Saturated Linkers in Two-Dimensional Covalent Organic Frameworks Boost Their Luminescence

The development ofhighly luminescent two-dimensional covalentorganic frameworks (COFs) for sensing applications remains challenging.To suppress commonly observed photoluminescence quenching of COFs,we propose a strategy involving interrupting the intralayer conjugationand interlayer interactions using cyclohexane as the linker unit.By variation of the building block structures, imine-bonded COFs withvarious topologies and porosities are obtained. Experimental and theoreticalanalyses of these COFs disclose high crystallinity and large interlayerdistances, demonstrating enhanced emission with record-high photoluminescencequantum yields of up to 57% in the solid state. The resulting cyclohexane-linkedCOF also exhibits excellent sensing performance for the trace recognitionof Fe3+ ions, explosive and toxic picric acid, and phenylglyoxylic acid as metabolites. These findings inspire a facile andgeneral strategy to develop highly emissive imine-bonded COFs fordetecting various molecules.