Electrochromic cyanophenylparaquat (CPQ: 1,1′-bis-cyanophenyl-4,4′-bipyridilium) studied voltammetrically, spectroelectrochemically and by ESR

• Published in: Solar energy materials and solar cells 1992-02, Vol.25 (3), p.201-210
• Main Authors: Rosseinsky, David R., Monk, Paul M.S.
• Format: Article
• Language: English
• Subjects: Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; Miscellaneous (electroosmosis, electrophoresis, electrochromism, electrocrystallization, ...)
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/0927-0248(92)90068-Z

Bipyridilium salts show two electron-transfer steps yielding differently coloured products, the colours themselves depending on the N-substituents. The species studied here have the cyanophenyl substituent - C 6H 5CN, which is one of the stabler members of the group. Standard electrochemistry has been the traditional probe. Here we present a variety of methods: spectroelectrochemistry on transparent electrodes, diffuse-reflectance voltammetry from the electrochromic surfaces, in situ ESR studies of both solution phase and solid-plus-solution-phase systems, and rotating ring-disc electrode studies on solutions, all of which allow of new insights into rates and processes of bipyridilium electrochromics. The possibilities and problems of bielectrochromicity and polyectrochromicity are revealed, amongst the latter being the electron-transfer interaction between different charge states such as the comproportionation of species summarised as ((2+)+(0) → 2(1+) where the parentheses encompass the species' charges.