Near-Infrared and Two-Wavelength Electrochromism Based on Nanocrystalline TiO2 Films Functionalized with Ruthenium-Amine Conjugated Complexes

• Published in: Inorganic chemistry 2017-07, Vol.56 (14), p.8538-8546
• Main Authors: Li, Zhi-Juan, Shao, Jiang-Yang, Zhong, Yu-Wu
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.7b01297

Two cyclometalated ruthenium complexes 2 and 4 containing a redox-active amine substituent and three carboxylic acid groups were synthesized, where the ruthenium ion and the amine site were separated by a phenyl or biphenyl bridge for 2 and 4, respectively. Nanocrystalline TiO2 films on fluorine doped SnO2 (FTO)/glass substrates anchored with 2 or 4 were prepared. These films display two consecutive anodic waves in the potential region between +0.1 and +1.0 V vs Ag/AgCl. Among four organic solvents examined, the FTO/TiO2/2 film displays the best cyclic electrochemical stability in ClCH2CH2Cl. Both films exhibit promising two-step electrochromism in the near infrared region. A contrast ratio (ΔT%) of 42% at 1000 nm and 40% at 680 nm was achieved for the FTO/TiO2/2 film in the single- and double-oxidation process, respectively. In contrast, the FTO/TiO2/4 film shows electrochromism at 1300 nm (ΔT% = 58%) and 780 nm (ΔT% = 59%) in the single- and double-oxidation process, respectively. The coloration efficiency of these processes varies in a range of 150–270 cm2/C. These films are potentially useful as variable optical attenuators for telecommunications.