Development of new multi-color electrochromic system by use of redox-active pi conjugated compounds

随着新型显示系统的发展，具有多色变化的有机化合物引起了人们的兴趣。本研究项目的目的是利用以下具有氧化还原活性的π偶联化合物：(1)四（2,6-二叔丁基-4-羟基苯基）-噻吩[3,2-b]噻吩(1),(2)1,3-二噻吩-[n]放射烯（n= 3,4,5,6）(2)和(3)1,3-二噻吩-[n]树突烯（n= 3,4）(3)，开发这种多色有机电致变色体系。对于1，用相应的二电子和四电子氧化化合物单醌（1′）和二醌（1′）构建了可逆的氧化还原体系。在三个组成部分之间观察到很大的颜色变化：1（淡黄色），1‘（蓝色）和1’'（棕红色）。令人惊讶的是，1‘和1’'在相当长的波长区域有最大的吸收，尽管它们的共轭系数不是很大。一些研究结果表明，激发态（双基结构）可能位于较低的能级，从HOMO到LUMO的跃迁能量可能非常小。从1'和1 "的详细esr测量中获得了这一建议的间接证据，其中肯定地认识到二元参与。此外，2和3在其自由基阳离子和指示物之间表现出电致变色。特别是，在3（黄色）和自由基阳离子（深蓝色）和阳离子（绿色）之间观察到比较大的三色变化。

Organic compounds with multi-color change are of current interest from development of new types of display systems. This research project has been carried out with aim of developing such multi-color organic electrochromic systems by use of the following redox-active pi conjugated compounds: (1) tetrakis(2,6-di-tert-butyl-4-hydroxyphenyl)- thieno[3,2-b]thiophene (1), (2) 1,3-dithiole-[n]radialenes (n=3, 4, 5, 6) (2), and (3) 1,3-dithiole-[n]dendralenes (n=3, 4) (3). As for 1 a reversible redox system was constructed with the corresponding two- and four-electron oxidized compounds, the mono- quinone (1') and diquinone (1''). Between the three components a large color change was observed: 1 (pale yellow), 1' (blue), and 1'' (brown red). It was very surprising that 1' and 1'' have absorption maxima at fairly long wavelength region, in spite of their not so large pi conjugation. As a result of some investigations, it was suggested that the excited state (biradical structure) might be located at comparatively low energy level and the transition energy from HOMO to LUMO might become very smaller. The indirect evidence to this suggestion was obtained from the detailed esr measurement of 1' and 1'', in which certainly the biradical involvement was recognized. Also, 2 and 3 exhibited electrochromism between their radical cations and dications. In particular, a comparatively large three color change was observed between 3 (yellow), and the radical cation (dark blue) and dication (green).