Highly photoluminescent two-dimensional imine-based covalent organic frameworks for chemical sensing.

The strong π-π interactions in the stacking layers of two-dimensional covalent organic frameworks (2D-COFs), together with rotationally labile imine linkages, make most of the solid state imine-linked COFs non-fluorescent due to fluorescence quenching processes. Here, we report the successful synthesis of highly photoluminescent imine-based 2D-COFs by integrating a non-planar building unit with a pyrene-based unit and transforming the COF into spherical, sub-micron particles. High photoluminescence quantum yields (PLQY) were achieved with COF sub-micron particles dispersed in organic solvents. The as-prepared COF sub-micron particles can be used as a chemical sensor for the detection of explosive chemicals, with high sensitivity and selectivity (up to ppm level).