of the conventional methods5 attempted met with success in
our hands, and an original synthetic pathway had to be devel-
oped. The products failed to crystallize and formed gels in a
variety of poor solvents, at ambient temperature, as anticipated.
Here we report the synthesis of 2,3-di-n-decyloxytetracene
(DDOT) and 2,3-di-n-hexadecyltetracene (DHDOT) and
describe their gelling ability as well as some distinct
spectroscopic properties attesting to the π interaction between
the molecules in the aggregates.
the last step and protect the phenol groups as methoxy ethers,
stable in basic media. The strategy consisted of starting from
1,4-dihydroxy-6,7-dimethoxynaphthalene (3) as the main
building block and constructing 2,3-dimethoxytetracene-
quinone (4) using the condensation of orthodiformylbenzene
with 3 in the presence of Na2CO3. Smooth demethylation
was followed by a classical Williamson alkylation with the
long chains to give 6 in reasonable yields. DDOT and
DHDOT were finally isolated after Meerwein-Pondorff-
Verley reduction. The preparation was repeated several times,
and gram quantities were obtained. Spectroscopic data,
detailed in Supporting Information (1), are consistent with
the proposed structures.
As outlined in Scheme 2, DDOT and DHDOT have been
Scheme 2. Synthetic Pathway to 2,3-Di-n-alkoxytetracenesa
Upon drop casting of warm solutions of dissolved gelator at
a concentration (1.4 × 10-3 M) higher than the critical gel con-
centration (cc, i.e., the lowest concentration at which a gel can
be obtained at ambient temperature) and then cooling to room
temperature, the topography images obtained by AFM of a
thick deposit revealed a network of entangled fibers and fiber
bundles, whereas no fiber termination was observed (Figure 1).
Figure 1. AFM topography (left) and signal error images (right)
of DHDOT in C14H30, concentration ) 1.4 × 10-3 M, after casting
on mica; fiber width ca. 100-200 nm.
a Overall yields from p-benzoquinone: DDOT and DHDOT ca.
20%.
Solvent screening for gel-forming ability was performed
with a variety of solvents, using the inverted tube method.6
A selection of solvents and critical concentrations are listed in
Table 1. One observes than DHDOT is more efficient than
prepared in six steps, starting from benzoquinone, a com-
mercial compound, in satisfactory overall yields (ca. 20%).
Since tetracene and hydroxytetracenes are very sensitive
to oxidation, it was advisable to form the tetracene core in
Table 1. Selected Solvents and Concentrations at Which Room
Temperature Gels Are Found for DDOT and DHDOT, from
Light Diffusion Measurementa
(4) Our synthetic work was achieved before the preparation of 2,3-
dihydroxytetracene was reported: Tulewski, G. S.; Miao, Q.; Fukuto, M.;
Abram, R.; Ocko, B.; Pindak, R.; Steigerwald, M. L.; Kagan, C. R.;
Nuckolls, C. J. Am. Chem. Soc. 2004, 126, 15048-15050. Our method
differs in several ways from that of the authors.
DDOT
concn ) 10-3
DHDOT
concn ) 10-3
M
solvent
M
(5) (a) Chemistry of Carbon Compounds; Rodd, E. H., Ed.; Elsevier:
Amsterdam, 1956; Volume 3, Part B, pp 1485-1489. (b) Traite´ de Chimie
Organique; Grignard, V., Dupont, G., Locquin, R., Eds.; Masson: Paris,
1949; Vol. XVII (II), pp 1241-1298. (c) Clar, E. Polycyclic Hydrocarbons;
Academic Press: London, 1964; Volume 1, Chapter 23, pp 386-422. (d)
Zander, M. Polycyclische Aromaten Kohlenwasserstoffe und Fullerene;
Teubner: Stuttgart, 1995. (e) Houben-Weyl Methoden der Organischen
Chemie; Thieme: New York, 1981; Bd 5/2b, Chapter 4, pp 359-470. (f)
Gupta, D. N.; Hodge, P.; Khan, N. J. Chem. Soc., Perkin Trans. 1 1981,
689-696. (g) Mallouli, A.; Lepage, Y. Synthesis 1980, 9, 689. (h) Franck,
R. W.; Gupta, P. B. J. Org. Chem. 1985, 50, 4632-4635. (i) Serpaud, B.;
Lepage, Y. Bull. Soc. Chim. Fr. 1977, 539-542. (j) Pozzo, J.-L.; Clavier,
G. M.; Colomes, M.; Bouas-Laurent, H. Tetrahedron 1997, 53, 6377-6390.
(k) Bowles, D. M.; Anthony, J. E. Org. Lett. 2000, 2, 85-87.
n-hexanol
n-heptane
n-C14H30
0.4*
0.3*
0.9
1.4*
0.5
cyclohexane
1.9
a Concentrations are critical concentrations (cc) except for those marked
with an asterisk (*), for which the cc values were not determined. Gels were
also formed in DMSO and for DHDOT, in dichloromethane and acetone
DDOT; in addition, DHDOT gelifies dichloromethane and ace-
tone, in contrast to DDOT. DHDOT shows a cc of 0.5 × 10-3
972
Org. Lett., Vol. 7, No. 6, 2005