A regulating surface functional groups strategy of multi-color solid-state fluorescent carbon dots for food...

Ultraviolet (UV) radiation can induce fresh food oxidation, discoloration and nutrient loss, but carbon dots (CDs) can convert UV to longer wavelength light to reduce the damage to fresh food. CDs with aggregation-induced emission (AIE) effect have been identified as an effective strategy for the direct synthesis of solid-state fluorescent (SSF) CDs. Nevertheless, due to the wide variety of reaction precursors, the relationship between the structure and properties of SSF CDs remains ambiguous, which presents challenges for their stable synthesis and application. Herein, we report a general and stable strategy for the controlled synthesis of multicolor SSF CDs by different carbonyl compounds. The structure and luminescence mechanism of the CDs were thoroughly investigated, and the enhanced solid-state fluorescence properties were attributed to the intramolecular motions restricting the surface fluorophores. Carbonyl groups act as strong electron-withdrawing groups and form conjugated domains when attached to the carbon core. The spatial separation of electrons and holes is facilitated by intramolecular charge transfer (ICT), which induces the fluorescence redshift of CDs. Meanwhile, the precise tuning of the fluorescence wavelength of CDs can be realized by adjusting the remaining surface functional groups in the carbonyl compounds. In addition, based on the excellent optical properties of AIE CDs in the solid state, composite films that can be used for food preservation packaging were prepared using them as dopants. This work presents a promising technique to guide us in designing the synthesis of SSF CDs, and it provides a new approach to producing innovative fresh food packaging.