Electron donors and acceptors based on 2,7-functionalized pyrene-4,5,9,10-tetraone

Article abstract of DOI:10.1039/c3cc39141h

An efficient synthesis of 2,7-dibromo- and diiodo-pyrene(4,5,8,19)- tetraones led to strong donors and acceptors based on pyrene. They are versatile building blocks for conjugated materials and can be further applied in molecular electronics. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3cc39141h

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Electron donors and acceptors based on
,7-functionalized pyrene-4,5,9,10-tetraone†
2
Cite this: DOI: 10.1039/c3cc39141h
Shin-ichiro Kawano,z Martin Baumgarten,* Dennis Chercka, Volker Enkelmann
Received 21st December 2012,
Accepted 10th April 2013
and Klaus M u¨ llen*
DOI: 10.1039/c3cc39141h
www.rsc.org/chemcomm
An efficient synthesis of 2,7-dibromo- and diiodo-pyrene(4,5,8,19)-
tetraones led to strong donors and acceptors based on pyrene.
They are versatile building blocks for conjugated materials and can
be further applied in molecular electronics.
Polycyclic aromatic hydrocarbons (PAHs) have long played an
important role in modern organic chemistry from a synthetic,
1
theoretical and applied viewpoint. More recently, PAH deriva-
tives have been intensively studied as active components of
2
electronic and optoelectronic devices. In this regard, pyrenes
3
are probably the best known organic chromophores, while
4
anthracenes are used as emitters in organic light emitting
5
diodes and pentacenes are outstanding semiconductors in
field effect transistors. Optimizing PAHs for electron and hole
transport requires the synthesis of derivatives with either an
electron rich or electron poor character. In the family of PAHs,
Scheme 1 (i) (2a) N-bromosuccinimide, H
2
SO
4
, at 45 1C, 2 h, 78%; (2b)
6
N-iodosuccinimide, H SO , at 45 1C,
2
h, 74%; (ii) Na S O , (n-Bu) NBr,
2
4
2
2
4
4
pyrene itself is known as an electron donor, and the conven-
(
CH
3
O)
2
SO
2
, KOH, THF, H
2
O, 40 1C, 1 h, 82%; (iii) CuCN, NMP, at 180 1C, 10 h,
O, THF, at 50 1C, 30 min, 20% for
CH (7) Pd DBA , toluene, 95 1C,
tional approach to functionalise this molecule is applied pre-
5
6%; (iv) AlCl
3
, CH
2
Cl
2
, at 40 1C, 4 days; (v) Ag
in THF (6), HN(p-C
2
7
dominantly at the 1,3,6,8-positions. There exist very few
two steps; (vi) HN(CH
3
)
2
6
H
5
3
)
2
2
3
reports where other positions have been tackled, like the 18 h; (vii) NaOMe, CuI, toluene–DMF, 95 1C, 18 h, 62%.
inactive 2,7 positions (due to the nodal plane of the frontier
orbitals) by introducing tert-butyl or pinacolborone both direc-
ted by steric demands, or the 4,5,9,10-positions which most can be prepared in gram scales. While pyrenes are usually
9
easily became accessible via the pyrene tetraone and its con- halogenated in the 1,3,6,8-positions, our approach utilized the
8
,9
densation with diamines. Here, we present a new synthetic direct bromination or iodination in the 2,7-positions of 1,
strategy for creating a variety of both, electron deficient and opening a new pathway for derivatives of pyrenes. The synthesis
electron rich pyrene derivatives 2–8.
of 2,7-dibromopyrene-4,5,9,10-tetraone (2a) and 2,7-diiodo-
The synthesis of the target structures 2–8 is depicted in pyrene-4,5,9,10-tetraone (2b) was easily performed by halo-
Scheme 1 and is based on pyrene-4,5,9,10-tetraone (1) which genation with N-bromo- or N-iodosuccinimide in sulfuric acid,
1
0
respectively. Direct cyanation of 2a using CuCN to synthesize
,7-dicyano-pyrene-4,5,9,10-tetraone (5) was not successful and
resulted in an unidentified black solid. Therefore, the ketone-
2
Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz,
Germany. E-mail: baumgart@mpip-mainz.mpg.de, muellen@mpip-mainz.mpg.de;
Fax: +49 6131 379100
functions of compound 2a were protected with methyl groups
1
1
†
Electronic supplementary information (ESI) available: Experimental details, via reductive alkylation with Na S O and dimethyl sulfate.
2 2 4
fluorescence spectra, cyclic voltammograms, X-ray structures and details, DFT
The resulting product, 2,7-dibromo-4,5,9,10-tetra-methoxypyrene
3a), was obtained in a very good yield (82%). Subsequently,
cyanation of compound 3a with CuCN led to 2,7-dicyano-
calculations. CCDC 847344 (2a), 857532 (5), 857533 (6), 857534 (7), 857535 (8),
(
8
57537 (and mixed TCNQ cocrystals with 8) and 857536 (9). For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c3cc39141h
Present address: Department of Chemistry, Graduate School of Science, Nagoya
1
2
4,5,9,10-tetramethoxypyrene (4) (56%).
After deprotection
‡
University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
with aluminium trichloride and subsequent oxidation with
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silver oxide, 2,7-dicyano-pyrene-4,5,9,10-tetraone (5) was suc- pronounced blue shift when the donor residue in positions 2
cessfully isolated in 20% yield. and 7 were changed from the amino groups in 6 (lmax = 483 nm)
The diiodo derivative 3b was prepared in analogy to 3a using or 7 (lmax = 495 nm) to methoxy 8 (lmax = 402 nm), respectively
the precursor compound 2b. 3b turned out to be an excellent (see ESI,† Fig S2).
1
3
14
precursor for Ullmann and Buchwald–Hartwig -type cross
The reduction properties of 1–5 were investigated in DMF
NClO ] = 0.1 M,
based on pyrene. The amino-derivatives 2,7-bis(dimethylamino)- 100 mV s ). All molecules showed two reversible one-electron
coupling reactions, thus opening a viable route to strong donors solutions using cyclic voltammetry ([n-Bu
4
4
ꢀ1
4
4
,5,9,10-tetra-methoxypyrene (6) and 2,7-bis(di-p-tolylamino)- reduction steps (ESI,† Fig. S3). The pyrene-4,5,9,10-tetraone
,5,9,10-tetramethoxypyrene (7) were synthesized via palladium derivative 1 had a low first reduction potential, ER1, at ꢀ0.41 V
catalyzed amination using the appropriate secondary amine. (vs. SCE for all the compounds discussed below), which was
1
5
When applying a copper(I)-catalyzed methoxylation 2,4,5,7,9,10- 0.19 V lower than that of 9,10-phenanthrenedione (ꢀ0.60 V).
hexamethoxypyrene (8) was obtained (67%). As a reference Further electron-withdrawing substituents such as halogens or
for the donors 6–8, 4,5,9,10-tetramethoxy-pyrene (9) was syn- cyano groups led to more easy reduction of 2a and 5, with ER1
thesised to compare the effects of additional substituents in of ꢀ0.24 V and ꢀ0.16 V, respectively. For direct comparison
positions 2 and 7.
The products were identified using H- and
the strong electron-acceptor 7,7,8,8-tetracyanoquinodimethane
C-NMR (TCNQ) was also studied under these conditions. Thereby,
1
13
16
spectroscopy as well as field desorption mass spectroscopy TCNQ still demonstrated more easy reduction by 0.42 V due to
1
7
(
FD-MS, see ESI†). The tetraone acceptors 1, 2a/b, and 5 are the quinoidal structure which is missing in the dicyano
soluble in polar solvents such as THF, 1,4-dioxane, DMF, and derivative 5. Cyclic voltammetry investigations of the donors
DMSO, while the donor derivatives 6–8 showed improved 6–8 were conducted in DCM solutions ([n-Bu NPF ] = 0.1 M
4
6
ꢀ
1
solubility in chlorinated solvents (DCM, chloroform) as well 50 mV s ). A two-electron oxidation was observed in the case of
as in THF. the amino donors 6 and 7 (see Table 1). For 8 a one-electron
The UV-Vis absorption spectra of the pyrene tetraones 1, 2a, oxidation was observed. The half wave oxidation potential
and 5 recorded in DMF are shown in Fig. 1a. Similar to 9,10- was determined to be E = +0.85 V. In none of the three
O
1
5
phenanthrenedione, they are characterized by the p–p* tran- studied donors the reduction wave was resolved before solvent
sitions at around 290 nm and the n–p* transitions at around decomposition.
350–380 nm which are considerably less intense than the
For the acceptors, it is noteworthy that the LUMO of the dicyano
former. The UV-Vis absorption properties of the donors 6–8 derivative 5 reached ꢀ4.24 eV which is comparable with many
1
6
were studied in dichloromethane and are depicted in Fig. 1b. other strong acceptors as benzo-TCNQ (ꢀ4.10 eV), 11,11,12,
1
7
Strong p–p* absorptions (300 to 350 nm) attributed to the 12-tetracyano-9,10-anthraquinodimethane (TCAQ) (ꢀ3.70 eV),
1
8
pyrene core were observed. Here the maximum extinction bis[1,2,5]thiadiazolo-tetracyanoquinodimethane (BTDA) (ꢀ4.38 eV),
1
9
coefficient of compounds 6 (log e = 5.42) and 7 (log e = 5.43), dicyano-substituted perylene-tetracarboxydiimide (ꢀ4.33 eV),
2
0
however, was one order of magnitude larger than the one for and a perfluorinated copper phthalocyanine at ꢀ4.27 eV. As
2
1
compound 8 (log e = 4.11). The longest wavelength transition suggested by Marks et al. the requirement for n-type semicon-
was observed above 450 nm for 6 and 7 due to the higher ductors with thermodynamically air-stable charge carriers is a
HOMO level, while it occurred at 399 m for the hexamethoxy- LUMO level within the range of ꢀ4.0 to ꢀ4.4 eV as found here.
pyrene 8. Therefore the fluorescence spectra also showed a
Single crystals of compounds 2a and 5 were grown by slow
evaporation of a THF solution at room temperature. The
dibromo derivative 2a exhibits p–p stacking with a distance of
0.34–0.35 nm (ESI,† Fig. S4). The dicyano derivative 5 shows a
stacking with the cyano groups oriented in an anti-parallel
fashion (Fig. 2a). The closest C–C distance between the molecules
Table 1 Optical absorption maxima, optical gap, redox potentials vs. SCE,
together with HOMO and LUMO energies of the main targets
a
b
c
c
d
Compd lmax /nm DE /eV ER1 /V ER2 /V EO1 /V HOMO/eV LUMO/eV
f
1
2
5
6
7
8
290, 371 2.65
290, 380 2.49
290, 336 2.48
ꢀ0.41 ꢀ0.76 —
ꢀ0.24 ꢀ0.55 —
ꢀ0.16 ꢀ0.44 —
ꢀ6.64
ꢀ6.65
ꢀ6.72
ꢀ3.99
ꢀ4.16
ꢀ4.24
ꢀ2.26
ꢀ2.48
ꢀ2.12
f
f
a
e
e
e
462
465
399
2.59
2.55
3.02
—
—
—
—
—
—
+0.55 ꢀ4.85
+0.69 ꢀ5.03
+0.85 ꢀ5.14
a
c
b
Optical absorption maxima (in DMF). Onset of optical absorptions.
d
E
R1 or E eR 2 = (Epa + Epc)/2, reduction potentials vs. SCE. Oxidation potential
Fig. 1 Absorption spectra of (a) pyrene tetraones 1, 2a, and 5, (b) pyrene
donors 6–8.
vs. SCE. Determined vs. vacuum level from EHOMO = ꢀ4.40 eV ꢀ EO1.
f
Determined from vacuum level from ELUMO = ꢀ4.40 eV ꢀ ER1
.
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pyrene-4,5,9,10-tetraone and its direct halogenation in posi-
tions 2 and 7 (Br, I) which otherwise is difficult to address in
1
1
1
pyrene chemistry. They even enable their insertion in the
main chain donor and alternating donor acceptor conjugated
1
0a
copolymers. CV measurements revealed that the LUMO level
of 2,7-dicyanopyrene-4,5,9,10-tetraone 5 (ꢀ4.24 eV) is compar-
able to that of dicyano-perylene derivatives and PCBM. New
donor moieties 6–8 were developed from the pyrene core with
high lying HOMO but yet air stable. From the above outline
there are two further options to follow: (i) the combination of
these building blocks with other extended conjugated systems
2
2
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based on the pyrene core.
We gratefully acknowledge support from the SFB TR49 and
the former CIBA Inc. now BASF-Switzerland.
Chem. Soc., 2012, 134, 4694.
This journal is c The Royal Society of Chemistry 2013
Chem. Commun.