U.S. patent application number 15/219747 was filed with the patent office on 2016-11-17 for graphene nanoribbon precursors and monomers suitable for preparation thereof.
This patent application is currently assigned to BASF SE. The applicant listed for this patent is BASF SE, Max-Planck-Gesellschaft zur Foerderung der Wissenschaften e.V.. Invention is credited to Lukas DOESSEL, Xinliang FENG, Klaus MUELLEN, Matthias Georg SCHWAB.
Application Number | 20160333141 15/219747 |
Document ID | / |
Family ID | 48167206 |
Filed Date | 2016-11-17 |
United States Patent
Application |
20160333141 |
Kind Code |
A1 |
SCHWAB; Matthias Georg ; et
al. |
November 17, 2016 |
GRAPHENE NANORIBBON PRECURSORS AND MONOMERS SUITABLE FOR
PREPARATION THEREOF
Abstract
Provided are graphene nanoribbon precursors comprising repeated
units of the general formula (I) in which R.sup.1, R.sup.2 are each
H, halogen, --OH, --NH.sub.2, --CN, --NO.sub.2 or a hydrocarbyl
radical which has 1 to 40 carbon atoms and may be linear or
branched, saturated or unsaturated and mono- or poly-substituted by
halogen (F, Cl, Br, I), --OH, --NH.sub.2, --CN, and/or --NO.sub.2,
where one or more CH.sub.2 groups may also be replaced by --O--,
--S--, --C(O)O--, --O--C(O)--, --C(O)--, --NH-- or --NR--, in which
R is an optionally substituted C.sub.1C.sub.40-hydrocarbyl radical,
or an optionally substituted aryl, alkylaryl or alkoxyaryl radical.
##STR00001##
Inventors: |
SCHWAB; Matthias Georg;
(Mannheim, DE) ; MUELLEN; Klaus; (Koeln, DE)
; FENG; Xinliang; (Mainz, DE) ; DOESSEL;
Lukas; (Darmstadt, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE
Max-Planck-Gesellschaft zur Foerderung der Wissenschaften
e.V. |
Ludwigshafen
Muenchen |
|
DE
DE |
|
|
Assignee: |
BASF SE
Ludwigshafen
DE
Max-Planck-Gesellschaft zur Foerderung der Wissenschaften
e.V.
Muenchen
DE
|
Family ID: |
48167206 |
Appl. No.: |
15/219747 |
Filed: |
July 26, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14354430 |
Apr 25, 2014 |
9434619 |
|
|
PCT/IB2012/055845 |
Oct 24, 2012 |
|
|
|
15219747 |
|
|
|
|
61551466 |
Oct 26, 2011 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01B 32/184 20170801;
C01B 2204/065 20130101; C08G 2261/314 20130101; B82Y 40/00
20130101; C08G 61/10 20130101; C08G 2261/1412 20130101; C08G
2261/148 20130101; C07C 25/18 20130101; C01B 2204/06 20130101; H01L
51/102 20130101; C07C 25/18 20130101; H01L 51/0558 20130101; C08G
2261/312 20130101; C07C 17/30 20130101; C07C 15/14 20130101; C08G
2261/412 20130101; H01L 51/0045 20130101; B82Y 30/00 20130101; C07C
17/30 20130101 |
International
Class: |
C08G 61/10 20060101
C08G061/10; H01L 51/10 20060101 H01L051/10; H01L 51/00 20060101
H01L051/00; C07C 25/18 20060101 C07C025/18; C07C 15/14 20060101
C07C015/14 |
Claims
1. A graphene nanoribbon obtained by cyclodehydrogenation, in
solution or on a metal surfgace, of a precursor comprising repeat
units of the general formula (I) ##STR00012## in which R.sup.1,
R.sup.2 are each H, halogen, --OH, --NH.sub.2, --CN, --NO.sub.2 or
a hydrocarbyl radical which has 1 to 40 carbon atoms and may be
linear or branched, saturated or unsaturated and mono- or
poly-substituted by halogen (F, Cl, Br, I), --OH, --NH.sub.2, --CN,
and/or --NO.sub.2, where one or more CH.sub.2 groups may also be
replaced by --O--, --S--, --C(O)O--, --O--C(O)--, --C(O)--, --NH--
or --NR--, in which R is an optionally substituted
C.sub.1C.sub.40-hydrocarbyl radical, or an optionally substituted
aryl, alkylaryl or alkoxyaryl radical.
Description
[0001] The invention relates to graphene nanoribbon precursors, to
graphene nanoribbons obtainable therefrom by oxidative
cyclodehydrogenation (intramolecular Scholl reaction), to processes
for preparing the graphene nanoribbon precursors, to monomers
suitable for preparation of the graphene nanoribbon precursors, and
to a process for preparing the monomers.
[0002] Graphene nanoribbons (GNRs) are a defined section from the
structure of graphene. They consist of monolayer ribbons of
sp.sup.2-hybridized carbon atoms arranged in a honeycomb and have a
high side ratio of length:width, such that they are a
quasi-one-dimensional carbon polymorph. Due to the low width of the
ribbons in relation to their length, the influence of the edge
structure on the electronic properties of the graphene cannot be
neglected in graphene nanoribbons. Through the edge structure, it
is possible to influence the electronic properties of graphene
nanoribbons in a controlled manner.
[0003] Graphene itself has already been used in organic
electronics, for example as a transparent electrode material or as
an active material in field-effect transistors. Graphene, however,
does not have a natural band gap, which opposes use as a
semiconductor in electronics circuits. However, it has been shown
by theoretical models that it is possible in graphene nanoribbons,
by controlling the width and the edge structure, to obtain a
synthetic band gap. In order to obtain such semiconductive graphene
nanoribbons, defect-free graphene ribbons of defined structure with
an "armchair" edge structure and a width of <10 nm are needed.
These have not been available to date.
[0004] It is not possible by "top-down" methods, such as the
reduction of graphene oxide (S. Stankovich, D. Dikin, R. Piner, K.
Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S. Nguyen, R. Ruoff,
Carbon 2007, 45, 1558), lithography (M. Han, B. Ozyilmaz, Y. Zhang,
P. Kim, Phys. Rev. Lett., 2007, 98, 206805, Z. Chen, Y. Lin, M.
Rooks, P. Avouris, Physica E, 2007, 40, 228), the unzipping of
carbon nanotubes (a) L. Jiao, X. Wang, G. Diankov, H. Wang, H. Dai,
Nat. Nanotechnol. 2010, 5, 321; b) D. Kosynkin, A. Higginbotham, A.
Sinitskii, J. Lomeda, A. Dimiev, B. Price, J. Tour, Nature 2009,
458, 872) or mechanical exfoliation of graphene (X. Li, X. Wang, L.
Zhang, S. Lee, H. Dai, Science 2008, 219, 1229), to control the
size and edge structure of the graphene nanoribbons obtained. An
organic "bottom-up" synthesis, in contrast, allows structural
control at the atomic level and is thus suitable for producing GNRs
with exactly defined structure.
[0005] X. Yang, X. Dou, A. Rouhanipour, L. Zhi, H. Rader, K.
Mullen, J. Am. Chem. Soc. 2008, 130, 4216 disclose the production
of a graphene nanoribbon by cyclodehydrogenation of a suitable
polymer precursor according to Scheme 1 below.
##STR00002##
The synthesis is based on the development of a tailored polymer
precursor which is converted to the two-dimensional graphene
structure in the last reaction step by oxidative
cyclodehydrogenation (intramolecular Scholl reaction). However,
full cyclodehydrogenation could not be achieved, and so a study of
the electronic properties was not possible due to the presence of
defects.
[0006] Scheme 2 shows the polymerization to give the polymer
precursor.
##STR00003##
[0007] The maximum length of the polymer at about 10 nm is caused
by strong steric hindrance during the Suzuki polycondensation from
the monomers, since the iodine function in the monomer 3 is
screened significantly by two phenyl radicals in the ortho
positions, which makes the coupling reaction more difficult. In
addition, thermal scission of the carbon-iodine bond is easily
possible, and causes chain termination. At the same time, there is
spatial hindrance in the polymer as a result of overlapping alkyl
radicals, which, in the subsequent cyclodehydrogenation step,
hinders formation of aryl-aryl bonds adjacent to these radicals and
leads to incomplete cyclodehydrogenation. Another disadvantage is
found to be the poly(para-phenylene) structure of the polymer
backbone, which allows only a low level of flexibility along the
polymer chain. This can result in enhanced aggregation and
precipitation of the molecules even during the polymerization,
before relatively high molecular weights are attained.
[0008] In addition, in the case of polymerization reactions of the
A.sub.2+B.sub.2 type, the monomers have to be used in exactly
stoichiometric amounts, since only low degrees of polymerization
are otherwise achieved.
[0009] It is an object of the invention to provide a process for
producing graphene nanoribbons and suitable graphene nanoribbon
precursors, which do not have the disadvantages of the prior art.
It is a particular object of the invention to provide graphene
nanoribbon precursors which give defect-free graphene nanoribbons
with an "armchair" edge structure.
[0010] The object was achieved by graphene nanoribbon precursors
comprising repeat units of the general formula (I)
##STR00004##
in which
[0011] R.sup.1, R.sup.2 are each H, halogen, --OH, --NH.sub.2,
--CN, --NO.sub.2, a hydrocarbyl radical which has 1 to 40 carbon
atoms and may be linear or branched, saturated or unsaturated and
mono- or polysubstituted by halogen (F, Cl, Br, I), --OH,
--NH.sub.2, --CN and/or --NO.sub.2, where one or more CH.sub.2
groups may also be replaced by --O--, --S--, --C(O)O--,
--O--C(O)--, --C(O)--, --NH-- or --NR--, in which R is an
optionally substituted C.sub.1-C.sub.40-hydrocarbyl radical, or an
optionally substituted aryl, alkylaryl or alkoxyaryl radical,
and the graphene nanoribbons obtainable therefrom by oxidative
cyclodehydrogenation.
[0012] The object was also achieved by a process for preparing
graphene nanoribbon precursors, comprising the Yamamoto coupling
reaction of monomer units of the general formula (II)
##STR00005##
in which
[0013] R.sup.1, R.sup.2 are each H, halogen, --OH, --NH.sub.2,
--CN, --NO.sub.2 or a hydrocarbyl radical which has 1 to 40 carbon
atoms and may be linear or branched, saturated or unsaturated and
mono- or polysubstituted by halogen (F, Cl, Br, I), --OH,
--NH.sub.2, --CN and/or --NO.sub.2, where one or more CH.sub.2
groups may also be replaced by --O--, --S--, --C(O)O--,
--O--C(O)--, --C(O)--, --NH-- or --NR--, in which R is an
optionally substituted C.sub.1-C.sub.40-hydrocarbyl radical, or an
optionally substituted aryl, alkylaryl or alkoxyaryl radical,
and
[0014] X is halogen, trifluoromethylsulfonate or diazonium
and by the monomer units of the general formula (II)
themselves.
[0015] In general, R.sup.1, R.sup.2 are each H or a saturated or
mono- to pentaethylenically and/or -acetylenically unsaturated
hydrocarbyl radical which may be mono- to pentasubstituted by the
substituents specified.
[0016] Preferably, R.sup.1, R.sup.2 is H or a linear or branched
saturated hydrocarbyl radical which may be mono- to
pentasubstituted by the substituents specified.
[0017] Preferably, R.sup.1, R.sup.2 are each independently
hydrogen, C.sub.1-C.sub.30-alkyl, C.sub.1-C.sub.30-alkoxy,
C.sub.1-C.sub.30-alkylthio, C.sub.2-C.sub.30-alkenyl,
C.sub.2-C.sub.30-alkynyl, C.sub.1-C.sub.30-haloalkyl,
C.sub.2-C.sub.30-haloalkenyl and haloalkynyl, for example
C.sub.1-C.sub.30-perfluoroalkyl.
[0018] C.sub.1-C.sub.30-Alkyl may be linear or, if possible,
branched.
[0019] Examples are methyl, ethyl, n-propyl, isopropyl, n-butyl,
sec-butyl, isobutyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl,
2,2-dimethylpropyl, 1,1,3,3-tetramethylpentyl, n-hexyl,
1-methylhexyl, 1,1,3,3,5,5-hexamethylhexyl, n-heptyl, isoheptyl,
1,1,3,3-tetramethylbutyl, 1-methylheptyl, 3-methylheptyl, n-octyl,
1,1,3,3-tetramethylbutyl and 2-ethylhexyl, n-nonyl, decyl, undecyl,
dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl,
octadecyl, eicosyl, heneicosyl, docosyl, tetracosyl or
pentacosyl.
[0020] C.sub.1-C.sub.30-Alkoxy groups are straight-chain or
branched alkoxy groups, for example methoxy, ethoxy, n-propoxy,
isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, amyloxy, isoamyloxy
or tert-amyloxy, heptyloxy, octyloxy, isooctyloxy, nonyloxy,
decyloxy, undecyloxy, dodecyloxy, tetradecyloxy, pentadecyloxy,
hexadecyloxy, heptadecyloxy and octadecyloxy.
[0021] The term "alkylthio group" means the same as alkoxy group,
except that the oxygen atom in the ether bridge has been replaced
by a sulfur atom.
[0022] C.sub.2-C.sub.30-Alkenyl groups are straight-chain or
branched, for example vinyl, allyl, methallyl, isopropenyl,
2-butenyl, 3-butenyl, isobutenyl, n-penta-2,4-dienyl,
3-methyl-but-2-enyl, n-oct-2-enyl, n-dodec-2-enyl, isododecenyl,
n-dodec-2-enyl or n-octadec-4-enyl.
[0023] C.sub.2-C.sub.30-Alkynyl is straight-chain or branched, such
as ethynyl, 1-propyn-3-yl, 1-butyn-4-yl, 1-pentyn-5-yl,
2-methyl-3-butyn-2-yl, 1,4-pentadiyn-3-yl, 1,3-pentadiyn-5-yl,
1-hexyn-6-yl, cis-3-methyl-2-penten-4-yn-1-yl,
trans-3-methyl-2-penten-4-yn-1-yl, 1,3-hexadiyn-5-yl, 1-octyn-8-yl,
1-nonyn-9-yl, 1-decyn-10-yl, or 1-tetracosyn-24-yl.
[0024] C.sub.1-C.sub.30-Perfluoroalkyl is branched or unbranched,
such as --CF.sub.3, --CF.sub.2CF.sub.3, --CF.sub.2CF.sub.2CF.sub.3,
--CF(CF.sub.3).sub.2, --(CF.sub.2).sub.3CF.sub.3 or
--C(CF.sub.3).sub.3.
[0025] The terms "haloalkyl, haloalkenyl and haloalkynyl" mean
partly or fully halogen-substituted alkyl, alkenyl and alkynyl
groups.
[0026] Aryl is typically C.sub.6-C.sub.30-aryl and may optionally
be substituted, for example phenyl, 4-methylphenyl,
4-methoxyphenyl, naphthyl, biphenylyl, terphenylyl, pyrenyl,
fluorenyl, phenanthryl, anthryl, tetracyl, pentacyl and
hexacyl.
[0027] Preferably, X=Cl or Br. More preferably, R.sup.1, R.sup.2
are each H or C.sub.8-C.sub.30-alkyl, especially H or
C.sub.10-C.sub.26-alkyl.
[0028] Preferably, R.sup.2=H.
[0029] Through the Yamamoto coupling reaction proceeding from the
inventive monomer units (II), it is possible to produce graphene
nanoribbons with generally 3 to 100 and preferably 5 to 50 repeat
units (I). The Yamamoto polymerization reaction is additionally not
stoichiometry-sensitive like a polymerization reaction of the
A.sub.2+B.sub.2 type.
[0030] The angled backbone of the graphene nanoribbon precursor
molecule reduces steric hindrance during the polymerization step to
form the graphene nanoribbon precursor, and during the subsequent
cyclodehydrogenation of the precursor to give the graphene
nanoribbon. This allows sterically demanding alkyl radicals to be
introduced, which additionally induce increased solubility. The
relatively high level of twisting of the angled polymer backbone,
which has relatively high flexibility, suppresses the aggregation
of the molecules during the polymerization, as a result of which
relatively high molecular weights can be achieved.
[0031] The synthesis scheme for preparation of monomers of the
general formula (II) is shown in Scheme 3.
##STR00006##
[0032] Proceeding from 1,3-di(biphenyl-3-yl)propan-2-one 7, which
already comprises the two flexible meta-biphenyl units, Knoevenagel
condensation with 4,4'-dihalobenzil introduces two halogen
functions for the later Yamamoto polymerization to obtain the
tetraarylcyclopentadienone 8. The cyclopentadienone 8 is converted
by Diels-Alder cycloaddition with optionally functionalized tolane
10 to give the monomer 6. This reaction can be performed in a
microwave reactor.
[0033] The graphene nanoribbon precursors are synthesized from the
monomer 6 by Yamamoto polymerization in the presence of a nickel
catalyst corresponding to Scheme 4. A suitable catalyst system
comprises Ni(COD).sub.2, 1,5-cyclooctadiene and 2,2'-bipyridine in
a toluene/DMF mixture as a solvent. The polymers formed can be
"end-capped", i.e. the terminal halogen functions can be exchanged
for phenyl, by addition of chlorobenzene or bromobenzene.
##STR00007##
[0034] The cyclodehydrogenation of the graphene nanoribbon
precursors 11 to give the graphene nanoribbons can be effected by
means of intramolecular Scholl reaction using, for example,
iron(III) chloride as a Lewis acid and oxidizing agent.
[0035] In general, the molecular weight of the graphene nanoribbons
obtained is 2000 to 100 000, preferably 4000 to 50 000, these
molecular weights being determinable by means of GPC.
[0036] Graphene nanoribbons can also be produced on metal surfaces.
This is done by depositing the monomer on the surface by
sublimation. This gives rise to diradicals which are polymerized by
a temperature increase to give the graphene nanoribbon precursor.
In the last step, further thermal treatment of the substrate
results in the cyclodehydrogenation to give the finished graphene
nanoribbons (see Cai, J.; et al. Nature 466, 470-473 (2010)).
[0037] The invention is illustrated in detail by the examples
below.
EXAMPLES
[0038] The figures show:
[0039] FIG. 1 the superimposed MALDI-TOF mass spectra of the
synthesized monomers 6a-c;
[0040] FIG. 2 the relevant aromatic region of the .sup.1H NMR
spectra of the synthesized monomers 6a-c;
[0041] FIG. 3 MALDI-TOF mass spectra of the polymer precursors
11a-c;
[0042] FIG. 4 the Raman spectrum of the GNR 12b;
[0043] FIG. 5 IR spectra of the GNR 12a, b.
EXAMPLES 1 TO 3
Monomer Synthesis
[0044] The synthesis scheme for preparation of monomers of the
general formula (II) 6a to 6c is shown in Scheme 5.
##STR00008##
[0045] Proceeding from 1,3-di(biphenyl-3-yl)propan-2-one 7, which
already comprises the two flexible meta-biphenyl units, Knoevenagel
condensation with 4,4'-dibromobenzil 9a or 4,4'-dichlorobenzil 9b
using tetrabutylammonium hydroxide as a base introduces two halogen
functions for the later Yamamoto polymerization. The
tetraarylcyclo-pentadienones 8a and 8b could not be removed from
the reactants by column chromatography, but selected precipitation
of the products was possible from DCM in methanol. Thus, 8a was
obtained with a yield of 77%, and 8b with 53%, as violet solids. In
the last reaction step, the solubility-imparting groups were
introduced and the cyclopentadienones were converted by Diels-Alder
cycloaddition with functionalized tolanes to give the target
compounds. Due to the high steric demands, this reaction had to be
performed in a microwave reactor at 220.degree. C. at 300 watts and
over a reaction time of 24 h. After column chromatography
purification with silica gel and repeated reprecipitation, all
monomers were purified by means of recycling GPC. In spite of an
associated reduction in yield, this high purity was necessary for
the achievement of high molecular weights in the polymerization.
Monomer 6a without alkyl radicals was thus obtained in 40% yield as
a colorless solid. Addition of 8b with 4,4'-didodecyltolane 10b
gave monomer 6b with a yield of 56%, and a reaction with
4,4'-bis(2-decyltetradecyl)tolane 10c gave monomer 6c with 41%
yield. Both alkylated products were obtained as colorless oils.
EXAMPLES
Example 1a
[0046]
2,5-Di([1,1'-biphenyl]-3-yl)-3,4-bis(4-bromophenyl)cyclopenta-2,4-d-
ienone (8a)
[0047] To a degassed solution of 2.84 g of 4,4'-dibromobenzil (7.73
mmol) and 2.80 g of 1,3-di(biphenyl-3-yl)propan-2-one (7, 7.73
mmol) in 30 ml of tert-butanol was added, at 80.degree. C., a
methanolic tetrabutylammonium hydroxide solution (1 M, 2.84 ml,
2.84 mmol). The reaction solution was stirred at 80.degree. C. for
20 minutes and then stopped by adding water. Extraction was
effected three times with dichloromethane, and the collected
organic phases were washed with saturated sodium chloride solution
and dried over magnesium sulfate before the solvent was distilled
off under reduced pressure. The crude product was purified by
column chromatography (silica gel, eluent: hexane with 20% DCM) and
gave 2.85 g of the tetraarylcyclopentadienone 8a as a violet wax
(53%, 4.10 mmol). Elemental analysis measured: C 70.5; H 3.3%
(calculated for C.sub.41H.sub.26Br.sub.2O: C, 70.9; H, 3.8%);
.sup.1H NMR (700 MHz, d.sub.8-THF) .delta.=7.51-7.49 (m, 4H, CH),
7.49-7.46 (m, 4H, CH), 7.41 (dd, J=8.2, 1.1 Hz, 4H, CH), 7.36 (t,
J=7.8 Hz, 4H, CH), 7.32 (t, J=8.0 Hz, 2H, CH), 7.29-7.25 (m, 2H,
CH), 7.25-7.22 (m, 2H, CH), 7.01-6.99 (m, 4H, CH); .sup.13C NMR
(175 MHz, d.sub.8-THF) .delta.=154.28, 141.92, 141.83, 133.58,
132.72, 132.34, 132.30, 132.12, 129.99, 129.89, 129.71, 129.53,
128.26, 127.80, 127.21, 126.74, 123.92; MS (FD, 8 kV): m/z (%):
693.8 (100) [M.sup.+] (calculated for C.sub.41H.sub.26Br.sub.2O:
694.0); Rf (hexane with 6% ethyl acetate)=0.47.
Example 1b
[0048]
1,2-Bis(4-bromophenyl)-3,6-bis(biphenyl-3-yl)-4,5-diphenylbenzene
(6a)
[0049] A degassed solution of 300 mg of
2,5-di([1,1'-biphenyl]-3-yl)-3,4-bis(4-bromophenyl)cyclopenta-2,4-dienone
(8a, 0.432 mmol) and 77.0 mg of 4,4'-dibromotolane (0.432 mmol) in
3 ml of diphenyl ether was heated to 230.degree. C. in a microwave
reactor at power 300 watts and a maximum pressure of 7 bar for
3.times.12 h. After cooling to room temperature, the reaction
solution was diluted with hexane and purified by column
chromatography (silica, hexane with 6% ethyl acetate). After
purification by means of recycling GPC and drying under high
vacuum, 145 mg of monomer 6a were obtained in the form of colorless
crystals (40%, 0.172 mmol). Elemental analysis measured: C 76.7; H
3.1% (calculated for C.sub.54H.sub.36Br.sub.2: C, 76.8; H, 4.3%);
.sup.1H NMR (700 MHz, d.sub.8-THF) .delta.=7.30-7.25 (m, 4H, CH),
7.23-7.17 (m, 6H, CH), 7.13 (d, J=1.5 Hz, 1H, CH), 7.12-7.11 (m,
1H, CH), 7.11-7.09 (m, 4H, CH), 7.09-7.06 (m, 2H, CH), 6.95 (s, 1H,
CH), 6.94 (br s, 2H, CH), 6.93 (s, 1H, CH), 6.91 (t, J=4.1 Hz, 2H,
CH), 6.89 (d, J=8.0 Hz, 2H, CH), 6.85 (d, J=7.0 Hz, 4H, CH), 6.83
(d, J=2.0 Hz, 2H, CH), 6.81 (d, J=1.4 Hz, 1H, CH), 6.79 (d, J=8.3
Hz, 2H, CH), 6.78 (s, 1H, CH); .sup.13C NMR (125 MHz, d.sub.2-TCE)
.delta.=141.05, 140.74, 140.20, 140.00, 139.44, 139.03, 138.52,
133.03, 132.92, 131.30, 131.15, 130.26, 129.92, 129.85, 128.42,
127.17, 126.87, 126.62, 126.52, 125.20, 124.15, 120.18, 119.51; MS
(MALDI-TOF): m/z (%): 845.1 (100) [M.sup.+] (calculated for
C.sub.54H.sub.36Br.sub.2: 844.1); Rf (hexane with 6% ethyl
acetate)=0.40; m.p. (.degree. C.): decomposition at >400.degree.
C.
Example 2a
[0050]
2,5-Di([1,1'-biphenyl]-3-yl)-3,4-bis(4-chlorophenyl)cyclopenta-2,4--
dienone (8b)
[0051] To a degassed solution of 940 mg of 4,4'-dichlorobenzil
(3.37 mmol) and 1.22 g of 1,3-di(biphenyl-3-yl)propan-2-one (7,
3.37 mmol) in 20 ml of tert-butanol was added, at 80.degree. C., a
methanolic tetrabutylammonium hydroxide solution (1M, 1.7 ml, 1.7
mmol). The reaction solution was stirred at 80.degree. C. for 20
minutes, and the reaction then stopped by adding water. The mixture
was extracted three times with dichloromethane and the collected
organic phases were washed with saturated sodium chloride solution
and dried over magnesium sulfate, before the solvent was distilled
off under reduced pressure. The crude product was purified by
column chromatography (silica gel, eluent: hexane with 20% DCM) and
gave 1.56 g of the tetraarylcyclopentadienone 8b as a pale violet
solid (77%, 2.58 mmol). Elemental analysis measured: C 81.3; H 3.3%
(calculated for C.sub.41H.sub.26Cl.sub.2O: C, 81.3; H, 4.3%);
.sup.1H NMR (700 MHz, d.sub.8-THF) .delta.=7.52 (s, 2H, CH), 7.50
(d, J=7.8 Hz, 2H, CH), 7.42 (d, J=7.2 Hz, 4H, CH), 7.36 (t, J=7.7
Hz, 4H, CH), 7.32 (m, 6H, CH), 7.27 (t, J=7.3 Hz, 2H, CH), 7.23 (d,
J=7.8 Hz, 2H, CH), 7.06 (d, J=8.5 Hz, 4H, CH); .sup.13C NMR (175
MHz, d.sub.8-THF) .delta.=199.86, 154.28, 141.91, 141.82, 135.61,
133.14, 132.14, 132.10, 129.98, 129.90, 129.70, 129.69, 129.52,
128.27, 127.78, 127.20, 126.73; MS (MALDI-TOF): m/z (%): 604.6
(100) [M.sup.+] (calculated for C.sub.41H.sub.26Cl.sub.2O: 604.1);
Rf (hexane with 10% ethyl acetate)=0.47.
Example 2b
[0052]
1,2-Bis(4-chlorophenyl)-3,6-bis(biphenyl-3-yl)-4,5-bis(4-dodecylphe-
nyl)benzene (6b)
[0053] A degassed solution of 1.84 g of
2,5-di([1,1'-biphenyl]-3-yl)-3,4-bis(4-chlorophenyl)cyclopenta-2,4-dienon-
e (8b, 3.03 mmol) and 1.72 g of 4,4'-didodecyltolane (3.34 mmol) in
12 ml of diphenyl ether and 5 ml of propylene carbonate was heated
to 230.degree. C. in a microwave reactor at power 300 watts and a
maximum pressure of 7 bar for 2.times.12 h. After cooling to room
temperature, the reaction solution was diluted with hexane and
purified by column chromatography (silica, hexane with 6% ethyl
acetate). After purification by means of recycling GPC and drying
under high vacuum, 1.85 g of monomer 6b were obtained as a
colorless oil (56%, 1.69 mmol). Elemental analysis measured: C
85.6; H 7.9% (calculated for C.sub.78H.sub.84Cl.sub.2: C, 85.8; H,
7.8%); .sup.1H NMR (700 MHz, d.sub.8-THF) .delta.=7.27 (dt, J=7.7,
4.0 Hz, 4H, CH), 7.22-7.16 (m, 6H, CH), 7.10 (d, J=10.0 Hz, 4H,
CH), 6.94 (t, J=7.7 Hz, 4H, CH), 6.91 (s, 2 Hv), 6.88 (d, J=8.4 Hz,
2H, CH), 6.87-6.81 (m, 2H, CH), 6.81-6.77 (m, 2H, CH), 6.77-6.70
(br m, 6H, CH), 6.66 (d, J=7.5 Hz, 2H, CH), 2.41-2.28 (m, 4H,
.alpha.-CH.sub.21), 1.44-1.34 (m, 4H, .beta.-CH.sub.2), 1.34-1.03
(m, 36H, --CH.sub.2--), 0.89 (t, J=6.9 Hz, 6H, --CH.sub.3);
.sup.13C NMR (175 MHz, d.sub.8-THF) .delta.=142.44, 142.42, 142.27,
141.88, 141.74, 140.76, 140.74, 140.68, 140.59, 140.56, 140.14,
140.10, 139.09, 139.05, 134.18, 134.14, 134.06, 134.01, 132.56,
132.50, 132.47, 132.30, 132.26, 131.69, 131.41, 129.37, 128.20,
128.07, 127.90, 127.88, 127.84, 127.81, 127.80, 127.74, 125.14,
125.12, 36.36, 36.33, 33.06, 32.37, 32.34, 30.85, 30.81, 30.77,
30.75, 30.61, 30.60, 30.51, 30.00, 29.98, 25.94, 25.82, 23.74,
14.62; MS (MALDI-TOF): m/z (%): 1091.0 (100) [M.sup.+] (calculated
for C.sub.78H.sub.84Cl.sub.2: 1090.6); Rf (hexane with 6% ethyl
acetate)=0.65.
Example 3
[0054]
1,2-Bis(4-chlorophenyl)-3,6-bis(biphenyl-3-yl)-4,5-bis(4-(2-decylte-
tradecyl)dodecylphenyl)benzene (6c)
[0055] A degassed solution of 636 mg of
2,5-di([1,1'-biphenyl]-3-yl)-3,4-bis(4-chlorophenyl)cyclopenta-2,4-dienon-
e (8b, 1.05 mmol) and 895 mg of 4,4'-bis(2-decyltetradecyl)tolane
(1.05 mmol) in 10 ml of diphenyl ether was heated to 230.degree. C.
in a microwave reactor at power 300 watts and a maximum pressure of
7 bar for 2.times.12 h. After cooling to room temperature, the
reaction solution was diluted with hexane and purified by column
chromatography (silica, hexane with 6% ethyl acetate). After
purification by means of recycling GPC and drying under high
vacuum, 613 mg of monomer 6c were obtained as a colorless oil (41%,
0.429 mmol). Elemental analysis measured: C 86.0; H 9.7%
(calculated for C.sub.102H.sub.132Cl.sub.2: C, 85.8; H, 9.3%);
.sup.1H NMR (700 MHz, d.sub.8-THF) .delta.=7.29-7.25 (m, 4H, CH),
7.20 (m, 6H, CH), 7.14 (s, 1H, CH), 7.11 (d, J=10.0 Hz, 3H, CH),
6.95-6.88 (m, 9H, CH), 6.85 (d, J=8.4 Hz, 1H, CH), 6.81 (d, J=8.0
Hz, 1H, CH), 6.79 (d, J=7.8 Hz, 2H, CH), 6.77 (d, J=7.7 Hz, 1H,
CH), 6.73 (d, J=7.8 Hz, 2H, CH), 6.69 (t, J=7.6 Hz, 2H, CH), 6.64
(d, J=7.9 Hz, 2H, CH), 2.33-2.24 (m, 4H, .alpha.--CH.sub.2),
1.44-1.37 (m, 2H, .beta.--CH.sub.2), 1.35-0.95 (br m, 80H,
--CH.sub.2--), 0.89 (m, 12H, --CH.sub.3); .sup.13C NMR (175 MHz,
d.sub.8-THF) .delta.=142.43, 142.41, 142.20, 142.18, 141.94,
141.77, 140.69, 140.65, 140.55, 140.52, 140.10, 140.07, 139.61,
139.08, 134.13, 134.04, 133.98, 132.48, 132.31, 132.13, 131.70,
131.37, 129.41, 128.67, 128.53, 128.21, 128.07, 127.87, 127.77,
125.08, 40.92, 40.61, 33.94, 33.86, 33.81, 33.08, 33.06, 31.20,
31.12, 31.10, 30.89, 30.86, 30.82, 30.54, 30.52, 27.49, 27.45,
25.93, 25.82, 23.76, 23.75, 14.63; MS (MALDI-TOF): m/z (%): 1427.8
(100) [M.sup.+] (calculated for C.sub.102H.sub.132Cl.sub.2:
1428.0); Rf (hexane with 6% ethyl acetate)=0.76.
[0056] FIG. 1 shows the superimposed MALDI-TOF mass spectra of the
synthesized monomers 6a-c. It was possible in all three cases to
obtain the products in pure form and to ensure that no by-products
which could have caused termination of chain growth during the
later polymerization were present any longer. The exact structure
of the monomers was confirmed by .sup.1H NMR spectroscopy.
[0057] FIG. 2 shows the relevant aromatic region of the .sup.1H NMR
spectra of monomers 6a-c, recorded in d.sub.8-THF (700 MHz, RT).
The .sup.1H NMR spectra of monomers 6a-c can be resolved only with
difficulty since all 34 to 36 aromatic protons exhibited a very
similar chemical shift. The signals are within a narrow range from
6.6 to 7.3 ppm, and some are superimposed. By means of DOSY
(diffusion-ordered spectroscopy), the diffusion properties of the
molecules in the sample can be determined, and COSY experiments can
determine couplings between the signals of conjugated protons in
the NMR.
Examples 4 to 6
Polymer Synthesis
[0058] Once the structure and purity of monomers 6a-c had been
confirmed, the corresponding polymers were synthesized by Yamamoto
polymerization according to Scheme 6.
##STR00009## ##STR00010##
[0059] Scheme 6 shows the synthesis of the graphene nanoribbon
precursors 11a-c by Yamamoto polymerization of the dihalogenated
monomers 6a-c with catalysis by Ni(COD)2, 1,5-cyclooctadiene and
2,2'-bipyridine in toluene/DMF. The yields were (i) 84%, (ii) 86%,
(iii) 67%. Since the catalytically active nickel(0) reagent in the
Yamamoto polycondensation is very sensitive to water and oxygen,
all monomer units 6 were dried under high vacuum before they were
used for the polymerization. The catalyst mixture composed of 59.4
mg of Ni(COD).sub.2, 23.4 mg of 1,5-cyclooctadiene and 33.7 mg of
2,2'-bipyridine (0.216 mmol of each) was weighed out in a glovebox
under an argon atmosphere and prepared together with the solvents
in a microwave-compatible glass reaction vessel, sealed with a
gas-tight aluminum lid with septum and protected from any incident
light. The use of a microwave reactor to conduct the reaction gives
the advantage of a distinctly increased reaction rate and a
reaction temperature above the boiling point of the solvents. After
the thermal activation of the catalyst at 60.degree. C. for 20
minutes, a degassed solution of 0.09 mmol of the monomer in 1 ml of
anhydrous toluene was introduced into the reaction vessel through
the septum, and the polymerization was performed at microwave power
300 watts and 80.degree. C. over a period of 10 hours. A monomer
concentration of about 50 mg/ml was used to promote the attainment
of high molecular weights. To end-cap the polymers, a degassed
solution of bromo-/chlorobenzene in toluene (0.5 ml, 0.01 molar)
was finally added, and the mixture was heated again to 80.degree.
C. for 20 minutes. To purify the products and remove catalyst
residues, the reaction solution was added dropwise to an
HCl/methanol mixture and stirred overnight. The resulting
precipitate was removed in a centrifuge and repeatedly
reprecipitated with THF in methanol, before it was filtered off and
dried under reduced pressure. The polymers 11a without alkyl
radicals and 11b with dodecyl chains were obtained in yields of 84
to 86% as colorless solids. Only by the introduction of branched
2-decyltetradecyl radicals was the melting point lowered to such an
extent that the polymer 11c was present as a colorless oil at room
temperature. Before the subsequent cyclodehydrogenation to give the
corresponding GNRs, low molecular weight oligomers were removed by
a manual preparative GPC fractionation. This was possible since all
three polymers were fully soluble in common organic solvents such
as THF, DCM or toluene.
Example 4
[0060] The monomer used was 76.0 mg of
1,2-bis(4-bromophenyl)-3,6-bis(biphenyl-3-yl)-4,5-diphenylbenzene
(6a, 0.09 mmol). After conclusion of the reaction and cooling to
room temperature, a colorless precipitate had already formed. After
purification of the crude product, 43.7 mg of the polymer 11a were
obtained as a colorless solid (84%). GPC analysis:
Mn=0.11.times.10.sup.4 g/mol, M.sub.w=0.15.times.10.sup.4 g/mol,
polydispersity D=1.35 (UV detector, PS standard), DSC (.degree.
C.): no transitions.
Example 5
[0061] The monomer used was 98.3 mg of
1,2-bis(4-bromophenyl)-3,6-bis(biphenyl-3-yl)-4,5-bis(4-dodecylphenyl)ben-
zene (6b, 0.09 mmol). After conclusion of the reaction and cooling
to room temperature, the reaction solution had turned dark brown,
and there was a black precipitate on the flask wall. After
purification of the crude product, 79.0 mg of polymer 11b were
obtained as a colorless solid (86%). GPC analysis:
M.sub.n=0.93.times.10.sup.4 g/mol, M.sub.w=1.25.times.10.sup.4
g/mol, polydispersity D=1.34 (UV detector, PS standard), DSC
(.degree. C.): no transitions.
Example 6
[0062] The monomer used was 128.6 mg of
1,2-bis(4-bromophenyl)-3,6-bis(biphenyl-3-yl)-4,5-bis(4-(2-decyltetradecy-
l)dodecylphenyl)benzene (6c, 0.09 mmol). After conclusion of the
reaction and cooling to room temperature, the reaction solution had
turned dark brown, and there was a black precipitate on the flask
wall. After purification of the crude product, 81.9 mg of polymer
11c were obtained as a colorless oil (67%). GPC analysis:
M.sub.n=0.35.times.10.sup.4 g/mol, M.sub.w=0.48.times.10.sup.4
g/mol, polydispersity D=1.37 (UV detector, PS standard), DSC
(.degree. C.): no transitions.
[0063] The molecular weights attained in polymers 11a-c were
determined by MALDI-TOF MS and GPC analysis. Since no suitable
standard was available for a GPC analysis, a polystyrene standard
was used due to the angled backbone of the polymers. MALDI-TOF MS
is subject to the limitation that detection of high molecular
weight species was impossible due to the polydispersity of the
samples. The data obtained here therefore permit only conclusions
about the minimum molecular weights in the sample. The MALDI-TOF
mass spectra recorded for polymer precursors 11a-c are reproduced
in FIG. 3.
[0064] The analysis of polymers 11a-c by means of MALDI-TOF MS
showed that very regular signal patterns were observed in all
cases, for which there was a high level of correspondence between
the spacings of the signals and the calculated molecular weights of
the respective repeat units. In the case of 11a, the intense
signals were assigned to the fully debrominated product. The weak
signals arose through adsorption of silver ions during the
ionization, and were not observed in reflector mode. It was
possible to detect molecular weights up to 5000 g/mol, which
corresponded to a maximum of seven repeat units. In the case of
polymer 11b with dodecyl chains, molecular weights of up to 20 000
g/mol (19 repeat units) were detected. In the case of polymer 11c,
seven repeat units with a molar mass up to 10 000 g/mol were
detected.
[0065] Since all three polymers 11a-c (apart from the alkyl
radicals) had the same repeat unit, it was easily possible to
convert the molecular weights to the chain length. This length
corresponded to the later longitudinal dimension of the GNRs after
the cyclodehydrogenation. For the graphene nanoribbon precursor 11b
with dodecyl chains, the molar mass of 20 000 g/mol corresponded to
a later graphene ribbon with a width of 2.1 nm and a length of
about 12 nm (.about.1.2 nm/repeat unit).
Examples 7 to 9
Cyclodehydrogenation
[0066] The cyclodehydrogenation of the polymer precursors 11a-c to
give the corresponding GNRs 12a-c according to Scheme 7 was
performed by means of intramolecular Scholl reaction using
iron(III) chloride as the Lewis acid and oxidizing agent.
##STR00011##
[0067] Typically, the reaction was performed with a very low
polymer concentration of 1 mg/ml in unstabilized dichloromethane in
order to prevent the occurrence of intermolecular aryl-aryl
couplings. The reaction solutions were degassed with an argon
stream over the entire reaction time in order to drive out oxygen
and the HCl which formed. At the start of the reaction, six
equivalents of iron(III) chloride per bond to be formed (90
equivalents per repeat unit) were added rapidly as a concentrated
solution in nitromethane, and the mixture was stirred at room
temperature for three days. After the cyclodehydrogenation had
concluded, the GNRs were precipitated with methanol and purified
further.
[0068] GNR 12a without alkyl radicals and GNR 12b with dodecyl
radicals were obtained with a yield of 64 and 98% as black solids,
which were insoluble in standard organic solvents such as toluene,
THF, tetrachloroethane or chloroform. With a width of the graphene
ribbon of 2.1 nm, there were such strong p-p interactions that two
dodecyl radicals per repeat unit in the case of 12b were
insufficient to prevent aggregation. For workup, the crude products
were therefore freed of all soluble impurities by Soxhlet
extraction with THF and methanol, and finally dried under high
vacuum. GNR 12c with 2-decyltetradecyl chains, in contrast, was
obtained in a yield of 81% as a black solid, which was soluble in
standard organic solvents such as THF or toluene. The purification
was therefore effected by repeated reprecipitation from THF in
methanol and subsequent Soxhlet extraction with acetone, in order
to remove impurities, by-products products and inorganic
residues.
Example 7
[0069] 50 mg of polymer precursor 11a were reacted with 1.12 g of
FeCl.sub.3 (6.87 mmol, dissolved in 4 ml of nitromethane). After a
reaction time of three days, a black precipitate had already
formed, which was removed in a centrifuge. For purification, the
crude product was in each case subjected to a two-day Soxhlet
extraction with THF and methanol, and finally dried under high
vacuum. Thus, 32.0 mg of the GNR 12a were obtained as a black
insoluble solid (64%). DSC (.degree. C.): no transitions.
Example 8
[0070] 76.6 mg of polymer precursor 11b were reacted with 1.10 g of
FeCl.sub.3 (6.76 mmol, dissolved in 3.5 ml of nitromethane). After
a reaction time of three days, a black precipitate had already
formed, which was removed in a centrifuge. For purification, the
crude product was in each case subjected to a two-day Soxhlet
extraction with THF and methanol, and finally dried under high
vacuum. Thus, 72.9 mg of the GNR 12b were obtained as a black
insoluble solid (98%). DSC (.degree. C.): no transitions.
Example 9
[0071] 38.11 mg of polymer precursor 11c were reacted with 410 mg
of FeCl.sub.3 (2.53 mmol, dissolved in 1.3 ml of nitromethane).
After addition of the methanol, a black precipitate formed, which
was removed in a centrifuge and freed of all impurities,
by-products and inorganic residues by reprecipitation from THF in
methanol and subsequent two-day Soxhlet extraction with acetone.
After drying under high vacuum, 30.2 mg of the GNR 12c were
obtained as a black solid (81%). DSC (.degree. C.): no
transitions.
[0072] The complete cyclodehydrogenation and the defect-free
structure of the GNRs 12a-c were demonstrated by means of Raman and
IR spectroscopy. FIG. 4 shows the Raman spectrum of the GNR 12b,
recorded in a thin powder film with laser excitation at .lamda.=488
nm. Raman spectroscopy allowed relevant information about the
extent of the .pi.-system within the GNRs to be obtained, and thus
the conjugation length to be calculated. By IR absorption
measurements, it was possible to examine the presence of a band at
4050 cm.sup.-1 for all samples, which was characteristic of the
free rotation of phenyl rings and, in the case of full
cyclodehydrogenation, was no longer detectable. GNR 12b was the
only sample which showed no fluorescence in the solid state, and
thus allowed the recording of Raman spectra on thin powder films
with a laser excitation wavelength of 488 nm. The spectrum obtained
is shown in FIG. 4. Good resolution was obtained both for the
characteristic D band at 1331 cm.sup.-1 and the sharp G band at
1579 cm.sup.-1. The position of these bands corresponded to a high
degree with values known from literature for graphene ribbons,
which confirmed the graphene character of the sample. At multiples
of these wavenumbers, it was also possible to find the second- and
third-order signals. For a calculation of the dimensions L.sub.a of
the GNR 12b, the ratio of the integrals (I) of first-order D and G
bands was converted by the formula I(D)/I(G)=C(.lamda.)/L.sub.a.
C(.lamda.) was a wavelength-dependent factor, which assumed the
value C(.lamda.)=4.4 nm for .lamda.=488 nm. Thus, a dimension of
4.6 to 4.7 nm was calculated, which corresponded to a graphene
ribbon with about eight repeat units and a molecular weight of
about 8000 g/mol.
[0073] The completeness of the cyclodehydrogenation of the GNRs 12a
and 12b was additionally confirmed by IR spectroscopy. FIG. 5 shows
the IR spectra of the GNRs 12a and 12b. The band at 4050 cm.sup.-1
was characteristic in each case of the free rotation of phenyl
rings, and it was observed clearly in the spectrum of the polymer
precursors 11a and 11b (upper lines). After conclusion of the
cyclodehydrogenation, complete absence of this band (lower lines)
ruled out the presence of uncondensed phenyl rings in the
molecules, and hence proved the complete cyclodehydrogenation.
* * * * *