Core-extended rylene dyes via thiophene annulation

Article abstract of DOI:10.1039/c2cc33529h

Annulation of thiophenes directly into the bay regions of rylene dyes through effective Stille coupling and subsequent ring-fusion under Scholl conditions leads to core-extended rylene tetracarboxylic diimides with interesting electro-optical properties.

Full text of DOI:10.1039/c2cc33529h

View Article Online / Journal Homepage / Table of Contents for this issue
This article is part of the
Aromaticity
web themed issue
Guest editors: Nazario Martín, Michael Haley and
Rik Tykwinski
All articles in this issue will be gathered together
online at
www.rsc.org/cc/aroma

Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2012, 48, 8204–8206
www.rsc.org/chemcomm
COMMUNICATION
Core-extended rylene dyes via thiophene annulationwz
Yan Li,a Wei Xu,a Simone Di Motta,bc Fabrizia Negri,*bc Daoben Zhua and Zhaohui Wang*a
Received 16th May 2012, Accepted 27th June 2012
DOI: 10.1039/c2cc33529h
Annulation of thiophenes directly into the bay regions of rylene dyes
through effective Stille coupling and subsequent ring-fusion under
Scholl conditions leads to core-extended rylene tetracarboxylic
diimides with interesting electro-optical properties.
work, we report the facile synthesis of a novel PDI that is
S-heterocyclic annulated in two bay-regions (SPDI, 2, Fig. 1).7
The palladium-catalyzed reaction of bis(tributylstannyl) sulfide
with aryl chloride easily converts an extremely twisted precursor
molecule to a planar product. Herein, we present a new synthetic
approach combining the palladium-catalyzed Stille cross-coupling
of halogenated rylene dyes with 2-(tributylstannyl) thiophene and
subsequent ring-fusion under Scholl conditions, which lead to a
series of thiophene-annulated core-extended rylene dyes with
interesting electro-optical properties.
Rylene dyes are based on naphthalene units linked at the peri-
position. The most important representatives are perylene-
3,4:9,10-tetracarboxylic acid diimides (PDIs, n = 2, Fig. 1).
Due to their remarkable electro-optical properties, PDIs have
received a great deal of attention as promising organic n-type
semiconducting materials which have found widespread
applications.1 Chemical modifications both at the imide groups
and in the perylene core are two different successful synthetic
strategies for a diverse library of perylene diimides.2 However,
the dramatic change of optical and electronic properties can only
be achieved by the bay-functionalization because of nodes in the
HOMO and LUMO orbitals at the imide nitrogen atoms. While
the effective synthesis of terrylene- (TDIs, n = 3, Fig. 1) and
quaterrylene tetracarboxylic diimides (QDIs, n = 4, Fig. 1) was
described in the last decade,3 modifications in the bay region to
achieve extension of the conjugation are rarely reported.4
The synthesis of thiophene-annulated rylene dyes is outlined
in Scheme 1. As reported by Wurthner et al., the regioisomerically
¨
pure 1,7-dibromo PDI is prepared by repetitive recrystallization
from a mixture of 1,6- and 1,7-dibromo PDIs.8 Tetrabromo-TDI
and hexabromo-QDI are prepared by using the procedures
reported in ref. 9. Although the aryloxylated TDIs and QDIs
can be facilely prepared by simple aryloxylation of halogenated
rylene dyes,10 the transition-metal catalyzed cross-coupling
reaction of halogenated TDIs and QDIs is rarely investigated.
Stille cross-coupling of halogenated rylene dyes with 2-(tri-
butylstannyl)thiophene proceeds smoothly to introduce thio-
phene units directly into the bay regions of TDI in good yields.
It is remarkable that the regioisomerically pure 1,6,8,11,16,18-
hexa-thiopheneyl substituted QDI could be separated from it’s
isomer 1,6,9,11,16,18-hexa-thiopheneyl substituted QDI (less
quantity) in moderate yields, while the hexa-brominated QDIs
contain unseparated mixtures of isomers.
Significant progress has been achieved in the development of
high performance organic semiconductors based on thiophene
and its derivatives due to their synthetic availability, widespread
possibility, and tunable electronic properties.5 We are particularly
interested in the bay-region functionalization of rylene dyes and
hetero-atom decorated organic semiconductors.6 In previous
Remarkably, when brominated PDIs are treated with 2-(tri-
butylstannyl)thiophene under the standard Stille conditions, they
directly afford the desired heterocyclic annulated PDIs in a yield
of 75%. As reported quite recently for pyridyl substituted
PDIs,11 the thiopheneyl substituted PDIs are also highly inclined
to cyclization probably promoted by visible light.
Differing from the thiopheneyl substituted PDIs, the thiopheneyl
substituted TDIs (6) and QDIs (7) are obtained in 73% and 36%
yield respectively. Following the critical final cyclodehydrogenation
step under Scholl conditions using ferric chloride, the desired
thiopheneyl annulated TDI (9) and QDI (10) are achieved in high
yields. It should be noted that oxidative cyclodehydrogenation with
ferric chloride is sometimes limited by the electronic character of
the substituents.12 Typically, phenyl rings bearing electron-
withdrawing groups are less active in the cyclodehydrogenation
reaction. Thus, the successful cyclodehydrogenation of 6 and 7
to afford the desired product is particularly significant.
Fig. 1 Rylene dyes (n = 1,2,3,4) and S-annulated PDI.
a Beijing National Laboratory for Molecular Sciences,
Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, P. R. China. E-mail: wangzhaohui@iccas.ac.cn
b
`
Dipartimento di Chimica ‘G. Ciamician’, Universita di Bologna,
via F. Selmi, 2, 40126 Bologna, Italy. E-mail: fabrizia.negri@unibo.it
c INSTM, UdR Bologna, Italy
w This article is part of the ChemComm ‘Aromaticity’ web themed
issue.
z Electronic supplementary information (ESI) available: Experimental
details and characterization of compounds 6 to 10, and computational
details. See DOI: 10.1039/c2cc33529h
In order to gain insight into the structure of molecules 8, 9 and
10, B3LYP/6-31G* calculations were carried out. The optimized
c
8204 Chem. Commun., 2012, 48, 8204–8206
This journal is The Royal Society of Chemistry 2012

Fig. 2 Comparison between TD-B3LYP/6-31G* computed (bottom)
and observed (top) UV/vis absorption spectra of 8 (black line),
9 (green line) and 10 (red line) in CHCl3 (1 ꢁ 10ꢀ5 M) at room
temperature. Inset: emission spectra of 8 (black line), 9 (green line) and
10 (red line).
rich character of the thiophene substituents that results in
higher energy HOMO orbitals of 6 and 7 compared to their
parent rylene diimides (Fig. S7, ESIz). Finally, the broadening is
attributed to the rotational flexibility of thiophene substituents
and to the availability of a number of low energy conformational
isomers of 6 and 7.
Scheme 1 Synthesis of the regiospecifically thiophene-annulated
rylenes: (i) 2-(tributylstannyl)thiophene, Pd(PPh3)4, toluene, 110 1C,
24 h. Yields: 75% for 8; 73% for 6; 36% for 7. (ii) FeCl3, dichloro-
methane, room temperature. Yields: 92% for 9; 90% for 10.
Thiopheneyl annulated rylenes 8, 9 and 10 show a limited
solubility in common organic solvents. The orange solution
structures are shown in Fig. S2 (ESIz). Owing to the steric
encumbrance effect between thiophene rings and neighbouring
hydrogens, optimized geometries of 9 and 10 are markedly
non-planar while the extended conjugated core in 8 is
fully planar. Similarly to PDI derivatives featuring large
substituents in the bay region, the twisted core in the lowest
energy conformers of 9 and 10 is associated with thiophenic
substituents in anti.
of 8 shows three major bands at 360, 472, 524 nm (el
=
max
25 310 Mꢀ1 cmꢀ1) with a slight hypsochromic shift relative to
parent PDI (N,N0-di(2,6-diisopropylphenyl) perylene-3,4:9,10-
tetracarboxylic acid diimide), the shape of which is in contrast to
that of dibenzo- and dipyrido-coronene diimides.9b,11 Inspection
of the computed lowest energy transitions of 8 reveals, however,
a close parentage with those of unsubstituted coronene diimide
CDI.11b The more extended conjugation driven by the thiophene
moieties, coupled with their electron rich character, pushes the
HOMO and HOMO ꢀ 1 levels of 8 to higher energies such that
the electronic transitions to the two lowest energy singlet excited
states of 8 are bathochromically shifted compared to those of
CDI (see Fig. S9, ESIz). The red solution of 9 and olive solution
of 10 exhibit also three major bands at 418, 530, 600 nm
Room-temperature absorption and emission spectra of
these compounds are shown in Fig. 2 and Fig. S6 (ESIz),
where a comparison with TD-B3LYP/6-31G* spectra, computed
at the optimized geometries, are also reported. Both 6 and 7
display broad absorption peaks with a maximum at 738 nm and
876 nm (see Fig. S6, ESIz), bathochromically shifted by 88 nm
and 116 nm compared with parent terrylene diimides and
quaterrylene diimides,3b,c respectively. Inspection of the
computed lowest-energy electronic transition of 6 and 7 reveals
that it is dominated by the HOMO - LUMO excitation, with
frontier orbitals conserving the rylene diimide character. The
observed bathochromic shift is therefore ascribed to the electron
(el = 17 872 Mꢀ1 cmꢀ1), and 454, 568, 634 nm (el
=
max
max
27 296 Mꢀ1 cmꢀ1) bathochromically shifted 76 nm and 110 nm
in comparison with 8, respectively, as a reflection of largely
extensive conjugation over the p-electronic system.
It should be also noted after the annulation that 9 and 10 are
hypsochromically-shifted relative to the corresponding parent
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 8204–8206 8205

Table 1 Electro-optical properties of thiophene-annulated rylene dyes
em/nm E1reda/V E2reda/V Eo1xb/V Eo2xb/V Egc/eV
the 973 Program (2011CB932301 and 2012CB932903), NSFC-
DFG joint project TRR61, the Chinese Academy of Sciences,
and Italian PRIN 2008, project JKBBK4.
labs/nm
l
8
9
524
600
532
612
644
ꢀ0.78
ꢀ0.87
ꢀ1.00
ꢀ1.00
—
1.37
1.19
—
—
1.46
2.30
2.00
1.88
d
d
10 634
—
—
Notes and references
a
Half-wave reductive potential (in V vs. Ag/AgCl) measured in CH2Cl2
at a scan rate of 0.1 V sꢀ1 with ferrocene as an internal potential marker.
1 (a) H. Zollinger, Color Chemistry, VCH, Weinheim, 3rd edn, 2003;
(b) F. Wurthner, Chem. Commun., 2004, 1564; (c) L. Schmidt-
¨
Mende, A. Fechtenkotter, K. Mullen, E. Moons, R. H. Friend and
b
Half-wave oxidative potential (in V vs. Ag/AgCl) measured in CH2Cl2
c
¨
¨
at a scan rate of 0.1 V sꢀ1
.
spectra. The CVs of compound 10 did not provide well-defined
Obtained from the edge of the absorption
J. D. Mackenzie, Science, 2001, 293, 1119; (d) B. A. Jones,
M. J. Ahrens, M.-H. Yoon, A. Facchetti, T. J. Marks and
M. R. Wasielewski, Angew. Chem., Int. Ed., 2004, 43, 6363;
d
reduction peaks probably because of poor solubility.
(e) F. Wurthner, P. Osswald, R. Schmidt, T. E. Kaiser,
¨
H. Mansikkamaki and M. Konemann, Org. Lett., 2006, 8, 3765;
¨
nemann,
¨
(f) R. Schmidt, M. M. Ling, J. H. Oh, M. Winkler, M. Ko
¨
TDIs and QDIs (50 nm for 9 and 126 nm for 10 respectively) as a
reflection of the extended rylene core along the short molecular
axis. Meanwhile, thiopheneyl annulated rylenes 8, 9 and 10
possess small Stokes shifts (8–12 nm) and high fluorescence
quantum yields (0.56 for 9 and 0.14 for 10 using cresyl violet as
a standard, and around 1 for 8 using parent PDI as a standard,
see ESIz), which means that the introduction of thiophene units
into the bay region of rylenes could effectively modulate the
absorption in keeping high fluorescence quantum yields.
Z. Bao and F. Wurthner, Adv. Mater., 2007, 19, 3692.
¨
2 See recent examples: (a) S. Nakazono, S. Easwaramoorthi,
D. Kim, H. Shinokubo and A. Osuka, Org. Lett., 2009, 11, 5426;
(b) W. Yue, Y. Li, W. Jiang, Y. Zhen and Z. Wang, Org. Lett.,
2009, 11, 5430; (c) A. Wicklein, A. Lang, M. Muth and
M. Thelakkat, J. Am. Chem. Soc., 2009, 131, 14442.
3 (a) H. Quante and K. Mullen, Angew. Chem., Int. Ed. Engl., 1995,
¨
S. D. Feyter, F. C. D. Schryver and K. Mullen, Chem.–Eur. J.,
¨
34, 1323; (b) F. O. Holtrup, G. R. J. Muller, H. Quante,
¨
1997, 3, 219; (c) Y. Geerts, H. Quante, H. Platz, R. Mahrt,
M. Hopmeier, A. Bohm and K. Mullen, J. Mater. Chem., 1998,
¨
8, 2357.
4 C. L. Eversloh, Z. Liu, B. Muller, M. Stangl, C. Li and K. Mullen,
Org. Lett., 2011, 13, 5528.
5 (a) B. O. Ong, Y. Wu, P. Liu and S. Gardner, Adv. Mater., 2005,
128, 4911; (b) I. McCulloch, M. Heeney, C. Bailey, K. Genevicus,
I. Macdonald, M. Shkunov, D. Sparrowe, S. Tierney, R. Wagner,
W. Zhang, M. L. Chabinyc, R. J. Kline, M. D. Mcgehee and
M. F. Toney, Nat. Mater., 2006, 16, 328; (c) X. Guo and
M. D. Watson, Org. Lett., 2008, 10, 5333; (d) H. Yan, Z. Chen,
The electrochemical properties of thiopheneyl annulated
rylenes are also investigated by cyclic voltammetry in dichloro-
methane (vs. Ag/AgCl), and their reductive and oxidative
potentials are given in Table 1. Cyclovoltammograms of 8, 9
and 10 are shown in Fig. S1 (ESIz). The thiopheneyl annulated
PDI 8 exhibits two reversible reduction waves, whereas within
the accessible scanning range in dichloromethane no oxidation
waves could be detected. The first reduction wave for 8 is
observed at ꢀ0.78 V vs. Ag/AgCl, whereas the second
reduction wave appeared at ꢀ1.00 V. In contrast to 8,
thiopheneyl annulated TDI 9 shows two reversible reduction
waves and one reversible oxidation wave, and thiopheneyl
annulated QDI 10 has two reversible oxidation waves in the
absence of well-defined reduction peaks probably because of
poor solubility. The first reduction wave of 9 is at a slightly
lower potential than that of 8, whereas the first oxidation wave
of 10 is at a lower potential than that of 9, indicating that
the introduction of thiopheneyl units into the bay region
of rylene dyes makes them suitable electron donors and
acceptors. This conclusion is strongly supported by the energy
trend displayed by the frontier molecular orbitals of 8, 9 and
10 (see Fig. S10, ESIz) and showing a modest energy change of
the LUMO level and a remarkable energy increase of the
occupied orbitals of 9 and 10.
¨
¨
Y. Zheng, C. Newman, J. R. Quinn, F. Dotz, M. Kastler and
¨
A. Facchetti, Nature, 2009, 457, 679.
6 (a) H. Qian, Z. Wang, W. Yue and D. Zhu, J. Am. Chem. Soc.,
2007, 129, 10664; (b) H. Qian, F. Negri, C. Wang and Z. Wang,
J. Am. Chem. Soc., 2008, 130, 17970; (c) H. Qian, W. Yue,
Y. Zhen, S. Di Motta, E. Di Donato, F. Negri, J. Qu, W. Xu,
D. Zhu and Z. Wang, J. Org. Chem., 2009, 74, 6275; (d) Y. Zhen,
H. Qian, J. Xiang, J. Qu and Z. Wang, Org. Lett., 2009, 11, 3084;
(e) Y. Li, L. Tan, Z. Wang, H. Qian, Y. Shi and W. Hu, Org. Lett.,
2008, 10, 529; (f) Y. Li, C. Li, W. Yue, W. Jiang, R. Kopecek, J. Qu
and Z. Wang, Org. Lett., 2010, 12, 2374; (g) W. Yue, J. Gao, Y. Li,
W. Jiang, S. Di Motta, F. Negri and Z. Wang, J. Am. Chem. Soc.,
2011, 133, 18054; (h) W. Yue, A. Lv, J. Gao, W. Jiang, L. Hao,
C. Li, Y. Li, L. E. Polander, S. Barlow, W. Hu, S. Di Motta,
F. Negri, S. R. Marder and Z. Wang, J. Am. Chem. Soc., 2012,
134, 5770.
7 H. Qian, C. Liu, Z. Wang and D. Zhu, Chem. Commun., 2006,
4587.
8 (a) F. Wurthner, V. Stepanenko, Z. Chen, C. R. Saha-Moller,
¨
¨
N. Kocher and D. Stalke, J. Org. Chem., 2004, 69, 7933;
(b) A. Bohm, H. Arms, G. Henning and P. Blaschka, (BASF
¨
AG) German Pat. DE 19547209 Al, 1997; Chem. Abstr., 1997,
127, 96569g; (c) L. Fan, Y. Xu and H. Tian, Tetrahedron Lett.,
2005, 46, 4443.
In summary, we report a new synthetic approach combining
the palladium-catalyzed Stille cross-coupling of halogenated
rylene dyes with 2-(tributylstannyl) thiophene and subsequent
ring-fusion under Scholl conditions. The introduction of
thiopheneyl groups directly into the core has drastically
influenced the optical and electronic properties of rylenes
which shows a modest energy change of the LUMO level
and a remarkable energy increase of the occupied orbitals.
Further studies on functionalization of thiopheneyl annulated
rylenes and their applications as ambipolar materials in electronic
devices are currently underway.
9 (a) T. Weil, E. Reuther, C. Beer and K. Mullen, Chem.–Eur. J.,
¨
2004, 10, 1398; (b) Y. Avlasevich, S. Muller, P. Erk and K. Mullen,
¨
Chem.–Eur. J., 2007, 13, 6555; (c) J. Qu, M. Koenemann,
¨
W. Helfer, K. Mullen, J. Romeis and A. Bohm, US 2007155968,
¨
2007; (d) M. Koenemann and N. G. Pschirer, US 2008058526, 2008.
10 (a) J. Qu, C. Kohl, M. Pottek and K. Mullen, Angew. Chem., Int.
¨
Ed., 2004, 43, 1528; (b) F. Nolde, J. Qu, C. Kohl, N. G. Pschirer,
E. Reuther and K. Mullen, Chem.–Eur. J., 2005, 11, 3959.
¨
11 (a) W. Jiang, Y. Li, W. Yue, Y. Zhen, J. Qu and Z. Wang, Org.
Lett., 2010, 12, 228; (b) U. Rohr, P. Schlichting, A. Bohm,
¨
¨
M. Gross, K. Meerholz, C. Brauchle and K. Mullen, Angew.
¨
Chem., Int. Ed., 1998, 37, 1434.
12 X. Dou, X. Yang, G. J. Bodwell, M. Wagner, V. Enkelmann and
For financial support of this research, we thank the National
Natural Science Foundation of China (91027043 and 21190032),
K. Mullen, Org. Lett., 2007, 9, 2485.
¨
c
8206 Chem. Commun., 2012, 48, 8204–8206
This journal is The Royal Society of Chemistry 2012