Chemistry Reference
In-Depth Information
Fig. 6.4 a
The monomers for the synthesis of TP-COF;
b
schematic representation of TP-COF
(structure is based on quantum calculation and crystal lattice parameters; B
purple
, O
red
, tri-
phenylene
green
, pyrene
blue
, H atoms are omitted for clarity). Reprinted with permission from
Ref. [
13
]. Copyright 2008, Wiley-VCH
states (excitons). Therefore, 2D COFs could be considered as a new platform to
molecularly design semiconducting and photoconducting materials.
In this research area, Jiang et al. have made a large contribution. In 2008, they
demonstrated the use of COFs for the construction of electronic and optoelectronic
materials [
13
]. It is notable that TP-COF is the first material for this novel prop-
erty. The p-electronic 2D TP-COF consisting of interlocking hexagons is synthe-
sized using HTTP molecules and pyrene-2,7-diboronic acid (PDBA) monomers
(Fig.
6.4
). Based on the XRD pattern and simulations, structural determinations
show that the planar sheet is layered. TP-COF can harvest a wide range of pho-
tons from the ultraviolet to the visible regions. Therefore, fluorescence micros-
copy shows that TP-COF has an intense blue luminescence owing to the excitation
of the pyrene units. TP-COF is electrically conductive, which is ascribed to the
eclipsed stacking structure of the p-electronic components. It guarantees the hole
transport and is capable of on-off switching of the electric current as revealed by
the I-V curve measurements (Fig.
6.5
).
Because phthalocyanine derivatives have abundant
π
-electronic cores, the syn-
thesis of
π
-electronic COFs has been achieved by the introduction of metallophth-
alocyanine units into the skeletons. For example, the condensation of [(OH)8PcNi]
with BDBA produces a 2D NiPc-COF (Fig.
6.6
) [
14
]. NiPc-COF adopts a flake-
like morphology and consists of eclipsed 2D sheets. The test reveals that NiPc-
COF is hole-conducting and with a high carrier mobility of 1.3 cm
2
V
−
1
s
−
1
.
Except for the p-type NiPc-COF, 2D-NiPc-BTDA-COF [
15
], a nickel phthalocy-
anine COF using the electron-deficient benzothiadiazole as the linker (Fig.
6.7
),
indicated different charge carrier-transport behaviors, which is an n-type semicon-
ductor with electron mobilities as high as 0.6 cm
2
V
−
1
s
−
1
.
