responding free radical, DMV+·. It would destroy the
CT complex and lead to the formation of aggregate consisting of
DMV+· itself, turning the color from red to purple.
However, DMV+· was unstable in the atmosphere and
spontaneously oxidized by O2 under the catalysis of
glucose oxidase (GOx), resulting in the recovery of the color. Thus, a
temporary pattern can be obtained by “writing” or “drawing” with SDT
on the red-colored CT gels. More importantly, the temporary pattern is
well repeatable and its lifetime can be modulated by the concentration
of SDT, GOx, or glucose. Similarly, A. Quintard and coworkers prepared a
self-erased writing by using a trichloroacetic acid (TCA)-driven
reaction network. [64] Upon the addition of TCA, the
NH2-containing organogelators were immediately
protonated, converting the green gel into a yellow sol. (Figure 10b)
Meanwhile, the alkaline amine groups of organogelators can catalyze the
decarboxylation of TCA, yielding volatile CO2 and
CCl3. The decrease of acidity induced the recovery of
the green gel without any residual. Hence, temporary words or patterns
can be repeatedly written on the surface of the green gel by the
addition of TCA. Furthermore, except for writing on the gel surface, it
was reported that the gel itself can be applied as self-erased ink as
well. J. Jiang and L. Wang et al. presented
a writable temporary gel, the
precursor of the temporary gelator was a star-shaped molecule containing
four carboxyl groups. [65] (Figure 11a) The addition of EDC
crosslinked the precursor by catalyzing the condensation of the carboxyl
groups, yielding a pulpous and plastic hydrogel. After a while, the
anhydride bridges formed by the condensation of carboxyl groups slowly
hydrolyzed, causing the collapse of the crosslinking network structure
as well as the hydrogel. Due to its good plasticity, the hydrogel showed
a good application in 3D printing. Materials in which fluorescence can
be temporarily changed by the drive of chemical fuel are also potential
self-erased inks. Therefore, the temporary fluorescent emission
aggregate reported by D.-S. Guo and coworkers should also be noted.
[66] The AIEgens shown in Figure 11b can generate significant
fluorescent emission after co-assembly with DNA. However, the DNase I
that existed in the solution led DNA to slowly decompose to
oligonucleotides, bringing about the disappearance of the fluorescence.
Although the author did not provide direct experimental evidence to
illustrate its application in self-erased ink. It is still to be
expected that this solution can be used in transferring confidential
information.