We herein report the tuning of mechanical plasticity of a series of 2-benzylidene-1-indanone derivative crystals through controlling intermolecular interactions for the first time. The roles of intermolecular interactions on plastic properties are rationalized by nanoindentation and energy framework calculations.

Flexible organic crystals (elastic and plastic) are important materials for optical waveguides, tunable optoelectronic devices, and photonic integrated circuits. Here, we present highly elastic organic crystals of a Schiff base, 1-((E)-(2,5-dichlorophenylimino)methyl)naphthalen-2-ol (1), and an azine molecule, 2). These microcrystals are highly flexible under external mechanical force, both in the macroscopic and the microscopic regimes. The mechanical flexibility of these crystals arises as a result of weak and dispersive CÀ H•••Cl, Cl•••Cl, Br•••Br, and π•••π stacking interactions. Singly and doubly-bent geometries were achieved from their straight shape by a micromechanical approach using the AFM cantilever tip. Crystals of molecules 1 and 2 display a bright-green and red fluorescence (FL), respectively, and selective reabsorption of a part of their FL band. Crystals 1 and 2 exhibit optical-path-dependent low loss emissions at the termini of crystal in their straight and even in extremely bent geometries. Interestingly, the excitation position-dependent optical modes appear in both linear and bent waveguides of crystals 1 and 2, confirming their light-trapping ability.

Mechanically dual-responsive molecular crystals substantially gained interest among researchers due to their significant application in various fields. Incorporation of disparate mechanical responses in the same crystalline material is still a...

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