Bis-N-annulated quaterrylenebis(dicarboximide) as a new soluble and stable near-infrared dye

Article abstract of DOI:10.1021/ol902027b

A new ladder-type bis-W-annulated quaterrylenebls(dlcarboxlmlde) (1) was synthesized, and It exhibits excellent solubility In common organic solvents, high molar absorptivity, and good stability. Moreover, It absorbs and emits light In the near-IR spectra

Full text of DOI:10.1021/ol902027b

ORGANIC
LETTERS
2009
Vol. 11, No. 20
4508-4511
Bis-N-annulated
Quaterrylenebis(dicarboximide) as a
New Soluble and Stable Near-Infrared
Dye
Chongjun Jiao, Kuo-Wei Huang, Jing Luo, Kai Zhang, Chunyan Chi, and
Jishan Wu*
Department of Chemistry, National UniVersity of Singapore, 3 Science DriVe 3,
Singapore 117543
chmwuj@nus.edu.sg
Received July 12, 2009
ABSTRACT
A new ladder-type bis-N-annulated quaterrylenebis(dicarboximide) (1) was synthesized, and it exhibits excellent solubility in common organic
solvents, high molar absorptivity, and good stability. Moreover, it absorbs and emits light in the near-IR spectral region with a high fluorescence
quantum yield. All these properties qualify it as a promising NIR dye for many applications.
Sunlight, the rich and green resource, possesses about 50%
of its radiation intensity in the near-infrared (NIR) region
ranging from 700 to 2000 nm. Thus, the development of
dyes and pigments that function in the NIR spectral region
is essential for diverse applications, such as optical recording,
can absorb and/or emit light in the NIR region are highly
desirable. However, many commercially available NIR dyes
suffer from inevitable drawbacks due to their insufficient
photostability.6
Rylenes and their dicarboxylic imide derivatives are key
chromophores in dye chemistry due to their excellent
chemical and photostability. Up to now, perylenebis(dicar-
boximide)s7 and higher rylenes, namely terrylene,8 quater-
rylene,9 pentarylene,10 and hexarylene,10 have been synthe-
sized, and the higher order rylene bis(dicarboximide)s can
laser filter, NIR photography, bioassays, and medicine.1,2
A
recent rising interest is to use low band gap NIR dyes for
solar cells,3 bioimaging,4 and two-photon absorption (TPA)
based optical limiting at telecommunications wavelength.5
For all of these applications, soluble and stable dyes which
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10.1021/ol902027b CCC: $40.75
Published on Web 09/22/2009
 2009 American Chemical Society

serve as good NIR dyes due to extended π-conjugation. A
general problem for the higher order rylene dyes is their poor
solubility even though some bulky groups are attached to
the peri-positions of the terminal naphthalene units. To
further improve their solubility, substitution by phenoxy
groups at the bay positions has been done, and materials with
good solubility have been obtained.9,10 One limit is that ring
cyclization reactions sometimes suffer from the dealkylation
of the phenoxy group under strong basic conditions.9b
Alternative substitution groups at the bay positions of higher
order rylene dyes are desired to facilitate an easy organic
synthesis of highly soluble NIR dyes. In addition, the
substituents with either electron-donating or electron-
withdrawing character can further tune their electronic and
spectral properties for applications such as n-channel FETs,
solar cells, and laser absorbing dyes.11
N-annulated quarterrylenebis(dicarboximide) such as com-
pound 1 (Figure 1). The design is based on the following
considerations: (1) The electron-withdrawing dicarboxylic
imide groups can significantly lower the high-lying HOMO
energy level of the respective N-annulated perylene and
quarterrylenes, which are expected to be unstable upon long-
term exposure to air and light. (2) The molecule 1 has a
typical acceptor-donor-donor-acceptor (A-D-D-A) mo-
tif which may show large two-photon absorption in long IR
wavelengths.13 On the other hand, a bis-N-annulated quar-
terrylene such as molecule 2 has a donor-donor (D-D,
Scheme 1) motif. (3) Substitution of the bulk 2,6-diisopro-
pylphenyl groups on the imides and the attachment of the
branched dove-tailed chains at the amine sites will largely
improve the solubility of the quarterrylene dyes. In this paper,
we report the successful synthesis of compound 1 which
shows the desired photophysical and electrochemical proper-
ties. For comparison, compound 2 was also prepared.
The synthesis of compounds 1 and 2 is shown in Scheme 1.
There are two major challenges for the synthesis of 1: (1) the
synthesis of N-annulated perylene dicarboxylic imide (NPDI)
6 and (2) the subsequent ring cyclization of the NPDI dimer 7.
Although perylene dicarboxylic imide (PDI) can be readily
obtained by one-step reaction from the cheap perylene tetra-
carboxylic dianhydride,14 there is no efficient way to synthesize
NPDIs such as 6. We and other researchers recently found that
arenedicarboxylic anhydride could be prepared by Friedel-Crafts
reaction of oxalyl chloride with active aromatic compounds such
as anthracene followed by oxidation of the as-formed diketone
to the carboxylic anhydride group in good yields.15 Herein, this
method was used, and the key intermediate compound 6 was
prepared in a convenient synthetic route.
Figure 1. Molecular structures of bis-N-annulated quarterrylene (2)
and quarterrylenebis(dicarboximide) (1).
The synthesis commenced with N-alkylation reaction of the
N-annulated perylene (NP) 312 with a dove-tailed alkyl bro-
mide16 in the presence of KOH and KI to give 4 in 97% yield.
Regioselective bromination of 4 with 1 equiv of NBS at 0 °C
gave the monobrominated NP 5 in 80% yield. Friedel-Crafts
reaction of 5 with oxalyl chloride promoted by AlCl3 then
generated an orange solid as a mixture containing different
isomers of diketone compounds, which were directly converted
to their corresponding anhydride compounds using oxone15,15c
without purification. Separation of the NPDI 6 from other
isomers was successful after the introduction of the 2,6-
diisopropylaniline to the anhydride group with an overall
yield of 48% for three steps. The precursor 7 was then
prepared by Yamamoto coupling of 6 in a nearly quantitative
yield. The last cyclization reaction was performed under
different conditions such as (1) KOH in ethanol with glucose,
(2) tert-BuOK/DBN in diglyme, (3) FeCl3 in nitromethane
and dichloromethane, and (4) K2CO3 in ethanolamine. It was
found out that the first three methods all failed, and
complicated mixtures were usually obtained probably due
to the decomposition of NPDI units. Fortunately, method 4,
using mild base K2CO3-promoted cyclization, worked well,
and our target compound 1 was obtained in 35% yield.
Compound 2 was prepared following a route similar to that
N-Annulation of perylene12 in which the nitrogen atoms
are annulated at the bay position becomes one option for
such a purpose because additional flexible alkyl chains can
be easily introduced by alkylation reaction and thus improve
the solubility. In addition, the electron-donating character
of amines can increase the electron density of the entire
π-system and lead to new opto-electronic properties. Wang
et al. reported several N-annulated perylenes,12b-e and very
recently, a bis N-annulated quaterrylene with good solubility
was also synthesized.12d In parallel to those studies, in the
past year we have been working on the synthesis of a bis-
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Org. Lett., Vol. 11, No. 20, 2009
4509

characterizations in solution. In particular, dye 1 has a
solubility of over 100 mg per mL in dichloromethane at room
temperature, which is much higher than the quarterrylenebi-
s(dicarboximide)s without bay substitution.9b The high
solubility of 1 can account for the introduction of two bulk
2,6-diisopropylphenyl groups which inhibit the formation of
π-stacks,9b the two dove-tailed alkyl chains, and the bent
structure as disclosed by the calculated geometric structure
(Figure S6 in the Supporting Information). Both dyes exhibit
a deep green color in solution, their UV-vis-NIR absorption
and fluorescence spectra recorded in chloroform are shown
in Figure 2, and the data are collected in Table 1. Dye 1
exhibits intense absorption in the NIR spectral region with
an absorption maximum at 760 nm, together with two
shoulders at 690 and 632 nm, which are similar to the
nonfunctionalized quarterrylene (λabs, max ) 764 nm).9b The
molar extinction coefficient (ε) of 1 is extremely high with
εmax ) 259540 M-1 cm-1 at 760 nm. In comparison,
compound 2 without electron-withdrawing dicarboxylic
imide groups shows absorption peaks at 685, 628, and 575
nm with εmax ) 90080 M-1 cm-1. A large bathochromic shift
of 75 nm was observed for 1 compared with 2, owing to the
substitution by electron-withdrawing dicarboxylic imide
groups in 1 which leads to a convergence of HOMO-LUMO
energy gap as previously calculated.13a,17 Both 1 and 2
display very small Stokes shifts (255 and 313 cm-1,
respectively) due to the rigid and planar quarterrylene
structure (Figure S6, Supporting Information). The photo-
luminescence quantum yields (Φ) of dyes 1 and 2 were
determined according to an optically dilute method (A < 0.05)
by using cardiogreen dye (λabs (max) ) 780 nm, Φ ) 0.13
in DMSO) as a standard.18 The Φ values of 0.55 and 0.83
were obtained for 1 and 2, respectively, and these values
are higher than for other quaterrylene compounds.12d,19 Time-
dependent DFT calculations (B3LYP/6-31G**) predict that
compounds 1 and 2 will show intense absorption in the NIR
region with maxima at 708.5 and 663.4 nm and large oscillator
strengths with f ) 1.7567 and 1.5452, respectively (see the
Supporting Information). These data agree well with our
experimental results and explain the observed large ε values.
Scheme 1
found in the literature.12d Regioselective bromination of 4
with 2 equiv of NBS at room temperature gave the dibro-
minated NP 8 in 98% yield. Suzuki coupling reaction of 8
with 1 equiv of tert-butylphenylboronic acid afforded mono-
substituted NP compound 9 in 44% yield. Yamamoto
coupling of 9 provided the precursor 10 in a nearly
quantitative yield, which was finally cyclized into the bis-
N-annulated quarterrylene 2 in 62% yield by using a
Sc(OTf)3-DDQ system.12d
Figure 2
.
Normalized UV-vis-NIR absorption spectra (3 × 10-6
M) and photoluminescence spectra (4 × 10-7 M) of compounds 1
and 2 in chloroform.
Both compounds 1 and 2 are highly soluble in common
organic solvents, and this allows us to perform various
Figure 3. Cyclic voltammograms of compounds 1 and 2 in
dichloromethane with 0.1 M Bu4NPF6 as supporting electrolyte,
AgCl/Ag as reference electrode, Au disk as working electrode, Pt
wire as counter electrode, and scan rate at 50 mV/s. Fc/Fc+ was
used as internal reference.
(14) Feiler, L.; Langhals, H.; Polborn, K. Liebigs. Ann. 1995, 1229–
1244.
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9302. (b) Langhals, H.; Schonmann, G.; Polborn, K. Chem.sEur. J. 2008,
14, 5290–5303. (c) Yan, J.; Travis, B. R.; Borhan, B. J. Org. Chem. 2004,
69, 9299–9302.
The electrochemical properties of compounds 1 and 2 were
investigated by cyclic voltammetry (CV) in dry DCM (Figure
(16) Pisula, W.; Kastler, M.; Wasserfallen, D.; Pakula, T.; Mu¨llen, K.
J. Am. Chem. Soc. 2004, 126, 8074–8075.
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Org. Lett., Vol. 11, No. 20, 2009

Table 1. Summary of Photophysical and Electrochemical Properties of Compound 1 and 2a
εmax (M-1cm-1
)
λem (nm) QY Eox (V) Eox (V) Eox (V) Ered (V) HOMO (eV) LUMO (eV) Eg (eV)
1
2
3
compd
λabs (nm)
1
2
632 690 760
575 628 685
259540
90080
775
700
0.55
0.83 -0.29
0.30
0.64
0.16
-1.26
-1.89
-5.10
-4.51
-3.54
-2.91
1.56
1.60
0.32
a Eoxn and Eredn are half-wave potentials for respective redox waves with Fc/Fc+ as reference. HOMO and LUMO energy levels were calculated from the
first oxidation and reduction waves according to the equations HOMO ) -(4.8 + Eox1) and LUMO ) -(4.8 + Ered1).20
3 and Table 1). The cyclic voltammogram of 1 exhibits two
addition, one quasi-reversible reduction wave was also
observed for 2 at a negative potential of -1.89 V, indicating
that although this molecule is electron-rich, it is still possible
to store negative charge by electron delocalization along the
large π-conjugated framework. Compared with 2, molecule
1, having an A-D-D-A motif, exhibits a smaller band gap
(1.56 eV), which is in agreement with their absorption
spectra.
In summary we have described the efficient synthesis of
a new NIR dye, the bis-N-annulated quarterrylenebis(dicar-
boximde) 1, which shows remarkable properties such as
excellent solubility, high molar absorptivity, NIR absorption
and emission, high fluorescence quantum yield, and good
photostability in comparison with the electron-rich analogue
2. Further studies on their NLO properties such as TPA and
synthesis of higher order N-annulated rylene carboximides
are in progress, and this research will likely lead to useful
materials for applications such as optical limiting5 and
photovoltaic windows.21
n
reversible oxidation waves with half-wave potentials (Eox
)
at 0.30 and 0.64 V (vs Fc/Fc+), while three oxidative waves
n
were observed for 2, with Eox at - 0.29, 0.16, and 0.32 V
(vs Fc/Fc+). The very low first half-wave oxidation potential
(- 0.29 V) of 2 indicates a highly electron-rich character of
this π-conjugated system due to the electron-donating
property of the amines. A high-lying HOMO energy level
of - 4.51 eV was calculated for 2 based on the Eox1, and
this implies that compound 2 can be easily oxidized by many
oxidants.20 In fact, we found that the green solution of 2 in
toluene became dark in a few hours when the solution was
exposed to ambient conditions, and significant decomposition
was observed as followed by UV-vis-NIR spectroscopic
measurements. In contrast, the first oxidative half-wave
potential of 1 with electron-withdrawing imide groups
appears at a much higher potential (0.30 V) with a HOMO
energy level of -5.10 eV. As a result, the UV-vis-NIR
absorption spectrum of 1 in toluene does not show any
change upon exposure to ambient air and light for weeks
and even under irradiation of 4 W UV lamp (emitting at
254 nm) for 5 days, suggesting a good photostability of dye
1, and this is important for practical applications. Compound
1 also exhibits two reversible reduction waves around -1.26
V which are overlapped together but distinguishable by
differential pulse voltammetry. Accordingly, a LUMO energy
level of -3.54 eV was calculated, indicating a high electron
affinity of dye 1 due to the carboximide substitution. In
Acknowledgment. This work was financially supported
by the Singapore DSTA DIRP (DSTA-NUS-DIRP/2008/03),
NUS Young Investigator Award (R-143-000-356-101), and
NRF Competitive Research Program (R-143-000-360-281).
Supporting Information Available: Experimental details
and characterization data of all new compounds. This
material is available free of charge via the Internet at
http://pubs.acs.org.
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OL902027B
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