Hydrazones are compounds widely studied.  They can be made by several synthetic pathways, such as a condensation reaction between a hydrazine or hydrazide with a ketone or aldehyde [1].  These molecules are constituted by an azomethine group, characterized by the fragment C=N-N, allowing the use of hydrazones in various fields of chemistry.  These molecules have many potential applications: they are used in dyes and in conductive materials to name a few [1].  In pharmaceutical field, several hydrazone-based prodrugs of isoniazid have shown less undesired side effects when compared with isoniazid [2].  These molecules can also be studied for their potential thermo- and photochromic properties.
 

Thermo- and photochromism are color change phenomena induced by temperature variation and absorption of electromagnetic radiations, respectively.  These phenomena have many applications: information storage, optical switching devices (optical glasses), etc. [3].

In this work, we are interested in a hydrazone system obtained by a condensation reaction between isoniazid and o-vanillin. This molecule is cocrystallized with various cocrystal formers with the aim to modulate its photo- and thermochromism [3].  Both syntheses of the chromophore and of its cocrystals are accomplished by mechanosynthesis.  All obtained solid forms are characterized by powder X-ray diffraction and single-crystal X-ray diffraction.  Photochromism is studied by UV-Vis diffuse reflectance.