oligoacenes in organic solvents at room temperature has been
a hurdle in fully realizing the advantages of organic electron-
ics, such as low-cost patterning and low-temperature pro-
cessing. Therefore, it is necessary to develop new, soluble,
π-stacking organic semiconductors for OFETs.11
Scheme 1. Syntheses of 5a-d
In this work, we report a family of partially fluorinated
and alkyl/alkoxy-substituted tetracene molecules that are
soluble in common organic solvents and have significant
π-stacking motifs in crystal lattices. Fluorine has been applied
extensively to tune the electronic and structural properties
of organic semiconducting materials because of its strong
electronegativity and significantly small size.7a,12 Recently,
Watson and co-workers have reported that partial fluorination
overcame the herringbone crystal packing of tetracyclic
aromatic compounds, leading to a cofacial packing with a
π-distance of 3.37 Å.12a Partially fluorinated silylethynyl
pentacenes were also found to reduce the intermolecular
distances.7a Incorporation of long alkyl or alkoxy chains is
widely used to improve the solubility of small molecules
and polymers and to facilitate formation of semiconductor
thin films by cost-effective solution deposition techniques.13
In our studies, we found that the regiochemistry of the side-
chain attachment on the tetracene backbone not only
improved the solubilities but also tuned the electrochemical
properties and packing motifs. Furthermore, the incorporation
of both donor and acceptor substituents to the main chain
was added to induce a strong dipole moment. Strong dipole-
dipole interactions between neighboring molecules were
previously demonstrated to afford π-stacking with short
intermolecular distances and self-assembly properties.9
solution of 4a-d and phase-transfer catalyst benzyltriethyl-
ammonium chloride at room temperature. This reaction was
proposed to proceed by way of the in-situ-formed dichlo-
rocarbene, which combined with 4a-d to form ammonium
ylide intermediates.16 The aromatic acenes were then gener-
ated from the rapid cheletropic loss of methyl isocyanide
dichloride. Tetracene derivatives 5a-d were obtained as red
or orange crystals from recrystallization in hexane, with
yields of 15-35% over three steps. The solubility of 5a-d
in organic solvents, such as methylene chloride, chloroform,
and toluene, was found to be much better than that of their
parent tetracene, owing to the long linear side chains.
Scheme 2 shows the synthetic routes to dibromonaphtha-
lenes (3a-d), which are used in Scheme 1. Hexyloxy-
substituted naphthalenes were prepared from corresponding
naphthoquinone (6 and 7) via a reduction to naphthalene-
hydroquinone and then alkylation under basic conditions.17
The bromination of 1,4-bis(hexyloxy)naphthalene (8) was
carried out by a treatment of N-bromosuccinimide (NBS) in
methylene chloride.18 Both 3a and 3b were obtained as
colorless crystals. Dioctyl-substituted dibromonaphthalenes
(3c-d) were prepared in two steps with good yields. In the
presence of an excess of furans, tetrabromobenzenes (9a-
b) were treated with n-butyllithium (n-BuLi) at low tem-
perature, leading to the epoxides (10a-b) via a D-A
reaction between corresponding benzynes and furans.19 Low-
valent Ti, prepared in situ from a reaction between zinc and
The key steps of our synthetic strategy to the tetracene
derivatives, as outlined in Scheme 1, were adapted from a
methodology previously reported by Gribble.14 N-Methyl-
4,5,6,7-tetrafluoroisoindole (2), which is a moderately stable
compound and should be prepared freshly, could be easily
prepared from a reaction between 1 and 3,6-di(2-pyridyl)-
1,2,4,5-tetrazine, via a Diels-Alder (D-A) reaction and
subsequent thermally allowed electrocyclic fragmentation.15
In the presence of 2, dibromonaphthalenes 3a-d were treated
with phenyllithium (PhLi) at 0 °C, leading to the formation
of corresponding naphthalyne, which readily reacted with 2
via the D-A reaction. Imines (4a-d) were obtained as
colorless or slightly yellow solids in 40-65% yields. The
deamination was carried out by the treatment of an aqueous
solution of NaOH (50%, w/w) to the stirred chloroform
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Siegrist, T.; Kloc, C.; Bao, Z. J. Am. Chem. Soc. 2004, 126, 15322.
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T.; Kobayashi, M.; Gao, Y.; Fukai, Y.; Inoue, Y.; Sato, F.; Tokito, S. J.
Am. Chem. Soc. 2004, 126, 8138.
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N. R.; Slayton, R. I. J. Org. Chem. 1981, 46, 1025.
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D. R. J. Med. Chem. 1985, 28, 822.
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