Mechanochromic behavior of a pyridine-containing pyrene derivative

Abstract

Pyrene-based hydrazone derivative (PYI) which was synthesized from 1-pyrene formaldehyde and isoniazid presented a mechanochromic (MC) behavior and self-recovery performance at room temperature. Mild grinding of a PYI crystal would convert its fluorescence from weak blue to yellow. The metastable grinded PYI powders could revert to the original stable state at room temperature (RT) in 24 h. However, under the same conditions, the control molecule PYB did not exhibit MC property. The results showed that the MC behavior of PYI was caused by mechanical induced slippage of the pyrene dimers in the lattice, which altered the stacking behavior and molecular interactions. Because the two pyrene units in PYB dimer almost exhibited a sandwich-type arrangement, mechanical stimulus had little influence on the stacking state of PYB. Therefore, it did not exhibit the MC property. In addition, when mixed with oxalic acid and malonic acid, the fluorescence of pristine PYI was turned off, meanwhile with a visible color change from yellow to orange red. The phenomenon was a result of enhanced ICT effect between acidifying pyridine and pyrene unit.