Side-Chain Engineering for Modulating Fluorescence and Mechanical Properties of Single Crystals

Molecular engineering of organic single crystals via minimal structural modification remains a key challenge in the development of multifunctional crystalline materials. A side-chain engineering strategy is reported for simultaneously regulating optical emission and mechanical adaptability in acetophenone derivatives: 2′-hydroxy-5′-methylacetophenone (HMAP) and 2′-hydroxy-5′-methoxyacetophenone (HMOAP). This approach enables unprecedented molecular-level control, facilitating concurrent modulation of optical emission with a notable shift (Δλ = 47 nm) through single substituent variation. Specifically, the fluorescence exhibits a notable blue shift from 552 nm (yellow, HMAP) to 505 nm (green, HMOAP). Distinct mechanical properties have been achieved, and HMAP single crystals exhibited two-dimensional plastic deformation when subjected to external force, whereas the elongated plate-like single crystals of HMOAP demonstrated two-dimensional elastic deformation under mechanical force, with elastic strains reaching up to 4.9% and 14.3%, respectively. Beyond their elastic limits, they experience permanent plastic deformation. Our findings establish a viable strategy for expanding the organic flexible single crystal system, enabling easy modulation of the single crystal properties.