Facile transformation of 1-aryltriphenylenes into dibenzo[fg,op]tetracenes by intramolecular Scholl cyclodehydrogenation: synthesis, self-assembly, and charge carrier mobility of large π-extended discogens

Article abstract of DOI:10.1039/c6tc04530h

The search for new organic semiconductors with enhanced charge transport properties and self-organizing abilities plays a pivotal role in the development of new applications in the emerging field of organic electronics. We have synthesized two series of d

Full text of DOI:10.1039/c6tc04530h

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Materials Chemistry C
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Facile transformation of 1-aryltriphenylenes into
dibenzo[fg,op]tetracenes by intramolecular Scholl
cyclodehydrogenation: synthesis, self-assembly,
and charge carrier mobility of large p-extended
discogens†
Cite this:DOI: 10.1039/c6tc04530h
a
a
a
a
a
a
Ke-Qing Zhao,* Min Jing, Ling-Ling An, Jun-Qi Du, Yan-Hong Wang, Ping Hu,
a
b
c
c
Bi-Qin Wang, Hirosato Monobe,* Benoıt Heinrich and Bertrand Donnio*
ˆ
The search for new organic semiconductors with enhanced charge transport properties and self-
organizing abilities plays a pivotal role in the development of new applications in the emerging field of
organic electronics. We have synthesized two series of discotic mesogenic materials derived from
hexasubstituted triphenylene, including (i) 1-aryl-2,3,6,7,10,11-hexakis(pentyloxy)triphenylenes (14 new
compounds) by
precursor and various arylboronic acids and (ii) unsymmetrical facial dibenzo[fg,op]tetracene discotic
molecules (11 new compounds) by an FeCl -oxidized cyclodehydrogenation reaction of the former. The
a Suzuki cross-coupling reaction between the appropriate 1-bromotriphenylene
3
mesomorphism has been investigated by polarizing optical microscopy, differential scanning microscopy,
and small-angle X-ray scattering. Most aryl-substituted triphenylene derivatives exhibit a single hexagonal
columnar mesophase, enantiotropic over small temperature ranges or monotropic, with this low stability
being likely attributed to the free-rotating bulky side-on arene group that disrupts a perfect stacking. The
corresponding more rigid and flat dibenzo[fg,op]tetracene derivatives also self-organize into a hexagonal
columnar mesophase, but with a larger mesophase stability than their parents, and occurring slightly
above room temperature. The UV/vis absorption and fluorescence emission spectra have been measured.
Tetracenes show stronger photoluminescence than aryltriphenylene in solution, while the reversed is
observed in thin films, where a strong excimer emission for one of the polar 1-aryltriphenylenes is
observed. The charge carrier mobility of two representative discogens has been measured by the time-of-
flight photocurrent technique. The results show that the discogen with a lateral nucleus dipole displays a
Received 18th October 2016,
Accepted 13th December 2016
À4
2
À1 À1
hole mobility of 10 cm
V s
in the mesophase, while the non-polar compound exhibits a hole
À1 À1
V s in its metastable-induced ordered phase. The charge carrier mobility is
DOI: 10.1039/c6tc04530h
À2
2
mobility of 10 cm
www.rsc.org/MaterialsC
discussed as a function of the supramolecular organization.
gaining enormous interest as attractive functional components
for their potential insertion in electronic devices, including photo-
Introduction
One-dimensional columnar liquid crystalline semiconductors voltaic cells, light emitting diodes, or field effect transistors.1,2
formed by the self-organization of discotic molecules are Discotic liquid crystals (DLCs) are usually composed of polycyclic
aromatic hydrocarbons equipped with several diverging paraffinic
a
College of Chemistry and Material Science, Sichuan Normal University,
chains. These supramolecular 1D conductive pathways, which
consist of the regular stacks of disc-like p-conjugated polycyclic
aromatic cores, possess both dynamical property and efficient
Chengdu 610066, China. E-mail: kqzhao@sicnu.edu.cn
b
Inorganic Functional Materials Research Institute, National Institute of Advanced
Industrial Science and Technology (AIST), Ikeda, Osaka 5638577, Japan.
E-mail: monobe-hirosato@aist.go.jp
charge carrier transporting ability along the columns, a required
condition for the functioning and operation of such devices.
The efficiency of the charge transport, which determines the
ultimate device performances, is however intimately connected
to the molecular structure of the discogen as well as with the
strength of the intermolecular interactions. This challenge thus
c
3,4
Institut de Physique et Chimie des Mat ´e riaux de Strasbourg (IPCMS),
CNRS-Universit ´e de Strasbourg (UMR 7504), 67034 Strasbourg, France.
E-mail: bertrand.donnio@ipcms.unistra.fr
†
Electronic supplementary information (ESI) available: Experimental techni-
1
13
ques, POM, DSC, H and C NMR, HRMS, IR, SAXS, and HOMO–LUMO analysis.
See DOI: 10.1039/c6tc04530h
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29
motivates intense research activity in this area, essentially focused proceed at all. Finally, unexpected regio-isomers may occasionally
5–7
on the molecular design and synthesis of new efficient systems,
their self-organization and optoelectronic properties. It is there-
be produced.
In this paper, we report two novel series of discotic mesogens,
fore essential to explore new discogenic structures with higher derived from hexasubstituted triphenylene by the facial attach-
8–10
charge carrier mobility
for the development of efficient, cheap ment of various phenylene, naphthalene and thiophene moieties,
and robust molecular electronic materials. The results reported in thereafter referred to as 1-aryltriphenylenes (Ar-TP) and unsym-
the literature seem to indicate that the carrier mobility is propor- metrical dibenzo[fg,op]tetracenes (DBT), which are effectively
tional to the size of the conjugated discogen core: the larger the synthesized by Suzuki cross-coupling reaction and aryl oxidative
aromatic core, the higher the molecule overlaps and the higher cyclodehydrogenation, respectively. The mesomorphic properties
1
1
the charge carrier mobility. Another approach consists in of all Ar-TP and DBT compounds were investigated, and most of
modifying the electronic properties of the core by attachment the derivatives exhibit hexagonal columnar mesophases, whose
of various electro-active substituents.
temperature ranges vary as a function of the molecular structure.
An extensively studied class of DLCs is based on hexa- Moreover, as the dibenzotetracene discotic core is a larger
5
substituted triphenylenes, but also includes for the most common p-extended polycyclic aromatic hydrocarbon, higher charge
4
6
ones, hexabenzocoronene and phthalocyanine derivatives. The carrier mobility than that of common triphenylene discogens
great progress in modern organic synthesis methods in the last may therefore be expected. In addition, the presence of electron-
decades has made the synthesis of more structurally challenging donating or electron-withdrawing substituents can impact both
discotic mesogens accessible, and therefore rendered the fine- the self-organization behaviors and the charge carrier mobility.
tuning of their physical properties by subtle modifications The charge carrier mobility of two DBT representatives was
possible. Transition metal catalyzed organic reactions, namely investigated by the time-of-flight photocurrent technique, and hole
1
2
13
À4
À2
2
À1 À1
Suzuki cross-coupling and Sonogashira reactions, have mobility values lying in the range of 10 to 10 cm V
s
were
been playing pivotal roles in the synthesis of such DLC systems. measured. The effects of dipolar functionalization on mesophase
Some classical reactions, such as the aryl oxidative cyclo- stability and charge carrier mobility are discussed.
1
4,15
dehydrogenation reaction, also known as the Scholl reaction,
have been widely used in the construction of DLCs and shown
high efficiency. Such an oxidative cyclodehydrogenation reaction
can form multiple aromatic C–C bonds in one step to yield
planar polycyclic aromatics, and has found many successful
Results and discussion
Synthetic methodology
applications in the synthesis of variants of DLCs, including 14 new 1-aryl-2,3,6,7,10,11-hexakis(pentyloxy)triphenylenes were
1
6
17
triphenylenes,
hexabenzocoronenes,
thiophene-fused prepared by a Pd-catalyzed Suzuki cross-coupling reaction between
peripherally fused the lipophilic 1-bromotriphenylene derivative and various aryl-
1
8
19
discogens,
tetrabenzoanthracenes,
20
21
porphyrins, triphenylene-fused triazatruxene, and triphenylene- boronic acids (Scheme 1). Then, in the next stage, intramolecular
crown ether discogens. Oxidative reagents, such as FeCl
CH Cl and/or MeNO , being low-cost and environmentally- using the FeCl
2
2
3
in cyclodehydrogenation was applied to these 1-aryltriphenylenes
/H SO pair, which after zinc reduction and
2
2
2
3
2
4
friendly, have been widely used in aryl oxidative cyclodehydro- O-alkylation resulted in 11 new dibenzo[ fg,op]tetracene deriva-
genation, though other chemical reagents have also been tives (Scheme 2). In the literature, dibenzo[ fg,op]tetracene is also
2
3
27
29,30
reported.
named as dibenzo[ fg,op]pyrene or dibenzonaphthacene.
As said, the Scholl reaction has greatly contributed to the The structures of the final compounds were fully characterized
synthesis of original DLCs, although, this reaction frequently by NMR, MS and IR (Fig. S3–S5 in ESI†).
competes with other mechanisms and its use still remains an
Synthesis of 1-aryltriphenylenes (Ar-TP) by Suzuki cross-
important synthetic challenge. For example, the direct trans- coupling. a-Bromination of hexaalkyloxytriphenylenes has
formation of hexakis(4-alkoxyphenyl)benzene under the oxida- allowed the synthesis of a wide variety of new p-extended
31
tive intramolecular cyclodehydrogenation conditions does not arenes. The key compound of this study, 1-bromo-2,3,6,7,10,11-
lead to the alkoxy-substituted hexa-peri-hexabenzocoronene hexakis(pentyloxy)triphenylene, 2, was synthesized in 40% yield
2
4
(
HBC) but rather unexpectedly to spirocyclic dienones or from 2,3,6,7,10,11-hexa(pentyloxy)triphenylene, 1, by a modified
3
2
indenofluorenes as main products. In some cases, semi-fused reported method. The bromination was carried out at low
2
5
HBC intermediates could be isolated. Similarly, the synthesis temperature (below 0 1C) and by slow addition of a bromine
of hexakis(alkoxy)triphenylenes and related discogens by solution in CCl . The Suzuki cross-coupling reaction of 2 with
a direct trimerisation of 1,2-dialkoxybenzenes was found various commercial arylboronic acids (including naphthyl and
to produce monohydrolyzed coupling products, or excess thiophene moieties) produced 1-aryl-2,3,6,7,10,11-hexa(pentyloxy)-
oxidized quinone derivatives when FeCl was used in excess. triphenylenes 3a–n in very high yields (79–95%, Scheme 1); the
4
2
6
2
7
3
1
5
Chlorinated byproducts were occasionally isolated when synthetic yields were hardly affected by the stereo- and electronic
FeCl was used as the oxidant. Another important challenge effects of the substrates and reagents.
3
faced by the cyclodehydrogenation reaction is the oxida-
Synthesis of dibenzo[fg,op]tetracenes (DBT) by intramolecular
2
8
tive potential dependence on the substrates,
as for aryl oxidative cyclodehydrogenation. As mentioned above, the aryl
some electron-deficient substrates, the reaction does not cyclodehydrogenation faces challenges for the electro-deficient
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Scheme 1 Synthesis, yields and molecular structures of the 1-aryl-2,3,6,7,10,11-hexa(pentyloxy)triphenylene derivatives (Ar-TP, 3).
1
5
aryl substrates.
The oxidative cyclodehydrogenation of Dibenzotetracenes 4 were obtained in moderate to high yields
1-aryltriphenylenes 3 to dibenzo[fg,op]tetracenes 4 was opti- (40–75%, Scheme 2).
mized. For complete cyclization, excess FeCl was used and a It is interesting to note that 1-aryltriphenylenes with very
3
few drops of sulfuric acid were added. However, the dealkylation strong electron-withdrawing substituents, such as 3d (with
and/or formation of quinones were simultaneously observed, and three fluorine substituents) and 3l (with a cyanide substituent),
both isolation and purification were tedious. These synthetic were not oxidized under the same conditions to the corres-
difficulties were circumvented by one-pot tandem reactions of ponding dibenzotetracenes, and the starting compounds were
reduction–realkylation with Zn powder/1-bromopentane/K
2
CO
3
.
recovered from the reaction mixtures. The thiophene-substituted
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Scheme 2 Synthesis, yields and molecular structures of the dibenzo[fg,op]tetracene derivatives (DBT, 4).
triphenylene 3n was transformed to dibenzotetracene 4n, but
was unstable in the air, thus limiting the mesophase characteri-
zation by optical microscopy only. 1-Naphthalenetriphenylene
3m was transformed, but not into the expected dibenzotetracene
derivative according to the structural characterization. Finally,
only the stereo less-bulky isomers were isolated in pure form
(as drawn in Scheme 2).
Liquid crystalline properties
Fig. 1 Typical optical textures of two representatives of the Ar-TP and
DBT series: 3k at 60 1C; 4k at 65 1C, on cooling from the isotropic liquid,
respectively (scale bars are 200 and 150 mm, respectively).
The mesomorphism of 1-aryltriphenylenes 3 and dibenzotetracenes
4
has been investigated by a combination of polarized optical
microscopy (POM, Fig. 1 and Fig. S1 in ESI†), differential scanning
calorimetry (Fig. S2 and Table S1 in ESI†), and small-angle X-ray enantiotropic hexagonal columnar (Colhex) range from 65 to
33
scattering (SAXS, Fig. 4, Fig. S6 and Table S2 in ESI†). As displayed 121 1C. In the Colhex phase, the disc-like cores stack face-to-face
in Fig. 1, most compounds of both series 3 and 4 show fluid, into columns, disposed at the nodes of a two-dimensional lattice
birefringent, fan-shaped optical textures with large homeotropic and nanosegregated from peripheral molten chains merging
domains characteristic of the formation of a columnar hexagonal to a continuum. Although of the same chemical nature,
mesophase (Colhex).
the appending phenyl unit of the aryltriphenylene cores is a
3
4
Mesomorphism of 1-aryltriphenylenes, 3. Hexakis(pentyloxy)tri- typical segment of rod-like mesogens, because of the rapid
phenylene 1 is an archetypal columnar liquid crystal, with a broad rotation around the sigma bond axis conferring an average
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positions, as such an angle is logically unfavorable for directed
intermolecular interactions. In liquid crystalline mesophases,
the cyano group shows the highest potential for dipolar
3
8
association, and the isotropization temperature of the cyano
derivative 3l consistently lies 50 1C above that of the fluoro
analogue 3a, for a 25 1C enlargement of the enantiotropic range
(Fig. 2) and the largest mesomorphic range.
Mesomorphism of the functionalized dibenzo[ fg,op]-
tetracenes, 4. After cyclodehydrogenation, the substituted phenyl
and triphenylene segments fuse to yield a unique large-size
conjugated discotic mesogen. The self-organization process is
therefore deeply modified from bare phenyl derivative 3f to 4f, in
consistency with a substantial increase of the isotropization
temperature and with the appearance of an enantiotropic Colhex
range (Fig. 3). In contrast, the isotropization temperature is
Fig. 2 Phase diagram of compounds of series 3. Cr: crystalline phase;
Colhex: enantiotropic hexagonal columnar phase; [Colhex]: monotropic already relatively high in 3n and stays roughly the same in 4n,
hexagonal columnar phase.
in accordance with the expected p-stacking of the entire core
before and after cyclodehydrogenation.
The variation of the number and size of chains (4g, h, j, and k)
3
5
cylindrical shape. The rigid linking between two mesogenic proved a maximum extension of the mesomorphous range for the
units self-associating in a different way is inevitably detrimental derivative with eight pentyl chains (4h). In contrast, the presence
to mesomorphism, and the bare phenyl derivative 3f only of two methoxy groups is detrimental to mesomorphism for 4i.
shows a monotropic Colhex phase with ca. 80 1C drop of the The influence of polar groups follows the same trend as that of
transition to the isotropic liquid (the isotropization) with precursors: high isotropization temperatures for the derivatives
respect to pure discotic 1 (Fig. 2). Conversely, the mesophase with fluoro or chloro groups in the para and meta positions
is still enantiotropic and the drop is limited to 40 1C in 3n, due (4a, b, and e), and the absence of mesomorphism for the
to the propensity for face-to-face stacking of its thiophenyl derivative with fluoro groups in both meta positions (4c) (Fig. 3).
3
6
substituent. In contrast, the increase of the substituent size
Characterization of the mesophases by small angle X-ray
from phenyl to naphthyl (3m) does not promote the Colhex scattering (SAXS). SAXS patterns could be recorded for four
phase, which is monotropic, with just upward shifts of melting derivatives of the aryltriphenylene series, namely 3f and 3k
and isotropization temperatures.
(with phenyl and methylphenyl substituents) in the monotropic
Beyond the impeded stacking, the expansion of the core by bare Colhex phase, and 3b and 3l (the difluorophenyl and cyano deriva-
substituents introduces an imbalance with the number of chains, tives) in their enantiotropic Colhex range (Fig. 4, Fig. S6 and Table S2
37
beforehand optimal in unsubstituted 1. A single pentyl tail on in ESI†). The signature of the nanosegregated structure at small
phenyl cancels this lack of chains and explains that the isotropiza- angles proves in both cases a hexagonal lattice with one single
tion temperature of 3g is 40 1C above that of 3f. Intermediate column, with an intense first-order reflection (10) around 17 Å and a
transition temperatures are logically found with a single methyl or series of weaker, higher-order reflections, according to spacing
methoxy group (3k and 3j), since the insertion of such short tails ratios O3, 2, O7 and indexations (11), (20) and (21), respectively.
between longer tails is less beneficial for a cohesive lateral
packing. The space requirement of two chains clearly exceeds
the void created by the core expansion as shown by the total
disappearance of the mesomorphism for derivatives 3h and 3i.
The use of phenyl substituents bearing polar groups could
induce more cohesive structures through the dipolar inter-
actions within and between the columns, and also through
the repelling of the tails and the denser periphery. In that line,
the isotropization temperatures of derivatives with fluoro or
chloro groups in the meta and para positions of the protruding
phenyl ring (3a–e) were found to extend far beyond that of 3f
and to result in enantiotropic Colhex ranges when at least one
meta position stays unsubstituted (3a, b, and e). The isotropiza-
tion temperature shift is not so large when both meta positions are
substituted (3c and d), while the melting temperature increases
quite regularly with the number of halogens. The effect on the
columnar range is therefore canceled in this particular case,
presumably in relation with the 1201 angle between meta Fig. 3 Phase diagram of compounds of series 4.
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Table
1
SAXS results of the representative 1-aryltriphenylenes and
a
dibenzo[fg,op]tetracenes
Compounds
Phase and parameters
2
2
2
2
2
2
2
2
2
2
3
3
3
3
4
4
4
4
4
4
b
k
l
Colhex, a = 19.36 Å, Scol = 324.7 Å
3
Vmol = 1360 Å , hmol = 4.2 Å
Colhex, a = 19.79 Å, Scol = 339.4 Å
3
V
mol = 1336 Å , hmol = 3.9 Å
Colhex, a = 19.54 Å, Scol = 331.0 Å
3
V
mol = 1430 Å , hmol = 4.3 Å
f
Colhex, a = 19.64 Å, Scol = 334.1 Å
3
V
mol = 1309 Å , hmol = 3.9 Å
b
e
f
Colhex, a = 20.18 Å, Scol = 352.5 Å
3
V
mol = 1319 Å , hmol = 3.74 Å
Colhex, a = 20.01 Å, Scol = 346.8 Å
3
V
mol = 1339 Å , hmol = 3.86 Å
Colhex, a = 20.23 Å, Scol = 354.4 Å
3
V
mol = 1298 Å , hmol = 3.66 Å
j
Colhex, a = 20.06 Å, Scol = 348.8 Å
3
V
mol = 1331 Å , hmol = 3.82 Å
k
h
Colhex, a = 20.04 Å, Scol = 348.0 Å
3
V
mol = 1325 Å , hmol = 3.81 Å
Colhex, a = 21.94 Å, Scol = 416.8 Å
3
V
mol = 1585 Å , hmol = 3.80 Å
P
a
2
2
1/2
À1
a = 2 Â [dhk(h + k + hk) (NhkO3) ], where Nhk is the number of hk
reflections for the Colhex phase; Vmol is the molecular volume, Scol is the
lattice area and hmol = Vmol/Scol is the molecular thickness (see Table S2
in the ESI).
Fig. 4 Representative SAXS patterns of one derivative of each series:
The SAXS patterns (Fig. 4) turned out to be very similar for all
compounds, with the same sharp small-angle reflections series
3
p
f and 4f at 25 1C (har, hch, htp and h are defined in the text).
(
10), (11), (20) and (21) from a hexagonal lattice with one single
column, and with nearly identical wide-angle regions. In particular,
The packing features inside domains can be taken from the wide- the semi-diffuse h scattering signal re-appears next to broad
angle region, in which the absence of the characteristic semi-diffuse scattering hch, which confirms the transformation of the core into
scattering maximum from p-stacked triphenylene h (usually located a unique p-stacking mesogen. The comparison of hmol (4f: E3.6 Å;
around 3.5 Å) is immediately noticed. This peculiarity is obviously 4j, k, h, b, and e: E3.8 Å, Table 1) and h (E3.6 Å) ends up with
related to the rigid bond with the phenyl substituent, which as a minor differences, compatible with the absence of tilting or small
p
p
33
p
40
sub-unit of calamitic mesogens is associated with larger lateral tilt angles of cores within the columns. The molecular packing in
39
distances (typically 4.5–4.8 Å, har).
the Colhex phase is therefore similar to that of 1, except that the
Triphenylene rings therefore accommodate this mismatch aspect ratio is close to 1.2 for the new dibenzotetracene core, which
between natural distances through their piling in a very irregular implies that the mesogen orientations vary inside columnar
way (htp), which explains the disappearance of the characteristic domains to preserve the hexagonal symmetry.
h
p
signal. Instead, the entire rigidly linked mesogens give rise to a
Interestingly, it is worth mentioning that some other structu-
unique broad scattering (har + htp), whose ill-defined maximum is rally related DBT DLCs (Fig. S9 in ESI†) have already been reported
27,29,30
located at intermediate distances and overlaps with the contribu- in the literature.
The symmetrical hexa(pentyloxy)-DBT dis-
tion from the molten aliphatic continuum, hch. Consistently, the plays an ordered Colhex mesophase between 121 and 223 1C (with
3
0
molecular slice thicknesses hmol (=Vmol/Scol, where Vmol is the a stacking distance of 3.55 Å at 150 1C), that is at much higher
calculated molecular volume from reference density data and temperatures than compounds 4, and particularly with respect to
Scol, the lattice area) are also intermediate between both natural its structural isomer 4f, highlighting the importance of the
distances (hmol E 3.9 Å for 3f and 3k and 4.2–4.3 for 3b and 3l, substituent positions and nature. Similarly, octakis(pentyloxy)-
Table 1), while a coincidence between hmol and h
found for the neat triphenylene compound 1.
p
(E3.5 Å) was DBT, a symmetrical isomer of 4h, shows in contrast a lower
clearing temperature of 94 1C, with a slightly larger aryl core–
3
3
2
7
SAXS patterns were recorded for six derivatives of the core distance value of 3.81 Å (at 67 1C). This result can be
dibenzotetracene series, namely the unsubstituted derivative explained by the stereo perturbation of the two extra alkoxy
4f, compared on the one hand to derivatives with one methyloxy peripheral chains, which weaken the p–p interactions and the
group (4j), one methyl group (4k) and two pentyloxy chains (4h), discotic staking with respect to compounds with lesser chains.
following the order of isotropization temperatures, and on the Mesomorphic properties are apparently strongly dependent on
other hand, to derivatives with fluoro or chloro groups in the the chains anchoring positions too (as compared with 4h). Most
meta and para positions (4b and 4e), for which the Colhex phase recently, a series of tetra-substituted dibenzo[fg,op]tetracenes has
is maintained at high temperature (Fig. 3).
been synthesized and reported to possess smectic A (SmA) and C
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3
0
(
SmC) phases, as well as the hexatic-B phase. It is obvious that
the semiconducting properties of 1-dimensional columnar and
-dimensional smectic mesophases based on this polycyclic
2
aromatic core are highly worth further studying. This study
indeed emphasizes once more the importance of molecular
engineering of mesogens to tune the transport properties of
liquid crystalline semiconductors. All DBT 4 synthesized here,
exhibiting a Colhex mesophase at room temperature and low
phase transition temperatures, are advantageous for thermal
annealing for homeotropic alignment of the samples and self-
healing the defects formed during self-assembly, and offer novel
perspectives for the fabrication of high performance active layers
for organic optoelectronic devices.
Charge transport properties investigated by the time-of-flight
(
TOF) photocurrent technique
The charge carrier mobility is the most important parameter
for organic semiconductors as it essentially determines their
future performance in devices. For liquid crystalline semi-
conductors, main factors such as the mesogenic core- and its
electronic properties, as well as the mesomorphic supramolecular
structure, have a direct and important effect on the charge
transport properties. We have investigated the charge carrier
mobility of two representative discogens, 4b and 4i, by the time-
of-flight (TOF) photocurrent technique, and the results are
shown in Fig. 5 and 6.
Fig. 6 Charge carrier (hole) mobility of 4b (measured by time-of-flight
photocurrent technique, cell thickness 16.2 mm). Top: Electric field depen-
dency of positive photocurrent curves (log–log plot) at 130 1C; bottom:
temperature dependence of charge carrier mobility for positive (circle) and
negative (square) charge carrier transports on cooling.
First, the liquid crystalline homeotropic aligned sample 4i in
an ITO cell was irradiated with an N laser (337 nm) and the
2
transient photocurrent decay curves were non-dispersive for
positive charges (holes) at various electric fields (Fig. 5). The
measured positive charge mobility value, mhole, is of the order of
À2
2
À1 À1
10
cm
V
s . Considering the distance of 16.8 mm for
the charge carrier hopped along the supramolecular discotic
columns, this TOF mobility value is quite high, and one to
two orders of magnitude higher than the transport value of
À4
À3
2
À1 À1
41
10
–10 cm V
s
exhibited by triphenylene discogens.
More interestingly, the hole mobility was temperature- and
electric-field-independent. However, the negative charge (electron)
photocurrent was not detected for 4i, feasibly due to the higher
sensitivity of the electron to oxygen, moisture, and organic
impurity. 4i, as an electron-rich discogen, favors hole transport
and is thus a p-type discotic semiconductor. Furthermore, as this
discogen has a low clearing temperature and a mesophase
temperature range covering the operational-significant room
temperature, it posits as a very useful candidate for electronic
device applications.
The charge mobility measurement of one dipolar homolog,
b, reveals both positive and negative charge transport abilities,
Fig. 5 Charge carrier mobility of 4i (measured by the time-of-flight
photocurrent technique, cell thickness 16.8 mm). Top: Bias-dependent
photocurrent decay curves at 55 1C with the drift times labeled on the
curves (hole, log–log plot). Bottom: Temperature dependence of charge
carrier mobility on cooling (hole).
4
and the photocurrent decay curves are non-dispersive (Fig. 6).
À4
2
À1 À1
Its hole charge mobility value reaches 2 Â 10 cm V
s
in
the mesophase. Both positive negative charge mobilities are
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.2 Â 10 cm V
Journal of Materials Chemistry C
À5
2
À1 À1
1
s
in the isotropic phase indicating the
existence of ionic charge transport. The photocurrent decay
curves are non-dispersive and the mobility value is slightly
temperature dependent.
These two discogens possess the same aromatic core, and
both discogens are hole transporters. However, their carrier
mobility values differ by two orders of magnitude. 4b has a
strong dipolar nucleus, with two fluoro-substituents on one
side pulling electrons and six pentyloxy groups on the other side of
the molecule pushing electrons. Therefore, in the supramolecular
discotic columns, discs 4b likely stack on top with an antiparallel
orientation. Thus, the charged carriers (holes) hope along these
electronically disordered columns at a low rate. On the contrary, 4i
is non-polar, with no preferential orientation, and the discotic
columns as charged-carrier pathways are electronically neutral,
therefore promoting a much faster hole mobility rate.
Related results have been reported in the literature. For
instance, the charge transport property of a few dipolar discotic
liquid crystalline systems, e.g. triphenylene discogens substituted
42
43
44
with nitro- or ester groups, and a discotic quinone, was found
to decrease as well as be temperature- and electric field-dependent.
The electronic and energetic disorder in the columns was sug-
gested to be responsible for this decreased charge transport value.
45
However, 1,4-difluoro-2,3,6,7,10,11-hexa(pentyloxy)triphenylene
showed enhanced mobility with a slight temperature and electric
field-dependence. The authors argued that the dipole benefited
the ordered staking of the discogens into the columns and
therefore improved the charge transport. So, dipoles seem to
have two opposite effects: one enhancing the discotic columnar
superstructures, and the other causing electronically dis-
ordered antiparallel orientation of the molecules in the discotic
columns. Which of these two opposite effects dominates is still
a puzzle and might be discotic system dependent, therefore
more explorations are needed.
In our case, the difference in the thermal stability of meso-
phases may offer an alternative explanation. A careful investigation
of the thermal behavior reveals that the mesophase of 4i is indeed
metastable, whilst it is enantiotropic for 4b, with this enhanced
stability being associated with the presence of the lateral fluoro
dipoles. For 4i, crystallization begins once in the (monotropic)
mesophase, with no temperature change, with this tendency being
Fig. 7 UV/vis (top) and fluorescence (middle in solution, bottom in film)
2 2
amplified in the thin film morphology. A columnar structure- spectra of 1-aryltriphenylene and dibenzotetracene derivatives (in CH Cl ,
1
.0 Â 10À5 M).
orientated crystallization process would therefore contribute to
this difference, likely by favoring a perfect stacking of the
mesogens into columns while reducing the formation of grain
boundaries during this gradual mesophase-to-crystalline phase solution and fluorescence emission in both solution and solid
transformation and the consequent rigidification, therefore film are shown in Fig. 7 and the results are summarized Table 2.
improving the charge transport properties within columns, with
The absorption spectra of 1-aryltriphenylenes (3b, h, and i)
respect to 4b which is still fluid and subjected to perturbations. and tetracene (4i) display the strongest absorption at l = 284 nm
that originates from the absorption of the triphenylene core
Photophysical properties of 1-aryltriphenylene and
dibenzotetracene derivatives – UV/vis absorption and
fluorescent emission
46,47
(Fig. 7).
4b shows a strong broad absorption band between
2
4
50–310 nm and several weak absorptions between 310 and
00 nm. All discogens exhibit molar absorption coefficients in
4
À1
À1
The photophysical properties of 1-aryltriphenylenes 3 and the range of 5–10 Â 10 L mol cm
dibenzotetracenes 4 are interesting as their p-conjugated In solution, the photoluminescence of tetracenes (4b and 4i)
systems varied from triphenylene. The UV/vis absorption in is stronger than that of 1-aryltriphenylenes 3 (Fig. 7), possibly
.
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Paper
Table 2 Summary of the UV/vis absorption and fluorescence spectro- DBT discogens display broad mesophase ranges covering the
scopic properties of discogens in solutions and films
operationally-significant room temperature. The isotropization
temperatures of these mesogens are dependent on the electronic
em [nm] QY (%) Film lem [nm] properties of the substituents: electron-withdrawing groups
Solution
l
À1
À1
l
abs [nm] e [L mol cm
]
5
increase the isotropization temperature, while electron-donating
groups decrease the T . The strong lateral nucleus dipole feasibly
i
3
3
3
3
4
b
h
i
l
b
284
284
283
279
228
1 Â 10
8 Â 10
8 Â 10
8 Â 10
7 Â 10
5 Â 10
5 Â 10
4 Â 10
4 Â 10
5 Â 10
8 Â 10
4 Â 10
403 (1.59)
398 (1.32)
398 (0.98)
472 (2.33)
403 (3.19)
433
255, 422
389
390
447
420
4
4
4
4
4
4
4
3
4
4
4
induces the antiparallel alignment of discogens into in the
columns and therefore stabilizes the columnar mesophase.
These 1-aryltriphenylenes and dibenzotetracenes display UV
absorption similar to triphenylene discogens and possess
strong fluorescence emission of blue or green light in both
solution and thin film. Unexpectedly the film of 3l exhibits
strong excimer emission of green light. Importantly, the semi-
conducting properties of two representative dibenzotetracene
discogens, 4i and 4b, have been investigated by the time-of-
flight photocurrent technique, they display hole mobility rates
258
297
310
398
4
i
232
401 (2.65)
422
413
427
2
3
83
12
For the emission measurement, the samples were excited with lex
84 nm, expect for 4b, which was excited with 297 nm. QY: quantum
yield efficiency.
=
2
À2
2
À1 À1
À4
2
À1 À1
of 10 cm V
s
and 10 cm V
s , respectively. The
introduced lateral molecular dipole in 4b and the resultant
due to the later exhibiting partial fluorescence quenching antiparallel molecular orientation promote strong stability of
caused by free rotation of the sigma bond between phenyl the Colhex mesophase with respect to 4i, but the charge carrier
and triphenylene core. It is noted that 3l shows a broad transport, due to the energetic and electronic disorder within the
emission band with a peak at 472 nm, larger than all discogens supramolecular columns, is disfavoured. In contrast, the low
studied here, and likely corresponds to the excimer emission of thermodynamic stability of the phase of 4b is actually very useful
3l, due to the natural tendency for antiparallel dimerization of as it permits the pre-organization of the molecules into columns
the polar molecule, as shown above.
whilst preserving the columnar structure during crystallization.
In this study, we emphasize once more the importance of
On the contrary, the fluorescence emission of 3 in film is
stronger than that of 4 (Fig. 7), as this time the p–p stacking of the molecular design to tune the transport properties of liquid
tetracenes 4 results in partial emission quenching. Obviously 3l crystalline semiconductors. The facile synthetic method described
shows the strongest green light emission with a peak centered here to generate a wide range of substituted dibenzotetracene
at 447 nm, blue-shifted by 25 nm from the emission in solution. discogens offers novel perspectives for the fabrication of high
Thus, as expected tetracenes 4 display higher quantum yield performance active layers for organic optoelectronic devices.
efficiency than 1-aryltriphenylene 3 in solution, but this is
reverted in films. In addition, it was found that polar com-
pounds show higher QY than non-polar compounds (Table 2).
The strong light emitting property of 1-aryltriphenylenes 3 as
Experimental section
well as their self-organization into a columnar mesophase General instruments and compounds characterization are reported
16b
implies their potential applications in sensors for explosive in the ESI.† 1,2-Di(pentyloxy)benzene and 2,3,6,7,10,11-hexakis-
chemicals (nitro-substituted arenes such as TNT) and light (pentyloxy)triphenylene, 1 were prepared according to a reported
1
6b
emitting and electronic charge carrier materials in OLEDs.
method.
: 1-bromo-2,3,6,7,10,11-hexakis(pentyloxy)triphenylene, 2,
2
3
2a
was synthesized by a modified reported method. To a stirred
solution of 2,3,6,7,10,11-hexa(pentyloxy)triphenylene (1, 20 g,
Conclusions
2
6.9 mmol) in CCl4 (150 mL) cooled to À10 1C, Br2 (4.4 g,
Fourteen members of 1-aryl-2,3,6,7,10,11-hexakis(pentyloxy)- 27.5 mmol) in CCl (20 mL) was added slowly, and the mixture
4
triphenylenes have been synthesized in high yields by the was stirred below 0 1C for 10 h. Then, a sodium metabisulfite
Suzuki cross-coupling reaction of 1-bromo-2,3,6,7,10,11-hexakis- solution (20%) was added. The organic extracts were combined,
(
pentyloxy)triphenylene with arylboronic acids. Quite surpris- washed with brine, dried over MgSO
ingly, most aryltriphenylenes are still capable of self-organizing The residue was purified by column chromatography on silica gel,
into a columnar hexagonal mesophase, but display lower isotro- eluted with light petroleum ether/CH Cl (3 : 2, v/v), and crystal-
4
, and concentrated in vacuo.
2
2
1
pization temperatures than the parent compound 2,3,6,7,10,11- lized from ethanol to yield a white solid (8.2 g, 37%). H NMR
hexakis(pentyloxy)triphenylene. The only exception is the (CDCl , TMS, 400 MHz) d: 9.00 (s, 1H, 1ArH), 7.81 (s, 1H, 1ArH),
3
4
-cyanophenyl-substituted triphenylene, which shows the highest 7.77 (s, 3H, 3ArH), 4.23 (t, J = 6.4 Hz, 10H, 5ArOCH ), 4.11
2
isotropization temperature.
(t, J = 6.8 Hz, 2H, 1ArOCH ), 1.94 (m, 12H, 6CH ), 1.55 (m, 12H,
2
2
The intramolecular oxidative cyclodehydrogenation by FeCl
3
6CH
2
), 1.45 (m, 12H, 6CH
2
3
), 0.98 (t, J = 7.2 Hz, 18H, 6CH ).
oxidation, followed by realkylation have successfully yielded eleven
3a: under argon atmosphere, to a flask containing 2 (500 mg,
novel dibenzo[ fg,op]tetracene discogens. These unsymmetrical 0.61 mmol), (4-fluorophenyl)boronic acid (169.81 mg, 1.21 mmol),
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anhydrous K
2
CO
3
powder (1.26 g, 9.13 mmol), Pd(PPh
3
)
4
3f: 2 (660 mg, 0.80 mmol), phenylboronic acid (145 mg,
1
(69.78 mg, 0.061 mmol), deoxygenated THF (12 mL) and dis- 1.2 mmol). 3f: 620 mg, 94%. H NMR (CDCl
3
, TMS, 400 MHz) d:
tilled water (3 mL) were added. The mixture was stirred at 80 1C 7.88 (d, J = 8.4 Hz, 2H, ArH), 7.83 (s, 1H, ArH), 7.78 (s, 1H, ArH),
for 18 h. Then, the mixture was cooled, poured into 2 N HCl 7.71 (s, 1H, ArH), 7.39–7.43 (m, 3H, ArH), 7.30–7.35 (s, 1H, ArH),
aqueous solution, and extracted with CH Cl . The organics 7.23 (s, 1H, ArH), 4.13–4.27 (t, J = 6.4 Hz, 8H, ArOCH ), 4.14
2
2
2
were dried over MgSO
The residue was purified by silica gel column chromatography, 3.15–3.17 (m, 2H, CH
eluted with light petroleum/CH Cl (3 : 2, v/v), and crystallized (m, 12H, CH ), 1.34–1.49 (m, 12H, CH
from ethanol to give a white solid, 3a (463.4 mg, 91%). H NMR 15H, CH ), 0.81 (t, J = 7.2 Hz, 3H, CH
3g: 2 (520 mg, 0.63 mmol), (4-pentylphenyl)boronic acid
4
, filtered, and concentrated in vacuum. (t, J = 6.4 Hz, 2H, ArOCH
2
2
), 3.59 (t, J = 6.4 Hz, 2H, ArOCH ),
2
), 1.84–1.99 (m, 10H, CH
), 0.92–1.00 (t, J = 7.2 Hz,
).
2
), 1.54–1.65
2
2
2
2
1
3
3
(
(
7
CDCl
s, 1H, 1ArH), 7.72 (s, 1H, 1ArH), 7.39 (d, J = 8.4 Hz, 2H, 2ArH), (144 mg, 0.91 mmol). 3g: 456 mg, 84%. H NMR (CDCl3,
.13 (s, 3H, 3ArH), 4.27 (t, J = 6.4 Hz, 8H, 4ArOCH ), 3.60 TMS, 400 MHz) d: 7.88 (d, J = 2.8 Hz, 2H, ArH), 7.78 (s, 1H,
3
, TMS, 400 MHz) d: 7.87 (d, J = 8.0 Hz, 2H, 2ArH), 7.78
1
2
(
t, J = 6.4 Hz, 2H, 1ArOCH ), 3.25 (t, J = 6.4 Hz, 2H, 1ArOCH ), ArH), 7.71 (s, 1H, ArH), 7.31 (s, 1H, ArH), 7.28 (d, J = 3.6 Hz, 2H,
2
2
1
6
0
.87–1.97 (m, 8H, 4CH
H, 3CH
.95 (t, J = 7.2 Hz, 15H, 5CH
2
), 1.66–1.69 (m, 2H, 1CH
2
), 1.52–1.59 (m, ArH), 7.25 (s, 1H, ArH), 7.22 (s, 1H, ArH), 4.23 (t, J = 6.4 Hz, 6H,
2
), 1.36–1.50 (m, 16H, 8CH
), 0.83 (t, J = 7.2 Hz, 3H, 1CH
2
), 1.06–1.17 (m, 4H, 2CH
).
2
), ArOCH
ArOCH
2
2
), 4.14 (t, J = 6.4 Hz, 2H, ArOCH
), 3.18 (t, J = 6.4 Hz, 2H, ArOCH
2
2
), 3.58 (t, J = 6.4 Hz, 2H,
), 2.64 (t, J = 8.0 Hz, 2H,
3
3
All the other 1-aryl-triphenylene derivatives, 3b–n, were ArCH
2
), 1.85–1.99 (m, 8H, CH
2
), 1.57–1.69 (m, 12H, CH
2
), 1.33–
synthesized and purified accordingly. 1.49 (m, 18H, CH
2
), 1.03–1.17 (m, 4H, CH ), 0.93 (t, J = 7.2 Hz,
2
3
b: 2 (130 mg, 0.16 mmol), (3,4-difluorophenyl)boronic acid 18H, CH ), 0.80 (t, J = 7.2 Hz, 3H, CH ).
3
3
1
(
49.83 mg, 0.32 mmol). 3b: 108.18 mg, 80%. H NMR (CDCl ,
TMS, 400 MHz) d: 8.17 (s, 1H, 1ArH), 8.13 (s, 1H, 1 ArH), 8.05 acid (429 mg, 1.46 mmol). 3h: 900 mg, 93%. H NMR (CDCl ,
3h: 2 (800 mg, 0.97 mmol), (3,4-bis(pentyloxy)phenyl)boronic
3
1
3
(s, 1H, 1ArH), 7.99 (s, 1H, 1ArH), 7.52 (d, J = 6.0 Hz, 1H, 1ArH), TMS, 400 MHz) d: 7.88 (s, 2H, ArH), 7.78 (s, 1H, ArH), 7.71
7
6
.48 (d, J = 6.4 Hz, 1H, 1ArH), 7.36 (s, 2H, 2ArH), 4.51 (t, J = (s, 1H, ArH), 7.34 (s, 1H, ArH), 6.98 (d, J = 2.0 Hz, 1H, ArH), 6.91
.4 Hz, 6H, 3ArOCH ), 4.43 (t, J = 6.4 Hz, 2H, 1ArOCH ), 3.88 (d, J = 8.4 Hz, 1H, ArH), 6.83 (s, 1H, ArH), 4.23 (t, J = 6.4 Hz, 6H,
), 3.55 (t, J = 6.4 Hz, 2H, 1ArOCH
), 1.96–1.99 (m, 2H, 1CH ), 1.63–1.84 ArOCH
2
2
(t, J = 6.4 Hz, 2H, 1ArOCH
2
2
), ArOCH
2
), 4.15 (t, J = 6.8 Hz, 2H, ArOCH
), 3.63 (t, J = 6.4 Hz, 1H, ArOCH
2
), 3.85 (t, J = 6.4 Hz, 4H,
), 3.53 (t, J = 6.8 Hz, 1H,
2.21–2.24 (m, 8H, 4CH
2
2
2
2
(
m, 22H, 11CH ), 1.36–1.44 (m, 4H, 2CH ), 1.21 (t, J = 7.2 Hz, ArOCH ), 3.26 (t, J = 6.4 Hz, 2H, 1ArOCH ), 1.83–1.99 (m, 10H,
2 2 2 2
1
5H, 5CH ), 1.13 (t, J = 7.2 Hz, 3H, 1CH ).
CH ), 1.72–1.79 (m, 2H, CH ), 1.61–1.67 (m, 2H, CH ), 1.55–1.60
2 2 2
3
3
3
c: 2 (200 mg, 0.24 mmol), (3,5-difluorophenyl)boronic acid (m, 10H, CH ), 1.30–1.50 (m, 20H, CH ), 1.09–1.20 (m, 4H, CH ),
2 2 2
1
(
76.66 mg, 0.49 mmol). 3c: 181.01 mg, 87%. H NMR (CDCl
TMS, 400 MHz) d: 7.92 (s, 1H, ArH), 7.87 (s, 1H, ArH), 7.79
s, 1H, ArH), 7.74 (s, 1H, ArH), 7.15 (s, 1H, ArH), 6.98 (s, 1H, acid (166 mg, 0.91 mmol). 3i: 427 mg, 80%. H NMR (CDCl
ArH), 6.79 (s, 1H, ArH), 4.18 (t, J = 6.4 Hz, 8H, ArOCH ), 3.70 TMS, 400 MHz) d: 7.93 (d, J = 4.0 Hz, 2H, ArH), 7.83 (s, 1H, ArH),
), 3.35 (t, J = 6.4 Hz, 2H, ArOCH ), 7.77 (s, 1H, ArH), 7.37 (s, 1H, ArH), 7.06 (s, 1H, ArH), 6.93 (s, 2H,
.88–1.98 (m, 8H, CH ), 1.68–1.75 (m, 2H, CH ), 1.55–1.59 ArH), 4.28 (t, J = 6.8 Hz, 6H, ArOCH ), 4.20 (t, J = 6.8 Hz, 2H,
3
,
3 3
0.88 (t, J = 7.2 Hz, 21H, CH ), 0.82 (t, J = 6.8 Hz, 3H, CH ).
3i: 2 (500 mg, 0.61 mmol), (3,4-dimethoxyphenyl)boronic
1
(
3
,
2
(
1
t, J = 6.4 Hz, 2H, ArOCH
2
2
2
2
2
(
m, 8H, CH ), 1.37–1.49 (m, 14H, CH ), 1.12–1.21 (m, 4H, ArOCH ), 3.97 (s, 3H, ArOCH ), 3.85 (s, 3H, ArOCH ), 3.72
2 2 2 3 3
CH ), 0.95 (t, J = 7.2 Hz, 15H, CH ), 0.85 (t, J = 7.2 Hz, 3H, CH ). (t, J = 6.4 Hz, 1H, ArOCH ), 3.58 (t, J = 6.8 Hz, 1H, ArOCH ),
2
3
3
2
2
3
d: 2 (200 mg, 0.24 mmol), (3,4,5-trifluorophenyl)boronic 3.30 (t, J = 6.8 Hz, 2H, ArOCH
2
), 1.90–2.04 (m, 8H, CH
2
), 1.66–
1
acid (85.39 mg, 0.48 mmol). 3d: 176.31 mg, 83%. H NMR 1.72 (m, 2H, CH
CDCl , TMS, 400 MHz) d: 7.91 (s, 1H, 1ArH), 7.85 (s, 1H, 1ArH), CH
.78 (s, 1H, ArH), 7.73 (s, 1H, ArH), 7.06 (s, 3H, ArH), 4.18 (t, J = 7.2 Hz, 15H, CH
t, J = 6.4 Hz, 8H, ArOCH ), 3.70 (t, J = 6 Hz, 2H, ArOCH ), 3.38 3j: 2 (200 mg, 0.24 mmol), (4-methoxyphenyl)boronic acid
t, J = 6.8 Hz, 2H, ArOCH ), 1.92–1.98 (m, 8H, CH ), 1.70–1.75 (73.77 mg, 0.48 mmol). 3j: 179.75 mg, 87%. H NMR (CDCl ,
2
), 1.60–1.63 (m, 8H, CH
2
), 1.45–1.55 (m, 10H,
(
7
(
(
3
2
), 1.38–1.41 (m, 4H, CH
2
), 1.12–1.24 (m, 4H, CH
).
2
), 0.96
3
), 0.87 (t, J = 6.8 Hz, 3H, CH
3
2
2
1
2
2
3
(
m, 2H, CH ), 1.37–1.49 (m, 22H, CH ), 1.14–1.21 (m, 4H, CH ), TMS, 400 MHz) d: 7.88 (d, J = 6.4 Hz, 2H, ArH), 7.78 (s, 1H, ArH),
2 2 2
0
.93–0.99 (t, J = 7.2 Hz, 15H, CH ), 0.86 (t, J = 7.2 Hz, 3H, CH ). 7.72 (s, 1H, ArH), 7.30 (s, 3H, ArH), 6.97 (d, J = 8.8 Hz, 2H, ArH),
3
3
HRMS (m/z) calcd for C54
H
73
F
3
O
6
: 874.5359; found: 874.5348.
4.16–4.26 (t, J = 6.4 Hz, 8H, ArOCH
), 3.27 (t, J = 6.4 Hz, 2H, ArOCH
), 1.35–1.58 (m, 24H, CH ), 1.08–1.16
), 0.82 (t, J = 7.2 Hz,
2
), 3.85 (s, 3H, ArOCH
3
), 3.60
3e: 2 (200 mg, 0.24 mmol), (3,4-dichlorophenyl)boronic acid (t, J = 6.4 Hz, 2H, ArOCH
2
2
),
1
(92.63 mg, 0.48 mmol). 3e: 177.15 mg, 82%. H NMR (CDCl
3
,
1.94–1.98 (m, 10H, CH
2
2
TMS, 400 MHz) d: 7.91 (s, 1H, ArH), 7.86 (s, 1H, ArH), 7.78 (m, 2H, CH
2
), 0.93–1.00 (t, J = 7.2 Hz, 15H, CH
3
(
(
(
s, 1H, ArH), 7.72 (s, 1H, ArH), 7.63 (d, J = 2 Hz, 1H, ArH), 7.48 3H, CH
d, J = 8 Hz, 1H, ArH), 7.17 (s, 1H, ArH), 7.07 (s, 1H, ArH), 4.23 3k: 2 (500 mg, 0.61 mmol), p-tolylboronic acid (165 mg,
t, J = 6.0 Hz, 6H, 3ArOCH ), 4.16 (t, J = 6.4 Hz, 2H, ArOCH ), 1.21 mmol). 3k: 430.79 mg, 85%. H NMR (CDCl , TMS, 400 MHz)
3
).
1
2
2
3
3
1
.58 (t, J = 6.4 Hz, 2H, ArOCH ), 3.22 (t, J = 6.0 Hz, 2H, ArOCH ), d: 7.91 (d, J = 4.4 Hz, 2H, ArH), 7.81 (s, 1H, ArH), 7.74 (s, 1H, ArH),
2
2
.86–1.99 (m, 8H, 4CH
2
), 1.67–1.74 (m, 2H, CH
2
), 1.53–1.61 7.29 (d, J = 6.4 Hz, 2H, ArH), 7.25 (s, 3H, ArH), 4.24 (t, J = 6.4 Hz,
(
0
m, 8H, CH
2
), 1.38–1.48 (m, 14H, CH
2
), 1.06–1.18 (m, 4H, CH
).
2
), 6H, ArOCH
2H, ArOCH
2
), 4.17 (t, J = 6.4 Hz, 2H, ArOCH
), 3.21 (t, J = 6.8 Hz, 2H, ArOCH ), 2.43 (s, 3H, ArCH
3
2
), 3.64 (t, J = 6.4 Hz,
.94 (t, J = 7.2 Hz, 15H, CH ), 0.85 (t, J = 7.2 Hz, 3H, CH
3
3
2
2
),
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2 2
1.89–2.00 (m, 8H, CH ), 1.47–1.59 (m, 12H, CH ), 1.37–1.45
All the other dibenzo[fg,op]tetracene discogens were prepared
(
m, 12H, CH ), 1.07–1.16 (m, 4H, CH
2
2
), 0.95 (t, J = 6.4 Hz, 15H, and purified accordingly.
4b: 3b (200 mg, 0.22 mmol), FeCl (364. 8 mg, 2.24 mmol);
CH ), 0.83 (t, J = 7.2 Hz, 3H, CH ).
3
3
3
3
l: 2 (100 mg, 0.12 mmol), (4-cyanophenyl)boronic acid zinc powder (400 mg); 1-bromopentane (270 mg, 1.79 mmol),
1
1
(
35.67 mg, 0.24 mmol). 3l: 97.56 mg, 95%. H NMR (CDCl , K CO (309 mg, 2.24 mmol). 4b: 97.83 mg, 52%. H NMR
3 2 3
TMS, 400 MHz) d: 7.93 (s, 1H, ArH), 7.86 (s, 1H, ArH), 7.75 (d, J = (CDCl
3
, TMS, 400 MHz) d: 9.62 (s, 2H, ArH), 8.10 (s, 2H, ArH),
.6 Hz, 2H, ArH), 7.72 (s, 2H, ArH), 7.56 (d, J = 8.4 Hz 2H, ArH), 7.91 (s, 2H, ArH), 4.34 (t, J = 6.4 Hz, 8H, OCH ), 3.98 (t, J =
.90 (s, 1H, ArH), 4.22 (t, J = 6.4 Hz, 6H, ArOCH ), 4.15 (t, J = 6.4 Hz, 4H, OCH ), 1.90–2.05 (m, 12H, CH ), 1.41–1.63 (m, 24H,
.8 Hz, 2H, ArOCH ), 3.62 (t, J = 6.4 Hz, 2H, ArOCH ), 3.14 (t, J = CH ), 1.03 (t, J = 7.2 Hz, 18H, CH ). C NMR (CDCl , 100 MHz)
.8 Hz, 2H, ArOCH ), 1.87–1.98 (m, 8H, CH ), 1.64–1.71 (m, 2H, d: 151.06, 150.10, 149.95, 149.64, 147.63, 147.48, 144.94, 127.72,
9
6
6
6
2
2
2
2
1
3
2
2
2
3
3
2
2
CH ), 1.55–1.59 (m, 10H, CH ), 1.36–1.50 (m, 14H, CH ), 1.12– 127.67, 127.62, 124.64, 123.79, 121.86, 119.61, 116.18, 116.10,
2
2
2
1.18 (m, 2H, CH ), 0.92 (t, J = 7.2 Hz, 15H, CH ), 0.83 (t, J = 116.05, 115.97, 107.27, 106.58, 77.35, 77.03, 76.71, 73.79, 69.59,
2 3
7
.2 Hz, 3H, CH ). HRMS (m/z) calcd for C H NO : 845.5594; 69.32, 30.14, 29.37, 29.13, 28.52, 28.47, 28.41, 22.63, 14.15,
3
55 75
6
found: 845.5586.
14.06. HRMS (m/z) calcd for C54
H
72
F
2
O
6
: 854.5297; found:
3
m: 2 (500 mg, 0.61 mmol), naphthalene-2-ylboronic acid 854.5284.
1
(
4
(
208 mg, 1.21 mmol). 3m: 450 mg, 85%. H NMR (CDCl
3
, TMS,
00 MHz) d: 7.94 (d, J = 6.4 Hz, 2H, ArH), 7.91 (s, 1H, ArH), 7.88 zinc powder (400 mg); 1-bromopentane (228.26 mg, 1.51 mmol),
CO powder (347.68 mg, 2.52 mmol). 4c: 43.77 mg, 40%.
H NMR (CDCl , TMS, 400 MHz) d: 9.25 (s, 1H, ArH), 8.04
4c: 3c (220 mg, 0.25 mmol), FeCl (409.41 mg, 2.52 mmol);
3
s, 1H, ArH), 7.86 (d, J = 7.2 Hz, 1H, ArH), 7.78–7.79 (m, 2H,
K
2
3
1
ArH), 7.71 (s, 1H, ArH), 7.44–7.50 (s, 3H, ArH), 7.15 (s, 1H, ArH),
3
4
3
1
.22 (t, J = 6.4 Hz, 6H, ArOCH ), 4.11 (t, J = 6.4 Hz, 2H, ArOCH ), (s, 2H, ArH), 7.91 (s, 2H, ArH), 7.08 (s, 1H, ArH), 4.34 (t, J =
2 2
.55 (t, J = 6.4 Hz, 2H, ArOCH ), 2.51 (t, J = 6.4 Hz, 2H, ArOCH ), 6.4 Hz, 8H, ArOCH ), 4.04 (t, J = 6.8 Hz, 2H, ArOCH ), 3.85 (t, J =
2
2
2
2
.92–2.00 (m, 6H, CH
2
), 1.82–1.86 (m, 2H, CH
2
), 1.55–1.60 6.4 Hz, 2H, ArOCH
2
), 1.96–2.02 (m, 10H, CH
2
), 1.57–1.62
), 1.21–1.25 (m, 2H,
).
: 854.5297; found: 854.5291.
4e: 3e (300 mg, 0.34 mmol), FeCl (547.7 mg, 3.37 mmol);
n: 2 (100 mg, 0.12 mmol), thiophen-3ylboronic acid (31 mg, zinc powder (500 mg); 1-bromopentane (305.37 mg, 2.02 mmol),
(m, 8H, CH
2
), 1.43–1.48 (m, 10H, CH
), 1.06–1.21 (m, 2H, CH ), 0.95–1.00 (m, 4H, CH
), 0.53 (t, J = 7.2 Hz, 3H, CH ). HRMS HRMS (m/z) calcd for C54
: 870.5798; found: 870.5795.
2
), 1.20–1.28 (m, 4H, (m, 12H, CH
2
), 1.34–1.50 (m, 12H, CH
2
CH
2
2
2
), 0.81 CH ), 1.02 (t, J = 7.2 Hz, 15H, CH ), 0.85 (t, J = 7.6 Hz, 3H, CH
2 3 3
(
(
t, J = 7.2 Hz, 15H, CH
m/z) calcd for C58
3
3
72 2 6
H F O
H
78
O
6
3
3
1
0.24 mmol). 3n: 79.3 mg, 79%. H NMR (CDCl , TMS, 400 MHz) K CO powder (465.14 mg, 3.37 mmol). 4e: 142 mg, 47.5%.
3 2 3
1
d: 7.89 (d, J = 6.0 Hz, 2H, ArH), 7.86 (s, 2H, ArH), 7.81 (s, 1H,
H NMR (CDCl , TMS, 400 MHz) d: 9.92 (s, 2H, ArH), 8.14
3
ArH), 7.75 (s, 1H, ArH), 7.36 (s, 1H, ArH), 7.28 (s, 1H, ArH), 4.24 (s, 2H, ArH), 7.94 (s, 2H, ArH), 4.34 (t, J = 6.4 Hz, 4H, ArOCH
2
2
),
),
(
t, J = 6.4 Hz, 6H, ArOCH
t, J = 6.4 Hz, 2H, ArOCH
.90–2.01 (m, 8H, CH ), 1.55–1.63 (m, 12H, CH
m, 12H, CH ), 1.19–1.24 (m, 4H, CH ), 0.95–1.02 (t, J = 7.2 Hz, for C54
5H, CH ), 0.88 (t, J = 7.2 Hz, 3H, CH ). HRMS (m/z) calcd for
2
), 4.19 (t, J = 6.4 Hz, 2H, ArOCH
), 3.47 (t, J = 6.4 Hz, 2H, ArOCH
), 1.40–1.53 (m, 12H, CH
2
), 3.66 4.28 (t, J = 6.4 Hz, 4H, ArOCH
), 1.91–2.05 (m, 12H, CH ), 1.52–1.64 (m, 12H, CH
), 1.01 (t, J = 7.2 Hz, 18H, CH ). HRMS (m/z) calcd
: 886.4706; found: 886.4708.
2
), 3.99 (t, J = 6.4 Hz, 4H, ArOCH
(
2
2
2
2
), 1.42–1.51
1
2
2
2
3
(
2
2
2 6
H72Cl O
1
4f: 3f (100 mg, 0.12 mmol), FeCl (189.65 mg, 1.16 mmol);
3
3
3
C H O S: 826.5206; found: 826.5195.
zinc powder (200 mg); 1-bromopentane (270 mg, 1.79 mmol),
5
2
74 6
1
4a: to a solution of 3a (310 mg, 0.37 mmol) in dry CH Cl
K CO (309 mg, 2.24 mmol). 4f: 60.54 mg, 62%. H NMR
2
2
2
3
(
H
15 mL), FeCl
SO were added; the mixture was stirred at room temperature (s, 2H, ArH), 7.96 (s, 2H, ArH), 7.57–7.61 (m, 2H, ArH), 4.36
for 40 min. Then, methanol (2 mL) and water (2 mL) were added. (t, J = 6.4 Hz, 8H, OCH ), 3.98 (t, J = 6.4 Hz, 4H, OCH ), 1.87–
After extraction with CH Cl , the organic extracts were washed 2.03 (m, 12H, CH ), 1.38–1.63 (m, 24H, CH ), 1.02 (t, J = 7.2 Hz,
with a saturated NaCl solution, dried over MgSO , filtered, and 18H, CH ). HRMS (m/z) calcd for C54 : 818.5485; found:
concentrated in vacuo to give a residue. DMF (20 mL) was added to 818.5377.
the residue, followed by 1-bromopentane (334.68 mg, 2.22 mmol), 4g: 3g (656 mg, 0.73 mmol), FeCl (788.6 mg, 7.28 mmol);
K CO powder (509.79 mg, 3.69 mmol) and zinc powder (500 mg). zinc powder (500 mg); 1-bromopentane (881.84 mg, 5.84 mmol),
3 3
(600.28 mg, 3.69 mmol) and a drop of concentrated (CDCl , TMS, 400 MHz) d: 9.68 (d, J = 6.4 Hz, 2H, ArH), 8.12
2
4
2
2
2
2
2
2
4
3
74 6
H O
3
2
3
1
The mixture was stirred at 80 1C for 16 h. After the reaction
2 3 3
K CO (1.01 g, 7.3 mmol). 4g: 324.6 mg, 50%. H NMR (CDCl ,
mixture was cooled, it was filtered through a thin layer of silica gel TMS, 400 MHz) d: 9.58 (s, 1H, ArH), 9.52 (s, 1H, ArH), 8.11
and the solvent was concentrated in vacuo. The residue was (d, J = 6.4 Hz, 2H, ArH), 7.96 (s, 2H, ArH), 7.44 (s, 1H, ArH), 4.34
purified by silica gel column chromatography, eluted with light (t, J = 6.4 Hz, 8H, OCH
petroleum ether/CH Cl (3 : 2, v/v) and recrystallized from ethanol (m, 2H, CH ), 1.90–2.04 (m, 12H, CH
to yield a white solid, 4a (184.8 mg, 60%). H NMR (CDCl , TMS, 1.37–1.59 (m, 28H, CH ), 0.94–1.00 (t, J = 7.2 Hz, 21H, CH ).
2
), 4.00 (t, J = 6.4 Hz, 4H, OCH
2
), 2.82–2.84
2
2
2
2
), 1.76–1.82 (m, 2H, CH
2
),
1
3
2
3
4
1
6
00 MHz) d: 9.68 (s, 1H, ArH), 9.47 (s, 1H, ArH), 8.15 (d, J = HRMS (m/z) calcd for C H O : 888.6268; found: 888.6265.
59 84 6
4.8 Hz, 2H, ArH), 7.96 (s, 2H, ArH), 7.34 (s, 1H, ArH), 4.36 (t, J =
.4 Hz, 8H, ArOCH ), 4.03 (t, J = 6.4 Hz, 4H, ArOCH ), 1.89–2.05 zinc powder (400 mg); 1-bromopentane (190.26 mg, 1.26 mmol),
), 1.38–1.63 (m, 24H, CH ), 1.02 (t, J = 7.2 Hz, 18H,
). HRMS (m/z) calcd for C54 : 836.5391; found: 836.5385. TMS, 400 MHz) d: 9.27 (s, 2H, ArH), 8.10 (s, 2H, ArH), 7.98
4h: 3h (200 mg, 0.21 mmol), FeCl (341.3 mg, 2.1 mmol);
3
2
2
1
(m, 12H, CH
2
2
2 3 3
K CO (289.8 mg, 2.1 mmol). 4h: 157 mg, 75%. H NMR (CDCl ,
CH
3
H73FO
6
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J. Mater. Chem. C

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Journal of Materials Chemistry C
(
s, 2H, ArH), 4.35 (t, J = 6.4 Hz, 4H, ArOCH
2
), 4.29 (t, J = 6.8 Hz, 1.90–2.20 (m, 12H, CH
), 3.97 (t, J = 6.8 Hz, 7.2 Hz, 18H, CH ).
H, ArOCH ), 1.89–2.09 (m, 16H, CH ), 1.35–1.67 (m, 32H, CH ),
2 2
), 1.40–1.80 (m, 24H, CH ), 1.10 (t, J =
4
4
1
1
2
1
1
H, ArOCH
2
), 4.23 (t, J = 6.4 Hz, 4H, ArOCH
2
3
2
2
2
1
3
.02 (t, J = 7.2 Hz, 24H, CH3). C NMR (CDCl , 100 MHz) d:
3
Acknowledgements
4.05, 14.10, 14.13, 22.56, 22.59, 22.63, 22.71, 28.34, 28.39, 28.52,
9.10, 29.14, 29.37, 30.35, 68.82, 69.14, 69.65, 76.70, 77.01, 77.33,
11.21, 111.24, 111.25, 119.56, 124.49, 124.52, 124.54, 147.98,
48.04, 149.47, 149.50, 149.55. Elemental analysis calcd for
This research was financially supported by the National Natural
Science Foundation of China (grant no. 51273133, and 51443004).
BD and BH thank the CNRS and the University of Strasbourg for
support.
C
(
96 130 8
H F O
16: C, 77.53; H, 9.56; found: C, 77.37; H, 9.56. HRMS
m/z) calcd for C64 : 990.6949; found: 990.6942.
i: 3i (200 mg, 0.23 mmol), FeCl (373.75 mg, 2.3 mmol);
94 8
H O
4
3
zinc powder (400 mg); 1-bromopentane (208.38 mg, 1.38 mmol),
References
1
K CO (317.4 mg, 2.3 mmol). 4i: 131 mg, 65%. H NMR (CDCl ,
2
3
3
TMS, 400 MHz) d: 9.30 (s, 2H, ArH), 8.11 (s, 2H, ArH), 7.98
s, 2H, ArH), 4.36 (t, J = 6.4 Hz, 4H, ArOCH ), 4.29 (t, J = 6.8 Hz,
H, ArOCH ), 4.10 (s, 6H, ArOCH ), 3.98 (t, J = 6.8 Hz, 4H,
ArOCH ), 1.91–2.07 (m, 12H, CH ), 1.60–1.68 (m, 8H, CH ),
.47–1.53 (m, 12H, CH ), 1.35–1.40 (m, 4H, CH ), 0.97–1.02
m, 12H, CH ), 0.92 (t, J = 7.2 Hz, 6H, CH ). C NMR (CDCl3,
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(
4
2
2
3
2
2
2
1
(
2
2
1
3
3
3
1
2
7
1
00 MHz) d: 14.05, 14.13, 22.59, 22.63, 22.66, 28.35, 28.39,
8.51, 29.13, 29.35, 30.35, 55.81, 69.14, 69.65, 73.99, 76.69,
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24.57, 124.74, 144.34, 147.91, 149.53, 150.94. HRMS (m/z) calcd
+
for C56
H O
78 8
[MH] : 879.5697; found: 879.5771.
3
4j: 3j (150 mg, 0.18 mmol), FeCl (286.35 mg, 1.76 mmol);
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1
K CO (243.19 mg, 1.76 mmol). 4j: 89.78 mg, 60%. H NMR
2
3
(
(
(
4
(
CDCl , TMS, 400 MHz) d: 9.66 (d, J = 9.6 Hz, 1H, ArH), 9.31
d, J = 2.4 Hz, 1H, ArH), 8.17 (s, 1H, ArH), 8.12 (s, 1H, ArH), 8.00
3
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s, 2H, ArH), 7.29 (s, 1H, ArH), 4.40 (t, J = 6.4 Hz, 8H, ArOCH
.05 (t, J = 6.4 Hz, 4H, ArOCH ), 4.04 (s, 3H, ArOCH ), 1.92–2.12
m, 12H, CH ), 1.41–1.69 (m, 24H, CH ), 1.06 (t, J = 7.2 Hz, 18H,
CH ). HRMS (m/z) calcd for C55 : 848.5591; found: 848.5588.
k: 3k (300 mg, 0.36 mmol), FeCl (583.68 mg, 3.59 mmol);
2
),
2
3
2
2
3
76 7
H O
4
3
zinc powder (400 mg); 1-bromopentane (325.42 mg, 2.15 mmol),
1
K CO (495.69 mg, 3.59 mmol). 4k: 183.3 mg, 61%. H NMR
2
3
(
CDCl , TMS, 400 MHz) d: 9.59 (s, 2H, ArH), 8.14 (d, J = 7.2 Hz,
3
2
8
H, ArH), 8.00 (s, 2H, ArH), 7.45 (s, 1H, ArH), 4.40 (t, J = 6.4 Hz,
H, ArOCH ), 4.02 (t, J = 6.4 Hz, 4H, ArOCH ), 2.61 (s, 3H,
), 2.00–2.09 (m, 8H, CH ), 1.90–1.98 (m, 4H, CH ), 1.60–
.69 (m, 12H, CH ), 1.43–1.57 (m, 12H, CH ), 1.06 (t, J = 7.2 Hz,
8H, CH ). HRMS (m/z) calcd for C55 : 832.5642; found:
32.5641.
n: to a stirred solution of 3n (115 mg, 0.14 mmol) in CH Cl
2
2
ArCH
3
2
2
1
1
8
2
2
3
76 6
H O
4
2
2
(
105 mL) at 0 1C, a solution of FeCl (67.8 mg, 0.42 mmol) in
3
MeNO
stirred at 0 1C for 1.5 h. Then, cold methanol (2 mL) and water
2 mL) were added to quench the reaction and the mixture was
extracted in CH Cl . The residue was purified by silica gel column
chromatography, eluted with petroleum ether/dichloromethane
2
(1.5 mL) was added under argon atmosphere and
(
2
2
(
(
3 : 2, v/v) and crystallized in ethanol to yield the product
44 mg, 38%). Repeated purification by column chromatography
and re-crystallization resulted in the oxidation of the product to a
1
black powder. H NMR (CDCl
ArH), 8.22 (s, 1H, ArH), 8.17 (s, 1H, ArH), 8.05 (s, 1H, ArH), 8.00
s, 1H, ArH), 7.69 (s, 1H, ArH), 4.60 (t, J = 6.4 Hz, 12H, ArOCH ),
3
, TMS, 400 MHz) d: 8.86 (s, 1H,
(
2
J. Mater. Chem. C
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Journal of Materials Chemistry C
Paper
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