Engineering covalent organic frameworks for tailored encapsulation and controlled release of fragrances

The inherent volatility of fragrances leads to rapid fading, poor stability, low availability, potential health, and environmental issues, necessitating the development of effective fragrance carriers for stable storage and controllable release. Herein, we presented a strategy for finely tuning the encapsulation and release profiles of fragrant molecules through engineering the pore surface properties of covalent organic frameworks (COFs). Three imine-based COFs with variable functional groups (TAPB-DHTP-COF, TAPB-DMTP-COF, and TAPB-DVA-COF) were rationally designed and constructed via solvent evaporation method, which exhibited stable crystallinity, uniform morphology, and tunable surface areas (152-1056 m² g^-1), and pore sizes (2.3-3.9 nm). Notably, the polar COFs demonstrated significantly higher loading capacities for polar aldehyde-type fragrances (anisaldehyde, Ani; and citral, Cit) compared to nonpolar terpene-type (limonene, Lim). Density functional theory (DFT) calculations revealed that the superior adsorption of polar fragrances into the COFs was governed by strong hydrogen bond interactions, with adsorption energies of -1.16 eV (Ani) and -1.17 eV (Cit) versus -0.37 eV (Lim). All fragrance-loaded COFs exhibited sustained release profiles over 48 h, in stark contrast to the rapid release of free fragrances. Importantly, the release rate was tunable by modulating host-guest interactions, stronger hydrogen bonding led to more prolonged release. This pioneering research established COFs as a heavy metal-free, designable platform for the encapsulation and controllable release of volatile fragrances, showcasing promising applications in cosmetics and personal care industries.