Herein,two compounds,4-2′-hydroxybenzylidenehydrazinyl-N-butyl-1,8-naphthalimide(BN-1)and 4-benzylidenehydrazinyl-N-butyl-1,8-naphthalimide(BN-2),were synthesized to explore the hydrogen bonding effect on mechanoresponsive luminescent(MRL).The results showed that compound BN-1 exhibited strong emission in solution and solid-state compared with compound BN-2.After grinding,the emission intensity of compound BN-1 sharply decreased by as much as 15 times with an obvious red-shift from 552 nm to 577 nm.The control compound BN-2,by contrast,did not change so much before and after grinding.Single crystal analysis suggests that BN-1 molecule formed strong intramolecular interaction via-N=N⋯H-O hydrogen bond with a distance of 0.2632 nm.An excited-state intramolecular proton transfer(ESIPT)based fluorophore featured this intramolecular hydrogen bond.The intramolecular hydrogen bond as well as other intermolecular interactions can rigidify the molecular conformation of compound BN-1 in solid-state,and thus suppress the nonradiative pathways,resulting in strong emission.These intra-and intermolecular interactions were destroyed by mechanical stimuli,accompanied by molecular conformation change that decreases the luminescence and blocks the ESIPT process.The MRL process was also demonstrated by scanning electron microscopy and powder X-ray diffraction.The molecular stacking mode changed from crystalline to a disordered amorphous state after grinding.
ZHANG BingyiZHANG XiaoleSU RuochenSUN YueDUAN Lian
