Layer-Stacking-Driven Fluorescence in a Two-Dimensional Imine-Linked Covalent Organic Framework

Schiff-condensation
reactions carried out between 1,6-diaminopyrene (DAP) and the tritopical
1,3,5 benzenetricarbaldehyde (BTCA) or 2,4,6-triformylphloroglucinol
(TP) ligands give rise to the formation of two-dimensional imine-based
covalent-organic frameworks (COFs), named IMDEA-COF-1 and -2, respectively. These materials show dramatic
layer-packing-driven fluorescence in solid state arising from the
three-dimensional arrangement of the pyrene units among layers. Layer
stacking within these 2D-COF materials to give either eclipsed or
staggered conformations can be controlled, at an atomic level through
chemical design of the building blocks used in their synthesis. Theoretical
calculations have been used to rationalize the different preferential
packing between both COFs. IMDEA-COF-1 shows green emission
with absolute photoluminescence quantum yield of 3.5% in solid state.
This material represents the first example of imine-linked 2D-COF
showing emission in solid state.