Saturated\nLinkers in Two-Dimensional Covalent Organic\nFrameworks Boost Their Luminescence

The development of\nhighly luminescent two-dimensional covalent\norganic frameworks (COFs) for sensing applications remains challenging.\nTo suppress commonly observed photoluminescence quenching of COFs,\nwe propose a strategy involving interrupting the intralayer conjugation\nand interlayer interactions using cyclohexane as the linker unit.\nBy variation of the building block structures, imine-bonded COFs with\nvarious topologies and porosities are obtained. Experimental and theoretical\nanalyses of these COFs disclose high crystallinity and large interlayer\ndistances, demonstrating enhanced emission with record-high photoluminescence\nquantum yields of up to 57% in the solid state. The resulting cyclohexane-linked\nCOF also exhibits excellent sensing performance for the trace recognition\nof Fe3+ ions, explosive and toxic picric acid, and phenyl\nglyoxylic acid as metabolites. These findings inspire a facile and\ngeneral strategy to develop highly emissive imine-bonded COFs for\ndetecting various molecules.