Biomedical Engineering Reference
In-Depth Information
Table 9.5
Phase transition behavior of unsymmetrical pyridine 31a-e and guani-
dinium chloride substituted ionic triphenylenes
32a-e
.
Compound
R
n
Phase transition behavior
31a
C
4
H
9
3
S-Col 110.0 I
31b
C
5
H
11
3
SS 75.7 SS 96.2 Col 112.8 Col 121.2 I
31c
C
6
H
13
3
SS 75.3 SS 91.7 Col 143.8 I
31d
C
4
H
9
4
S 83.7 Col 95 I
31e
C
4
H
9
5
S 83.4 SS 112.4 I
32a
C
5
H
11
2
Cr 53
58 I
32b
C
6
H
13
2
Cr 46 Col
r1
81 Col
r2
106 I
32c
C
7
H
15
2
r
1
47 Cr
2
55 Col
r
95 I
32d
C
8
H
17
2
Cr 44 Col
r
103 I
32e
C
9
H
19
2
r
1
41 Cr
2
49 Col
r
115 I
32f
C
10
H
21
2
Cr 45 Col
r
91 I
peripheral lengths have been synthesized. h e compound with the short-
est peripheral chain was found to be non-mesomorphic (Table 9.5). An
interesting point to note here is that all the odd chain length compounds
exhibited polymorphism in the crystalline state. Mesophase observed was
Col
r
with varying symmetry (
P2/m
,
C2/m
).
9.3.1.2.3 Ionic Discotic Dimers Based on Triphenylene
Pal and Kumar [79] synthesized triphenylene-imidazole-based ionic
dimers
33
in which they hybridized two triphenylene and one imidazole
moiety to form dimer under microwave dielectric heating, since classical
reaction did not give the desired product (Figure 9.13). h is dimer exhib-
ited Col mesophase at 84 C on heating, which i nally cleared at 95 C. On
cooling, mesophase appeared at 92 C and no crystallization was observed
up to room temperature. Interestingly, the calamitic-discotic hybrid made
by the authors was found to be non-liquid crystalline.
A series of symmetrical gemini dimers based on imidazole and triphe-
nylene moieties have been synthesized by Kumar
et al.
[80] using micro-
wave dielectric heating. Dimers
34
with shorter spacer length displayed
Col
h
mesophase over a wide range of temperature. Transition temperatures
of these compounds are given in Table 9.6.
