Chemistry Reference
In-Depth Information
Fig. 22 Structures of
N
-annulated rylenes [
72
-
74
]
ends and bay regions. The important role of rylene bisimides as fluorescent dyes in
biological systems have attracted considerable attention because of their excellent
chemical and photostability compared to commercial dyes. Moreover, higher order
rylene bisimides display absorption and strong emission at the far-red to NIR region
which prevents interference from self-absorption of biomolecules. The largest
obstacle for aromatic organic dyes to be used in biological systems is to achieve
sufficient water solubility while maintaining a high fluorescence quantum yield, as
aromatic chromophores are prone to aggregate in aqueous media. Endeavors are
made in this area in M¨ llen's group and some water soluble terrylene bisimide dyes
such as 86 and 87 are already available for protein labeling (Fig.
23
)[
75
].
Applications of high order rylene bisimides as semiconducting materials in the
fields of organic solar cells and field-effect transistors (FETs) have also been
examined. Higher rylenes are expected to display a larger
-conjugation and a
concomitant better light-harvesting property, so compound 88 (Fig.
23
) was
prepared and tested in dye-sensitized solar cell (DSSC) devices [
76
]. Despite a
remarkably broad photocurrent action spectrum arising from its absorption behav-
ior, a moderate efficiency of 2.4% has been achieved, which is attributed to the low
voltage caused by the dye's incompatibility with additives. The field effect transis-
tor property was initially studied based on an
n
-type semiconductor molecule 89
(Fig.
23
), and the vapor-deposited films of 89 on Si-SiO
2
substrates exhibited a
maximum FET electron mobility of around 0.07 cm
2
V
1
s
1
and an on/off ratio in
excess of 10
4
, indicating the potential of terrylene molecule for FET applications
[
77
]. Recently, Bao's group successfully developed a scalable synthesis of swallow
tailed quaterrylene bisimides 90a and 90b (Fig.
23
) which can be processed from
solution [
78
]. The pressure-assisted thermal cleavage of swallow tails yielded films
p
