Stimuli-responsive behavior of naphthyl acylhydrazone derivative and its application in information security...

Acylhydrazone derivatives containing naphthyl group, namely, 3,5-bis-octyloxy-benzoic acid naphthalen-1-ylmethylene-hydrazide (NTH-mB8) and 4-methoxy-benzoic acid naphthalen-1-ylmethylene-hydrazide (NTH-P1) were synthesized. π-π interactions between naphthalene groups and -N-H···O=C- intermolecular hydrogen bondings were observed in NTH-P1 single crystal, in which -C=N- bonds exhibited trans-isomer. NTH-mB8 showed photo-responsive behavior due to photo-induced trans-cis isomerizations of -C=N- bonds. Interestingly, the NTH-mB8 films fumed by trifluoroacetic acid (TFA)/triethylamine (TEA) (or standing at room temperature) vapors show reversible fluorescence on/off switching property. The cast film of NTH-mB8 exhibited almost no fluorescence. The NTH-mB8 film fumed by TFA vapor exhibited intensive cyan emission, which was quickly quenched by TEA vapor. The reversible remarkable fluorescence on/off switching properties suggested that the organic solution of NTH-mB8 could be used as security ink without needing a covering reagent in information security protection.