Isomerically Pure Star-Shaped Triphenylene–Perylene Hybrids Involving Highly Extended π-Conjugation

Article abstract of DOI:10.1002/chem.201705872

The synthesis and characterization of a new type of a highly conjugated heterocyclic π-chromophore, consisting of a central triphenylene core fused with three perylene monoimide units (star-shaped molecules), is described. By judicious bay functionalizati

Full text of DOI:10.1002/chem.201705872

A Journal of
Accepted Article
Title: Isomerically Pure Star-Shaped Triphenylene-Perylene Hybrids
Involving Highly Extended π Conjugation
Authors: Edurne Nuin, Vicent Lloret, Konstantin Amsharov, Frank
Hauke, Gonzalo Abellán, and Andreas Hirsch
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To be cited as: Chem. Eur. J. 10.1002/chem.201705872
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Isomerically Pure Star-Shaped Triphenylene-Perylene Hybrids
Involving Highly Extended π Conjugation
Edurne Nuin[1], Vicent Lloret[1,2], Konstantin Amsharov[1], Frank Hauke[1,2], Gonzalo Abellán[1,2] and
Andreas Hirsch[1,2]
*
Abstract: The synthesis and characterization of a new type of a
highly conjugated heterocyclic π-chromophore, consisting of
studied as exciting building blocks for the supramolecular
construction of aggregates, but when it comes to π-extended
PDI-based macromolecules, like n-type disk-shaped molecular
systems, the number of studies is very scarce. These molecules
endowed with C3 symmetry exhibit appealing spectroscopic
effects of interest in highly anisotropic media like liquid crystals
as well as in molecular electronics.[1,3] Usually, disk-shaped
molecules containing polycyclic aromatic cores have a strong
tendency to aggregation into 1D columns, endowing them with
anisotropic charge transport properties. Along this front, Liu and
co-workers developed a PDI-based C3-symmetric star-shaped
molecular skeleton exhibiting good electron mobility with a
remarkably charge transport anisotropy.[24,25] However, these
systems strongly aggregate and are almost insoluble in common
organic solvents, severely limiting their characterization (e.g. by
1H NMR) and processability. Moreover, as a consequence of the
condensation reaction between hexaaminotriphenylene and the
corresponding anhydrides, these trimeric molecules are
obtained as a statistical mixture of cis- (symmetric) and trans-
(asymmetric) isomers, which to the best of our knowledge, have
never been successfully separated.
a
central triphenylene core fused with three perylene–monoimide units
(star-shaped molecule) is described. By judicious bay-
functionalization with tert-butylphenoxy substituents, aggregation
was completely prevented in common organic solvents, allowing for
a straightforward purification and, for the very first time, the complete
separation of the constitutional isomers by HPLC. Both isomers can
be easily distinguished by means of several conventional
spectroscopic techniques. Furthermore, we have illustrated the
absence of supramolecular aggregates and enhanced processability
by noncovalent functionalization of graphene substrates, showing an
outstanding homogeneity and observing a different doping behavior
in both isomers, being possible to distinguished by Raman
spectroscopy.
Introduction
Perylenetetracarboxylic diimide (PDI)-based materials have
become increasingly attractive due to their good charge-carrier
mobilities, excellent light absorption in the wavelength range of
the visible light, as well as high thermal, chemical, and
photostability.[1–9] Beyond optoelectronics, PDIs have been
extensively used in the dispersion and noncovalent
functionalization of synthetic carbon allotropes such as carbon
nanotubes or graphene and in novel 2D materials.[10–13]
Moreover, in the last years several efforts have been devoted to
the design and synthesis of highly extended heterocyclic π
Herein, we designed and synthesized
a highly extended
conjugated star-shaped molecule (see Scheme 1) that contains
a triphenylene core fused with three bay-functionalised twisted
peryleneimide imidazole “arms”. Although these architectures do
not contain long and highly flexible side groups in their imide
periphery they are highly soluble in organic solvents.[26]
Moreover, we successfully separated constitutional isomers by
means of HPLC for the very first time, and differentiated them
using several spectroscopic techniques including NMR and
Raman spectroscopy. Further we have found that these isomer-
pure star-shaped molecules form densely packed molecular
films on CVD graphene with exceptionally high homogeneity.
systems with extraordinarily large seas of conjugated
π
electrons.[14,15] A characteristic feature of this family is the
continuous bathochromic shift of the absorption and
fluorescence emission bands as a consequence of the extension
of the conjugated π-system.[1,16–21]
The arrangement of PDI-based molecules can be tailored by
supramolecular design, inducing perylene core twisting enforced
by bay substituents, by the attachment of trialkoxyphenyl
wedges, or by a head-to-tail alignment through hydrogen-
bonding interactions.[22,19,23,9] PDIs have been extensively
Results and Discussion
The targeted star-shaped PDI (Scheme 1) was assembled by
the condensation of hexamino triphenylene and perylene
monoimide building blocks requiring
a multistep synthetic
sequence. One of the most common features in highly extended
π systems is their tendency to aggregate via π-π stacking
leading to virtually insoluble materials that complicate their
purification, characterization, and processing.[27–30] To overcome
this hurdles, a widespread approach to obtain soluble aromatic
system derivatives is based on the incorporation of bulky
solubilising groups or long alkyl chains in the periphery[19,31] as
well as by distortion of their planarity.[28,32] Specifically, the
methodology for the synthesis of soluble PDI derivatives is the
introduction of branched or long alkyl tails at the imide
positions[19,30] and bulky groups like p-tert-butilphenoxy at the
bay positions.[20,33,19,23] As expected, the incorporation of four
bulky aryloxy groups attached to the bay positions of each PDI
[a]
[b]
Dr. E. Nuin, V. Lloret, Dr. K. Amsharov, Dr. F. Hauke, Dr. G.
Abellán, Prof. Dr. A. Hirsch
Chair of Organic Chemistry II
Friedrich-Alexander-Universität Erlangen-Nürnberg
Henkestr. 42
91054 Erlangen, Germany
V. Lloret, Dr. F. Hauke, Dr. G. Abellán, Prof. Dr. A. Hirsch
Joint Institute of Advanced Materials and Processes
Friedrich-Alexander-Universität Erlangen-Nürnberg
Dr.-Mack-Str. 81
90762 Fürth, Germany
Supporting information for this article is given via a link at the end of
the document.
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derivative arm lead to a significant distortion of the planar
geometry of the PDI moiety. This is attributed to the repulsive
interactions between these sterically encumbered substituents
and consequently the PDI twisted out position from the plane
preventing the intermolecular π-π stacking.[34–36] Hence,
according to Scheme 1, the first part of the synthetic approach
started
from
the
1,6,7,12-tetrachloroperylene-3,4:9,10-
tetracarboxylic dianhydride 1
O
N
O
O
O
O
O
O
N
O
O
N
O
a)
b)
c)
O
O
O
O
Cl
Cl
Cl
Cl
O
O
O
O
Cl
Cl
Cl
Cl
O
O
O
O
O
O
N
3
O
O
N
O
g)
1
4
2
N
H2N
Br
Br
NH2
N
x 6 HCl
NH2
d)
e)
f)
N
H2N
H2N
Br
Br
N
N
Br
Br
NH2
N
5
8
6
7
O
N
O
Constitutional isomers
O
N
N
O
O
O
O
C3h
O
N
N
O O
O O
O
N
O
N
g)
N
O
N
N
O
O
O
O
O
Cs
O
O
N
N
O
N
N
N
O
9
Scheme 1. Synthetic sequence of 9. Reagents and conditions: a) 3-Pentylamine, imidazole, 3 h, 100 ºC, N2; b) 4-tert-butylphenol, K2CO3, NMP, 16 h, 120 °C; c)
KOH, isopropanol:H2O mixture, 1.5 h, 100 °C; d) Br2, Fe powder, nitrobenzene, 16 h, 205 °C; e) benzophenone imine, Pd2(dba)3, rac-BINAP, NaOC(CH3)3,
toluene, 16 h, 110 °C, N2; f) HCl 2M, THF, 30 min, rt; g) Zn(OAc)2, dry quinoline, 18 h, 180 ºC, N2.
Thus, an imidization reaction of
1
with 3-pentylamine in
monoanhydride 4 in 18 % yield as a red solid (see Figures S1–
2).
imidazole at 100 ºC under N2 provides, after acidic work-up, the
symmetrically N,N-substituted PDI (2) as a red solid with 83 %
yield. The subsequent nucleophilic substitution of bay chlorine
atoms by 4-tert-butylphenolate in deaerated NMP at 120ºC
yielded tetraphenoxyperylene dimide 3, which was subsequently
partially hydrolyzed to afford the perylene monoimide
Once 4 was obtained, the second part of the synthetic procedure
consisted in the preparation of the triphenylene core (Scheme 1
center).[37,38] Thus, reaction of triphenylene
5 with Br2 in
nitrobenzene at 205°C in the presence of Fe powder provides 6
with 85% yield. Then, cross coupling reaction of the brominated
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were explored and despite the good solubility of the molecule,
the 1H NMR spectra resulted to be very broad even at high
temperatures (see Figure S3). This is due to the interactions
with the solvent and the balance of π–π interactions between
the extended π systems. However, the strong π–π interactions
could be overcome by using 1,1,2,2-tetrachloroethane-d2,
resulting in sharper NMR signals, indicative of a reduced
aggregation. Additionally, the behavior of 9 under temperature-
dependent 1H NMR spectra was investigated. Figure 1 shows
the 1H NMR spectrum of 9 in 1,1,2,2-tetrachloroethane-d2
measured at 363 K, in which the aromatic proton signals
became sharpened and a much better resolution was observed
(see Figures 1 and S4). Nonetheless, despite all the dilution
conditions applied in the spectroscopic measurements, the full
characterization based on the analysis of 13C NMR spectroscopy
failed to reliably confirm the proposed structure. This may be
attributed to the residual aggregation of the molecules in the
selected deuterated solvent even at elevated temperatures.
Further characterization by high-resolution mass spectrometry
measurements was conducted to verify the composition of the
final product (see Figure 2 inset).
N
O
O
O
O
O
O
O
O
O
O
O
O
O
N
O
N
O
O
O
O
As can be seen in the inset of Scheme 1, a mixture of all-trans-
(C3h symmetry) and mono-cis (Cs symmetry) isomers resulting
from the random orientation of the perylene monoimide during
the condensation reaction on the central hexaminotriphenylene
of compound 9 was formed. Analysis of the 1H NMR spectrum of
the final compound presented in Figure 1 revealed two sets of
signals with different intensities in the aromatic region indicating
that 9 was a statistical mixture of the C3h and Cs isomer with
yields of ca. 25 % and 75 %, respectively.
The separation of the isomers of 9 was expected to be very
challenging. Indeed, only a few reports on the separation of 1,6-
and 1,7-regioisomers of dibromo, diphenoxy, and dipyrrolidinyl
substituted perylene diimides derivatives have been reported so
far. Typical separation routes consist of crystallization[39] or
differences in solubility.[40] In the case of π-extended molecules
the separation of individual isomers appears to be challenging,
firstly because of relatively poor solubility, and secondly due to a
very similar chromatographic mobilities.
Figure 1. 1H NMR spectrum of compound 9 in 1,1,2,2-tetrachloroethane-d2 at
363 K.
triphenylene with benzophenone imine in toluene catalyzed by
Pd2(dba)3 using rac-BINAP as ligand in the presence of
NaOC(CH3)3 afforded 7 as a yellow solid in good yield. The last
stage in building up the structure of the star-shaped target
molecule consisted in linking the individual perylene monoimide
monoanhydride 4 with 7.
To face this challenge, high-performance liquid chromatography
(HPLC) with a COSMOSIL-5PBB-R semi preparative column (10
× 250 mm) using CH2Cl2:toluene:MeOH - (25:35:40) mixture as
selected mobile phase was employed. Figure 2 shows the HPLC
profile of 9, whose peaks could be assigned to the C3h and Cs
isomer based on their relative intensities. The configurations of
isolated isomers were unambiguously assigned on the basis of
1H NMR analysis of signals of the perylene core and
After deprotection of the amino groups, which was carried out
with 2M HCl in THF to furnish 8 in 81 % yield. Finally, the target
molecule was successfully obtained in one step from 4 by
reaction with 8 in dry quinoline in the presence of Zn(OAc)2 at
180 ºC for 18 h. Under these conditions, final 9 was isolated as a
dark blue solid in 53% yield (Scheme 1 bottom). As expected
this large π-conjugated architecture exhibits a pronounced
aggregation leading to difficulties in its processing and
characterization.[24] Indeed, despite the introduction of the bay-
functional tert-butoxy moieties – which remarkably improved the
1
triphenylene core protons. The H NMR spectra of the C3h and
Cs isomer of 9 as well as its statistical mixture in 1,1,2,2-
tetrachloroethane-d2 at 363 K are presented in Figures 3 and
S5–6. The 1H NMR of the Cs isomer (Figure 3 top) exhibits 6
singlets between 9.05–9.85 ppm (bay region in the
triphenylenecore). As expected 12 protons of the perylene
moiety appears in the region of 8.18–8.70 ppm (according
integration), although only 11 singlets can be detected because
of overlapping of two signals. Hence, the
1
solubility of the molecule – the H NMR spectrum of 9 recorded
in chloroform-d1 at room temperature showed a significant
signal broadening in the aromatic region caused by aggregation.
One approach to circumvent this problem is to change the
deuterated reference solvent. Along this front, different organic
solvents like benzene-d6 or dichloromethane-d2 among others
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Figure 4. AFT-IR spectra of the C3h (red) and Cs (blue) isomer of 9 in the
region between 1600-1850 cm-1.
Figure 2. HPLC profile of 9 COSMOSIL-5PBB-R (10 × 250 mm; eluent
CH2Cl2:toluene:MeOH 25:35:40; flow rate 5.0 mL/min; 50 ºC; detection 630
nm). The collection regions are highlighted by blue (Cs isomer) and green (C3h
isomer). Insert: MALDI mass spectrum of 9 and calculated and experimentally
observed isotopic distribution MS pattern.
isomers, respectively (Figure 4). It is worth noting that, in
addition to these vibrations, the FT-IR spectrum displayed an
additional signal at 1735 cm-1, which is remarkable more intense
for the Cs isomer. The lower molecular symmetry increases the
molecular dipole moment, which typically enhance IR active
vibrational modes. Thus, the band at 1735 cm-1 is assigned to
C=O vibration of the asymmetric N-imine carbonyl because of
the C3 symmetry breaking in the Cs isomer.[41]
Steady-state absorption studies in 1,1,2,2-tetrachloroethane at
298 K of the target molecule as well as the different building
blocks were carried out. The UV-Vis absorption spectrum of 4
and 9 is dominated by characteristic π–π* transitions showing a
maximum absorption at 592 and 645 nm, respectively (Figure 5).
It is noteworthy to mention that 9 exhibited a bathochromic shift
of 53 nm in the absorption maximum, attributed to the extensive
conjugation of its 156 π electrons in the star-shaped molecule,
higher than those previously observed for benz-bimidazole-
bridged perylenes[15] or fused perylene–phthalocyanine
hybrids.[14]
assignment of the first elution phase at 6.1 min to the isomer
with Cs symmetry based on the peaks intensity of the HPLC
chromatogram was confirmed. For the minor isomer (second
elution phase at 7.2 min) 2 and 4 singlets (triphenylene and
perylene protons, respectively), were detected in agreement with
the expected C3h symmetry (Figure
3 center). The NMR
spectroscopic data recorded for 9 (Figure 3 bottom) exhibited
the combination of both isomer signals in the spectrum.
The successful isomers separation was further evidenced by
attenuated total reflectance infrared spectroscopy (ATR-FTIR).
The direct comparison of the spectra of the C3h and Cs isomers
revealed a rather similar behavior (see Figure 4 and S7). In both
cases, characteristic stretching vibrations of perylene derivatives
at 1694(1690) cm-1 and 1654(1653) cm-1 corresponding to the N-
imides carbonyl groups were observed for the C3h and Cs
Figure 3. Selected sections of the 1H NMR spectra of C3h and Cs isomer of 9 as well as its statistical isomers mixture in 1,1,2,2-tetrachloroethane-d2 at 363 K.
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yields were 0.09 ±0.01 and 0.03 ±0.01 for the C3h and Cs
isomers, respectively. Such a pronounced quenching of the
emission has been previously observed for related PDIs
endowed with 3,4,5-tridodecyloxyphenyl substituents on
theimide N-atoms and having four tert-butilphenoxy substituents
in the bay position.[44]
To further confirm the solubility of 9 and its respective isolated
isomers in 1,1,2,2-tetrachloroethane, concentration-dependent
UV-Vis experiments were carried out.
Figure SI8 shows the spectra collected in
a range of
concentration comprising 5·10-5–2·10-4 M for both isomers,
highlighting the increased processability of these extended
aromatic macrocycles. Furthermore, temperature-dependent
analysis in the 298–353 K range only revealed slight changes in
the absorbance, in excellent agreement with the NMR studies
(see Figure S9).
At this point, we decided to explore the processability of these
pure isomers on surfaces in order to discover whether these
molecules presented supramolecular aggregates or not. Firstly,
both isomers were spin-coated at 2,000 rpm on SiO2/Si
substrates and thoroughly analysed by means of optical
microscopy, scanning Raman microscopy (SRM), and atomic
force microscopy (AFM) showing an inhomogeneous covering of
the surface, with no signatures of specific supramolecular
aggregation motifs and the presence of fluorescence in the
Raman spectra (see Figures SI10–11). Moreover, when CVD
graphene substrates are used – in which π-aromatic molecules
tend to lie with the aromatic cores parallel to the surface,
stabilised by van der Waals interactions[48–53]
– a very
Figure 5. (A) UV-Vis absorption spectra of
9 (black) and the isolated
chromophores 4 (red) and 8 (green) in 1,1,2,2-tetrachloroethane at room
temperature. The concentration of each sample was 8 × 10-5 M. (B) Steady-
state emission spectra of the C3h (red) and Cs (blue) isomers of 9 in 1,1,2,2-
tetrachloroethane at room temperature.
homogeneous fluorescence quenching was detected by Raman
spectroscopy in the range of millimetres (Figure 6). It is worth to
remark that normally it is not possible to measure Raman
spectra of fluorescent molecules, however by non covalently
binding to graphene or related 2D materials, a fluorescence
quenching of the dye can be obtained as a consequence of an
electron/energy transfer.[49,54,55] The homogeneity of the films
was characterized by means of SRM in areas of 30×30 µm2,
measuring with 1 µm steps (> 900 single point spectra) and
using a grating of 1800 grooves·mm-1 (Figure 6a and Figures
S12–13). The isolated isomers of the star-shaped molecules
exhibited the characteristic Raman peaks associated to the
tetraryloxy-substitued PDI chromophores when resonantly
excited at 532 nm in backscattering geometry.[49] As recently
reported by Duesberg and co-workers, the ratio between the nAg
(ca. 1351 cm-1) and the G peak of the graphene substrate can
be efficiently used as an estimation of the packing density.[56,57]
Indeed, both isomers exhibited very homogeneous mean
PDInAg/G ratios of 1.03 and 0.93 (FWHM 0.10 and 0.11) for the
C3h and Cs isomers, respectively, indicative of a high packing
density (Figure 6b). Interestingly, thanks to the profound
quenching of the fluorescence, it was possible to distinguish
both isomers when analysing the PDI-related bands centered at
ca. 1351, 1403, 1447 and 1548 cm-1, showing a measurable
shift to lower frequencies (mode softening) of all the Raman
modes for the Cs with respect to the C3h isomer in the 1.5–6.7
cm-1 range (Figure 6c). To the best of our knowledge, this is the
first time that constitutional isomers of polycyclic aromatic
This fact indicates an utterly new arrangement of the electron
levels from which the optical excitation is facilitated. In the case
of tetraryloxy-substitued PDI chromophores, the maximum
absorption band indicates strongly allowed electronic S0àS1
transitions, generally found in the 400–600 nm range for these
sort of molecules, and is characterized by three well resolved
vibronic peaks.[42–46] The ratio between the (0,0) and (0,1)
transitions were remarkably larger than 1.6, indicative of
monomeric units in solution for both molecules.[47] The broad
absorption behavior of 9 covers a larger part of the UV and
visible region (250–750 nm), being of interest for those
applications requiring larger absorption crossections in the
visible region of the electromagnetic spectra (e.g., photovoltaic
devices).
When comparing the absorption spectra of the separated C3h
and Cs isomers, we observed a shift of ca. 4 nm in the (0,0) peak,
as well as an increased absorption (ca. twice) in the case of the
asymmetric isomer in the whole spectra. The fluorescence
emission spectra with a peak maximum at 669(680) nm for the
C3h and Cs isomers, respectively, revealed
a mirror-like image of the absorption spectra with a Stokes shift
of 26(22) nm with respect to 4. Remarkably, a shift of ca. 11 nm
between both isomers was detected. The calculated quantum
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C3h isomer. (D) Topography AFM images of the C3h and Cs isomers (RMS
values are 1.6±0.7 and 0.9±0.2, respectively) exhibiting the characteristic
corrugations and wrinkles of CVD graphene substrates.
molecules can be distinguished by Raman spectroscopy.
Interestingly, a detailed inspection of the main graphene Raman
modes revealed a shift in the position of the graphene bands as
a consequence of the interaction with the star-shaped isomers,
which is more remarkable in the case of the 2D band. The
increase in the Raman modes is indicative of a charge transfer
(molecular doping) and is in excellent agreement with previous
reports on electron acceptor molecules interactions with
graphene.[58,59] This shift to higher frequencies (stiffening) of the
G and 2D bands is related with changes in the electronic
structure of electron–phonon interactions and suggest a different
doping behavior for both isomers, being more intense for the C3h
one.[58]
Furthermore, we inspected the samples by AFM, revealing the
presence of the characteristic smooth graphene surfaces with
the presence of wrinkles, in which thin layers of 9 isomers of ca.
3 nm thick were clearly observed, in excellent agreement with
related water-soluble PDIs thicknesses determined by
spectroscopic ellipsometry.[57] The rough mean square values
(RMS) of the functionalized surfaces were 1.6±0.7 and 0.9±0.2
for the C3h and Cs isomers, respectively, indicative of a very
homogeneous and smooth surface (Figure 6d). Additionally, we
have performed Raman mappings with an increased resolution
of 200 nm demonstrating that the covering is completely
homogeneous and is not depending on the corrugations and
wrinkles of the graphene substrate (see Figures SI14–15).
Interestingly, the molecules deposited on the graphene
substrates where more resilient to washing steps than the ones
deposited on SiO2/Si.
To shine light on the stability of the star-shaped isomers of
molecule 9 adsorbed to the graphene surface, we performed
temperature-dependent statistical Raman spectroscopy (T-SRS).
Figure
7 shows the evolution of the Raman peaks with
temperature, surprisingly, the molecules start to be desorbed
from the graphene surface at ca. 475 °C, showing a very high
thermal stability. Finally, the pristine monolayer graphene
surface was recovered after heating to 500 °C.
These results demonstrate that the star-shaped PDIs 9 can be
used to produce homogeneous large areas of non-covalently
functionalised graphene, and can be distinguished not only by
means of NMR, UV-Vis, fluorescence or FT-IR, but also using
Raman spectroscopy. The more abundant asymmetric isomer
(Cs) exhibited the highest absorbance, the more pronounced
bathochromic shift in both UV-Vis and fluorescence, as well as a
characteristic amide peak in the FT-IR spectrum. Moreover, both
isomers exhibited homogeneous packing on graphene surfaces
exerting measurable G-band mode stiffening. Last but not least
we have been able to differentiate both isomers by Raman
spectroscopy showing a softening of all the Raman modes for
the Cs isomer with respect to C3h one.
Figure 7. (A) PDIνAg/G ratios Raman intensity mappings (measured over a
30×30 µm2 area) of the C3h and Cs isomers deposited on CVD graphene
substrates, exhibiting a very high uniformity and homogeneous covering. The
color code indicates the PDIνAg (ca. 1351 cm-1) and graphene G band intensity
ratios. (B) The corresponding PDIνAg/G histograms extracted from the
statistical analysis of the Raman mappings showing narrow distributions
centered at around ca. 1, indicative of a high packing density. (C) Top: Mean
Raman spectra of the C3h and Cs isomers highlighting the softening of the
Raman modes of the Cs with respect to the C3h isomer, allowing its clear
differentiation. Bottom: The characteristic G and 2D graphene Raman modes
are shifted as a consequence of the charge transfer (molecular doping). The
inset shows the 2D band mode stiffening, which is more intense in the case of
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Graphenea. 2,3,6,7,10,11-hexabromotriphenylene 6, N,N',N'',N''',N'''',N'''''-
(triphenylene-2,3,6,7,10,11-hexayl)hexakis(1,1-diphenylmethanimine) 7,
and 2,3,6,7,10,11-hexaaminotriphenylene hydrochloride
synthesized according to reported literature procedures.[37,38]
8
were
NMR spectra were recorded on a Bruker Avance 400 (400 MHz) and a
Jeol EX 400 (400 MHz) spectrometer. Chemical shifts are given in ppm
and referenced to solvent signals. NMR solvents were purchased from
VWR or DEUTERO. HRMS were recorded with Bruker microTOF II focus
and maXis 4G instruments.
MALDI-TOF HRMS were recorded with an UltrafleXtreme TOF/TOF
(Bruker Daltonics). Analytical and preparative HPLC was carried out on a
SHIMADZU Prominence system with CBM-20A system controller, LC-
20A solvent delivery unit, SIL-20A auto-sampler, CTO-20A column oven,
SPD-M20A photodiode array detector, and a DGU-20A on-line degassing
unit.
Figure 8. Temperature-dependent statistical Raman spectroscopy (T-SRS) of
9 in the temperature region between 25 and 500 °C. Remarkably the pristine
CVD graphene spectrum can be completely recovered after heating to 500 ºC
and cool down to room temperature.
The ATR-FTIR spectra were recorded on a BrukerTensor 27 (ATR or
ZnSe plate) spectrometer.
Optical extinction and absorbance was measured on a Perkin Elmer
Lambda 1050 spectrometer in extinction, in quartz cuvettes with a path
length of 0.2 cm.
Conclusions
Fluorescence was acquired on a Horiba Scientific Fluorolog-3 system
equipped with a 450 W Xe halogen lamp, double monochromator in
excitation (grating 600 lines/mm blazed at 500 nm) and emission (grating
1.200 lines/mm blazed at 500 nm) and a PMT detector using quartz
cuvettes with a path length of 0.2 cm.
In summary, we have designed and synthesized a highly soluble
and very π-extended molecule consisting of a triphenylene core
fused with three perylene derivatives yielding a macrocycle
endowed with an extended conjugation of 156 π-electrons. For
the very first time, the respective C3h and Cs isomers have been
completely separated by means of HPLC. Both isomers
exhibited a very high solubility in 1,1,2,2-tetrachloroethane and
have been unambiguously characterized and distinguished by
Raman spectra were acquired on a LabRam HR Evolution confocal
Raman microscope (Horiba) equipped with an automated XYZ table
using 0.80 NA objectives. All measurements were conducted using an
excitation wavelength of 532 nm, with acquisition times of 0.5–2.0 s and
a grating of 1.800 grooves/mm. Maps of 30x30 µm were recorded with a
step size of 1 µm, giving > 1.000 single-point spectra.
1
means of five spectroscopic techniques, namely H NMR, ATR-
FTIR, UV-Vis, fluorescence, and Raman spectroscopy. Finally,
we explored the self-assembly of these molecules on graphene
substrates by optical microscopy, scanning Raman microscopy,
and AFM, showing a favorable processability of this star-shaped
molecules. This work represents the first example of separation
of constitutional isomers of disk-shaped polycyclic aromatic
molecules, which can be clearly distinguished by means of
several spectroscopic techniques thanks to its enhanced
processability, and could be efficiently used for noncovalently
functionalize graphene and related 2D materials.[54],48
Temperature-dependent Raman measurements were performed in a
Linkam stage THMS 600, equipped with a liquid nitrogen pump TMS94
for temperature stabilization under a constant flow of nitrogen. The
measurements were carried out with a heating rate of 10 K.min−1
.
Atomic force microscopy (AFM) was carried out using
a Bruker
Dimension Icon microscope in tapping-mode. The samples were
prepared by spin coating a solution of the separated isomers of molecule
9 at 5.000 rpm.
Synthesis of 2. A mixture of Cl4-PTCDA (3.00 g, 5.63 mmol, 1 equiv.),
imidazole (9.38 g) and 3-pentylamine (1.76 mL, 14.87 mmol, 2.6 equiv.)
was refluxed at 100 °C under nitrogen atmosphere for 3 hours. After
cooling the crude product to room temperature, a solution of HCl in EtOH
(5 M, 225 mL) was added which resulted in the formation of a precipitate.
Stirring was continued for a further 12 h. The precipitate was filtrated,
washed with water until reaching neutrality, and dried in the oven at
100 °C overnight yielding 2 (3.11 g, 83%) as a red solid. The desired
perylene diimide was used in the next step without further purification.
Due to its low solubility in common organic solvents 1H NMR and 13C
NMR spectra were found to be coincident with those previously
reported.[60] HRMS: calculated. for C34H26Cl4N2O4 666.0647 [M]+; found
666.0642.
Experimental Section
General. Tetrachloroperylene tetracarboxylic acid dianhydride (Cl4-
PTCDA) was purchased from abcr. 3-Pentylamine and bromine were
provided from Acros Organics. Imidazole, t-butylphenol, N-methyl-2-
pyrrolidone (NMP), triphenylene, rac-BINAP, benzophenone imine,
sodium tert-butoxide (NaOC(CH3)3), zinc acetate (Zn(OAc)2), quinolone,
tris(dibenzylideneacetone)dipalladium(0), toluene, tetrahydrofuran (THF),
1,1,2,2-tetrachloroethane, nitrobenzene, and triethylamine (Et3N) were
obtained from Sigma-Aldrich. Potassium carbonate (K2CO3) was ordered
from SAFC. Acetic acid (HAc), hydrochloric acid (HCl), isopropanol, and
potassium hydroxide (KOH) were bought from Grüssing. Biobeads-SX3
was purchased from BIO-RAD. Monolayer CVD graphene films
deposited on 300 nm SiO2/Si substrates were purchased from
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10.1002/chem.201705872
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Synthesis of 3. Compound 2 (3.11 g, 4.64 mmol, 1 equiv.), t-butylphenol
(7.66 g, 51.02 mmol, 11 equiv.) and K2CO3 (8.33 g, 60.29 mmol, 13
equiv.) were dissolved in degassed anhydrous NMP (250 mL) and stirred
at 120 °C for 16 hours under nitrogen atmosphere. After cooling the
mixture to room temperature an aqueous solution of HCl (2 M, 120 mL)
was carefully added. The mixture was stirred for another 4 hours. The
isomer), 8.23 (s, 0.75 H, 1 CH, Cs isomer), 8.49 (s, 0.75 H, 1 CH, Cs
isomer), 8.50 (s, 0.75 H, 3 CH, C3h isomer), 8.57 (s, 0.75 H, 1 CH, Cs
isomer), 8. 58 (s, 0.75 H, 1 CH, Cs isomer), 8. 58 (s, 0.75 H, 1 CH, Cs
isomer), 8. 58 (s, 0.75 H, 1 CH, Cs isomer), 8. 64 (s, 0.75 H, 3 CH, C3h
isomer), 8. 65 (s, 0.75 H, 1 CH, Cs isomer), 9.07 (s, 0.75 H, 1 CH, Cs
isomer), 9.08 (s, 0.75 H, 1 CH, Cs isomer), 9.15 (s, 1.50 H, 1 CH of Cs
isomer and 3 CH of C3h isomer), 9.77 (s, 0.75 H, 1 CH, Cs isomer), 9.78
(s, 0.75 H, 1 CH, Cs isomer), 9.79 (s, 1.50 H, 1 CH of Cs isomer and 3
CH of C3h isomer) ppm. HRMS: m/z: calculated for C225H207N9O21
3370.5407 [M]+; found: 3370.5401.
precipitate
formed
was
filtered,
washed
with
water
until reaching neutrality, and dried in the oven at 100 °C overnight
yielding 3 (5.00 g, 96%) as a red solid, which was used for the next step
without further purification. 1H NMR (400 MHz, CDCl3, 25ºC): δ = 0.84 (t,
J = 7.5 Hz, 12H, CH3), 1.27 (s, 36H, CH3), 1.76-1.88 (m, 4H, CH2), 2.09-
2.20 (m, 4H, CH2), 4.90-4.98 (m, 2H, CH), 6.82 (d, J = 8.8 Hz, 8H, CH),
7.21 (d, J = 8.8 Hz, 8 H, CH), 8.19 (s, 4H, CH) ppm. 13C NMR (100 MHz,
CDCl3): δ = 11.3, 25.1, 31.5, 34.4, 57.6, 119.4, 119.7, 120.3, 126.6,
132.9, 147.2, 152.8, 156.0 ppm. HRMS: m/z: calculated for C74H78N2O8:
1122.4190 [M]-; found: 1122.4192.
9 (Cs): 1H NMR (400 MHz, C2D2Cl4, 90 ºC): δ = 0.88 (dd, J = 7.6 Hz and J
= 7.6 Hz, 6H, CH3), 0.88 (dd, J = 7.6 Hz and J = 7.6 Hz, 6H, CH3), 0.88
(dd, J = 7.6 Hz and J = 7.6 Hz, 6H, CH3), 1.30 (br. s, 36 H, CH3), 1.31 (s,
18H, CH3), 1.33 (s, 18H, CH3), 1.35 (s, 27 H, CH3), 1.35 (s, 9H, CH3),
1.81-1.95 (m, 6H, CH2), 2.04-2.19 (m, 6H, CH2), 4.85-4.96 (m, 3H, CH),
6.81-7.02 (m, 24H, CH), 7.20-7.32 (m, 24H, CH), 8.18 (s, 1H, CH), 8.19
(s, 1H, CH), 8.19 (s, 1H, CH), 8.22 (s, 1H, CH), 8.22 (s, 1H, CH), 8.23 (s,
1H, CH), 8.49 (s, 1H, CH), 8.57 (s, 1H, CH), 8.58 (s, 1H, CH), 8.58 (s, 2H,
CH), 8.66 (s, 1H, CH), 9.07 (s, 1H, CH), 9.07 (s, 1H, CH), 9.15 (s, 1H,
CH), 9.77 (s, 1H, CH), 9.78 (s, 1H, CH), 9.79 (s, 1H, CH) ppm. HRMS:
m/z: calculated for C225H207N9O21 3370.5407 [M]+; found: 3370.5401.
Synthesis of 4. To a solution of 3 (4.99 g, 4.44 mmol, 1 equiv.) in a
mixture of isopropanol (197 mL), and H2O (11 mL), KOH (0.88 g, 15.61
mmol, 3.5 equiv.) was added dropwise. The resulting solution was
refluxed at 100 °C with stirring for 1.5 hours. After cooling down the
solution, an aqueous solution of HCl (6 M, 230 mL) and AcOH (74 mL)
were added. The precipitate was filtered off, washed with water
until reaching neutrality, and dried in the oven at 100 °C overnight. After
double purification by plug of silica (CH2Cl2:n-hexaneꢀ34:66), 4 (0.84 g,
18%) was obtained as a pink solid. 1H NMR (400 MHz, CDCl3, 25ºC): δ =
0.86 (t, J = 7.4 Hz, 6H, CH3), 1.30 (s, 36H, CH3), 1.77-1.91 (m, 2H, CH2),
2.10-2.22 (m, 2H, CH2), 4.90-5.00 (m, 1H, CH), 6.83 (d, J = 8.8 Hz, 8H,
CH), 7.25 (d, J = 8.8 Hz, 8H, CH), 8.21 (s, 4H, CH) ppm. 13C NMR (100
MHz, CDCl3): δ = 11.4, 25.2, 31.6, 34.6, 57.9, 118.1, 119.6, 119.7, 121.9,
122.0, 122.6, 127.0, 127.1 133.4, 133.4, 147.9, 148.0, 152.8, 152.9,
156.0, 157.0, 160.4 ppm. HRMS: m/z: calculated for C69H67NO9:
1055,2710 [M]+; found: 1055,2711.
9 (C3h): 1H-NMR (400 MHz, C2D2Cl4, 90 ºC): δ = 0.88 (dd, J = 7.6 Hz and
J = 7.6 Hz, 18H, CH3), 1.30 (s, 54 H, CH3), 1.34 (s, 27H, CH3), 1.35 (s,
27H, CH3), 1.81-1.94 (m, 6H, CH2), 2.04-2.18 (m, 6H, CH2), 4.91 (tt, J =
13.1 Hz and J = 6.3 Hz, 3H, CH), 6.81-7.02 (m, 24H, CH), 7.20-7.31 (m,
24H, CH), 8.18 (s, 3H, CH), 8.21 (s, 3H, CH), 8.50 (s, 3H, CH), 8.64 (s,
3H, CH), 9.10 (s, 3H, CH), 9.79 (s, 3H, CH) ppm. HRMS: m/z: calculated
for C225H207N9O21 3370.5407 [M]+; found: 3370.5401.
Acknowledgements
Synthesis of 9. Et3N (0.07 mL, 0.52 mmol, 9 equiv.) was added
dropwise to a suspension of 8 (30.88 mg, 0.06 mmol, 1 equiv.) in dry
quinoline (6.20 mL) at room temperature under N2. The resulting mixture
was stirred for 30 min and the excess Et3N was removed under vacuum.
Then, 4 (0.20 g, 0.19 mmol, 3.3 equiv.) and dry Zn(OAc)2 (47.46 mg,
0.26 mmol, 4.5 equiv.) were added and the reaction was heated to 180
ºC with stirring overnight. Afterwards, the mixture was allowed to cool
down to room temperature and an aqueous solution of HCl (2 M, 10 mL)
was added dropwise to quench the reaction. After stirring for 30 min at 40
ºC, CH2Cl2 was added to the suspension and the layers were separated.
The combined organic layers were washed with an aqueous solution of
HCl (2 M), brine, dried over anhydrous magnesium sulfate, and
concentrated. The residue was dissolved in CH2Cl2 and passed through
a pad of silica gel. The crude mixture was further purified by size-
exclusion chromatography on Biobeads-SX3 using CH2Cl2 as eluent
yielding 9 as a dark blue solid (103.20 mg, 53.22 %). The individual
isomers of 9 were separated on a COSMOSIL- 5PBB-R column (10 ×
250 mm; eluent CH2Cl2:toluene:MeOH 25:35:40; flow rate 5.0 mL/min; 50
ºC; detection 630 nm) yielding the Cs isomer (75.64 mg, 73.31 %) and
the C3h isomer (27.55 mg, 26.80 %) as a dark blue solid.
The authors thank the Deutsche Forschungsgemeinschaft (SFB
953 “ Synthetic Carbon Allotropes”, projects A1 & A6) for the
financial support. In addition, the research leading to these
results has received partial funding from the European Union
Seventh Framework Program under Grant Agreement No.
604391 Graphene Flagship. G. A. thanks the FAU for the
Emerging Talents Initiative (ETI) grant. Dr. E. Nuin thanks the
Programm zur Förderung der Chancengleichheit für Frauen in
Forschung und Lehre (FFL) “Promoting Equal Opportunities for
Women in Research and Teaching” for a postdoctoral fellowship.
Keywords: perylene • isomers • π conjugation • graphene • non-
covalent functionalization
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We present a highly conjugated
heterocyclic π-chromophore,
consisting of a central triphenylene
core fused with three perylene–
monoimide arms. An unprecedented
separation of the constitutional
isomers was achieved by HPLC,
being distinguished by 1H NMR,
ATR-FTIR, UV-Vis, fluorescence,
and Raman spectroscopy. Its
outstanding processability was
demonstrated by noncovalent
functionalization of graphene.
Edurne Nuin, Vicent Lloret, Konstantin
Amsharov, Frank Hauke, Gonzalo
Abellán and Andreas Hirsch*
Page No. – Page No.
Isomerically Pure Star-Shaped
Triphenylene-Perylene Hybrids
Involving Highly Extended π
Conjugation
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