Endowing Hydrochromism to Fluorans via Bioinspired Alteration of Molecular Structures and Microenvironments and Expanding Their Potential for Rewritable Paper

Interest
and effort toward new materials for rewritable paper have
increased dramatically because of the exciting advantages for sustainable
development and better nature life cycle. Inspired by how nature works
within living systems, herein, we have used fluorans, as a concept
verification, to endow original acidochromic, basochromic or photochromic
molecules with broader properties, such as switchable with solvent,
water, heat, electricity, stress, other force, etc., via simplified
methods (i.e., via variation of submolecular structure or microenvironments).
The hydrochromic visual change and reversible behavior of selected
molecules have been explored, and the primary mechanism at the atomic
or subatomic level has been hypothesized. In addition, several newly
demonstrated hydrochromic fluorans have been utilized for water-jet
rewritable paper (WJRP), which exhibit great photostability,
high hydrochromic contrast, and fast responsive rate and which can
be reused at least 30 times without significant variation. The water-jet
prints have good resolution and various colors and can keep legibility
after a few months or years. This improved performance is a major
step toward practical applications of WJRP.