The development of
highly luminescent two-dimensional covalent
organic frameworks (COFs) for sensing applications remains challenging.
To suppress commonly observed photoluminescence quenching of COFs,
we propose a strategy involving interrupting the intralayer conjugation
and interlayer interactions using cyclohexane as the linker unit.
By variation of the building block structures, imine-bonded COFs with
various topologies and porosities are obtained. Experimental and theoretical
analyses of these COFs disclose high crystallinity and large interlayer
distances, demonstrating enhanced emission with record-high photoluminescence
quantum yields of up to 57% in the solid state. The resulting cyclohexane-linked
COF also exhibits excellent sensing performance for the trace recognition
of Fe3+ions, explosive and toxic picric acid, and phenyl
glyoxylic acid as metabolites. These findings inspire a facile and
general strategy to develop highly emissive imine-bonded COFs for
detecting various molecules.