Covalent organic framework as an efficient fluorescence-enhanced probe to detect aluminum ion

The fluorescence of two-dimensional (2D) covalent organic frameworks (COFs) are generally quenched by the strong layer-layer π-π stacking or the intramolecular rotation. However, the latter effect can be reduced if the intramolecular rotation in COFs can be restricted through the selective coordination with metal ions or small molecules. Herein, we demonstrate that the fluorescence of p-methoxyl group-substituted imine-based COFs can be dramatically enhanced after coordination with Al³⁺ compared with other metal cations (i.e. Fe³⁺, Ni²⁺, Cd²⁺, Mn²⁺, Co²⁺, Zn²⁺, Hg²⁺, Ba²⁺, Mg²⁺ and K⁺) while o-methoxyl group-substituted one has no such phenomena, which might be due to the rotation of the uncoordinated CN and C–O bonds in one side.