Molecular mechanics of elastic and bendable caffeine co-crystals

Complementing recent experimental results, here we report a computational study of remarkably flexible, elastically bendable caffeine cocrystals (cocrystal solvate 1), formed from caffeine (CAF), 4-chloro-3-nitrobenzoic acid (CNB), and methanol, and compare with its unsolvated brittle form, 1 (dry). We show that 1 is able to maintain stable cocrystal structures at temperatures between 100 K and 400 K. The tensile and compressive Young's modulus of 1 are close to similar to 10 GPa. The ultimate strength is more than 600 MPa in tensile and 400 MPa in compressive at temperature of 100 K. The simulation results of the structural and mechanical properties of 1 are in good agreement with our previous experimental work. Notably, before the ultimate tensile stress, the stress-to-strain curves of 1 show linear behavior, but 1 (dry) show nonlinear behavior. This study might explain the remarkable elasticity of 1 and is relevant to the design of high-performance organic materials with excellent self-healing or efficient stress dissipating properties.