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Two conformational polymorphs of 5-methyl-2-(2-nitrophenyl)amino-3-thiophenecarbonitrile (ROY) exhibited similar morphology but strikingly different mechanical flexibility, where the yellow needle (YN) is exceptionally elastic while orange needle (ON) is highly brittle. Similar to color differentiation, the distinct bending behaviors of YN and ON polymorphs are linked to different molecular conformations. Aided by crystal structural analysis, interaction energies, topology, nanoindentation, and elastic constant calculation, this study reveals new structural insights that explain the strikingly different mechanical behaviors of the two polymorphs.
Mishra et al. (Fri,) studied this question.