Flexible Multicolor Rewritable Paper Coated with Metallosupramolecular Polymers for Electrochromic Printing and Natural Erasing by Humidity

Stamping
an image on paper with ink is a conventional approach
to displaying information. As a next-generation display, stimuli-responsive
rewritable paper has attracted considerable attention. In this study,
we present an electrical color printing approach using electrochromic
(EC) Fe(II) and Ru(II)-based metallosupramolecular polymers (MSPs),
which were synthesized via complexation of the metal ions and a chelating
terpyridine ligand. The printing method involves a flexible ITO film
with a Fe(II)-based MSP layer (an EC film), an erasing unit, and a
printing unit. To conduct the writing or erasing process, the erasing
unit or the printing unit was stuck on the EC film and an oxidative
or reductive potential was applied to the EC layer of the EC film.
The printing and erasing of an image were caused by the oxidation
state changes between Fe(II) and Fe(III) in the EC layer. After printing,
the printed information remained for more than a week due to the memory
property of the Fe(III)-based MSP film. The printed information was
quickly erased through electrochemical reduction. The rewritable EC
film had a subsecond switching time (<1 s) and high stability for
repeated writing/erasing more than 2500 times. In addition, it was
also found that printed information could be naturally erased under
humid conditions. An EC film containing both Fe(II)- and Ru(II)-based
MSPs successfully displayed multiple colors by varying the potential
application time.