reported elsewhere soon. These properties indicate that the
smectic liquid crystal glass provides us with solid self-organized
molecular aggregates while keeping easy control over the
molecular alignment in smectic liquid crystals, which shows
promising advantages over both amorphous and crystalline
materials as a new type of organic semiconductors.
Table 1 Hole mobility of LCG-triester 8-PNP-O12 in different phases
Hole mobility
cmꢂ2 vꢂ1 sꢂ1 (at 25 V)
Phase
SmA
SmBhex
SmBhex glass
Polycrystal
1.25 ꢁ 10ꢂ4
5 ꢁ 10ꢂ4
3.5 ꢁ 10ꢂ4
—
Acknowledgements
The authors would like to thank Dr Hiroaki Iino and Dr Akira
Ohno for helpful discussions regarding experimental analysis,
and to thank Center for Advanced Materials Analysis (Suzuka-
kedai), Technical Department, Tokyo Institute of Technology,
for MS analysis. The authors are also grateful for the financial
supports from a Core Research for Evolutional Science and
Technology (CREST) program sponsored by Japan Science and
Technology Agency.
SmBhex phase. Each photocurrent is also non-dispersive and
shows a clear shoulder. The hole mobility is estimated to be 3.5 ꢁ
10ꢂ4 cm2 Vꢂ1 sꢂ1 at 25 V. This mobility is almost the same as that
in SmBhex phase, indicating that the charge transport properties
of the SmB phase are successfully maintained in solid state, i.e.,
glassy SmBhex phase.
On the other hand, the transient photocurrents in the poly-
crystalline phase decay rapidly as shown in Fig. 6(b). It indicates
that there are lots of defects or deep trap states in the bulk to stop
the carrier transport, which are possibly caused by grain
boundaries among the polycrystallites. Therefore, the carrier
transport properties were dramatically decreased in the poly-
crystal phase. We summarize the charge carrier transport prop-
erties of LCG-triester 8-PNP-O12 in Table 1.
Notes and references
1 P. M. Borsenberger and D. S. Weiss, Organic photoconductors for
Imaging System, Marcel Decker, New York, 1993.
2 C. W. Tang and S. A. van Slyke, Appl. Phys. Lett., 1987, 51, 12.
3 M. van der Auweraer, F. C. Schryver, P. M. Borsenberger and
€
H. Bassler, Adv. Mater., 1994, 6, 199.
€
4 H. Bassler, Phys. Status Solidi B, 1993, 175, 15.
As for the mobility in liquid crystal glass states, the relatively
high OFET mobility of 10ꢂ2 cm2 vꢂ1 sꢂ1 was reported in the
nematic glassy phase of oligofluorene derivatives.34 However, we
might expect higher mobility up to 0.1 cm2 vꢂ1 sꢂ1 or more if
highly ordered smectic mesophases were turned to glass, because
the charge carrier mobility in smectic mesophases depends on
molecular order in a smectic layer, as reported previously.35
The fixation of molecular motion in liquid crystalline phases is
one of continuous interest for device applications of liquid
crystalline organic semiconductors. In fact, various approaches
have been proposed, which include reactive mesogens with
polymerizable function groups,36 immobile liquid crystalline
composites with a cross-linker,37 polymeric liquid crystals,38 and
dried lyotropic liquid crystals reported more recently.39 Utiliza-
tion of the LC-glass is another approach, as demonstrated in
nematic and discotic glasses.26,34
5 J. Mort and A. I. Lakatis, J. Non-Cryst. Solids, 1970, 4, 117.
6 R. G. Kepler, Phys. Rev., 1960, 119, 1226.
7 E. A. Silinsh, Organic Molecular Crystals, 1980, Springer, Berlin.
8 M. Yamashita and Y. Amemiya, Jpn. J. Appl. Phys., 1978, 17, 1513.
9 K. Okamoto, S. Nakajima, A. Itaya and Kusabayashi, Bull. Chem.
Soc. Jpn., 1983, 56, 3930.
ꢁ
10 B. Blanzat, C. Barthou, N. Tercier, J.-J. Andre and J. Simon, J. Am.
Chem. Soc., 1987, 109, 6193.
11 N. Boden, R. J. Bushby, J. Clements, M. V. Jesudason, P. F. Knowles
and G. Williams, Chem. Phys. Lett., 1988, 152, 94.
ꢁ
12 A. Belarbi, M. Maitrot, K. Ohta, J. Simon, J. J. Andre and P. Petit,
Chem. Phys. Lett., 1988, 143, 400.
13 P. G. Schouten, J. M. Warman, M. P. de Haas, M. A. Fox and
H.-L. Pan, Nature, 1991, 252, 736.
14 P. G. Schouten, J. M. Warman, M. P. de Haas, J. F. van der Pol and
J. W. Zwikker, J. Am. Chem. Soc., 1992, 114, 9028.
15 J. Wu, T. Usui, A. Ohno and J. Hanna, Chem. Lett., 2009, 38, 592.
16 G. B. Vaughan, P. A. Heiney, J. P. MaCauley and A. B. Smith III,
Phys. Rev. B: Condens. Matter, 1992, 46, 2788.
17 D. Adam, F. Closs, T. Frey, D. Funhoff, D. Haarer, H. Ringsdorf,
P. Schuhmacher and K. Siemensmeyer, Phys. Rev. Lett., 1993, 70,
457.
Conclusions
€
18 D. Adam, P. Schuhmacher, J. Simmerer, L. Haussling,
K. Siemensmeyer, K. H. Etzbach, H. Ringsdorf and D. Haarer,
Nature, 1994, 371, 141.
In this study, we have successfully prepared a novel smectic glass,
1,3,5-benzenetricarboxylic acid, tris{12-[60-(400-octylphenyl)-20-
naphthyloxy]-1-dodecyl ester} containing a mesogenic 2-phe-
nylnaphthalene moiety. This material exhibited SmA and
SmBhex phases when cooled from an isotropic phase at slow
cooling rates, but exhibited a glassy SmBhex phase when cooled at
high cooling rates. This is the first reported case of the glass state
of the SmBhex phase in small moleclues, whose glass transition
temperature, Tg was as high as 60 ꢀC. We also report for the first
time, the charge carrier transport properties in smectic liquid
crystal glassy phases: the highest charge carrier transport
mobility in the SmBhex glass phase was around 3.5 ꢁ 10ꢂ4 cm2
Vꢂ1 sꢂ1 for holes, which is comparable to that for the SmBhex
phase. In addition, the mobility in the SmBhex glassy phase
depends on the temperature, but not on the electric field, which is
quite different from amorphous materials. The details will be
19 L. L. Chapoy, D. K. Munck, K. H. Rasmussen, E. J. Diekmann,
R. K. Sethi and D. Biddle, Mol. Cryst. Liq. Cryst., 1984, 105, 353.
20 M. Funahashi and J. Hanna, Appl. Phys. Lett., 2000, 76, 2574.
21 J. Hanna, Opto-Electron. Rev., 2005, 13, 259.
22 I. K. Iverson, S. M. Casey, W. Seo and S. W. T. Chang, Langmuir,
2002, 18, 3510.
23 H. Maeda, M. Funahashi and J. Hanna, Mol. Cryst. Liq. Cryst., 2000,
346, 183.
24 M. Funahashi and J. Hanna, Phys. Rev. Lett., 1997, 78, 2184.
25 K. Tokunaga, H. Iino and J. Hanna, J. Phys. Chem. B, 2007, 111,
12041.
€
26 D. Adam, P. Schuhmacher, J. Simmerer, L. Haussling, W. Paulus,
K. siemensmeyer, K. H. Etzbach, H. Ringsdorf and D. Haarer,
Adv. Mater., 1995, 7, 276.
27 F. Fan, S. W. Culligan, J. Mastrangelo, D. Katsis and S. H. Chen,
Chem. Mater., 2001, 13, 4584.
28 K. Yonetake, O. Habaand T. Takahashi, Jpn. Kokai Tokkyo Koho,
2008, JP 2008239987.
29 N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457.
8050 | J. Mater. Chem., 2011, 21, 8045–8051
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