Crafting defects in two-dimensional organic platelets via seeded coassembly enables emergent molecular recognition.

Defect engineering plays a pivotal role in materials science, as defects significantly influence material properties. However, achieving precise control over defects in pure organic systems remains a challenge. In this study, we demonstrate the creation of controllable defects in molecular crystals through supersaturated solution-fed seeded self-assembly of two strategically designed molecules. One molecule features 2-(2'-hydroxyphenyl)benzimidazole groups at both ends, enabling the formation of an intramolecular hydrogen bond on one side while leaving the hydrogen bond donors on the other side available for potential intermolecular interactions. When coassembled with a second molecule containing benzimidazole groups capable of continuous intermolecular hydrogen bonding, defects in the hydrogen-bonding network are introduced, resulting in the formation of defects within the resulting two-dimensional cocrystals. The defect density can be precisely tuned by adjusting the molar ratio of the two molecules. Remarkably, these defects exhibit shape-complementary hydrogen bonding with dimethoate enabling high sensitivity and selectivity molecular recognition.