Biomedical Engineering Reference
In-Depth Information
the number of alkoxy chains was increased, melting temperatures were
decreased. h ese moieties also show photoluminescence in a 500 nm to
650 nm range, but with lesser quantum ei ciencies in the condensed state.
9.3.1.2 Triphenylene
9.3.1.2.1 Symmetrical Hexasubstituted Monomeric Ionic Triphenylene
Aida and coworkers [59, 72] reported triphenylene derivatives carry-
ing parai nic side chains with ionic liquid pendants
26a-f
(Figure 9.11).
Hexahydroxy triphenylene
24
was converted to ω-bromo substituted tri-
phenylene which was then subjected to quarterization with imidazole.
h ese derivatives not only exhibited Col
h
phases, but also Cub
bi
in lower
temperature range than Col
h
mesophase. Phase behaviors are found to be
highly chain-length dependent (Table 9.3). Two derivatives with tetradecyl
spacer exclusively form Cub
bi
mesophase over a wide temperature range,
while derivative with the shortest side chain did not show any mesomor-
phic behavior. When the counterions are changed from BF
4
to PF
6
to Tf
2
N,
triphenylenes with longer side chains only form the cubic mesophases.
h e XRD studies indicate the presence of π-stacked columns in the Cub
bi
mesophase. Further, maximum transient conductivity for the Cub
bi
meso-
phase for compound
26a2
was found to be 3.5 × 10
-4
cm
2
V
-1
s
-1
. Such
high conductivity in the Cub
bi
mesophase makes them suitable as organic
semiconductors.
OMe
OR
OH
OMe
OH
OR
MeO
RO
HO
(i)
(ii)/(iii)
MeO
HO
RO
OMe
OH
OR
OMe
OH
OR
23
24
25
O
N
N
Y
-
R
R
H
NH
n
X
COO
-
C
12
H
25
O
26a-f
27
Figure 9.11
Synthesis of Symmetrical hexasubstituted monomeric ionic triphenylene
(i)
HBr, HAc; (ii) Br(CH
2
)
n
OH, then CBr
4
, PPh
3
, THF, and then 1-methylimidazole;
(iii) BrCH
2
COOC
2
H
5
, (CH
3
)
2
N(CH
2
)
3
NH
2
, dodecayloxybiphenylcarboxylic acid.
