Polymorph-Dependent Luminescence Response to Acid Vapors and Its Application in Safety Protection of File Information

A Schiff
base, (E)-1-(phenylimino)­methyl-2-hydroxylnaphthalene
(PIHN), was found to form both nonluminescent and luminescent polymorphs.
A unique luminescence “turn on” behavior was observed
when the nonluminescent polymorph was fumed with the vapor of aliphatic
acids with two or three carbons in the main chain, while the luminescent
polymorphs almost did not change the emission color under the same
condition. As we know, this is the first report on polymorph-dependent
acid response which discloses the influence of crystalline phase on
acid-responsive behavior. The formation of hydrogen bonds between
PIHN and aliphatic acid is proposed to be the reason for the responsive
behavior of the nonemissive polymorph, and such a mechanism is different
from the common protonation mechanism. A novel safety protection method
of file information has been developed based on the polymorph-dependent
luminescence response of PIHN. In addition, we disclose that a crystalline
form could show multiple responsive behaviors toward different acids,
which benefits the further design of novel acid sensors, such as the
sensors that can qualitatively analyze the species of the acid source
in an acidic environment.