Regioselective Ru-catalyzed direct 2,5,8,11-alkylation of perylene bisimides

Article abstract of DOI:10.1002/chem.200901318

A study was conducted to demonstrate the first selective synthesis of 2,5,8,11-substituted perlylene tetracarboxylic acid bisimides (PBI). A mixture of bis(N-ethylpropyl)PBI and trimethylvinylsilane was heated in mesitylene at 165°C for 60 hours in the pr

Full text of DOI:10.1002/chem.200901318

DOI: 10.1002/chem.200901318
Regioselective Ru-Catalyzed Direct 2,5,8,11-Alkylation
of Perylene Bisimides
Satomi Nakazono,[b] Yusuke Imazaki,[b] Hyejin Yoo,[c] Jaesung Yang,[c]
Takahiro Sasamori,[d] Norihiro Tokitoh,[d] Tassel Cꢀdric,[e] Hiroshi Kageyama,*[e]
Dongho Kim,*[c] Hiroshi Shinokubo,*[a] and Atsuhiro Osuka*[b]
Perylene tetracarboxylic acid bisimides (PBIs) are an im-
portant class of dyes and pigments for widespread practical
use, which have been extensively investigated for a long
time both in academia and industry.[1] Recently, they have
also received much attention as n-type semiconducting ma-
terials.[2] Furthermore, owing to high fluorescence quantum
efficiency and photostability, they have been a popular
motif for single-molecule spectroscopy.[3] Chemical modifica-
tions of PBIs are quite important to gain desirable photo-
physical and electronic properties as well as solubility. In
Scheme 1. Functionalization of perylene bisimides.
spite of their rich material chemistry, functionalization of
the perylene core of PBIs relies on halogenation of the bay
area (1,6,7,12-positions) and subsequent transformations
(Scheme 1).[4] Selective functionalization at 2,5,8,11-posi-
tions remains unavailable to date.[5]
of direct functionalization of PBIs by organometallic and
À
catalytic means: ruthenium-catalyzed C H bond activation
Here we wish to disclose the first selective synthesis of
2,5,8,11-substituted PBIs. We have envisioned the potential
and addition strategy, namely, the Murai–Chatani–Kakiuchi
protocol (Scheme 2).[6] This reaction can introduce alkyl
substituents to the proximal position of the directing groups.
Successful installation of alkyl chains at the 2,5,8,11-posi-
tions of PBIs would allow greater modification of properties
in the solid state or condensed phase.
[a] Prof. Dr. H. Shinokubo
Department of Applied Chemistry
Graduate School of Engineering, Nagoya University
Chikusa-ku, Nagoya 464-8603 (Japan)
E-mail: hshino@apchem.nagoya-u.ac.jp
The reaction procedure is quite simple. A mixture of
bis(N-ethylpropyl)PBI 1a and trimethylvinylsilane was
heated in mesitylene at 1658C for 60 h in the presence of
[b] S. Nakazono, Y. Imazaki, Prof. Dr. A. Osuka
Department of Chemistry, Graduate School of Science
Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)
E-mail: osuka@kuchem.kyoto-u.ac.jp
[c] H. Yoo, J. Yang, Prof. Dr. D. Kim
Department of Chemistry, Yonsei University
Seoul 120-749 (Korea)
E-mail: dongho@yonsei.ac.kr
[d] Dr. T. Sasamori, Prof. Dr. N. Tokitoh
Institute for Chemical Research
Kyoto University, Kyoto 611-0011 (Japan)
[e] T. Cꢀdric, Prof. Dr. H. Kageyama
Department of Chemistry, Graduate School of Science
Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)
E-mail: kage@kuchem.kyoto-u.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200901318.
Scheme 2. Ru-catalyzed selective alkylation of perylene bisimides.
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COMMUNICATION
6 mol% of [RuH2(CO)ACHTUNTRGNEG(UN PPh3)3]. After silica-gel separation,
tetraalkylated PBI 2a was obtained in 94% yield
(Scheme 2). The alkylation of N-(2,6-diisopropyl)phenylPBI
1b needed longer reaction times due to its lower solubility,
but afforded the desired product 2b in almost quantitative
yield. After tetraalkylation, solubility in organic solvents is
significantly enhanced: 2a is soluble in ethyl acetate and 3a
is soluble in warm hexane. A particularly attractive feature
is facile introduction of the alkoxylsilyl side chain (6a) that
serves as a docking group for inorganic substrates (see
below).
UV/Vis absorption and fluorescence spectra are shown in
Figure 1. As expected, the alkylation does not significantly
change the absorption and emission properties in the solu-
tion state, but somewhat lowers molar extinction coefficients
of the lowest energy absorption band. Fluorescence quan-
tum yields in toluene are almost the same as the parent
PBIs 1a and 1b. Importantly, alkylated PBIs fluoresce even
in the solid state with intense red emission.[7] For example, a
powder sample of 3a emits at 635 nm with a much enhanced
quantum yield of 0.59 (Table 1). The fluorescence spectra in
the solid state are broad and substantially red-shifted, sug-
gesting emission from aggregates of PBI. In sharp contrast
to the solution state, quantum yields in the solid state heavi-
ly depend on the introduced alkyl groups, implying the im-
portance of alkyl substituents that influence the crystal
packing. Absorption spectra in the solid state were mea-
sured for microdispersion of PBIs (Figure 1c).[8] PBI 1a ex-
hibits a broad and blue-shifted spectrum, which is typical for
H-type aggregates. For 3a and 4a, the absorption features in
solution including the vibronic bands were preserved in the
solid sate, but 3a showed 12 nm of red-shift. These results
indicate smaller intermolecular electronic interaction in
crystal than parent PBI 1a by the introduced alkyl substitu-
ents.
Figure 1. a) UV/vis absorption spectra in toluene. b) Emission spectra in
toluene and solid state emission spectra. c) Solid-state absorption spectra
of dispersion of PBIs in water.
The structure of PBI 4a has been clearly elucidated by
the X-ray analysis (Figure 2 and Figure S31).[9] Introduction
of four alkyl groups does not result in any distortion of the
flat perylene core. This is in sharp contrast to bay-area sub-
stitution, which often induces severe twist in perylene. Each
molecule of 4a aligns in a parallel manner without stacking.
Obviously, the interaction between alkyl groups is essential
to form this type of aggregation. In contrast, PBI 2a exhibits
the herringbone arrangement
Using trimethoxysilyl groups, 6a can be chemisorbed on a
glass surface via the following process: 1) recovery of the
OH groups on the glass surface, 2) dropping a toluene solu-
tion of 6a on the surface; 3) removal of the physisorbed
PBI. We were able to obtain a fluorescence image of single
molecules of 6a adsorbed on glass surface. The fluorescence
is still observable, even though the molecule is exposed to
with distinct p-stacking of an
interplanar distance of about
3.6 ꢂ.[10] Two molecules are
crossed with each other by 668,
resulting from steric hindrance
of bulky silylethyl substituents.
Although it was difficult to
obtain a nice single crystal of
3a, the synchrotron powder X-
ray diffraction (SXRD) re-
vealed a high crystallinity of 3a
with the triclinic symmetry.
Table 1. Photophysical properties of alkylated PBIs.
PBI e [mÀ1 cmÀ1 lmax [nm][a] lem [nm][b] Stokes shift [cmÀ1
]
]
Ff (solution) lem [nm] (solid) Ff (solid)[c]
1a
2a
3a
4a
5a
1b
2b
3b
8.43ꢃ104
5.97ꢃ104
6.42ꢃ104
5.30ꢃ104
5.19ꢃ104
8.50ꢃ104
6.29ꢃ104
6.80ꢃ104
526
522
521
521
525
527
524
523
533
533
533
533
534
534
534
533
250
414
380
451
339
249
357
358
1.0
676
640
635
644
634
–
0.07
0.41
0.59
0.24
0.08
0.01
0.02
0.09
0.91
0.94
0.95
0.92
0.97
0.94
0.94
584
591
[a] The longest absorption maxima. [b] Excited at the longest absorption maxima. [c] Excited at 470 nm. Abso-
lute quantum yields were determined by a calibrated integrating sphere system within Æ3% errors. Powder
samples were prepared by recrystallization of alkylated PBIs from CHCl3/CH3CN.
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H. Shinokubo, H. Kageyama, D. Kim, A. Osuka et al.
of a few seconds that is probably induced by interaction be-
tween PBI and covalent-bonded glass substrate, such as
electron transfer to the impurity sites in the glass (Figure 3
and Figure S34).[11]
In conclusion, we have developed a direct introduction of
alkyl groups to 2,5,8,11-positions of perylene bisimides on
À
the basis of ruthenium-catalyzed C H bond activation. Such
alkylations have a significant influence on the solid-state
properties as exemplified by the intense red emission. The
usefulness of this protocol has been demonstrated by pre-
liminary single-molecule spectroscopy of 6a on glass surface,
which was facilitated through facile introduction of alkoxyl-
silyl groups to PBI. Thus, we can study the inherent optical
properties of single molecules without any hindrance from
the surrounding polymer matrix. This direct protocol repre-
sents a promising perspective for a chelation-assisted strat-
egy for the selective functionalization of PBIs at 2,5,8,11-po-
sitions.
Acknowledgements
Figure 2. X-ray structure of 4a. a) Top view and b) side view. The ther-
mal ellipsoids are at the 50% probability level. Crystal packing of c) 4a
and d) 2a.
The work at Kyoto and Nagoya Universities was supported by a Grant-
in-Aid for Scientific Research (No. 21685011) from MEXT, Japan. Help-
ful discussion with Prof. Fumitoshi Kakiuchi (Keio University) is ac-
knowledged. We also thank Mr. Yoshihiro Tsujimoto (Kyoto University)
and Dr. Jungeun Kim (SPring-8) for the SXRD measurement at
BLO2B2 in SPring-8 and its analysis and Prof. Ryo Sasai and Mr. Hiroki
Kusumoto (Nagoya University) to obtain diffuse reflectance spectra. H.S.
gratefully acknowledges financial support from the Asahi Glass Founda-
tion. The work at Yonsei University was supported by the Star Faculty
and World Class University Programs (No. 2008-8-1955) from MEST of
Korea and the AFSOR/AOARD grant (No. FA4869-08-1-4097). H.Y.
and J.Y. acknowledge the fellowship of the BK21 program from the
MEST.
air and not in the polymer (PMMA) matrix where the single
molecules can be dispersed, immobilized, and fluoresce. We
measured the fluorescence intensity trajectories (FITs) of
single molecules both on glass surface and in the polymer
matrix. While one-step and stable FITs are observed in the
polymer matrix, the representative FIT of 6a on glass sur-
face shows fluorescence intensity fluctuation with off-states
Keywords: alkylation
·
fluorescence
·
perylenes
·
ruthenium · single-molecule studies
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Alkylation of Perylene Bisimides
COMMUNICATION
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1calcd =1.228 gcmÀ3, T=123(2) K, 12876 measured reflections, 5966
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35.381(14) ꢂ, V=10789(7) ꢂ3, Z=8, 1calcd =1.146 gcmÀ3
,
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90(2) K, 46252 measured reflections, 8468 unique reflections, R=
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These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif
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¯
P1 (No. 2), a=6.299(3), b=10.967(6), c=19.506(9) ꢂ, a=
Received: May 18, 2009
Published online: July 2, 2009
78.896(19), b=85.019(19), g=84.60(2)8, V=1313.2(11) ꢂ3, Z=1,
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