LAUSR

A Schiff base, (E)-1-(phenylimino)methyl-2-hydroxylnaphthalene (PIHN), was found to form both non-luminescent and luminescent polymorphs. A unique luminescence 'turn on' behaviour was observed when the non-luminescent polymorph was fumed with the vapour of aliphatic acids with two or three carbons in the main chain, while the luminescent polymorphs almost did not change the emission colour 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 behaviour. The formation of hydrogen bonds between PIHN and aliphatic acid is proposed to be the reason for the responsive behaviour of the non-emissive 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 behaviours towards different acids, which benefits the further design of novel acid sensors, such as the sensors that can qualitatively analyses the species of acid source in an acidic environment.