Syn th esis of High ly F lu or escen t Y-En yn e
Den d r im er s w ith F ou r a n d Six Ar m s†
into structures with columnar order and liquidlike dy-
namics occurs in disk-shaped molecules with rigid aro-
matic cores and flexible peripheral side chains. Mol-
ecules with flat disklike cores and surrounding alkyl
substituents form columnar mesophases.18
In this paper, we report the synthesis of the first
generation of Y-enyne dendrimers with four and six
extended dodecyloxy arms, 9 and 10, respectively (Scheme
,‡
1
7
Bilal R. Kaafarani,§,| Brigitte Wex, Fei Wang,
§
§
⊥
⊥
Otilia Catanescu, L. C. Chien, and
Douglas C. Neckers*,§
Center for Photochemical Sciences, Bowling Green State
University, Bowling Green, Ohio 43403, Chemistry
Department, University of Arizona, Tucson, Arizona 85721,
and Liquid Crystal Institute, Kent State University,
Kent, Ohio 44242
1
). The synthetic approach of 9 and 10 is a combination
1
9
of both divergent (four and six couplings) and conver-
gent methods (acetylene 4 was synthesized separately).
4
-Hydroxybenzaldehyde 1 was refluxed with 1-bromo-
20
dodecane to afford 4-dodecyloxybenzaldehyde 2, which
was converted via Corey-Fuchs reaction to 4-dode-
cyloxy-â,â-dibromostyrene 3. The latter when reacted
2
1
Received November 14, 2002
2
2
with n-BuLi afforded 1-dodecyloxy-4-ethynylbenzene 4.
Abstr a ct: A first generation of dendrimeric Y-enynes with
extended flexible chains was synthesized using Sonogashira
coupling. Dendrimers 9 and 10 are highly fluorescent in the
solid state and in solution.
Terephthalaldehyde 5 and 1,3,5-benzenetricarboxalde-
hyde 7 were converted into 1,4-bis(2,2-dibromovinyl)-
benzene 6 and 1,3,5-tris(2,2-dibromovinyl)benzene 8.
Sonogashira23 couplings of 6 and 4 as well as 8 and 4
afforded dendrimers 9 and 10, respectively. Differential
scanning calorimetry (DSC) and optical polarized micro-
scope measurements of 9 and 10 showed the absence of
mesophase in these two compounds. The electron accep-
tor 2,4,7-trinitro-9-fluorenone (TNF) is commonly used
in charge-transfer complexes to induce mesophase.
Preliminary results showed that charge-transfer com-
plexes of 9/TNF and 10/TNF induced discotic mesophases
in both systems.
2
4
Interest in cross-conjugated enynes (Y-enynes) has
grown recently as a result of their unique conjugation,
electronic, and photonic properties.1-3 Fomina4 first
reported that polymerization of â,â-dibromo-4-ethynyl-
styrene produced a conjugated Y-enyne hyperbranched
2
5
5
polymer. Dendrimers have been thought to have a wide
6
7,8
range of applications in biomedicine, electronics,
9
-11
12,13
26,27
sensors,
and coatings.
Twenty-five years ago,
A possible explanation for the
Chandrasekhar14 discovered discotic liquid crystals that
constitute a unique class of materials. Self-organization
15
absence of mesophase in 9 and 10 is the close proximity
1
6
(
12) Dusek, K.; Duskova-Smrckova, M. Prog. Polym. Sci. 2000, 25,
†
Contribution no. 493 from the Center for Photochemical Sciences.
This paper is dedicated to Prof. Dr. J . W. Neckers on the occasion
1215-1260.
‡
(13) Pettersson, B. Pigm. Resin Technol. 1996, 25, 4-14.
(14) Chandrasekhar, S.; Sadashiva, B. K.; Suresh, K. A. Pramana
1977, 9, 471-480.
of his 101st birthday.
§
Bowling Green State University.
University of Arizona.
Kent State University.
|
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Liq. Cryst. 1997, 23, 613-627. (c) Christ, T.; Glusen, B.; Greiner, A.;
Kettner, A.; Sander, R.; Stumpflen, V.; Tsukruk, V.; Wendorff, J . H.
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1
0.1021/jo026718+ CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/03/2003
J . Org. Chem. 2003, 68, 5377-5380
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