Achieving redox-responsive organic afterglow materials via a dopant–matrix design strategy

Abstract

Stimulus-responsive organic afterglow materials, when compared to their fluorescence counterparts, exhibit distinct advantages to function normally even in the presence of strong background fluorescence. However, the types of these afterglow materials are quite limited; to date, only pH-, ion-, mechanical force- and temperature-responsive afterglow materials have been developed. Here, we report the fabrication of redox-responsive organic afterglow materials via a dopant–matrix design strategy. Difluoroboron β-diketonate (BF₂bdk) luminescent compounds are selected as organic dopants, which possess intramolecular charge transfer characters and show large dipole moments in their S₁ states. Reductive organic matrices with small dipole moments are used to accommodate BF₂bdk dopants to show insignificant room-temperature organic afterglow. Upon the chemical oxidation of the reductive matrices, the organic afterglow can be switched on in the dopant–matrix systems at room temperature. Detailed studies reveal that the organic matrices in an oxidized form can interact with BF₂bdk S₁ states via dipole–dipole interactions, reduce S₁ energy levels with less influence on T₁ energy levels, and consequently decrease ΔE_ST and enhance the intersystem crossing of BF₂bdk excited states to give rise to significant room-temperature afterglow properties. The redox-responsive materials can be processed into desired shapes, diverse patterns, and even aqueous dispersion to serve as security inks.