Principles for the Synthesis of Porous Organic Frameworks - Porous Organic Frameworks - page 15

Fig. 2.3 Topology-directed synthesis of POF material via bottom-up and top-down approaches,
taking PAF-1 as example. Reproduced from Ref. [ 1 ] with permission from The Royal Society of
Chemistry
skills and RCSR database organized by Yaghi and O'Keeffe ( http://rcsr.anu.edu.
au/ ) , the underlying topological possibilities could be produced. Subsequently,
the suitable monomers would be selected and prepared to satisfy the demands.
From this point of view, a topology-based strategy offers guidelines for the
fabrication of POF architectures with interesting structural properties aiming at
diverse applications.
2.2.2 The Configuration of Monomers
According to the geometry of POF materials, they could be classified into three
types (one-, two-, and three-periodic nets). The final structures of POF materi-
als are directly decided by the original configurations of the monomers. To con-
struct POFs with high porosity, the monomers should have special configuration
such as planar triangle, octahedron, linear pattern, tetrahedron, and square, etc.
(Fig. 2.4 ).
The monomers listed in Fig. 2.5 could meet the requirements that are able to
satisfy the demands on the configuration of building units. It has been documented
that those monomers with the above-mentioned structures present good abilities
for constructing POFs.
Through selecting suitable building units and effective strategies, we could
obtain POF materials. The next step should be the determination of the structure
and porosity of POFs. Therefore, POFs are characterized by Fourier transform
infrared spectroscopy (FT-IR), 13 C solid-state NMR, powder X-ray diffraction
(PXRD), scanning electron microscopy (SEM), transmission electron microscopy
(TEM), thermogravimetric analysis (TGA), and N 2 gas sorption. According to the
pattern of PXRD, POFs are distinguished into two types, ordered crystalline POFs
or randomly amorphous POFs. To date, hundreds of POFs have been success-
fully designed and synthesized. In the following sections, POFs are discussed in
accordance with whether they are crystalline or not.