Electrochromic redox reactions of vapour-deposited thin films of tetrapyridotetraazaporphyrinatozinc(II)

✍ Scribed by Ruth Wahlster-Yoshida; Tsukasa Yoshida; Derck Schlettwein; Katsuhiko Tsukatani; Hisao Yanagi; Masao Kaneko; Hideki Minoura

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 163 KB
• Volume: 04
• Category: Article
• ISSN: 1088-4246
• DOI: 10.1002/(sici)1099-1409(200001/02)4:1<112::aid-jpp210>3.0.co;2-5

✦ Synopsis

Electrochromic redox reactions of vacuum-evaporated thin films of tetrapyridotetraazaporphyrinatozinc(II) ( TPyTAPZn ) have been studied in aqueous KCl electrolytes by in situ spectrocyclic voltammetry, which combines cyclic voltammetry and in situ monitoring of the absorption spectrum of the film. Although the voltammetric response of TPyTAPZn thin film electrodes can hardly be understood by the conventional electrochemical approach, the spectral information linked to the voltammetric information elucidated the presence of two-step reductions and reoxidations by each electron per TPyTAPZn molecule, which, however, take place with significant overlap during the voltammetric scan. Reduction of the film turned the color of the film from blue to purple and it changed reversibly to regenerate the original spectrum upon reoxidation. These reversible electrochromic reactions could be repeated many times without causing any noticeable change in the voltammetric and spectral responses. While use of electrolytes with various cations did not affect the redox behavior of the film, the effect of electrolyte pH was clearly seen, changing the ratio of the two reduction and two reoxidation peak magnitudes in the voltammogram. XPS analysis of the reduced film indicated that charge compensation upon reduction of the film occurred by protonation of reduced TPyTAPZn molecules at their aza and/or pyrido nitrogen atoms. A reaction scheme is presented to describe the observed redox reactions of the TPyTAPZn thin film from thermodynamic and kinetic viewpoints.