Synthesis of pyridine-fused perylene imides with an amidine moiety for hydrogen bonding

Article abstract of DOI:10.1021/ol401316q

Pyridine-fused perylene tetracarboxylic acid bisimides (PBIs) were synthesized via Suzuki-Miyaura coupling and acid condensation. The fused PBIs with electron-donating substituents exhibited an intramolecular charge transfer interaction. One of the N-alkyl substituents was selectively removed with BBr₃ to create an amidine guest binding site. A hydrogen bonding interaction with pentafluorobenzoic acid changed the absorption spectra and enhanced fluorescence.

Full text of DOI:10.1021/ol401316q

ORGANIC
LETTERS
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Vol. XX, No. XX
000–000
Synthesis of Pyridine-Fused Perylene
Imides with an Amidine Moiety for
Hydrogen Bonding
Satoru Ito, Satoru Hiroto, and Hiroshi Shinokubo*
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University,
Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8603, Japan
hshino@apchem.nagoya-u.ac.jp
Received May 11, 2013
ABSTRACT
Pyridine-fused perylene tetracarboxylic acid bisimides (PBIs) were synthesized via SuzukiꢀMiyaura coupling and acid condensation. The fused
PBIs with electron-donating substituents exhibited an intramolecular charge transfer interaction. One of the N-alkyl substituents was selectively
removed with BBr3 to create an amidine guest binding site. A hydrogen bonding interaction with pentafluorobenzoic acid changed the absorption
spectra and enhanced fluorescence.
Perylene tetracarboxylic acid bisimide (PBI) is an im-
portant class of dyes and pigments for widespread use in
both academia and industry.1 Since PBIs have unique
photophysical properties such as efficient visible light
absorption, strong emission, and high stability against
light and air, they have received much attention in wide
areas of material science such as organic solar cells,2
organic light-emitting diodes,3 single molecule spectros-
copy,4 field effect transistors,5 and biomedical sensors.6
PBIs are also a building block of supramolecules, con-
structing optically active H- or J-aggregated structures by
a πꢀπ stacking interaction with cooperating hydrogen-
bonding interaction.7
To control electronic and photophysical characteristics
of PBIs, a number of studies on functionalization of PBIs
have been conducted.8 In particular, extension of the
PBI core with fused structures is a current hot topic.9 Such
core extension has been mostly achieved at the 1,6,7,12-
positions, so-called “bay-areas.” In contrast, there are few
(1) For reviews on PBIs: (a) Li, C.; Wonneberger, H. Adv. Mater.
2012, 24, 613. (b) Huang, C.; Barlow, S.; Marder, S. R. J. Org. Chem.
€
2011, 76, 2386. (c) Wurthner, F. Chem. Commun. 2004, 14, 1564. (d)
Langhals, H. Heterocycles 1995, 40, 477.
(2) (a) Rajaram, S.; Shivanna, R.; Kandappa, S. K.; Narayan, K. S.
J. Phys. Chem. Lett. 2012, 3, 2405. (b) Raj, M. R.; Anandan, S.;
Solomon, R. V.; Venuvanalingam, P.; Lyer, S. S. K.; Ashokkumer, M.
J. Photochem. Photobiol. A 2012, 247, 52. (c) Keivanidis, P. E.; Kamm,
V.; Zhang, W.; Floudas, G.; Laquai, F.; McCulloch, I.; Bradley,
D. D. C.; Nelson, J. Adv. Funct. Mater. 2012, 22, 2318. (d) Liang, Z.;
Cormier, R. A.; Nardes, A. M.; Gregg, B. A. Synth. Met. 2011, 161,
1014. (e) Zhan, X.; Facchetti, A.; Barlow, S.; Marks, T. J.; Ratner,
M. A.; Wasielewski, M. R.; Marder, S. R. Adv. Mater. 2011, 23, 268.
€
(4) Rohr, U.; Schlichting, P.; Bohm, A.; Gross, M.; Meerholz, K.;
€
€
Brauchle, C.; Mullen, K. Angew. Chem., Int. Ed. 1998, 37, 1434.
€
(5) (a) Dossel, L. F.; Kamm, V.; Howard, I. A.; Laquai, F.; Pisula, W.;
Feng, X.; Li, C.; Takase, M.; Kudernac, T.; Feyter, S. D.; Mullen, K. J. Am.
€
Chem. Soc. 2012, 134, 5876. (b) An, Z.; Yu, J.; Domercq, B.; Jones, S. C.;
Barlow, S.; Kippelen, B.; Marder, S. R. J. Mater. Chem. 2009, 19, 6688.
(6) (a) Franceschin, M.; Alvino, A.; Casagrande, V.; Mauriello, C.;
Pascucci, E.; Savino, M.; Ortaggi, G.; Bianco, A. Bioorg. Med. Chem.
2007, 15, 1848. (b) Franceschin, M.; Alvino, A.; Ortaggi, G.; Bianco, A.
Tetrahedron Lett. 2004, 45, 9015.
€
(3) (a) Grozema, F.; Andrienko, D.; Kremer, K.; Mullen, K. Nat.
Chem. 2009, 8, 421. (b) Kraft, A.; Grimsdale, A. C.; Holmes, A. B.
Angew. Chem., Int. Ed. 1998, 37, 402. (c) Pan, J.; Zhu, W.; Li, S.; Zeng,
W.; Cao, Y.; Tian, H. Polymer 2005, 46, 7658.
r
10.1021/ol401316q
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reports on fused PBIs at the 2,5,8,11-positions instead of
bay areas, due to the lack of functionalization methods at
these positions.10
Scheme 2. Synthesis of Pyridine-Fused PBIs
Scheme 1. Synthetic Strategy for Pyridine Fusion
Recently, direct CꢀH borylation of PBIs at the 2,5,8,11-
positions has been accomplished under iridium and ruthe-
nium catalyses.11,12 The boryl group is useful for introduction
various functionalities through oxidation and cross-coupling
reactions13 We now designed a novel type of core-extended
PBIs, which could be prepared through SuzukiꢀMiyaura
cross-coupling followed by dehydrative condensation of
the carbonyl and amino groups (Scheme 1). The ring fusion
created an amidine moiety, which served as a hydrogen
bonding site. The imide moiety of PBIs has been utilized as
a guest-binding site in supramolecular chemistry. How-
ever, the binding at the imide group is not generally
strong.14 Incorporation of a more basic pyridine unit
would enhance the binding constant.
The synthesis of 1 began with direct CꢀH borylation of
PBI 2 according to our previous report.11c The yield of
monoborylated product 3 was improved up to a 57% yield
by using 1.0 equiv of bis(pinacolate)diboron (Scheme 2).
The cross-coupling reaction with 4-tert-butyl-2-bromo-
acetoanilide proceeded smoothly in the presence of a
catalyst combination of the Pd2dba3ꢀSPhos ligand to
furnish 4a in 97% yield. Deprotection and spontaneous
ring fusion occurred by hydrolysis with aqueous HCl to
afford pyridine-fused PBI 1a in 70% yield. The structure of
(7) Recent examples of supramolecular architectures with PBIs via
€
€
hydrogen bonding interactions. (a) Gorl, D.; Zhang, X.; Wurthner, F.
Angew. Chem., Int. Ed. 2012, 51, 6328. (b) Yagai, S.; Usui, M.; Seki, T.;
Murayama, H.; Kikkawa, Y.; Uemura, S.; Karatsu, T.; Kitamura, A.;
Asano, A.; Seki, S. J. Am. Chem. Soc. 2012, 134, 7983. (c) Seki, T.; Asano,
A.; Seki, S.; Kikkawa, Y.; Murayama, H.; Karatsu, T.; Kitamura, A.;
Yagai, S. Chem.;Eur. J. 2011, 17, 3598. (d) Yagai, S.; Seki, T.; Karatsu, T.;
1
1a was characterized by spectroscopic analysis. Its H
€
Kitamura, A.; Wurthner, F. Angew. Chem., Int. Ed. 2008, 47, 3367. (e)
NMR spectrum showed a downfield shifted singlet peak
at 9.65 ppm, which is assigned as a proton on the perylene
core proximal to the fused moiety. In addition, two broad-
ened signals were observed around 6 ppm, which gradu-
ally merged into a single peak at elevated temperatures
(Figure S10). These peaks are attributed to the methine
protons of the 3-pentyl group, whose rotation is constrained
by steric hindrance of the pyridine ring. According to the
same synthetic procedure, various pyridine-fused PBIs 1b,
1c, and 1d were obtained in excellent yields.
Figure 1a shows UV/vis absorption spectra of pyridine-
fused PBIs in CH2Cl2. As compared to parent PBI 2, no
obvious change was observed for fused PBIs 1b and 1c
which bear electron-withdrawing phenyl rings, while spec-
tra of 1a and 1d exhibited broadening and bathochromic
shifts of the lowest energy absorption bands. Fluorescence
spectra (Figure 1b) exhibited broadening and reduction of
the quantum yields for 1a and 1d, suggesting existence of
an intramolecular charge transfer interaction. To evaluate
€
Kaiser, T. E.; Wang, H.; Stepanenko, V.; Wurthner, F. Angew. Chem., Int.
Ed. 2007, 46, 5541.
(8) (a) Fan, L.; Xu, Y.; Tian, H. Tetrahedron Lett. 2005, 46, 4443. (b)
€
€
Wurthner, F.; Stepanenko, V.; Chen, Z.; Saha-Moller, C. R.; Kocher,
N.; Stalke, D. J. Org. Chem. 2004, 69, 7933. (c) Huang, C.; Barlow, S.;
Marder, S. R. J. Org. Chem. 2011, 76, 2386.
€
(9) (a) Eversloh, C. L.; Li, C.; Mullen, K. Org. Lett. 2011, 13, 4148.
(b) Jiang, W.; Li, Y.; Yue, W.; Zhen, Y.; Qu, J.; Wang, Z. Org. Lett.
2010, 12, 228. (c) Yan, Q.; Cai, K.; Zhang, C.; Zhao, D. Org. Lett. 2012,
€
€
14, 4654. (d) Muller, S.; Mullen, K. Chem. Commun. 2005, 4045. (e)
Alibert-Fouet, S.; Seguy, I.; Bobo, J.-F.; Destruel, P.; Bock, H. Chem.;
Eur. J. 2007, 13, 1746.
(10) One example of a π-extended PBI at 2,5,8,11-positions: Yao,
J. H.; Chi, C.; Wu, J.; Loh, K.-P. Chem.;Eur. J. 2009, 15, 9299.
(11) (a) Nakazono, S.; Imazaki, Y.; Yoo, H.; Yang, J.; Sasamori, T.;
ꢀ
Tokitoh, N.; Cedric, T.; Kageyama, H.; Kim, D.; Shinokubo, H.; Osuka,
A. Chem.;Eur. J. 2009, 15, 7530. (b) Nakazono, S.; Easwaramoorthi, S.;
Kim, D.; Shinokubo, H.; Osuka, A. Org. Lett. 2009, 11, 5426. (c) Teraoka,
T.; Hiroto, S.; Shinokubo, H. Org. Lett. 2011, 13, 2532.
€
(12) Battagliarin, G.; Li, C.; Enkelmann, V.; Mullen, K. Org. Lett.
2011, 13, 3012.
€
(13) Battagliarin, G.; Zhao, Y.; Li, C.; Mullen, K. Org. Lett. 2011, 13,
3399.
€
€
(14) Wurthner, F.; Thalacker, C.; Sautter, A.; Schartl, W.; Ibach, W.;
Hollricher, O. Chem.;Eur. J. 2000, 6, 3871.
B
Org. Lett., Vol. XX, No. XX, XXXX

presence of a RuH2CO(PPh3)3 catalyst furnished trialky-
lated PBI 6b and 6c in 32 and 80% yields, respectively.11a
During the reaction, no overalkylated products were de-
tected. The addition of BBr3 into a dichloromethane
solution of 6b and 6c provided dealkylated product 7b
and 7c in 95 and 98% yields, respectively. Interestingly,
dealkylation occurred exclusively on nitrogen adjacent to
the pyridine ring due to the directing effect of the pyridine
nitrogen. Both 7b and 7c were soluble enough in various
organic solvents.
Scheme 3. Regioselective Dealkylation and Alkylation of 1a
Figure 1. (a) UV/vis absorption and (b) fluorescence spectra
of 2, 1a, 1b, 1c, and 1d in CH2Cl2.
the charge-transfer character of 1d, the solvent effect on
optical properties was examined. Positive solvatochromic
behavior was observed for both UV/vis absorption and
emission spectra. A linear correlation with a positive slope
was confirmed between Stokes shifts and orientation po-
larizabilities ofsolvents(FigureS29). Theseresultsindicate
that the change of the dipole moment upon excitation is
dependent on solvent polarity. In addition, fluorescence
quenching occurred in polar media such as acetone and
ethyl acetate. We calculated the molecular orbitals of 1c
and 1d by the DFT method at the B3LYP/6-31G(d) level
(Figure S35). Both the HOMO and LUMO of 1c mainly
spread over the perylene core and there were small MO
coefficients on the fused rings. On the other hand, the
HOMO of 1d was mainly located on the fused rings, while
the LUMO was localized on the perylene part, indicating
the substantial charge-transfer interaction from the ben-
zene ring to the perylene core.
We then investigated the association behavior of 7c with
carboxylic acids. An amidine moiety has been well-known
to associate with carboxylic acid guests through formation
of a strong amidiniumꢀcarboxylate complex.16 The well-
defined structure of the amidiniumꢀcarboxylate complex
and strong hydrogen bonding would be useful for the
construction of supramolecular assemblies.17 An addition
of benzoic acid into a dichloromethane solution of 7c
induced no noticeable change on the UV/vis absorption
spectrum. In contrast, titration with C6F5CO2H (pKa =
1.6) caused an enhancement of the absorbance and a red
shift of the peak around 520 nm (Figure 2a). In addition,
an increase of the fluorescence intensity was observed. The
fluorescence quantum yield was enhanced from Φf = 0.35
to 0.61. The enhancement of the emission can be detected
We then attempted selective dealkylation of one of the
N-alkyl groups to create a hydrogen bonding site.7b Treat-
ment of 1a with BBr3 at room temperature afforded deal-
kylated product 7a in 65% yield (Scheme 3).15 Unfortunately,
however, 7a was not very soluble in common organic solvents.
To enhance the solubility, alkyl chains were introduced.
The reaction of1awith1-hexene orvinylcyclohexanein the
(16) Kraft, A.; Peters, L.; Powell, H. R. Tetrahedron 2002, 58, 3499.
(17) Recent examples of supramolecular assemblies with amidiniumꢀ
carboxylate bridges. (a) Yamada, H.; Wu, Z.-Q.; Furusho, Y.; Yashima, E.
J. Am. Chem. Soc. 2012, 134, 9506. (b) Ito, H.; Ikeda, M.; Hasegawa, T.;
Furusho, Y.; Yashima, E. J. Am. Chem. Soc. 2011, 133, 3419. (c) Yamada,
H.; Furusho, Y.; Ito, H.; Yashima, E. Chem. Commun. 2010, 46, 3487. (d)
Young, E. R.; Rosenthal, J.; Hodgkiss, J. M.; Nocera, D. G. J. Am. Chem.
Soc. 2009, 131, 7678. (e) Ito, H.; Furusho, Y.; Hasegawa, T.; Yashima, E.
J. Am. Chem. Soc. 2008, 42, 14008. (f) Maeda, T.; Furusho, Y.; Sakurai,
S.-I.; Kumaki, J.; Okoshi, K.; Yashima, E. J. Am. Chem. Soc. 2008, 130,
7938. (g) Otsuki, J.; Kanazawa, Y.; Kaito, A.; Islam, D.-M.-S.; Araki, Y.;
Ito, O. Chem.;Eur. J. 2008, 14, 3776.
(15) BBr3-mediated dealkylation was facilitated by a pyridine ring.
Palikov, E.; Strekowski, L. Tetrahedron Lett. 2004, 45, 4093.
Org. Lett., Vol. XX, No. XX, XXXX
C

faces the two nitrogen atoms of the amidine moiety.18
These results elucidated the formation of the amidiniumꢀ
carboxylate complex of 7c with pentafluorobenzoic acid,
which induced substantial changes in absorption and emis-
sion features because of the attenuation of intramolecular
charge transfer. DFT calculations at the ωB97XD/6-31G(d)
level revealeddiminishedMOcoefficientsaround the fused
rings in the HOMO of 7c by binding with C6F5CO2H
(Figure S36).
In summary, we have synthesized a series of pyridine-
fused PBIs 1 in excellent total yields from borylated PBI 3.
The ring fusion with electron-withdrawing aryl groups
does not significantly alter the optical properties from
the parent PBI 2, while fusion with the electron-donating
ones causes an intramolecular charge-transfer interaction,
resulting in broadening and bathochromic shifts of the
electronic absorption spectrum and lowering of the fluor-
escence intensity. Furthermore, selective removal of one
of the N-alkyl groups allows installation of an amidine
moiety, which serves as a hydrogen binding site. Infact, the
fused PBI 7c strongly binds to pentafluorobenzoic acid,
resulting in an enhancement of the fluorescence intensity.
The present amidiniumꢀcarboxylate strategy would en-
able construction of rigid supramolecules on the basis of
pyridine-fused PBIs.
Figure 2. (a) Change of UV/vis absorption spectra of 7c in
CH2Cl2 (6.4 ꢁ 10ꢀ5 M) upon the addition of C6F5CO2H. (b)
Change of fluorescence spectra of 7c in 1,2-dichloroethane. The
blue lines show the spectra of 7c, and the red lines show those of
7c þ excess C6F5CO2H.
Acknowledgment. This work was supported by Grants-
in-Aid for Scientific Research (Nos. 22750036 and 24350023)
and Program for Leading Graduate Schools “Integrative
Graduate Education and Research in Green Natural
Sciences”, MEXT, Japan. H.S. acknowledges Asahi Glass
Foundation for financial support.
by the naked eye (Figure 2b). The binding constant was
calculated to be 2640 Mꢀ1 in CH2Cl2. The addition of
C6F5CO2H to 6c resulted in no spectral change, excluding
the possibility of simple protonation of the pyridine moi-
ety. The binding structure was eventually determined
by preliminary X-ray diffraction analysis (Figure S33). A
pentafluorobenzoic acid molecule was aligned in the
same plane of 7c. The carboxylate moiety of C6F5CO2H
Supporting Information Available. General procedures,
spectral data for compounds, absorption and fluores-
cence spectra. CIF file for the preliminary X-ray analysis of
the complex of 7c with C6F5CO2H. This material is available
free of charge via the Internet at http://pubs.acs.org.
(18) Interestingly, a columnar packing structure is constructed by a
pair that includes one pentafluorobenzoic acid and one fused PBI in the
crystal (Figure S34).
The authors declare no competing financial interest.
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Org. Lett., Vol. XX, No. XX, XXXX