Electron acceptors based on functionalizable cyclopenta[hi]aceanthrylenes and dicyclopenta[de,mn]tetracenes

Article abstract of DOI:10.1021/ja304602t

We report the synthesis and selective functionalization of two externally fused cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs) and demonstrate their electron accepting behavior. 2,7-Bis(trimethylsilyl) cyclopenta[hi]aceanthrylene (1) and 2,8-

Full text of DOI:10.1021/ja304602t

Article
pubs.acs.org/JACS
Electron Acceptors Based on Functionalizable
Cyclopenta[hi]aceanthrylenes and Dicyclopenta[de,mn]tetracenes
Jordan D. Wood,‡ Jessica L. Jellison,‡ Aaron D. Finke,† Lichang Wang,‡ and Kyle N. Plunkett*,‡
‡Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, Illinois 62901, United States
†Department of Chemistry, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
S
* Supporting Information
ABSTRACT: We report the synthesis and selective functionaliza-
tion of two externally fused cyclopenta-fused polycyclic aromatic
hydrocarbons (CP-PAHs) and demonstrate their electron accepting
behavior. 2,7-Bis(trimethylsilyl)cyclopenta[hi]aceanthrylene (1) and
2,8-bis(trimethylsilyl)dicyclopenta[de,mn]tetracene (4) were pre-
pared in a one-pot, palladium-catalyzed cross-coupling of
(trimethylsilyl)acetylene and either 9,10-dibromoanthracene or
5,11-dibromotetracene, respectively. The trimethylsilyl groups were
selectively converted into bromides via substitution with N-
bromosuccinimide to create universal partners (2 and 6) for metal-catalyzed cross-coupling reactions. To demonstrate the
utility of the halogenated CP-PAHs, we successfully employed a Sonogashira cross-coupling between the CP-PAHs and a
phenylacetylene derivative. The resulting compounds (3 and 7) were found to be highly conjugated between the CP-PAH core
and the substituents, as demonstrated by large bathochromic shifts in the absorption spectra as well as density functional theory
calculations. Ethynylated CP-PAHs 3 and 7 were found to possess low optical bandgaps (1.52 and 1.51 eV, respectively) and
displayed two reversible reductions. We further demonstrated the fullerene-like electron-accepting behavior of 3 through
solution-phase fluorescence quenching of the prototypical electron donor, poly(3-hexylthiophene).
corannulene).5−10 The synthetic methods8,11,12 used to create
these five-membered ring-containing compounds are typically
INTRODUCTION
■
Fullerene derivatives are currently the most widely employed
laborious, not conducive to scaled up procedures, and often too
electron acceptor material because of their stability, their
harsh to maintain functionality for subsequent chemical
disposition to create charge percolation pathways through
transformations. Recent advances have led to new scalable
crystallization, and their generous capacity to accept
syntheses13 and new CP-PAHs such as indenofluorenes,14−17
electrons.1−3 Unfortunately, they are not conducive to chemical
modification that would lead to dramatically new morpho-
logical or electronic properties. Fullerenes can only be modified
dibenzopentalenes,18−20 emeraldicenes,21,22 and cyclopenta-
[hi]aceanthrylenes23 that show promise for functionalization
and possess relatively low bandgaps and good stability.
through addition reactions, which limit the interactions
However, comparison studies of the electron acceptor behavior
between the substituents and the fullerene to inductive effects
that are in general weak and fall off exponentially with
of CP-PAHs have shown that externally fused CP-PAHs are
distance.4 More importantly, fullerenes are not able to undergo
often more capable electron acceptors than their internally
fused counterparts.24 We were therefore interested in creating
substitution reactions that lead to new fully conjugated species.
It is therefore difficult to appreciably change the energies of the
highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) due to a lack of
acceptors based on externally fused CP-PAHs. We were
encouraged by the serendipitous discovery by Garcia-Garibay
and co-workers that externally fused aceanthrylenes (one five-
resonance effects.4 To accomplish such control, and to create
membered ring) and cyclopenta[hi]aceanthrylenes (two five-
membered rings) could be obtained in one step from the
new acceptor materials that can be electronically and/or
palladium-catalyzed cross-coupling of bromoanthracene deriv-
morphologically tailored, we envision creating conjugated
atives and a few terminal acetylenes.25,26 The resulting
species with the desirable cyclopenta-fused polycyclic aromatic
compounds were found to have fullerene-like electron affinity,
hydrocarbon (CP-PAH) character of fullerenes and universal π-
in that they could be reversibly reduced twice at low potentials.
donating or π-withdrawing aromatics. Using this strategy, small-
molecule variants that behave similarly to fullerenes but can
have their electronic properties systematically adjusted through
This observation is justifiable as the cyclopenta[hi]-
aceanthrylene27−29 subunit is a unique fragment in the oval-
shaped C70 fullerene (Figure 1). A resonance structure of
chemical synthesis will be prepared. This article describes our
initial work in creating such systems.
Traditional interest in CP-PAH synthesis has predominantly
Received: May 11, 2012
focused on fragments of C60 that have bowl-like structures (i.e.,
© XXXX American Chemical Society
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resulting compounds are fully conjugated, and therefore
systematic modulation of peripheral groups should readily
affect the frontier orbitals of the electron acceptor CP-PAH
core. We have prepared the previously unknown 2,7-
bis(trimethylsilyl)cyclopenta[hi]aceanthrylene30 (1) via a one-
pot, Pd-catalyzed cross-coupling between 9,10-dibromoanthra-
cene and (trimethylsilyl)acetylene (TMS-acetylene, Scheme 1).
As formerly demonstrated,26 heating the reaction in a sealed
tube at 110 °C in the absence of copper iodide minimizes the
typical Sonogashira cross-coupling product and promotes the
formation of a thermally stable alkenylpalladium intermediate.25
This intermediate is capable of undergoing an intramolecular
alkene insertion into the anthracene core to form a five-
membered ring. The reaction proceeds in high yield, and
multiple grams of product can be easily obtained. To create a
universal partner for metal-catalyzed cross-coupling reactions,
the resulting vinylic-TMS groups were substituted with N-
bromosuccinimide (NBS) to give 2,7-dibromocyclopenta[hi]-
aceanthrylene (2). The silyl-substitution strategy is preferable
because its ipso-selectivity is in contrast to simple electrophilic
bromination. Dibromide 2 was easily converted to the π-
extended, diethynyl CP-PAH derivative 3 by modified
Sonogashira cross-coupling with 1-(decyloxy)-4-ethynylben-
zene. The cross-coupling reaction was carried out at room
temperature using Pd(PhCN)2Cl2 and PtBu3 in toluene and
diisopropylamine to give 3 in 90% yield. The resulting CP-PAH
conjugate shows remarkable properties, including low bandgaps
and electron-accepting behavior that will be discussed shortly.
We also became interested in extending the described ring-
closure and bromination methodology to other polycyclic
aromatic hydrocarbons such as tetracene. We felt this new
Figure 1. Cyclopenta[hi]aceanthrylene is a fragment of C70 and can
accept two electrons through aromatic 4n+2 stabilization.
cyclopenta[hi]aceanthrylene details the chemical means for
reduction by forming a 4n+2 aromatic, benzocyclopentadienyl
anion (favorable) and a 4n anti-aromatic, benzocyclopenta-
dienyl cation (unfavorable). The addition of two electrons
creates a reduced structure with two stabilized aromatic,
benzocyclopentadienyl anions. These unique properties, as well
as the ability to scale up the synthesis, suggested new electron-
accepting compounds based on the cyclopenta[hi]-
aceanthrylene or other similar CP-PAHs scaffolds4 would be
of utility.
RESULTS AND DISCUSSION
■
In this work, we have developed a methodology to create two
new CP-PAH scaffolds that are capable of discrete function-
alization via transition metal-catalyzed cross-couplings. The
a
Scheme 1. Synthesis of Brominated CP-PAHs 2 and 6 and Conjugated Analogues 3 and 7
a
Reagents: (i) TMS-acetylene, Pd(PPh3)2Cl2, PPh3, benzene, triethylamine, 110 °C; (ii) NBS, THF; (iii) 1-(decyloxy)-4-ethynylbenzene,
Pd(PhCN)2Cl2, PtBu3, CuI, toluene, diisopropylamine.
B
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Figure 2. Crystal structure and columnar packing (looking down a-axis) of 4.
strategy would provide quick access to dicyclopenta[de,mn]-
tetracene31 scaffolds and provide opportunities for their
selective functionalization. Starting with 5,11-dibromotetracene,
we carried out the one-pot Pd-catalyzed cross-coupling with
TMS-acetylene and expected to find a mixture of 4 and 5 owing
to the central location of the bromides (Scheme 1).
Interestingly, we found 2,8-bis(trimethylsilyl)dicyclopenta-
[de,mn]tetracene (4) as the major product from the reaction,
with 5 present only in trace amounts. Crystals of 4 suitable for
X-ray analysis, grown from slow evaporation of CDCl3 solution,
confirmed the regioselectivity (Figure 2). The solid-state
packing shows π-stacked dimers propagating down the a-axis
and the column orientation along the c-axis offset by ∼90°. The
TMS groups appear to enforce π-stacking by blocking a more
typical “herringbone” interaction.32 The face-to-face arrange-
ment is similar to other trialkylsilane-pentacene derivatives.33
Bromination of 4 with NBS was also successfully employed to
create 2,8-dibromodicyclopenta[de,mn]tetracene (6). Unfortu-
nately, the reaction is not as straightforward as for 2 because
prolonged reaction times in the presence of NBS led to a
variety of side products that were not immediately identified.
However, we were able to successfully obtain a reasonable yield
of 6 by monitoring the reaction via NMR and then filtering the
precipitated product straight from the reaction mixture. Upon
purification, the product was air- and solution-stable and could
be carried forward with an analogous Sonogashira cross-
coupling of 1-(decyloxy)-4-ethynylbenzene to give 7.
It is immediately obvious by visual inspection that the
photophysical properties of the π-extended compounds 3 and 7
are dramatically altered from those of the TMS-functionalized
CP-PAHs 1 and 4. While 1 is a black solid that creates a tan-
colored solution, 3 is a dark green/black solid and forms a dark
green solution (Figure 3). Similarly, the tetracene derivative
transforms from an aqua-blue to a dark green solution upon
extending the conjugation from 4 to 7. The absorption spectra
for compounds 1, 3, 4, and 7 can be found in Figure 3. Similar
to a previous analogue,26 1 possessed three sets of absorption
bands: a prominent band centered at 248 nm, a medium range
band with fine structure from 340 to 480 nm, and a broad
transition centered at 560 nm with an absorbance onset of 682
nm. Upon the formation of the π-extended 3, a prominent
fourth transition emerged at 327 nm, and all other transitions
were slightly (or largely) bathochromically shifted. The most
striking change occurred to the longest wavelength transition
that dramatically red-shifted and grew in intensity at 680 nm
with an absorbance onset of 815 nm. The tetracene derivative
demonstrated a similar bathochromic shift, with the lowest
energy transition shifting from an absorbance onset of 693 nm
for 4 to an absorption onset of 822 nm for 7. Although the
Figure 3. Absorbance of anthracene-based 1 and 3 (top) and of
tetracene-based 4 and 7 (bottom).
spectra of 3 and 7 are not shown on the same plot, it is
apparent that the absorption spectra and optical bandgaps (1.52
and 1.51 eV, respectively) are very similar. The overall
bathochromic shifts upon functionalization suggest highly
delocalized states with communication between the central
CP-PAH core and the phenylacetylene substituents. To
confirm the delocalized character of 3 and 7, we explored
their electronic structure further with density functional theory
(DFT) calculations. Calculations were carried out using the
Becke’s three-parameter exchange functional with the Lee−
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Figure 4. DFT-calculated HOMO (left) and LUMO contours of 3 (top) and 7 (bottom).
Yang−Parr correlation functional (B3LYP)34−36 with a 6-
311G(d,p) basis set, which was shown to be sufficiently
accurate from our previous calculations.37,38 As shown in Figure
4, the HOMO contours of 3 and 7 illustrate the delocalized
character that extends from the CP-PAH core to the
phenylacetylene substituents. Further analysis of the time-
dependent DFT suggests the excitation from HOMO to
LUMO undergoes partial charge transfer. In this type of
excitation, DFT calculations typically do not provide accurate
absorption spectra simulation. However, the current calcu-
lations predicted the first absorptions for 3 and 7 to occur at
821 and 856 nm, respectively. These values agree reasonably
well with the experimental measurement of absorbance onset of
815 and 822 nm, respectively.
Cyclic voltammetry of the four CP-PAH compounds was
utilized to further elucidate the electronic structure and assign
energy levels to the frontier orbitals (Figure 5). Each
compound showed two reduction steps that can be assigned
to the two-step reduction process described in Figure 1. Upon
conversion of 1→3 and 4→7, the onset of the first reduction
wave was lowered by 0.23 and 0.17 V, respectively, suggesting
the reduced CP-PAH structures are further stabilized through
conjugation to the periphery substituents (Table 1). Each of
the compounds 1, 3, 4, and 7 showed irreversible oxidation
Table 1. Summary of Electrochemical and Optical
a
Properties
Egap (eV)
Eox/onset Ered/onset
HOMO
(eV)
LUMO
(eV)
e-
compd
(V)
(V)
chem optical
1
3
4
7
0.79
0.39
0.56
0.39
0.69
0.38
0.54
−1.39
−1.16
−1.35
−1.18
−
−5.59
−5.19
−5.36
−5.19
−5.49
−5.18
−5.34
−3.41
−3.64
−3.45
−3.62
−2.25
−2.61
2.18
1.55
1.91
1.57
1.82
1.52
1.79
1.51
3.24
2.57
2.79
b
anthracene
tetracene
perylene
−
−
−
b
−
−
b
−2.55
a
Potentials are measured relative to a ferrocenium/ferrocene redox
couple used as an internal standard (Figure 5 or Supporting
Information). Eox/onset is the onset of oxidation potential, Ered/onset is
the onset of reduction potential. HOMO and LUMO values calculated
on the basis of the oxidation of the ferrocene reference in vacuum (4.8
b
eV). From optical bandgap (Supporting Information).
steps that were modulated through substitution. Using an
internal ferrocene reference, the HOMO and LUMO levels of
each compound were calculated (Table 1). As demonstrated
from the optical bandgaps in the absorption spectra, the
experimentally obtained frontier orbitals of 3 (HOMO = −5.19
eV, LUMO = −3.64 eV) and 7 (HOMO = −5.19 eV, LUMO =
−3.62 eV) are surprisingly similar, even though they are based
on two separate acenes. This peculiarity may be rationalized by
noting the similarities of the chromophore length and structure
in the calculated frontier orbitals of 3 and 7 (Figure 4). An
interesting discrepancy between the optical bandgap and the
electrochemical bandgap is found for 1 and 4, while 3 and 7 are
relatively similar. Although we do not fully understand this
discrepancy at this time, the data suggest a substantial
difference between the exciton binding energy of these two
classes (TMS vs ethynylated) of compounds.39 These results
highlight the electronic ramifications of externally fused CP-
PAHs and how the five-membered ring can greatly influence
the electronic properties of PAHs.24 We have included the
electrochemical properties of anthracene, tetracene, and
perylene in Table 1. Perylene possesses a fused ring structure
similar to that of cyclopent[hi]aceanthrylene 1 with the
exception of substitution of five-membered rings for six-
Figure 5. Cyclic voltammograms of 1, 3, 4, and 7 in THF with 0.1 M
tetrabutylammonium hexafluorophosphate, glassy carbon electrode,
platinum counter electrode, and an Ag/AgCl reference electrode. Scan
rate = 50 mV/s. Ferrocene added as internal standard and referenced
to 0 V.
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Figure 6. Emission spectrum of P3HT (1.0 × 10−5 M) in chloroform with varying concentrations of the electron acceptor 3: (a) 0, (b) 1.00 × 10−6,
(c) 2.50 × 10−6, (d) 5.00 × 10−6, (e) 7.50 × 10−6 M, (f) 1.00 × 10−5, (g) 1.50 × 10−5, and (h) 2.00 × 10−5 M. The spectra were corrected for the
inner filter effect due to the absorbance of 3 at the excitation and emission wavelengths (Supporting Information).
membered rings. As can be seen in Table 1, the CP-PAH
analogues have LUMOs that are ∼1 eV lower in energy than
those of the parent PAHs (Supporting Information). The
B3LYP calculated energy levels of 3 (HOMO = −5.14 eV,
LUMO = −3.27 eV) and 7 (HOMO = −5.09 eV, LUMO =
−3.26 eV) as well as the calculated absorption spectra
(Supporting Information) agreed reasonably well with the
experimental results. As a final comparison, the low-lying
LUMOs described here are similar to the literature reported
values for PCBM-C60 (LUMO = −3.7 eV)40 and other small-
molecule acceptors such as perylene bisimide (LUMO = −3.8
eV).41
several favorable traits with fullerenes. They possess low-lying
LUMOs, exhibit minimal fluorescence, and act as electron
acceptors. Additionally, the structures are fully conjugated,
absorb broadly over the visible spectrum, and have remarkably
low bandgaps. We have also demonstrated that the electronic
properties of the CP-PAHs can be controlled via substitution of
the brominated compounds 2 and 6 and have recently utilized
2 as a monomer in the preparation of donor−acceptor
copolymers.46 Finally, electronic and morphological control
through side-chain variation presents opportunities to create
new functional materials that may have utility in organic
photovoltaics and field effect transistors, topics we are currently
pursuing.
None of the CP-PAH compounds prepared in this work
produce easily measured fluorescence, a property that is
consistent with the extremely small fluorescent quantum yields
found for other small-molecule CP-PAHs26,42 and full-
erenes.43,44 However, the lack of fluorescence was beneficial
in our attempt to further illustrate the similarity of the electron-
accepting behavior of the described compounds to fullerenes.
We performed fluorescence quenching experiments of a
prototypical donor material, poly(3-hexylthiophene) (P3HT),
with varying concentrations of 3 (Figure 6). We found that 3
was an excellent quencher for P3HT, as the observed
fluorescence intensity was markedly reduced upon addition of
the electron acceptor. Analysis of the quenching data using the
Stern−Volmer equation showed a linear trend and gave a
quenching constant KSV = 2.7 × 104 M−1, which was similar to
that of C60. A general electron-transfer scheme is summarized
in Figure 6 and shows the energetically favorable transfer from
the P3HT LUMO (−3.2 eV) to the LUMO of 3 (−3.64 eV).
The electron transfer described here is analogous to the well-
known P3HT/fullerene donor−acceptor pairing used in high-
efficiency photovoltaic cells.3 Although the energy difference
between the LUMOs of 3 and P3HT is not optimal for high
open-circuit voltages in photovoltaic cells,45 the described
system provides ample opportunities for tuning the frontier
orbitals through conjugation with the correct choice of
aromatic substituent added to 2 or 6.
EXPERIMENTAL SECTION
■
Unless otherwise noted, all reagents were used as received, and all
reactions were carried out under an argon atmosphere. Column
chromatography was performed on a CombiFlash Rf system with
Redisep normal phase silica columns (Teledyne ISCO Inc., Lincoln,
NE). Millipore filtrations were accomplished with a 47 mm Millipore
vacuum filter. 1H NMR and 13C NMR were recorded on a Varian 400
MHz NMR station at room temperature, unless otherwise noted.
Cyclic voltammetry was performed on a CH-Instruments 700D
potentiostat with a 0.1 M tetrabutylammonium hexafluorophosphate
solution (in THF) using a glassy carbon electrode, a platinum counter
electrode, and a Ag/AgCl reference electrode. Mass spectra and X-ray
crystallography were obtained from the University of Illinois Mass
Spectrometry Laboratory and the George L. Clark X-ray Facility,
respectively.
2,7-Bis(trimethylsilyl)cyclopenta[hi]aceanthrylene (1). In a
glovebox, 9,10-dibromoanthracene (2.0 g, 6.0 mmol), TMS-acetylene
(2.34 g, 3.30 mL, 23.8 mmol), Pd(PPh3)2Cl2 (190 mg, 0.27 mmol),
triphenylphosphine (370 mg, 1.4 mmol), benzene (15 mL), and
triethylamine (6 mL) were combined in a sealed tube. The reaction
mixture was stirred overnight at 110 °C. The reaction was cooled to
room temperature and filtered. The white solid was washed with
hexane, and the collected filtrate was concentrated. The residue was
purified by silica gel chromatography (Rf = 0.3, 100% hexane) followed
by recrystallization in ethanol to give 1.37 g (62%) of a black
crystalline material. Alternatively, the reaction can also be carried out
without the use of a glovebox. In a sealed tube, 9,10-dibromoan-
thracene and triphenylphosphine were dissolved in benzene and
triethylamine and bubbled with argon for 10 min. To this solution was
added the palladium followed by the TMS-acetylene, and the tube was
sealed. Similar yields can be achieved with this method. 1H NMR (400
MHz, CDCl3) δ 8.17 (d, J = 8.5 Hz, 2H), 7.82 (d, J = 6.5 Hz, 2H),
7.73 (s, 2H), 7.66 (dd, J = 8.5, 6.6 Hz, 2H), 0.45 (s, 18H). 13C NMR
CONCLUSIONS
■
We have presented a unique synthetic pathway to access
externally fused CP-PAHs (2 and 6) that can be further
modified through metal-catalyzed cross-coupling reactions. We
have prepared two such modified analogues, 3 and 7, that share
E
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(101 MHz, CDCl3) δ 144.4, 142.8, 138.5, 135.7, 130.7, 129.0, 136.2,
125.0, 124.0, 0.06. LRMS (EI+) 370.0; HRMS m/z for C24H26Si2 calcd
370.1573, found 370.1558.
7.51 (d, J = 8.7 Hz, 4H), 6.86 (d, J = 8.8 Hz, 4H), 3.94 (t, J = 6.6 Hz,
4H), 1.79−1.70 (m, 4H), 1.2−1.4 (m, 28H), 0.82 (t, J = 6.8 Hz, 6H).
13C NMR (101 MHz, THF-d8) δ 161.4, 142.5, 138.9, 134.6, 132.3,
131.9, 130.9, 129.9, 129.5, 127.3, 126.6, 126.4, 123.5, 117.3, 116.3,
98.0, 85.6, 55.7, 33.7,, 31.4, 31.4, 31.2, 31.1, 31.1, 27.9, 24.4, 15.3.
LRMS (MALDI) 788.51; HRMS m/z for C58H60O2 calcd 788.4593,
found 788.458.
2,7-Dibromocyclopenta[hi]aceanthrylene (2). To a 500 mL
round-bottom flask were added 1 (1.87 g, 5.05 mmol) and THF (200
mL). The solution was cooled to 0 °C, and NBS (1.96 g, 11.1 mmol)
was added all at once. The reaction was allowed to warm to room
temperature and stirred for 3 h. The solvent was removed, and the
residue was dispersed in 300 mL of hot ethanol and then filtered. The
solid was washed with ethanol and collected to give 1.27 g (66%) of a
black/green solid. Further purification could be accomplished via
recrystallization with chloroform. 1H NMR (400 MHz, CDCl3) δ 8.16
(d, J = 8.4 Hz, 2H), 7.80 (d, J = 6.7 Hz, 2H), 7.72 (dd, J = 8.4, 6.7 Hz,
2H), 7.58 (s, 2H). 13C was difficult due to solubility. LRMS (EI+)
383.8; HRMS m/z for C18H8Br2 calcd 381.8993, found 381.9002.
2,7-Bis((4-(decyloxy)phenyl)ethynyl)cyclopenta[hi]-
aceanthrylene (3). In a glovebox were combined 2 (50 mg, 0.13
mmol), Pd(PhCN)2Cl2 (3.0 mg, 0.0078 mmol), and CuI (1.5 mg,
0.0078 mmol) in a small vial. To these solids were added toluene (2
mL), diisopropylamine (0.33 mL), and PtBu3 (3.2 mg, 32 mg of a 10%
solution). The mixture was stirred for 2 min, and then a solution of 1-
(decyloxy)-4-ethynylbenzene (74 mg, 0.29 mmol) in toluene (1 mL)
was added. The vial was capped and stirred for 6 h at room
temperature. The solvent was removed, and the crude solid was
dissolved in a minimal amount of THF and precipitated into cold
methanol. The green/black solid was filtered to give 86 mg (90%). 1H
NMR (400 MHz, CDCl3) δ 8.19 (d, J = 8.5 Hz, 2H), 8.00 (d, J = 6.7
Hz, 2H), 7.72 (dd, J = 8.5, 6.7 Hz, 2H), 7.69 (s, 2H), 7.56 (d, J = 8.9
Hz, 4H), 6.92 (d, J = 8.9 Hz, 4H), 4.00 (t, J = 6.6 Hz, 4H), 1.86 − 1.76
(m, 4H), 1.29−1.47 (m, 28H), 0.89 (t, J = 6.8 Hz, 6H). 13C NMR
(101 MHz, CDCl3) δ 159.4, 140.5, 138.0, 134.0, 133.1, 129.4, 129.1,
128.0, 126.2, 124.2, 123.4, 115.3, 114.7, 97.5, 84.5, 68.1, 31.9, 29.6,
29.6, 29.4, 29.3, 29.2, 26.0, 22.7, 14.1. LRMS (MALDI) 738.5; HRMS
m/z for C54H58O2 calcd 738.4437, found 738.446
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthesis and characterization of precursor compounds, inner
filter effect correction, NMR spectra, computational methods
and spectra, molar absorption of compounds, electrochemistry
of acenes, and X-ray crystallography data. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
kplunkett@chem.siu.edu
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
K.N.P. thanks Southern Illinois University for startup funds and
a seed grant. The authors thank Danielle Gray for help with the
crystallography. She is a part of The Materials Chemistry
Laboratory at the University of Illinois, which was supported in
part by grants NSF CHE 95-03145 and NSF CHE 03-43032
from the National Science Foundation.
REFERENCES
■
2,8-Bis(trimethylsilyl)dicyclopenta[de,mn]tetracene (4). In a
glovebox, 5,11-dibromotetracene (600 mg, 1.55 mmol), TMS-
acetylene (763 mg, 7.77 mmol), bis(triphenylphosphine)palladium(II)
chloride (54.7 mg, 0.077 mmol), triphenylphosphine (94.0 mg, 0.360
mmol), triethylamine (630 mg, 77.0 mmol), and benzene (15 mL)
were combined in a sealed tube. The solution was stirred at 110 °C
overnight. After cooling to room temperature, solvent was removed
and the resulting residue was purified via silica gel chromatography (Rf
= 0.28, 100% hexane) to give 471 mg (72%) of a dark blue/black solid.
1H NMR (400 MHz, CDCl3) δ 8.99 (s, 2H), 8.02 (d, J = 8.5 Hz, 2H),
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7.97 (s, 2H), 7.84 (d, J = 6.4 Hz, 2H), 7.59 (dd, J = 8.5, 6.5 Hz, 2H),
0.48 (s, 18H). 13C NMR (101 MHz, CDCl3) δ 144.8, 140.2, 138.0,
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tube were dissolved 4 (27 mg, 0.064 mmol) and NBS (57 mg, 0.32
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1
black solid. H NMR (400 MHz, CDCl3) δ 8.82 (s, 2H), 8.08 (d, J =
8.6 Hz, 2H), 7.80 (d, J = 6.5 Hz, 2H), 7.79 (s, 2H), 7.64 (dd, J = 8.5,
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1
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