Molecular Packing Topology and Interactions to Decipher Mechanical Compliances in Dicyano-Distyrylbenzene Derivatives

Abstract

Flexible optoelectronics is the need of the hour as the market moves toward wearable and conformable devices. Crystalline pi-conjugated materials offer high performance as active materials compared to their amorphous counterpart, but they are typically brittle. This poses a significant challenge that needs to be overcome to unfold their potential in optoelectronic devices. Unveiling the molecular packing topology and identifying interaction descriptors that can accommodate strain offers essential guiding principles for developing conjugated materials as active components in flexible optoelectronics. The molecular packing and interaction topology of eight crystal systems of dicyano-distyrylbenzene derivatives are investigated. Face-to-face pi-stacks in an inclined orientation relative to the bending surface can accommodate expansion and compression with minimal molecular motion from their equilibrium positions. This configuration exhibits good compliance towards mechanical strain, while a similar structure with a criss-cross arrangement capable of distributing applied strain equally in opposite directions enhances the flexibility. Molecular arrangements that cannot reversibly undergo expansion and compression exhibit brittleness. In the isometric CT crystals, the disproportionate strength of the interactions along the bending plane and orthogonal directions makes these materials sustain a moderate bending strain. These results provide an updated explanation for the elastic bending in semiconducting pi-conjugated crystals. The molecular packing and interaction topology of eight crystal systems, including polymorphs, solvate crystal, and isometric charge transfer crystals of dicyano-distyrylbenzene derivatives with similar molecular structures but varying structural and interaction characteristics were investigated in detail to explore the key molecular arrangements necessary for mechanical compliance. The results provide an updated explanation for the elastic bending observed in semiconducting pi-conjugated crystals. image