Chemistry Reference
In-Depth Information
N
N
N
N
O
R
O
R
O
O
S
S
S
S
S
S
S
S
S
S
S
S
OC
12
H
25
R =
OC
12
H
25
OC
12
H
25
O
Figure 7.27
Chemical structures of some TTF-based gelators.
119
Low molecular weight gelators designed with extended functional p-conju-
gated oligomers have also attracted a great deal of attention, for example,
organogelators incorporating p-conjugated oligothiophenes moieties. Oli-
gothiophenes are attractive semiconductor moieties because of their excellent
ability to form conductive p-stacks systems and their relatively simple chemical
modification.
120-123
Recently, the synthesis of a quaterthiophene gelator
functionalised with a barbituric acid segment and a tridodecyl oxy-phenyl end
group was reported
124
(Figure 7.28). The formation of conductive self-
assembled nanorods and nanotape-like aggregates was demonstrated through
complementary hydrogen bonds with a flexible bis(melamine) receptor
(Figure 7.28). By controlling the temperature of the coaggregated solution, a
selective self-assembly towards nanorod or nanotape supramolecular objects
was reported. Flash-photolysis time-resolved microwave conductivity (FP-
TRMC) measurements performed with a laser pulse l
ΒΌ
355 nm, showed the
formation of long-lived charge carriers with maximum transient conductivities
of 1.0
10
-4
cm
2
V
-1
s
-1
for the quaterthiophene assembly and of 0.67
10
-4
cm
2
V
-1
s
-1
for the coassembled structure. The hole mobility of the coassembled
nanotape-like structure was calculated to be 0.57 cm
2
V
-1
s
-1
, whereas a value
of 1.3 cm
2
V
-1
s
-1
was estimated for the nanorods. The hole mobility of the
nanotape-like structures is one order of magnitude higher than the mobility
observed for lamellarly organised poly(hexylthiophene)s. This high mobility
value was attributed to the interchain transportation of charge carriers within a
lamella. Similar effects have also been seen in a quaterthiophene gelator.
125
A hairpin-shaped molecule containing two sexithiophene moieties employed
as charge-conducting segments has been prepared and studied
126
(Figure 7.29).
To determine the charge mobility of this thiophene-based organogelator,
OFETs from thin films were fabricated using an assembling solvent (toluene) or
nonassembling solvents (chlorobenzene or o-dichlorobenzene). All OFET
