Structure Property Correlation of a Series of Halogenated Schiff Base Crystals and Understanding Molecular Basis Through Nanoindentation

Organic molecular crystals were perceived as brittle and inelastic entity; however, very recently there is a sudden spurt of reports of soft molecular crystals. We describe a family of halogenated Schiff base molecular crystals with a design protocol aimed to achieve incorporation of structural features for desired mechanical property. We were able to achieve five crystals of which two were elastically bendable and remaining three were brittle. One of them is dimorphic means one form is brittle while other form is elastically bendable. Delicate rebalancing between weak and dispersive noncovalent interactions along with packing features ultimately give rise to two different polymorphs having different mechanical properties. Further, nanoindentation technique was employed to understand the role of weak interactions so that design of crystals with desired properties can be done more precisely in future. This combination of elastic bending flexibility and fluorescence optical properties of molecular crystals ...