Direct synthesis of highly pure perylene tetracarboxylic monoimide

Article abstract of DOI:10.1016/j.tetlet.2010.10.071

A series of perylene tetracarboxylic monoimides substituted with cycloalkanes were synthesized through a one-step reaction between cycloalkyl amines and the parent perylene dianhydride. The reaction demonstrates high selectivity for the production of mono

Full text of DOI:10.1016/j.tetlet.2010.10.071

Tetrahedron Letters 51 (2010) 6651–6653
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Direct synthesis of highly pure perylene tetracarboxylic monoimide
⇑
Helin Huang, Yanke Che, Ling Zang
Department of Material Science and Engineering, University of Utah, 122S. Central Campus Drive, Salt Lake City, UT 84112, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of perylene tetracarboxylic monoimides substituted with cycloalkanes were synthesized through
a one-step reaction between cycloalkyl amines and the parent perylene dianhydride. The reaction dem-
onstrates high selectivity for the production of monoimides with no formation of diimides. The high reac-
tion selectivity is primarily due to the insolubility of the monoimides in the reaction medium, which in
turn causes rapid precipitation of the products, shifting the reaction equilibrium to the right.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 6 September 2010
Revised 9 October 2010
Accepted 12 October 2010
Available online 19 October 2010
Keywords:
PTCDI
Perylene
Monoimide
Direct synthesis
Perylene tetracarboxylic diimides (PTCDIs) represent a robust
class of n-type organic semiconductor with high thermal and
photo-stability, and have long been used in various optoelectronic
materials and devices.1–4 As evidenced in recent research, appropri-
ate side-chain modification of PTCDIs facilitates one-dimensional
(1D) cofacial stacking of the molecules, leading to formation of
well-defined nanowires or nanobelts.4–7 Compared to the tradi-
tional bulk-phase materials, these 1D nanostructures often demon-
strate unique properties and unprecedented performance, such as
1D confined charge transport,8–10 linear emission polarization,11,12
and 1D enhanced exciton migration, and the resulted amplification
of emission quenching.13,14 Combination of these optoelectronic
properties enables applications in vapor sensing of gaseous
reagents through modulation of the emission intensity or electrical
conductivity of the nanofibers.4,15
(which could be extremely time-consuming and costly if the solu-
bility of imides is limited). This prevents large scale production of
the asymmetric PTCDIs for the necessary materials fabrication. To
overcome this bottleneck, it is critical to develop a synthetic proto-
col that allows for direct preparation of monoimides from the par-
ent dianhydride compound (Chart 1).
Herein we report on a one-step synthesis of highly pure cyclo-
alkyl substituted monoimides without further purification
(Scheme 1). Cycloalkanes represent a special class of side-chains
that possess a crossed orientation with the perylene plane at about
90°, thus enforcing rotated stacking between the molecular planes
so as to minimize the steric hindrance caused by the cycloalkanes
rings.12 The rotated stacking enables strong fluorescence emission
for the nanofibers thus fabricated from the molecules, though most
of other PTCDIs demonstrate very weak emission due to the H-type
The synthesis of PTCDIs takes advantages of the fact that
the two nitrogen positions at the imides of PTCDI are nodes in
p–p
interaction.3
In one typical reaction, perylene-3,4,9,10-tetracarboxylic dian-
the
p
-orbital wavefunction,16 providing enormous options for
hydride (0.2 g, 0.51 mmol), cyclohexylamine (0.5 mL, 4 mmol),
modifying the structures of the two side-chains (but without sig-
nificant altering of the electronic property of the PTCDI skeleton).
To construct supramolecular structures of PTCDI containing multi-
functional moieties (e.g., electron donor for charge separation,
hydrophilic side-chain for enhanced layer-by-layer stacking), it is
often demanded to make the monoimide as precursor so as to
synthesize the asymmetric PTCDIs with two different side-chain
substitutions (Chart 1). However, most of the monoimides have
thus far been synthesized through partial hydrolysis of the
symmetric PTCDI,17,18 followed by extensive column purification
⇑
Corresponding author.
E-mail address: LZANG@eng.utah.edu (L. Zang).
Chart 1. Synthetic pathways for PTCDIs.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.10.071

6652
H. Huang et al. / Tetrahedron Letters 51 (2010) 6651–6653
Scheme 1. One-step condensation leading to selective production of monoimides.
Scheme 3. One-step condensation with linear alkyl amines shows decreased
selectivity for the production of monoimides.
that performed with the cycloalkyl side-chains. In the best case
(14:6 ethanol/water), the production yield of the dodecyl monoi-
mide was only about 80%, with 20% parallel production of the dii-
mide. This less selective reaction is likely due to the increased
solubility of dodecyl monoimide in alcohols. Indeed, as previously
observed in propanol/water mixture, the same reaction also pro-
duced diimide as impurity.21
Scheme 2. Substituting the monoimides with long alkyl side-chains to improve the
solubility for NMR characterization.
In conclusion, a series of perylene tetracarboxylic monoimides
substituted with cycloalkyls were synthesized through a one-step
reaction between cycloalkyl amines and the parent perylene dian-
hydride, both of which are cheap and commercially available. The
high selectivity thus obtained for the reaction is primarily due to
the insolubility of the monoimides in the reaction medium, which
in turn causes rapid precipitation of the products. This precipita-
tion-driven synthesis may be extended to preparation of other per-
ylene monoimides, for which selection of appropriate reaction
medium is the most critical for achieving the high purity of prod-
uct. In general, an ideal reaction medium must possess minimal (if
not none) solubility for the monoimides, while still maintaining
sufficient solubility for the reactant amines.
and ethanol/water (20 mL, volume ratio of 4:1) were mixed and
heated at 70 °C for 6 h. The reaction mixture was cooled to room
temperature and acidified by adding 30 mL concentrated HCl
(12 M) and 20 mL water. After stirring overnight, the resultant so-
lid was collected by vacuum filtration through a 0.45 lm mem-
brane filter (Osmonics), followed by washing with methanol and
water until the pH of washings turned to be neutral. The collected
solid was dried in vacuum at 60 °C. The solid thus obtained was
proven pure with no formation of the diimide, which has signifi-
cant solubility in chloroform and can be spotted (if any) by alumina
TLC (eluent: chloroform/methanol of 9:1).
Since the solubility of cycloalkyl monoimide in common organic
solvents is very low, it is impossible to perform NMR characteriza-
tion directly on the monoimide products obtained. To improve the
solubility, the as-prepared monoimides were reacted with exces-
sive dodecylamine to convert into the asymmetric di-substituted
PTCDIs (Scheme 2), which turned to be sufficiently soluble in chlo-
roform, allowing for 1H NMR characterization.22 As evidenced for
all the three PTCDIs substituted with cyclopentyl, cyclohexyl, and
cycloheptyl, the NMR spectra showed clean assignment to a single
compound, which in turn indicated the high purity of the monoi-
mide as prepared in Scheme 1. The straight, highly selective pro-
duction of monoimides thus observed is largely due to its
insolubility in the mixed solvent of ethanol/water, which causes
rapid precipitation of the product out of the reaction medium. Such
precipitation-driven synthesis was previously employed in the
preparation of macrocyclic conjugated molecules through cyclo-
oligomerization.19,20
To further prove the concept of precipitation-driven synthesis,
we changed the reaction medium from ethanol/water mixture to
other alcohol based solvents, where the cycloalkyl PTCDIs remain
insoluble.12 These solvents include pure ethanol, methanol, and
their mixtures with water containing varying levels of water up
to 60%. As expected, the only product for the reaction following
the same protocol described above (Scheme 1) was the corre-
sponding monoimide. Increasing the water content above 60%
makes it difficult to dissolve the alkyl amines, thus significantly
slowing the reaction process.
Acknowledgments
This work was supported by DHS (2009-ST-108-LR0005), NSF
(CAREER CHE 0641353, CBET 730667) and USTAR Program.
References and notes
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The same reaction protocol was also tested for synthesizing
other monoimides substituted with different side-chains such as
dodecane (Scheme 3). The reaction turned out not as selective as
16. Kazmaier, P. M.; Hoffmann, R. J. Am. Chem. Soc. 1994, 116, 9684–9691.

H. Huang et al. / Tetrahedron Letters 51 (2010) 6651–6653
6653
17. Langhals, H. Heterocycles 1995, 40, 477–500.
0.45 membrane filter (Osmonics). The red solid was then washed
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thoroughly with methanol and water until the pH of washings turned to be
neutral. The collected solid was dried in vacuum at 60 °C. TLC: Rf (silica gel/
CH3Cl:methanol 95:5) = 0.60. The purity and structure of the three asymmetric
PTCDIs thus prepared (as shown in Scheme 2) were confirmed by 1H NMR as
presented below:
21. Geerts, Y.; Quante, H.; Platz, H.; Mahrt, R.; Hopmeier, M.; Bohmc, A.; Mullen, K.
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N-cyclopentyl-N0-dodecyl-perylene-3,4,9,10-tetracarboxylic
diimide.
1HNMR
(500 MHz, CDCl3): d = 0.87 (t, 3H, CH3), 1.24–2.28 (m, 28H, 14CH2), 4.11 (t,
22. The asymmetric PTCDIs substituted with dodecyl and three different cycloalkyl
groups were synthesized following the standard condensation method
2H, CH2), 5.53 (t, 1H, CH), 8.15 (m, 8H, perylene). Yield: 92%.
N-cyclohexyl-N0-dodecyl-perylene-3,4,9,10-tetracarboxylic
diimide.
1HNMR
previously developed (see Refs. 4,17). In
a
typical reaction, 193 mg
(500 MHz, CDCl3): d = 0.87 (t, 3H, CH3), 1.24–2.28 (m, 30H, 15CH2), 4.16 (t,
2H, CH2), 5.04 (t, 1H, CH), 8.44 (m, 8H, perylene). MALDI–TOFMS gave m/z
640.3 (calculated 640.33). Yield: 90%.
(0.41 mmol) of the cyclohexyl substituted monoimide, 113 mg (0.61 mmol)
of dodecylamine, and 2 g of imidazole were heated at 120 °C under argon for
4 h. The reaction mixture was cooled to room temperature and dispersed into
10 mL ethanol, followed by addition of 25 mL of 2 M HCl. After stirring
overnight, the resulting solid was collected by vacuum filtration through a
N-cycloheptyl-N0-dodecyl-perylene-3,4,9,10-tetracarboxylic
diimide.
1HNMR
(500 MHz, CDCl3): d = 0.87 (t, 3H, CH3), 1.24–2.28 (m, 32H, 16CH2), 4.17 (t,
2H, CH2), 5.20 (t, 1H, CH), 8.50 (m, 8H, perylene). Yield: 91%.