Inorganic Chemistry, Vol.56, No.14, 8538-8546, 2017
Near-Infrared and Two-Wavelength Electrochromism Based on Nanocrystalline TiO2 Films Functionalized with Ruthenium-Amine Conjugated Complexes
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 (Delta T %) 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 (Delta T% = 58%) and 780 nm (Delta T% = 59%) in the single- and double-oxidation process, respectively. The coloration efficiency of these processes varies in a range of 150-270 cm(2)/C. These films are potentially useful as variable optical attenuators for telecommunications.