Synthesis of Arylamine Tribenzopentaphenes and Investigation of their Hole Mobility

Article abstract of DOI:10.1002/open.201500064

We report the versatile synthesis of two tribenzo[fj,ij,rst]pentaphene (TBP) derivatives bearing two diarylamine substituents attached at the opposite ends of the aromatic core. Field effect transistor (FET) devices of the bis-diarylamine-TBP compounds we

Full text of DOI:10.1002/open.201500064

DOI: 10.1002/open.201500064
Synthesis of Arylamine Tribenzopentaphenes and
Investigation of their Hole Mobility
[
b]
[c]
[c]
[a]
Bassam Alameddine, Andrew H. Rice, Christine Luscombe, and Titus A. Jenny*
We report the versatile synthesis of two tribenzo[fj,ij,rst]penta-
phene (TBP) derivatives bearing two diarylamine substituents
attached at the opposite ends of the aromatic core. Field
effect transistor (FET) devices of the bis-diarylamine-TBP com-
pounds were fabricated using spin coating under different
concentrations, spin speed, and solvent conditions. Emission
spectra and surface investigation by atomic force microscopy
photovoltaic devices than the more symmetrical hexagonal
[
9,10]
disc-shaped hexa-peri-hexabenzocoronene.
In order to in-
crease hole transport efficiency of TBP, we have synthesized
the arylamine tribenzo[fj,ij,rst]pentaphene derivative 1 with
two nitrogen-containing groups attached at the opposite ends
of the aromatic core. Scheme 1 summarizes the few reaction
(
AFM) reveal the formation of aggregates induced by the
strong p–p stacking of the aromatic core leading to island fea-
tures, and thus, unexpected low hole mobilities. The synthetic
strategy we show herein, however, offers the possibility to dec-
orate the TBP core structure with various charge-carrier periph-
eral groups and optimized alkyl chains, which should improve
the crystalline property of their thin films upon deposition,
leading consequently to a better hole transport mobility.
A wide variety of one- and two-dimensional highly p-conjugat-
ed aromatic molecules have been thoroughly studied as po-
[1–4]
tential organic semiconductors.
Among these conjugated
compounds, polycondensed aromatic hydrocarbons with re-
duced symmetries are finding increasing interest, such as 1,4-
[
5]
diphenyl triphenylene-based derivatives whose macrocyclic
[
6]
and polymeric derivatives have shown superior electrolumi-
[
7]
nescent properties. We have recently disclosed the synthesis
of some derivatives based on the larger aromatic core triben-
zo[fj,ij,rst]pentaphene (TBP), whose trapezoidal structure offers
some major advantages over other polycondensed aromatic
hydrocarbons, most notably 1) their versatile synthesis and
[
8]
2
) the easy access to many possible functionalization sites.
Recently, TBP derivatives with alkoxy side chains have shown
better efficiency and photoconductive properties in organic
[
a] Prof. T. A. Jenny
Chemistry Department, University of Fribourg
Chemin du MusØe 9, 1700 Fribourg (Switzerland)
E-mail: titus.jenny@unifr.ch
Scheme 1. Synthesis of the arylamine pentaphene derivatives. Reagents and
conditions: a) KOH, EtOH, reflux, 1 h, 55%; b) phenylvinyl sulfoxide, toluene,
reflux, 2 d, 46%; c) FeCl
3 3 2 2 2
, CH NO , CH Cl , rt, 6 h, 76%; d) diarylamine,
Pd(OAc) , NaOtBu, tBu P, reflux, 2 d, 25% (1a), 50% (1b).
2
3
[
b] Prof. B. Alameddine
Department of Mathematics and Natural Sciences
Gulf University for Science and Technology, Hawally 32093 (Kuwait)
[
c] Dr. A. H. Rice, Prof. C. Luscombe
Materials Science and Engineering Department, University of Washington
Seattle, WA 98195-2120 (USA)
steps towards the target aryl amine pentaphene derivatives;
4
,4’-didodecylbenzil was prepared from the oxidation of 4,4’-
[
11,12]
didodecyltolane
in presence of iodine and dimethyl sulfox-
Supporting information and ORCID(s) from the author(s) for this article
are available on the WWW under http://dx.doi.org/10.1002/
open.201500064.
ide (DMSO) (see Supporting Information for synthetic de-
[
13]
tails).
The double Knoevenagel condensation reaction be-
[
14]
ꢀ
2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
tween the benzil and 1,3-bis(4-bromophenyl)acetone in re-
This is an open access article under the terms of the Creative Commons
Attribution-NonCommercial-NoDerivs License, which permits use and
distribution in any medium, provided the original work is properly cited,
the use is non-commercial and no modifications or adaptations are
made.
[13]
fluxing diphenyl ether
affords the tetraarylcyclopentadie-
none moiety 2 in 55% yield. This latter undergoes a [4+2]
[
15]
Diels–Alder cycloaddition reaction with phenylvinyl sulfoxide
in refluxing toluene yielding, via subsequent spontaneous de-
ChemistryOpen 2015, 4, 453 – 456
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carbonylation and hydrosulfinylbenzene elimination, the dibro-
minated tetraphenyl benzene 3 in 46%. Cyclodehydrogenation
[
16]
reaction of synthon 3 with iron(III) chloride in nitromethane
yields the dibrominated pentaphene 4. Buchwald–Hartwig
[17,18]
cross-coupling reaction
of 4 with diphenyl amine deriva-
tives gives 1a and 1b in 25% and 50% yield, respectively. It
should be noted that the excellent stability and moderate solu-
bility of 4 in common organic solvents offer the possibility to
employ it as a key building block to synthesize a wide variety
of TBP-based monomers and polymers similar to the less-ex-
[6,19]
tended triphenylene-based ones,
but bearing functional
groups such as alkoxy groups, whose attachment prior to the
cyclodehydrogenation step leads to the formation of only par-
[20,21]
tially aromatized compounds.
The two target compounds, 1a and 1b, were soluble
1
enough to be analyzed by H NMR, but a more useful tool for
their characterization was high-resolution matrix-assisted laser
desorption ionization–ion cyclotron resonance mass spectrom-
etry (MALDI-ICR MS) using trans-2-[3-(4-t-butyl-phenyl)-2-
methyl-2-propenylidene]malononitrile (DCTB) as the matrix,
which reveals the high purity of the two pentaphene deriva-
tives as shown from the measured isotopic patterns, as com-
pared to their respective calculated ones (Figure 1).
The bis-diarylamine TBP derivatives 1a and 1b show strong
UV/Vis absorption bands at 302 and 309 nm, respectively,
[8]
which is typical for these aromatic chromophores, in addition
to a series of less intense bands around ~395 nm (Figure 2).
The two new compounds, however, emit in the blue-green
region with a slight red shift for 1b of ~10 nm (Figure 2) as
compared to 1a.
It is worth mentioning that despite the very comparable ab-
sorption spectra of 1a and 1b with respect to the TBP chro-
mophore as mentioned above, the absorption and emission
spectra of the compounds we report herein are significantly
[
8]
Figure 1. a) MALDI-ICR spectrum of 1a in DCTB; inset: measured (up) and
+
red shifted from the alkyl-substituted TBP derivatives by
40 nm, which is explained by the additional conjugation due
calculated isotopic pattern (down), calculated for C78
82 2
H N . b) MALDI-ICR
~
spectrum of 1b in DCTB; inset: measured (up) and calculated isotopic pat-
to the presence of the aryl amines as shown by density func-
tional theory (DFT) calculations with B3LYP at the 6-31G* level
+
146 2
tern (down), calculated for C110H N .
(
Table 1). Likewise, the 0!0 transition bands for 1a and 1b
are clearly visible at 429 and 435 nm, respectively, also red
shifted from the typical value of a 3,12-dialkylated TBP chro-
between 30–50 nm, were made by spin-coating onto Si/SiO2
substrates. In order to improve the films’ smoothness and to
charge optimize mobility, various solutions of 1a and 1b were
prepared with different processing variables, such as the type
of solvent, molar concentration,
[
8]
mophore (~395 nm).
In spite of their moderate solubility in common organic sol-
vents, thin films of 1a and 1b, with thickness ranging typically
and spin speed (Table 2). All the
solutions were sonicated for
Table 1. DFT calculations (B3LYP at the 6-31G* level) of several TBP derivatives disubstituted at their opposite
ends.
3
0 min prior to spin-coating to
reduce aggregation induced by
the strong p–p stacking of the
pentaphene core and to im-
prove the molecules’ solution
processibility. A summary of the
film roughness and field-effect
transistor (FET) device per-
formance is shown in Table 2. It
is worth noting that the depict-
Tribenzopentaphene (TBP) (3,12-disubstituted)
Parent
Diethyl
Di-NMe
2
NMe
2
, NMePh
Di-NMePh
Di-NPh
2
Di-NTolyl
2
HOMO (eV)
LUMO (eV)
Gap
max (nm) calcd.
max (nm) exp.
À5.32
À1.54
3.78
362.32
—
À5.21
À1.47
3.74
À4.54
À1.16
3.38
À4.59
À1.23
3.36
À4.65
À1.31
3.34
À4.73
À1.47
3.26
425.87
429
À4.59
À1.38
3.21
433.29
435
[
a]
[a]
l
363.88
395
408.61
—
410.67
—
411.32
—
l
[
a] very weak transition.
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Table 2. Thin film spin-coating conditions, their root mean square (RMS)
surface roughness, and FET mobilities.
Entry PAH Solv.
Conc.
Spin speed RMS roughness Mobility
À4
2
À1 À1
[10 m] [rpm]
[nm]
[cm V
s ]
1
2
3
4
5
6
7
8
9
1a toluene
1a toluene
1b toluene
1a toluene
1a toluene
1b toluene
1a toluene
4.5
4.5
4.5
4.5
2.0
2.0
0.5
2.0
2.0
2500
19.7
18.4
1.9
21.4
14.5
1.2
13.2
22.7
2.3
n.a.
n.a.
8.3”10
n.a.
n.a.
3.4”10
n.a.
n.a.
4000
4000
5000
4000
4000
4000
4000
4000
À9
À8
À9
1a
1b
DCB
DCB
7.9”10
n.a.: not applicable
[
22]
strate. The growth of islands, and thus incomplete layers, is
known to limit the transport of charge carriers and cause
[
22]
lower carrier mobility. Given the lack of solubilizing groups
for 1a, it is not surprising that the intermolecular interactions
for 1a would be stronger than in 1b.
The mobility of 1b was improved by fourfold to 3.4”
Figure 2. Normalized absorption (red) and emission (green) spectra of the
À8
2
À1 À1
À7
10 cm V
s
when decreasing the solution concentration to
tribenzopentaphene derivatives in toluene: a) emission (c=10 m,
À8
À4
l
ex =302 nm) of 1a, b) emission (c=10 m, lex =309 nm) of 1b. Emission
2”10 m in toluene and keeping the spin speed unchanged
spectra were measured with a maximum intensity (internal scale) of 780 and
40, for 1a and 1b, respectively.
(
Table 2, entry 6). In attempt to improve the smoothness of the
4
films, and so the charge mobility, toluene was replaced by the
more polar o-dichlorobenzene (DCB), which is reported to
reduce aggregation for some other polycondensed aromatic
[
23,24]
ed results represent average values taken from four up to
eight different substrates that is, more than twenty FET devices
for each compound. It is worth-
hydrocarbon molecules.
However, in our hands, the sur-
face roughness of the films increased, suggesting that o-di-
while to mention that several at-
tempts to sublime 1a and 1b
under high vacuum were unsuc-
cessful, which prevented us from
employing thermal deposition
known to be a much better
technique
to
control
the
[4]
smoothness of thin films.
None of the FET devices pre-
pared from 1a showed a hole
mobility, whereas 1b reveals
a
1
mobility
of
8.3”
À9
2
À1 À1
0
cm V s
(Table 2, entry 3)
when spin coated at 4000 rpm
À4
from a 4.5”10 m solution in
toluene. This can be attributed
to the island formation that
takes place for 1a as can be
seen in the atomic force micros-
copy (AFM) images (Figure 3).
This kind of growth can be de-
scribed by the Volmer–Weber
growth mode, which occurs
when the deposited molecules
are more strongly bound to
À4
Figure 3. AFM topography image of a thin film prepared by spin-coating at 4000 rpm of a a) 0.5”10 m 1a in tol-
À4
À4
uene b) 2”10 m 1a in o-dichlorobenzene c) 2”10 m 1b in toluene, and d) its transfer characteristic curves
each other than to the sub- (gate-source voltage, VGS= +80 to À80 V).
ChemistryOpen 2015, 4, 453 – 456
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chlorobenzene is not effective at decreasing aggregation for
molecules 1a and 1b (Table 2, entries 8–9).
Keywords: conducting materials · cross-coupling · fused-ring
systems · Pi interactions · thin films
Figure 3b depicts the AFM investigation of the film topogra-
phy of 1a spin-coated from o-dichlorobenzene, showing
a poor film quality with consistent island features that display
an average surface roughness of ~23 nm. Replacing the sol-
vent with toluene, altering the spin speed, and decreasing the
concentration slightly improved the film quality to an average
surface roughness of ~13 nm, but without detecting any mobi-
lity for their FET devices. The lack of mobility for 1a could be
explained by the small number of number alkyl chains leading
to a lower solubility, and therefore, causing a more rapid ag-
gregation that produces the island features in the solid state.
The AFM investigation of thin films of 1b, on the other hand,
revealed smooth surfaces with no visible island features and
an average roughness of ~2 nm (Table 2, entries 3 and 9). This
later was decreased to ~1 nm when lowering the concentra-
[
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B. A. would like to thank the Kuwait Foundation for the Advance-
ment of Sciences for supporting this work (grant number 2011-
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1413-02), and C. L. acknowledges the US National Science Foun-
Received: March 9, 2015
dation (NSF) (DMR 1407815).
Published online on May 6, 2015
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ꢀ 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim