Structural effects on the electronic properties of extended fused-ring thieno[3,4-b]pyrazine analogues

Article abstract of DOI:10.1021/jo200850w

The synthesis and characterization of the extended thieno[3,4-b]pyrazine analogues acenaphtho[1,2-b]thieno[3,4-e]pyrazine (3a), 3,4-dibromoacenaphtho[1, 2-b]thieno[3,4-e]pyrazine (3b), 3-octylacenaphtho[1,2-b]thieno[3,4-e]pyrazine (3c), dibenzo[f,h]thieno[3,4-b]quinoxaline (4), and thieno[3′,4′:5, 6]pyrazino[2,3-f][1,10]phenanthroline (5) are reported. Comparison of structural, electrochemical, and photophysical properties to those of simple thieno[3,4-b]pyrazines are provided in order to provide structure-function relationships within this series of compounds.

Full text of DOI:10.1021/jo200850w

NOTE
pubs.acs.org/joc
Structural Effects on the Electronic Properties of Extended Fused-Ring
Thieno[3,4-b]pyrazine Analogues
Jon P. Nietfeld,† Ryan L. Schwiderski,† Thomas P. Gonnella,‡ and Seth C. Rasmussen*,†
†Department of Chemistry and Biochemistry, North Dakota State University, Dept. 2735, PO Box 6050, Fargo,
North Dakota 58108, United States
‡Division of Science and Mathematics, Mayville State University, Mayville, North Dakota 58257, United States
S Supporting Information
b
ABSTRACT: The synthesis and characterization of the extended
thieno[3,4-b]pyrazine analogues acenaphtho[1,2-b]thieno[3,4-e]-
pyrazine (3a), 3,4-dibromoacenaphtho[1,2-b]thieno[3,4-e]pyrazine
(3b), 3-octylacenaphtho[1,2-b]thieno[3,4-e]pyrazine (3c), dibenzo[f,
h]thieno[3,4-b]quinoxaline (4), and thieno[30,40:5,6]pyrazino[2,3-f]-
[1,10]phenanthroline (5) are reported. Comparison of structural,
electrochemical, and photophysical properties to those of simple
thieno[3,4-b]pyrazines are provided in order to provide structureꢀ
function relationships within this series of compounds.
he 2,3-disubstituted thieno[3,4-b]pyrazines (Chart 1, 1
and 2) have been shown to be excellent building blocks
over a period of hours or even minutes at higher temperatures,
the generation of the extended fused-ring analogues occurs much
more slowly and requires several hours at elevated temperatures.
As 3,4-diaminothiophene can be isolated in good yield from the
reduction of 2,5-dibromo-3,4-dinitrothiophene21 and unsubsti-
tuted diones such as 1,2-acenaphthenequinone or 9,10-phenan-
threnequinone are commercially available, these species are
relatively simple to produce for applications to organic materials.
Additional synthesis is required, however, to generate func-
tionalized derivatives, which are important for the generation of
processable materials, as well as additional tuning of the corre-
sponding electronic and optical properties.20 In order to generate
the halogenated 3b as a precursor for families of functionalized
acenaphtho[1,2-b]thieno[3,4-e]pyrazines, the production of
dione 6 was investigated (Scheme 2). Although previous
methods22 had heated acenaphthenequinone in a bromine slurry
to generate 6, attempts to reproduce these methods revealed
that bromination was not sufficiently selective. Attempts to
improve selectivity using NBS resulted in no reaction with the
applied conditions. Dione 6 was successfully produced from
acenaphthene23 (Scheme 2), but unfortunately both 6 and 3b
exhibited very low solubility, thus severely limiting the applica-
tion of 3b.
T
for the production of low band gap conjugated polymers.1ꢀ9
Poly(2,3-dialkylthieno[3,4-b]pyrazine)s have exhibited band
gaps as low as ∼0.7 eV,2ꢀ6 and thieno[3,4-b]pyrazine-based
copolymers have produced band gaps ranging from 0.36 to
2.1 eV.7ꢀ9 Control of the band gap is an important factor in the
production of technologically useful materials, and the applica-
tion of thieno[3,4-b]pyrazines has been one of the more
successful approaches to this goal.1
While the majority of new thieno[3,4-b]pyrazines utilize mod-
ified functionality at the 2- and 3-positions, a number of extended
fused-ring analogues (Chart 1, 3ꢀ5) have also been recently
applied as potentially improved building blocks.6c,9b,10ꢀ15 Such
extended fused-ring analogues have included acenaphtho[1,2-
b]thieno[3,4-e]pyrazines6c,10ꢀ12 (3), dibenzo[f,h]thieno[3,4-b]
quinoxalines9b,12ꢀ16 (4), thieno[30,40:5,6]pyrazino[2,3-f][1,10]
phenanthroline16,17 (5), and others.12b,18 As these studies have
focused on the resulting materials, full characterization of the
monomeric heterocycles has not been a priority and little effort has
been made to correlate the effect of chemical structure on the
electronic and optical properties. Collected herein is the complete
characterization of compounds 3ꢀ5, along with comparison to the
simple thieno[3,4-b]pyrazines 1 and 2. The goal is to provide a
better understanding of the structureꢀfunction relationships in
such thieno[3,4-b]pyrazines so that they may be better applied to
the production of advanced materials.
An alternate approach24 focused on enhancing the solubility of
the initial naphthalene in hopes to simplify purification for the
subsequent steps. Thus 1-octylnapthalene was produced and
then subjected to FriedelꢀCrafts acylation, forming mixtures of
dione 7 and 1,2-bis(4-octylnaphthalene-1-yl)ethane-1,2-dione
(8). Increasing the yield of 7 proved to be difficult because the
Synthesis. As with typical 2,3-dialkyl or 2,3-diaryl-thieno[3,4-
b]pyrazines,19 compounds 1ꢀ5 are all produced by the reaction
of 3,4-diaminothiophene20 and an R-dione via a double con-
densation process (Scheme 1). While the condensation of simple
thieno[3,4-b]pyrazines can be carried out at room temperature
Received: April 26, 2011
Published: June 29, 2011
r
2011 American Chemical Society
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|

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NOTE
Chart 1. Thieno[3,4-b]pyrazines and Extended Fused-Ring Analogues
is nearly identical to the parent thiophene, while the fused
pyrazine shows some bond fixation.19 Comparison of the ace-
naptho portion of 3a with acenaphthylene,26 however, reveals
significant differences. The exterior bonds C(8)ꢀC(9) and
C(10)ꢀC(11) of 3a exhibit shortening, while the interior bonds
C(7)ꢀC(12) and C(11)ꢀC(12) show elongation. As a result,
the average bond alternation in 3a is significantly reduced,
indicative of enhanced delocalization and conjugation within
the extended fused-ring system.
Scheme 1. Synthesis of Thieno[3,4-b]pyrazines and
Extended Fused-Ring Analogues
Electrochemistry. Electrochemical data of 1ꢀ5 are given in
Table 2, and cyclic voltammograms of 2ꢀ5 are shown in Figure 1.
As previously reported, thieno[3,4-b]pyrazines exhibit an irre-
versible thiophene-based oxidation and a quasireversible pyrazine-
based reduction.19 Typical of thiophene derivatives, the
irreversible nature of the oxidation results from the formation
and rapid coupling (τ < 10ꢀ5 s) of thiophene-based radical
cations, thus leading to oligomeric and polymeric products.27,28
Unlike typical thiophenes, however, thieno[3,4-b]pyrazine oxi-
dations occur at much lower potentials and agree well with the
oxidation potentials of other analogous fused-ring thiophene
systems (1.1ꢀ1.5 V).29 Comparing 1 to its diphenyl analogue 2
shows that the additional conjugation provided by the phenyl
groups results in a shift of both oxidation and reduction to lower
potentials. The greater effect on the reduction has been shown
to be due to the direct placement of the functional groups on
the pyrazine ring, which contributes more significantly to the
LUMO than the HOMO.20
Scheme 2. Synthesis of Fused-Ring Dione Precursors
Analogue 3a can be thought of as thieno[3,4-b]pyrazine 2 in
which the two phenyl groups have been fused to generate the
acenaphthylene group. As expected, this provides greater π-
overlap and a greater shift of the redox processes to lower
potentials. As the acenaphthylene unit does not exhibit oxidation
below 2 V and calculations of the radical cation of 3a predict the
highest spin density at the thiophene R-positions,10 the oxidation
of 3a is believed to be thiophene-based and analogous to that of
thieno[3,4-b]pyrazines. The functionalized analogues 3b and 3c
give shifts consistent with previously reported functional group
effects on thieno[3,4-b]pyrazines.20 For 3b, the electron-with-
drawing bromo functionalities result in stabilization of both the
HOMO and LUMO, thus lowering the potential for reduction
while increasing the potential for oxidation. In contrast, the octyl
group of 3c is weakly electron-donating and causes a slight
destabilization of HOMO and LUMO with corresponding shifts
in potential. As previously illustrated, the electronic nature of the
functional groups affects LUMO levels to a greater extent than
HOMO levels.
electrophilic nature of the oxalyl chloride/AlCl3 complex re-
sulted in enhanced reactivity para to the octyl substituent, thus
allowing the formation of the byproduct 8 even though 7 would
appear to be energetically more favorable. Some improvement in
yield was accomplished, however, by the slow addition of a dilute
1-octylnapthalene solution to the reaction mixture. The con-
densation of 7 with 3,4-diaminothiophene successfully allowed
the production of the first known alkylacenaptho[1,2-b]thieno-
[3,4-e]pyrazine 3c. However, although 3c proved to be more
soluble then 3a, it did not result in substantial increases in
solubility and more soluble analogues are still needed.
Crystallography. X-ray quality crystals of 3a were grown by
slow evaporation of hexane/ethyl acetate solutions, and selected
bond angles are given in Table 1, along with values for 1,
acenaphthylene, thiophene, and pyrazine. The thieno[3,4-b]-
pyrazine portion of 3a agrees well with the previous structure of
1,19 with minor elongation of several bonds, but no significant
differences. Thus as with all previously reported thieno[3,4-b]
pyrazine structures,19,20 comparison with the gas phase distances
of thiophene and pyrazine25 shows that the fused thiophene ring
Analogue 4 can be thought of as thieno[3,4-b]pyrazine 2 in
which the phenyl groups have been joined via a covalent bond,
rather than ring fusion. This results in another planar system with
an additional two π-electrons in comparison to 3a. As a result, 4
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NOTE
Table 1. Experimental Bond Lengths of Acenaphtho[1,2-
b]thieno[3,4-e]pyrazine (3a), 2,3-Dimethylthieno[3,4-
b]pyrazine (1), Acenaphthylene, Thiophene, and Pyrazine
Table 2. Electrochemical Data for Extended
Thieno[3,4-b]pyrazine Analoguesa
b
b
compound
Epa (V)
E1/2 (V)
ΔE (mV)
EHOMO
ELUMO
1
1.33
1.26
1.18
1.47
1.15
0.98
1.45
ꢀ2.04
ꢀ1.78
ꢀ1.67
ꢀ1.25
ꢀ1.75
ꢀ1.51
ꢀ1.27
90
75
6.38
6.33
6.23
6.52
6.20
6.03
6.50
3.01
3.34
3.38
3.80
3.30
3.54
3.78
2
3a
3b
3c
4
60
150
90
90
5
110
a Potentials measured vs Ag/Ag+ using 0.1 M TBAPF6 in CH3CN.
bond
3a
1a
acenaphthyleneb thiophenec pyrazinec
b Determined vs ferrocene (5.1 eV vs vacuum).
S(1)ꢀC(1)
1.706(2) 1.692(2)
1.714
1.370
C(1)ꢀC(2) 1.377(2) 1.372(3)
C(2)ꢀC(3) 1.443(2) 1.427(3)
C(2)ꢀN(1) 1.389(2) 1.377(2)
N(1)ꢀC(5) 1.309(2) 1.307(2)
C(5)ꢀC(6) 1.473(2) 1.460(3)
C(5)ꢀC(7) 1.473(2) 1.496(3)
C(7)ꢀC(8) 1.374(2)
1.423
1.403
1.339
1.339
1.403
1.5024(1)
1.489(2)
1.3238(2)
1.3505(4)
1.556(2)
1.3866(5)
1.5645(6)
1.198(1)
C(7)ꢀC(12) 1.420(2)
C(8)ꢀC(9) 1.416(2)
C(9)ꢀC(10) 1.377(2)
C(10)ꢀC(11) 1.420(3)
C(11)ꢀC(12) 1.400(2)
a Reference 19. b Reference 26. c Reference 25.
Figure 1. Comparative cyclic voltammograms in CH3CN.
exhibits even further decreases in potentials for oxidation and
reduction, providing the lowest potential of oxidation of the
series (ca. 1 V). While analogue 5 is isostructural to 4, the
additional nitrogens significantly modify the electronics to
stabilize the LUMO of 5, resulting in a reduction potential
of ꢀ1.27 V. However, the electron-withdrawing nature of the
phenanthroline unit also significantly stabilized the HOMO as
well, pushing the potential of oxidation to 1.45 V.
The strength of this transition in comparison to the rest of
the series suggests that this may be due to multiple over-
lapping transitions. In fact, both 4 and 5 exhibit a great many
more absorption bands than either 3a or 3c. The addition of
the octyl side chain in 3c has very little effect on the
absorption properties, as previously seen for simple thieno-
[3,4-b]pyrazines.30
Spectroscopy. Representative absorption spectra of 2ꢀ5 are
shown in Figure 2, and photophysical data of 1ꢀ5 are given
Table 3. Previous photophysical studies on 2,3-dialkylthieno[3,4-
b]pyrazines have shown four electronic transitions. The lowest
energy transition at ∼350 nm is a broad charge transfer (CT)
band resulting from a transition between a predominately
thiophene-localized HOMO and a LUMO of greater pyrazine
contribution.30 A second transition near 300 nm consists of
multiple bands of close energetic spacing, which are assigned as
various vibrational components of the same πfπ* electronic
transition. Two significantly stronger πfπ* transitions are also
exhibited at higher energy. The phenyl groups in 2 result in a red
shift of the simple πfπ* transitions, which now overlap with the
low energy CT transition. This overlap, combined with the
rotational freedom of the phenyl groups, results in two broad
bands, with the low energy transition centered at 340 nm.
In comparison to 2, the absorption onset of the fused analogue
3a is slightly red-shifted, exhibiting a weak and very broad CT
transition at 375 nm. The remaining higher energy transitions of
3a are fairly sharp, presumably due to its rigid structure, and the
transition near 320 nm exhibits significant intensity.
Consistent with the HOMO and LUMO energies determined
electrochemically (Table 2), both 4 and 5 exhibit a significant
red-shift in comparison to 3a. Interestingly, while the CT bands
of 4 and 5 are of similar energy with nearly identical absorption
onsets, the higher energy πꢀπ* transitions of the visible region
in 5 are significantly blue-shifted in comparison to 4. For those
transitions below 325 nm, however, we see the opposite trend,
with those of 5 red-shifted in comparison to 4. It should be
mentioned that absorption data for 5 in chloroform were
previously reported.17 While only two transitions were reported
(368 and 307 nm), they do correlate closely to two of the
multiple transitions given here. The corresponding extinction
coefficient given for the lower energy transition, however, was
nearly twice that given in the current study (25600 vs 13800
M
ꢀ1 cmꢀ1). The cause for this difference is uncertain as it has
been previously shown that there are little to no solvent effects on
thieno[3,4-b]pyrazine absorption spectra.30 In addition, compar-
ison of the spectra of 5 in both CH3CN and CHCl3 revealed no
significant differences with nearly identical energies and extinc-
tion coefficients in both solvents.
All species studied exhibited a single broad emission consistent
with that previously reported for 1 and 2.30 In comparison to 2,
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NOTE
efficiencies essentially twice that of 3a. As can be seen in Table 3,
the emission lifetimes of all fused-ring analogues are at least twice
that of 2, with compound 4 exhibiting the longest lifetime at
0.62 ns.
Conclusion. In conclusion, the synthesis and full characteriza-
tion of a series of extended thieno[3,4-b]pyrazines has been
reported. Careful comparison of the structural, electrochemical,
and photophysical properties of analogues 3ꢀ5 with those of
previously studied thieno[3,4-b]pyrazines provides clear rela-
tionships between the chemical structures of these species and
their resulting electronic properties. Such increased understand-
ing of such factors should allow the application of specific design
criteria when utilizing these building blocks in new conjugated
materials. For example, in analogous conjugated polymeric
materials, the application of the fused-ring analogues should
result in lower band gaps than conventional thieno[3,4-b]-
pyrazines, with 4 and 5 giving the lowest band gaps. While
analogous materials of 4 and 5 should exhibit similar band gaps,
materials of 5 should exhibit deeper HOMOs and LUMOs in
comparison to those of 4.
Figure 2. UVꢀvis spectra of extended thieno[3,4-b]pyrazine analogues
in CH3CN.
Table 3. Photophysical Data for Extended Thieno[3,4-b]-
pyrazine Analoguesa
abs
max
em
b
compound
λ
(nm) ε (Mꢀ1 cmꢀ1
)
λ
(nm)
max
Φem
τ (ns)
1
233
18300
429 (sh) 2.3 ꢁ 10ꢀ3
’ EXPERIMENTAL SECTION
292(sh)
304
7300
11000
10600
2400
468
Materials and Instrumentation. 3,4-Diaminothiophene,20 2,3-
dimethylthieno[3,4-b]pyrazine,19 and 2,3-diphenylthieno[3,4-b]pyra-
zine,19 were all prepared as previously reported. THF was distilled from
sodium/benzophenone prior to use. Chromatographic separations were
performed using standard column methods with silica gel (230ꢀ400
mesh). Unless otherwise stated, all other materials were reagent grade
and used without further purification, and all reactions were performed
under nitrogen atmosphere using oven-dried glassware. Melting points
are corrected and were obtained using a heating block with a thermo-
couple connected to a digital thermometer. Unless otherwise stated,
NMR spectra were obtained in CDCl3 on a 400 MHz spectrometer and
referenced to the chloroform signal. Electrochemical measurements
were performed on an EC Epsilon potentiostat using a Pt disk working
electrode and a Pt wire counter electrode. Solutions consisted of 0.1 M
TBAPF6 in CH3CN and were sparged with argon for 20 min prior to
data collection and blanketed with argon during the experiment. All
potentials are referenced to Ag/Ag+ reference (0.1 M AgNO3/0.1 M
TBAPF6 in CH3CN; 0.320 V vs SCE).31 UVꢀvis spectra were measured
on a dual beam scanning spectrophotometer using samples prepared as
dilute solutions in 1 cm quartz cuvettes. Emission spectroscopy was
performed on a Spex Fluorolog spectrofluorometer utilizing a Hama-
matsu R928 photomultiplier tube. All samples were measured as dilute
solutions (<10ꢀ5 M) at room temperature. Quantum yields were
determined using secondary methods with 9,10-diphenylanthracene as
the reference.32,33
314
350
2
252
26000
10500
31100
42900
69800
4300
478
479
3.3 ꢁ 10ꢀ3 0.21
5.5 ꢁ 10ꢀ3 0.42
340
3a
240
303(sh)
317
375
3c
4
241
31000
42700
69500
4200
479
519
3.5 ꢁ 10ꢀ3 0.45
309(sh)
321
376
244
37100
30600
21600
9200
1.5 ꢁ 10ꢀ2 0.62
281
296
362(sh)
380
13200
11800
2400
400
426
5
240
32900
30000
29700
9600
529
1.4 ꢁ 10ꢀ2 0.45
280
304
5,6-Dibromoacenaphthene. Modified from previously reported
procedures.23,35 Acenaphthene (77.1 g, 0.50 mol) and N-bromosucci-
nimide (222.5 g, 1.25 mol) were combined in DMF (500 mL) and
stirred overnight at 30ꢀ32 °C. The reaction was then cooled to room
temperature, filtered to obtain the crude product, and purified via
recrystallization from hexanes (25ꢀ30% yield). Mp 169ꢀ171 °C
(lit.23 168ꢀ171 °C). 1H NMR: δ 7.78 (d, J = 7.6 Hz, 2H), 7.07
(d, J = 7.6 Hz, 2H), 3.30 (s, 4H). 13C NMR: δ 147.3, 142.16, 136.0,
128.0, 121.1, 114.6, 30.3.
348
365
13800
11300
2500
383
418
a All spectra obtained from room temperature CH3CN solutions using
matched, 1 cm quartz cells. (sh) = shoulder. b (0.0005.
the emission of 3a is essentially identical in energy, although with
a slightly enhanced quantum efficiency. The quantum efficiency
of the octyl-functionalized 3c is reduced in comparison to 3a,
most likely due to an increase in high frequency modes as a result
of the side chain. The emission maxima of the remaining species
4 and 5 are both significantly red-shifted and exhibit quantum
5,6-Dibromo-1,2-acenaphthenequinone (6). Modified from
a previously reported procedure.23 A mixture of 5,6-dibromoace-
napthene (3.2 g, 10 mmol) and Na2Cr2O7 (17.5 g, 58 mmol) in acetic
acid (175 mL) was stirred at 80 °C for 2 h. The solution was then diluted
with 500 mL of water and filtered, and the resulting precipitate was
washed with 30 mL of boiling aqueous 6% Na2CO3. The crude material
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NOTE
was then dissolved in hot chlorobenzene (500 mL at 50ꢀ60 °C), 40%
aqueous NaHSO3 (20 mL) was added, and the mixture stirred for 1 h.
The precipitate was then collected by filtration, washed first with hot
chlorobenzene (2 ꢁ 50 mL) and then boiling 10% aqueous HCl
(25 mL). The resulting solid was then recrystallized from chlorobenzene
to give 6 as yellow crystals (20ꢀ25% yield). Mp 326ꢀ328 °C (lit.23
326ꢀ328 °C). 1H NMR: δ 8.25 (d, J = 7.5 Hz, 2 H), 7.92 (d, J = 7.5 Hz,
2 H). 1H NMR data agrees well with previously reported values.23
1-Octylnaphthalene. Modified from a previously reported
procedure.24 Octylmagnesium bromide (100 mmol) was added to
Ni(dppp)Cl2 (0.4 g, 1 mol %) and zinc chloride (10.2 g, 75 mmol) in
THF (100 mL) and allowed to stir for 30 min. 1-Bromonaphthalene
(10.4 mL, 75 mmol) was then slowly added, and the mixture was heated
at reflux overnight. Saturated aqueous ammonium chloride (150 mL)
was then added, and the solution was extracted with hexanes (3 ꢁ
50 mL). The combined organic fractions were then washed with H2O
(100 mL), dried with anhydrous MgSO4, filtered, and concentrated via
rotary evaporation. The resulting oil was diluted with hexanes (10 mL)
and purified by column chromatography (hexanes) to give a colorless oil
(90ꢀ95% yield). 1H NMR: δ 8.09 (d, J = 8.0 Hz, 1H), 7.89 (d, J = 8.0
Hz, 1H), 7.24 (d, J = 8.0 Hz, 1H), 7.52 (m, 2H), 7.43 (dd, J = 8.0 Hz, 6.8
Hz, 1H), 7.36 (d, J = 6.8 Hz, 1H), 3.10 (t, J = 7.2 Hz, 2H), 1.79 (p, J = 7.2
Hz, 2H), 1.48 (m), 1.34 (m), 0.93 (t, J = 7.2 Hz, 3H). 13C NMR: δ 139.3,
134.1, 132.2, 129.0, 126.6, 126.1, 125.8, 125.7, 125.6, 124.2, 33.4, 32.2,
31.1, 30.1, 29.8, 29.6, 22.9, 14.4.
5-Octylacenaphthylene-1,2-dione (7). Modified from a pre-
viously reported procedure.24 Oxalyl chloride (6.47 g, 50 mmol) was
added to a stirred suspension of AlCl3 (13.3 g, 100 mmol) in 300 mL of
CH2Cl2 at ꢀ5 °C. 1-Octylnaphthalene (12.02 g, 50 mmol) in 100 mL of
CH2Cl2 was then added dropwise, and the mixture was allowed to stir for
an additional 5 h (below 0 °C). The reaction mixture was then poured
over ice (200 g) and allowed to warm to room temperature. The
resulting layers were separated. The organic layer was isolated, washed
with a saturated Na2CO3 solution (1 ꢁ 100 mL), followed by a water
wash (1 ꢁ 100 mL), and then dried with anhydrous MgSO4. The
mixture was filtered, concentrated via rotary evaporation, and purified by
column chromatography (10% EtOAc in hexanes) to yield a yellow solid
(3.74 g, 30%). Mp 131ꢀ132 °C. 1H NMR: δ 8.33 (d, J = 8.0 Hz, 1H),
8.01 (d, J = 6.8 Hz, 1H), 7.98 (d, J = 7.2 Hz, 1H), 7.80 (dd, J = 8.0 Hz, 6.8
Hz, 1H), 7.62 (d, J = 7.2 Hz, 1H), 3.16 (t, J = 7.2 Hz, 2H) 1.78 (p, J = 7.2
Hz, 2H), 1.44 (m, 2H), 1.25 (m, 8H), 0.85 (t, J = 7.2 Hz, 3H). 13C NMR:
δ 189.1, 187.9, 147.8, 146.4, 130.1, 129.9, 129.1, 128.1, 127.2, 126.8,
122.4, 121.7, 33.3, 32.0, 30.8, 29.9, 29.6, 29.4, 22.8, 14.3. HRMS: m/z
317.1513 [M + Na]+ (calcd for C20H22NaO2 317.1518).
yellow needles (15ꢀ20% yield). Mp ∼130 °C (dec). 1H NMR: δ 8.21
(d, J = 7.6 Hz, 2H), 8.11 (d, J = 7.6 Hz, 2H), 8.04 (s, 2H). 13C NMR
spectrum not obtained due to poor solubility. Anal. Calcd for C16H6Br2N2S:
C, 45.96; H, 1.45; N, 6.70. Found: C, 46.22; H, 1.31; N, 6.69.
3-Octylacenaphtho[1,2-b]thieno[3,4-e]pyrazine (3c). The
crude product was purified by column chromatography (1:1 CH2Cl2/
hexanes) to yield 3c as a yellow solid (20ꢀ25% yield). Mp 114.5ꢀ
115.7 °C (lit.6c 114.5ꢀ115.7 °C). 1H NMR: δ 8.30 (d, J = 6.8 Hz, 1H),
8.24 (d, J = 7.2 Hz, 1H), 8.20 (d, J = 8.0 Hz, 1H), 7.99 (d, J = 8.4 Hz, 2H),
7.97 (d, J = 8.4 Hz, 2H), 7.82 (dd, J = 6.8, 7.2 Hz, 1H), 7.63 (d, J = 7.2 Hz,
1H) 3.19 (t, J = 7.6 Hz, 2H), 1.83 (p, J = 7.6 Hz, 2H), 1.47 (m, 2H) 1.31
(m, 8H), 0.83 (t, J = 7.2 Hz, 3H). 13C NMR: 154.7, 154.4, 143.6, 142.1,
142.0, 138.0, 132.0, 129.6, 129.5, 128.4, 128.3, 126.4, 121.2, 120.7, 117.6,
117.3, 32.8, 32.1, 31.6, 30.0, 29.7, 29.5, 22.9. NMR spectral data agrees
well with previously reported values.6c
Dibenzo[f,h]thieno[3,4-b]quinoxaline (4). Compound 4 was
prepared and purified as for 3a above, subsituting 9,10-phenanthrene-
quinone for 1,2-acenaphthenequinone (65ꢀ70% yield). Mp: ∼125 °C
(dec). 1H NMR: δ 9.20 (dd J = 7.2, 1.6 Hz, 2H), 8.44 (dd, J = 7.2, 0.8 Hz,
2H), 8.20 (s, 1H), 7.72 (dt, J = 7.2, 1.6, 2H), 7.66 (dt, J = 7.2, 0.8 Hz, 2
H). 1H NMR spectral data agrees with previously reported values.12
1,10-Phenanthroline-5,6-dione (9). Modified from previously
reported procedures.34 1,10-Phenanthroline (2.0 g, 11.1 mmol) and KBr
(3.0 g, 25.2 mmol) were slowly added to concentrated H2SO4 (20 mL)
cooled in an ice-bath, maintaining a temperature below 5 °C. Concen-
trated HNO3 (10 mL) was then added dropwise to give a red solution.
The mixture was stirred for 1 h and then heated to 80 °C for an
additional h. The solution was allowed to cool, poured over 100 g of ice,
and then carefully adjusted to pH 7 using Na2CO3. The neutralized
solution was extracted with dichloromethane, and the combined organic
layers were dried with anhydrous MgSO4 and concentrated by rotary
evaporation. The resulting solid was redissolved in CH2Cl2, run through
a 5 cm silica plug, and concentrated to give an orange solid (80ꢀ85%
yield). Mp 275ꢀ277 °C (lit.26 271ꢀ272 °C). 1H NMR: δ 9.12 (d, J = 4.8
Hz, 2H), 8.50 (d, J = 8.0 Hz, 2H), 7.59 (dd, J = 8.0, 4.8 Hz, 2H). 13C
NMR: δ 178.9, 156.3, 153.2, 137.5, 128.3, 125.8.
Thieno[30,40:5,6]pyrazino[2,3-f][1,10]phenanthroline (5).
3,4-Diaminothiophene (0.34 g, 3.0 mmol) was dissolved in 100 mL
of absolute ethanol. 1,10-Phenanthroline-5,6-dione (0.52 g, 2.4
mmol) was then added, and the solution was heated at reflux for
1 h. The mixture was then cooled to room temperature and filtered, and the
isolated solid was washed with cold ethanol. The filtrate was then diluted
with water and extracted with CH2Cl2. The combined organic layers were
dried with anhydrous Na2SO4, and the solvent was removed by rotary
evaporation. The resulting solid was then dissolved in CH2Cl2, run through
a 5 cm silica plug, and concentrated to give 5 as an orange solid (90ꢀ95%
yield). Mp ∼140 °C (dec). 1H NMR: δ 9.46 (dd J = 8.0, 2.0 Hz, 2H), 9.20
(dd, J = 4.4, 2.0 Hz, 2H), 8.29 (s, 1H), 7.72 (dd, J = 8.0, 4.4 Hz, 2H).
1H NMR data agrees with previously reported values.17 1H NMR (d6-
DMSO): δ9.29 (dd J= 8.0, 2.0 Hz, 2H), 9.08 (dd, J = 4.4, 2.0 Hz, 2H), 8.65
(s, 1H), 7.80 (dd, J = 8.0, 4.4 Hz, 2H). 13C NMR (d6-DMSO): δ 152.9,
149.0, 142.4, 141.6, 133.7, 128.3, 125.2, 119.3. HRMS: m/z 311.0358
[M + Na]+ (calcd for C16H8N4NaS 311.0362).
General Procedure for the Preparation of Acenaphtho[1,2-
b]thieno[5,4-e]pyrazines 3aꢀc. Modified from previously reported
procedures.6c,10 3,4-Diaminothiophene (0.51 g, 5.0 mmol) was dissolved in
50 mL of absolute ethanol. 1,2-Acenaphthenequinone, or its derivative 6 or
7 (5.0 mmol), was then added, and the solution was heated at reflux for 3 h.
The mixture was then cooled to room temperature, diluted with 100 mL of
water, and extracted with dichloromethane. The combined organic layers
were dried with anhydrous Na2SO4, and the solvent was removed by rotary
evaporation. The resulting solid product was then purified by recrystalliza-
tion or column chromatography.
Acenaphtho[1,2-b]thieno[3,4-e]pyrazine (3a). The crude
product was dissolved in CH2Cl2, run through a 5 cm silica plug, and
concentrated to give a yellow solid. Recrystallization from methanol gave
3a as yellow needles (55ꢀ60% yield). Mp ∼150 °C (dec); 1H NMR: δ
8.25 (dd, J = 7.2, 0.4 Hz, 2H), 8.03 (dd, J = 8.4, 0.4 Hz) 2H), 7.98 (s, 2H),
7.77 (dd, J = 8.4, 7.2 Hz, 2H). 13C NMR: δ 154.5, 142.1, 138.5, 131.7,
130.4, 129.3, 128.9, 121.1, 117.8. NMR spectral data agrees well with
previously reported values.10
’ ASSOCIATED CONTENT
S
Supporting Information. NMR spectra for 3ꢀ7 and
b
crystallographic data for 3a including CIF file. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: seth.rasmussen@ndsu.edu.
3,4-Dibromoacenaphtho[1,2-b]thieno[3,4-e]pyrazine (3b).
Recrystallization of the crude product in dichloromethane gave 3b as
6387
dx.doi.org/10.1021/jo200850w |J. Org. Chem. 2011, 76, 6383–6388

The Journal of Organic Chemistry
NOTE
’ ACKNOWLEDGMENT
(14) Huang, J.-H.; Velusamy, M.; Ho, K.-C.; Lin, J.-T.; Chu, C.-W.
J. Mater. Chem. 2010, 20, 2820.
(15) Mak, C. S. K.; Leung, Q. Y.; Chan, W. K.; Djurisic, A. B.
Nanotechnology 2008, 19, 424008.
The authors thank the National Science Foundation (DMR-
0907043) and North Dakota State University for support of this
research and NSF-CRIF (CHE-0946990) for the purchase of a
departmental XRD instrument. We wish to thank Dr. Angel
Ugrinov for assistance with the collection of the X-ray
crystal data.
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