electrochromic display applications.