Quinoidization of π-Expanded Aromatic Diimides: Photophysics, Aromaticity, and Stability of the Novel Quinoidal Acenes

Article abstract of DOI:10.1002/ejoc.201901456

We report the synthesis and photophysical characterization of π-expanded quinoidal triplet chromophores which exhibit attractive light-harvesting properties. The kinetic of the triplet excited state of quinoidal benzotetraphene 2 was found to be one order of magnitude higher than the lifetime of ³(1)* from the less conjugated parent chromophore 1. Furthermore, the evaluation of the optoelectronic properties indicates that π-expansion helps narrow the optoelectronic band gap, but the influence of the additional aromatic rings in the structure of 2 and 3 compromises the stability of the p-quinoidal ring. QDM 2 was isolated and fully characterized; however, it was found to rearomatize to a mixture of uncharacterized radical species.

Full text of DOI:10.1002/ejoc.201901456

A Journal of
Accepted Article
Title: Quinoidization of π-Expanded Aromatic Diimides: Photophysics,
Aromaticity, and Stability of the Novel Quinoidal Acenes
Authors: Nareshbabu Kamatham, Jingbai Li, Siamak Shokri, Guang
Yang, Steffen Jockusch, Andrey Yu Rogachev, and Anoklase
Jean-Luc Ayitou
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201901456
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10.1002/ejoc.201901456
European Journal of Organic Chemistry
COMMUNICATION
p
Quinoidization of -Expanded Aromatic Diimides: Photophysics,
Aromaticity, and Stability of the Novel Quinoidal Acenes
Nareshbabu Kamatham,[a] Jingbai Li,[a] Siamak Shokri,[a] Guang Yang,[a] Steffen Jockusch,[b] Andrey
Yu. Rogachev*[a] and A. Jean-Luc Ayitou*[a]
excited state aromaticity and photophysical properties.[13] Our
Abstract: We report the synthesis and photophysical characterization
previously reported quinoidal chromophore can also be employed
as a light-harvesting triplet sensitizer for photonic research such
as triplet-triplet annihilation photon upconversion.[14] From the
of p-expanded quinoidal triplet chromophores which exhibits attractive
light-harvesting properties. The kinetic of the triplet excited state of
quinoidal benzotetraphene 2 was found to be one order of magnitude
higher than the lifetime of 3(1)* from the less conjugated parent previous report, we showcased a new cycloaddition reaction of p-
acidic diimides in the presence of phosphine disulfide, as
Lawesson’s reagent, to afford QDM 1. Inspired by the earlier
success to convert readily available naphthalene diimides to the
corresponding triplet sensitizer by modulating the intrinsic
aromaticity of the p–core, we wish to extend the new
cycloaddition reaction to other p–expanded acene diimides[15-18]
to afford novel quinoidal acene triplet sensitizers quinoidal
benzotetraphene 2 and its thiophene analog 3 (Figure 1).
chromophore 1. Furthermore, the evaluation of the optoelectronic
properties indicates that p-expansion helps narrow the optoelectronic
bandgap; but, the influence of the additional aromatic rings in the
structure of 2 and 3 compromises the stability of the p–quinoidal ring.
QDM 2 was isolated and fully characterized; but, it was found to
rearomatize to a mixture of uncharacterized radical species.
Unexpectedly, quinoidal thiophene
purification.
3
decomposes during
Introduction
R
N
R
N
R
N
R
N
A
S
S
S
S
S
S
Polyaromatic rylene and acene chromophores are actively
researched owing to their attractive light-harvesting properties
and tunable optoelectronic bandgap, which dictates excitons
dynamics and kinetics in organic photonic materials/devices.[1-4]
Undeniably, the behavior, photo-kinetics, and stability of the
corresponding excited polyaromatic systems are essential to the
modulation and transformation of absorbed radiation in many
photonic materials. In recent years, significant contributions
aiming to alter the excited state behaviors and/or properties of
polyaromatic chromophores have been disseminated in the
chemical literature.[5-11] Yet, there is more room at the bottom to
explore other variables and factors that can be employed to tune
the photophysics of these chromophores. A known strategy that
allows to tune the photo-kinetics of polyaromatics relies on
perturbing the intrinsic ground state aromaticity by inserting
pro/non-aromatic units such as para-quinodimethyl ring (p-QDM)
in the backbone of organic polyaromatics with the expectation to
generate metastable triplet excited species via aromaticity
reversal.[13-14]
S
S
B
C
D
N
R
N
R
N
R
S
1
2
3
Figure 1. Chemical structures of QDM 1–3: R = n–C8H17
.
Results and Discussion
In the present investigation, we are particularly interested to
red-shift the absorption band of QDM 1 using the p–expansion
synthetic strategy. With this in mind, we hoped to isolate the new
QDM derivatives 2 and 3 which were proposed to absorb red
photons. The synthetic route leading to QDM 2 is depicted in
Scheme
1 (See Experimental Section & Supplementary
Information for the synthesis of diimide precursor to QDM 3).
Using well-documented procedures, we first converted
naphthalene dianhydride (NDA) to the corresponding brominated
NDA (Br–NDA and Br2–NDA) using dibromoisocyanuric acid.
Next, the combined brominated NDA was reacted with n-
octylamine to afford Br–NDI in quantitative yield after
separation/purification. The monobrominated NDI was reacted
with bis-tributyltin to afford the corresponding stannated NDI
(Sn–NDI) following a reported procedure.[19] Under Stille
coupling conditions, Sn–NDI and 2,2’–dibromophenyl were
reacted in refluxing Argon saturated toluene solution in the
presence of catalytic amount of Pd(PPh3)4 for 12 h. As reported by
Yue et. al.,[19] Stille coupling reaction will also induce a sp2C–H
activation to afford the expected annulated π-expanded diimide.
We recently demonstrated that the fusion of a p-QDM unit to a
phenylene ring can generate a new naphthoquinodimethane
chromophore 1 (Figure 1) which exhibits unusual ground and
[a]
[b]
Dr. Nareshbabu Kamatham, Dr. Jingbai Li, Dr. Siamak Shokri,
Guang Yang, Prof. Andrey Yu Rogachev, Prof. A. Jean-Luc Ayitou
Department of Chemistry
Illinois Institute of Technology
3101 S Dearborn St.
Chicago, IL 60616 USA
E-mail: arogache@iit.edu and aayitou@iit.edu
Dr. Steffen Jockusch
Department of Chemistry
Columbia University
New York, NY 10027 USA
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10.1002/ejoc.201901456
European Journal of Organic Chemistry
COMMUNICATION
Benzotetraphene diimide (BTDI) was isolated in 38% yield and
After isolating the expected quinoidal benzotetraphene 2, its
was further used in the Lawesson-reagent-mediated UV−vis absorption and emission profiles were recorded and
quinoidization reaction to obtain the expected QDM 2 in 22 % compared to the ones of the parent structure 1. As shown in Figure
yield as depicted in Scheme 1. A more detailed synthetic 2a, the absorption profile of QDM 2 is ca. 20 nm red-shifted, but
procedure for all compounds in Scheme 1 is also reported in the exhibits a decrease of ca. 200 M-1 cm-1 in molar absorptivity at
Experimental Section and Supplementary Information (Scheme
S1). QDM 2 was characterized by NMR, UV-vis and FTIR
spectroscopy methods (Supplementary Information).
lmax (Table 1). The slight red-shift in absorption is indicative of
the additional π-conjugation, which also helps decrease the
HOMO–LUMO gap from 3.18 to 2.95 eV (Figure 4 & Table 1).
Also shown in Figure 2b are the steady state and matrix isolated
emission bands of QDM 2, which again showcase similar vibronic
features similar to the ones seen in the emission bands of parent
QDM 1. Nonetheless, one can see that there is a ca. 15 nm shift in
both the fluorescence and phosphorescence bands which is
indicative of the presence of π-expanded core in QDM 2. We then
measured the phosphorescence decay kinetics of the two
compounds to ascertain the effect of π-expansion on the kinetics
of their corresponding aromatic triplet species. As shown in
Figure 2c, the lowest triplet excited state of QDM 2 gave a lifetime
value of 4.4 ms (Figure 2c, Table 1). This value is one order of
O
Br
Br
O
O
O
O
O
O
O
O
O
O
N
N
O
O
O
O
O
Br
Br
O
N
H
Oleum (20% SO3)
r.t , 5 h
Br
O
O
O
O
Br2–NDA
NDA
Br–NDA
AcOH
3
magnitude higher than the lifetime of (1)* indicating a likely
Reflux/120 ºC, 3 h
(then separation)
NH2
7
change/increase in aromaticity of the quinoidal ring B of QDM 2.
We had previously hypothesized aromaticity reversal of QDM
molecules in the excited states; in the case of QDM 2, one can see
that the additional two Clar’s sextets (from the phenanthro unit) is
mostly likely contributing in the stabilization of the triplet excited
state in comparison to the effect of only one Clar’s sextet: (See
Chart S2, Supplementary Information for the corresponding
resonance structures).
7
7
Sn2Bu6
Pd2(dba)3
P(o-Tol)3
O
O
N
O
O
O
O
N
O
Sn(Bu)3
Br
Toulene
130 ºC, 48 h
N
7
N
O
7
1.2
0.8
0.4
0.0
a)
UV-vis recorded in DCM
Sn–NDI
Br–NDI
1
2
Br
Pd(PPh3)4
CuI
Toluene,
reflux, 48 h
Br
300
400
500
600
7
7
Wavelength (nm)
N
S
S
O
N
O
O
7
S
O
P
N
b)
1.2
0.8
0.4
0.0
c)
LR
1Fl
τ
725 = 0.4 ms (1Phos
)
)
2Fl
Ar
τ745 = 4.4 ms (2Phos
S
0.8
Toluene
145 ± 5 ºC
48 h
1Phos
H
λExc = 470 nm
2Phos
N
in 50:50 DCM:EtOH
glass at 77 K
O
N
0.4
via
7
7
2
BTDI
LR = Lawesson reagent
0.0
0
10
20
30
500
600
700
800
Scheme 1. Synthesis scheme for QDM 2.
Time (ms)
Wavelength (nm)
Figure 2. a) Normalized UV-Vis absorption spectra of QDM 1 and 2 recorded in
dichloromethane (DCM). b) Steady state (fluorescence) and phosphorescence
emission bands in DCM and 50:50 DCM:EtOH glass at 77 K, respectively, of
QDM 1 and 2 (samples OD = 0.1 at lExc = 470 nm). c) Phosphorescence decay
For the reaction depicted in Scheme 1, we hypothesize that the
reaction pathway leading to QDM 2 (and 3) could also produce
the thermodynamic regio-isomers, where the thiocarbonyl groups
are outside the fjord of the π-expansion: a comprehensive
mechanistic rationale is depicted in the Supplementary
Information (Figure S18). Nonetheless, on the basis of our
previously reported mechanistic rationale (for QDM 1)[13] and
additional computational data, it was found that the pathway to
form the doubly de-aromatized phosphinine intermediate(s) that
would lead to the regio-isomers of 2 (and 3) is kinetically not
favored.
kinetic of QDM
1 and 2 recorded in 50:50 DCM:EtOH glass at 77 K.
Phosphorescence emissions and decay kinetics were recorded with time-gated
option (90 μs delay after pulse) and at 2 Hz lamp repetition.
Even though the π-expanded–phenanthro core was essential in
enhancing the lifetime of metastable 3(2)*, this moiety was found
to induce subsequent transformation of QDM 2 to form a mixture
1
of uncharacterized products 2’, which rendered the H NMR
signal to broaden after 24 h when kept under ambient light (Figure
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10.1002/ejoc.201901456
European Journal of Organic Chemistry
COMMUNICATION
3). Due to the broadening of the 1H NMR, we hypothesized that
2’ is most likely constituted of persistent radicaloids. Moreover,
it was possible to monitor the slow conversion of 2 to 2’ using
UV-vis absorption method as depicted in Figure 3b. After
complete decomposition of 2, we attempted unsuccessfully to
characterize the resulting material by NMR spectroscopy: the
signals were broad and uncharacteristic of the signals of QDM 2.
We also carried out EPR experiments to corroborate the formation
of persistent radical species 2’. As shown in Figure S17, an intense
EPR signal was observed after exposure of QDM 2 to light for just
2 min; from this result two conclusions can be made: a) the
additional resonance energy provided by the phenanthro moiety
would contribute to destabilize ring B in QDM 2 via
rearomatization, or b) the close proximity of the sulfur atom to
ring E would induce rearrangement or ArC-H insertion: (See Chart
S2, Supplementary Information for the resonance structures).
pentyl) optimized at PBE0/cc-pVTZ;[20,21] DEL–H = ELUMO
–
EHOMO
.
Next, we used computational tools to assess the impact of the
additional phenanthro unit on the energetics of the frontier
molecular orbitals as well as on the intrinsic ground state
aromaticity of the new quinoidal benzotetraphene 2. As shown
in Figure 4, the orbital pictures in the structure of QDM 2
exhibit similar features as the ones from the parent compound
1. Although the energy levels of the orbitals have slightly
increased for chromophore 2, the HOMO-LUMO gap has
shrunk from 3.18 to 2.95 eV. The decrease in electronic
bandgap energy is clearly in agreement with the decrease in
energy of the optical transitions as shown above in the UV-vis
and emission spectroscopy results. In order to shed light on the
nature of the triplet state, we also provided in Figure 4 the
pictures of singly-occupied MOs (SOMOs) and the 3D spin
density maps of QDM 1 and 2. These results clearly indicate
the high similarity of systems 1 and 2 in their triplet states.
Altogether, we ascertain that the π-expansion has helped in
narrowing the optoelectronic bandgap; on the other hand, the
π-expanded–phenanthro moiety impacted the ground state
global aromaticity and stability of the quinoidal
benzotetraphene 2 and the corresponding thiophene 3.
*
a)
2
0 h
4 h
amb.
light
8 h
24 h
radicaloids or
radical ionic
species
+1
b)
(2')
MO
U
Time
0 min
45 min
L
2'
2
amb.
light
-2.05
-2.07
0.6
0.3
0.0
• • •
270 min
315 min
24h
+1
MO
SO
)
(L
MO
U
L
-2.16
-2.26
360
450
540
630
Wavelength (nm)
)
MO
Figure 3. a) Partial 1H NMR spectra of QDM 2 at various times while the
NMR tube was kept at ambient conditions. b) UV-vis absorption spectra of
QDM 2 recorded at various times while the sample was kept under ambient
light. * residual NMR solvent peak.
(H
SO
MO
O
H
-5.21
-5.34
SPIN DENSITY
Table 1. Optoelectronic Characteristics for QDM 1
and 2.
1
–
ꢃꢄꢅ
MO
l
e
lꢃꢆ ꢄꢅ
lꢃꢇ ꢄꢅ
tꢇ
∆ꢈꢉꢊꢋ
(eV)[d]
ꢀꢁꢂ
O
Comp.
H
(nm) [a]
(M-1cm-1)[a]
(nm) [a]
(nm)[b]
(ms)[b],[c]
1
2
453
1631
1468
545
559
725
743
0.4
4.4
3.18
2.95
-5.74
2
-5.94
1
460
1
2
[a] UV-vis absorption and fluorescence emission. were recorded
ΔE L–H (eV)
3.18
2.95
[b]
in DCM.
Phosphorescence was recorded in 50:50 (v/v)
DCM:EtOH glass at 77 K and lexc = 470 nm. [c] Phosphorescence
lifetime. [d] Calculations were performed using geometries (N-3-
Figure 4. Frontier molecular orbital pictures and energies of QDM 1 and 2
in their singlet (left) and triplet (right) states. The latter is accompanied by
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3D spin density map (isosurface 0.0035 a.u.). Calculations were performed
current density vectors for the individual rings in the triplet
excited state is most likely due to middle/local Baird-type
aromaticity.[24] Surprisingly, ring B which is essentially non-
aromatic, in the ground state of both QDM 1 and 2, remains
using geometries (N-3-pentyl) optimized at PBE0/cc-pVTZ;[20a,21] DEL–H
=
ELUMO – EHOMO
.
3
non-aromatic in (1)* but this behavior is less pronounced in
ACID Isosurfaces
(only π–delocalization)
3(2)* presumably due to the decrease of aromaticity of rings D
and E.
a)
Furthermore, a closer look at the current density vectors in ring
B revealed its low involvement into total delocalization in the
singlet state (this ring could be described as essentially isolated
double bond in the ground/singlet state); whereas the presence of
diatropic ring current density vectors and significant
delocalization are obvious in the triplet spin state for both QDM 1
and 2. This finding agrees with spin density distribution (Figure 4
right), which shows delocalization of unpaired electrons in the
system and significant involvement of the ring B. From the
NICS(1)zz calculations for individual rings (Figure 5b and
Supplementary Information, Table S2 and Figure S20), one can
see that the NICS(1)zz values switch (from singlet to triplet excited
state) except for ring E; however, the NICS(1)zz values for rings
B indicate that these rings are notably non-aromatic in the singlet
spin state while all other rings (A, C, D) remain aromatic for both
QDM 1 and 2. While these characteristics seemed reversed in the
triplet excited state, it’s still not clear whether one would label
rings B as aromatic or non-aromatic, especially in the case of
QDM 1. Nonetheless, similar to QDM 1, QDM 2 is globally
aromatic; but, NICS(1)zz calculations indicate that ring B, which
is essentially non-aromatic, gains some aromaticity characters in
the triplet excited.
A
E
A
B
D
C
C
B
(S = 1); triplet state
A
B
E
A
C
D
C
B
(S = 0); singlet state
1
2
b)
NICS Values for individual rings
(+)
Conclusions
In summary, we report the synthesis of novel quinoidal
benzotetraphene 2 using our previously reported quinoidization
reaction from our group. The analogous thiophene system 3 was
found to decompose readily upon isolation. Chromophore 2 was
found to exhibit similar optoelectronic and aromaticity
characteristics in comparison with parent quinoidal compound 1.
Importantly, our investigation revealed that the π-expanded–
phenanthrene core was useful in producing long-lived triplet
species 3(2)* with lifetime value which is one order of magnitude
NICS
(-)
Aromatic (-) | Antiaromatic (+) | s = singlet state | t = triplet state
Figure 5. a) ACID[20b] isosurface plots of QDM 1 and 2 in the singlet spin
state (bottom) and triplet spin state (top): iso values are 0.03 for QDM 1, and
0.024 (singlet) and 0.0125 (triplet) for QDM 2; current density vectors are
plotted onto the ACID isosurface to indicate dia– (aromatic, clockwise) and
para–tropic (anti-aromatic, counterclockwise) ring currents. Applied
3
higher than the triplet lifetime of (1)*. But, extending the π–core
has also impacted the ground state stability of 2 to generate a
mixture of persistent radical species 2’, which were responsible
for the NMR signal broadening of 2. On the basis of
complementary computational results, it was found that the
additional phenanthro unit contributed in the reduction of the
optoelectronic bandgap. We are currently extending the
quinoidization method to other less conjugated polyacene
diimides to compile a library of novel triplet quinoidal acene
chromophores.
magnetic field direction is perpendicular to the molecular and toward outside.
[22,23]
b) NICS(1)zz
values for individual rings in QDM 1 and 2: NICS(1)zz
values are in ppm. Calculations were performed using geometries (N-3-
pentyl) optimized at PBE0/cc-pVTZ[20a,21]
.
To evaluate global and local aromaticity of 2, we performed
[22,23]
magnetic nucleus independent chemical shift: NICS(1)zz
calculations and ACID[20b] isosurface plots (Figure 5). As
depicted in Figure 5a, besides ring B in QDM 1 and 2, all other
rings exhibit diatropic ring current (in the singlet state) with
respect to the applied magnetic field (pointing outward), thus
supporting their aromatic character. The direction of the current
density vectors can be seen reversed as illustrated by the
paratropic vectors (counterclockwise) once the spin state is
changed (singlet → triplet). The change of tropicity of the
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10.1002/ejoc.201901456
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COMMUNICATION
ºC for 24 h. After cooling reaction mixture to room temperature,
the solvent was concentrated in vacuo and purified by silica gel
chromatography using mixture of DCM and Hexane (2 : 1) as
mobile phase to yield compound BTDI. Obtained as reddish solid
(400 mg, 38 %), m.p. 117-118 ºC; 1H NMR (300 MHz, CDCl3)
δ: 8.79 (s, 2H), 8.29 - 8.27 (d, J = 6 Hz, 2H), 8.16 - 8.14 (d, J = 6
Hz, 2H), 7.69 - 7.64 (t, J = 9 Hz, 2H), 7.43 - 7.38 (t, J = 9 Hz, 2H),
4.24 - 4.19 (t, J = 6 Hz, 4H), 1.78 - 1.73 (m, 4H), 1.31 - 1.25 (m,
20H), 0.89 - 0.84 (m, 6H);); 13C NMR (75 MHz, CDCl3) δ: 14.0,
22.6, 27.1, 28.1, 29.2, 29.3, 31.7, 41.4, 119.5, 123.6, 126.3, 126.4,
127.9, 130.50, 131.1, 132.5, 132.7, 140.4, 162.8, 163.3; ESI-
Experimental Section
General
Methods:
All
commercially
obtained
reagents/solvents were used as received without further
purification. Unless stated otherwise, reactions were conducted in
oven-dried glassware under argon atmosphere. 1H-NMR and 13C-
NMR spectra were recorded on Bruker® 300 MHz (75 MHz for
13C) spectrometer; data from the 1H-NMR spectroscopy are
reported as chemical shift (δ ppm) with the corresponding
integration values. Coupling constants (J) are reported in hertz
(Hz). Standard abbreviations indicating multiplicity were used as
follows: s (singlet), b (broad), d (doublet), t (triplet), q (quartet),
m (multiplet) and virt (virtual). Standard abbreviations in FTIR
spectra were used as fellows: (st = strong, wk = weak, br = broad
& sh= sharp). Data for 13C NMR spectra are reported in terms of
chemical shift (δ ppm). High-resolution mass spectrum data were
recorded on a Bruker microTOF II or Shimadzu IT-TOF
spectrometers in positive (ESI+) ion mode. UV-Vis absorption
spectra were recorded on Ocean Optics® spectrometer (DH-MINI
UV-VIS-NIR Light Source and QE-Pro detector using
OceanView® software package). Emission spectra were recorded
on an Edinburgh Instrument FLS980 spectrometer. Melting point
values were recorded on a Melt-Point II® apparatus. Infra-Red
spectra were recorded on PerkinElmer UATR FT-IR
spectrometer. EPR experiments were performed on a Buker EMX
X-band spectrometer.
HRMS: Calculated for C42H46N2O4
observed: 641.3374.
[M+H] 641.3374,
BT-NDI: A mixture of Sn-NDI (1.64 mmol, 1.28 g, 1 equiv.)
and 3,3’-Dibromo-2, 2’- bithiophene (1.37 mmol, 424 mg, 0.83
equiv.) was added to round bottom flask which contains dry
toluene (10 ml), and to this solution, Pd(PPh3)4 (159 mg, 0.137
mmol) and CuI (52 mg, 0.275 mmol) were added under Argonne
medium then refluxed at 140 ºC for 24 h. After cooling reaction
mixture to room temperature, the solvent was concentrated in
vacuo and purified by silica gel chromatography using mixture of
DCM and Hexane (2 : 1) as mobile phase to yield compound BT-
NDI. Obtained as reddish solid (400 mg, 38 %), m.p. 117-118 ºC;
1H NMR (300 MHz, CDCl3) δ: 8.77 - 8.74 (d, J = 3 Hz, 2H), 7.27
- 7.25 (d, J = 6 Hz, 2H), 7.14 - 7.12 (d, J = 6 Hz, 2H), 4.17 - 4.08
(m, 4H), 1.74 - 1.71 (m, 4H), 1.69 - 1.62 (m, 20H), 0.89 - 0.84
(m, 6H);); 13C NMR (75 MHz, CDCl3) δ: 14.6, 22.6, 27.0, 28.0,
29.1, 29.2, 31.7, 40.9, 111.8, 124.5, 126.8, 127.2, 128.7, 130.9,
131.0, 135.6, 142.2, 162.4, 162.8.
Br-NDA and Br2-NDA: A solution of dibromoisocyanuric acid
(6.39 g, 22 mmol 1 equiv.) in oleum (20% SO3, 100 mL) was
added at room temperature to 500 mL oleum solution of
naphthalene dianhydride NDA (15 g, 55.9 mmol, 0.4 equiv.) over
a period of 4 h. The resulting mixture was stirred at room
temperature for 1 h and then carefully poured onto ice (2 kg) to
give a bright yellow precipitate. After additional 1 L of water was
added to the cold solution, and the mixture was allowed to stand
for overnight under stirring. The expected yellow solid was
collected by suction filtration, washed with 1 N HCl solution, and
dried. The crude mixture of mono- and di-brominated NDA (Br-
NDA and Br2-NDA) weight 16.0 g and used without further
purification.
QDM 2: BP-NDI (150 mg, 0.234 mmol, 1 equiv.) and
Lawesson’s reagent (480 mg, 6.0 mmol, 4 equiv.) were added to
anhydrous toluene (30 mL) in round-bottom flask with an attached
condenser under an argon atmosphere. The mixture was stirred at
reflux (140 °C) for 48 h. The resulting solution was cooled to room
temperature and concentrated under reduced pressure to give a
dark red-brown sticky solid. The solid was then precipitated into
methanol (300 mL) and filtered to remove excess Lawesson’s
reagent and Lawesson’s reagent byproducts. After that product
was purified by silica gel chromatography using acetone and
toluene (1: 100) to yield compound 2. Obtained as reddish solid
(31 mg, 22 %). 1H NMR (300 MHz, CDCl3) δ: 8.51 - 8.49 (d, J =
6 Hz, 2H), 8.04 - 7.95 (m, 4H), 7.66 - 7.59 (q, J = 6 Hz & 9 Hz ,
2H), 7.53 - 7.46 (q, J = 6 Hz & 6 Hz , 2H), 7.04 - 7.00 (d, J = 6
Hz, 2H), 3.8 - 3.9 (m, 4H), 1.3 - 1.9 (m, 4H), 1.2 - 1.3 (m, 20H),
0.8 - 0.9 (m, 6H); 13C NMR (75 MHz, CDCl3) δ: 14.0, 22.6, 26.7,
26.9, 29.1, 29.2, 31.7, 55.6, 114.3, 114.5, 122.8, 124.9, 127.3,
127.6, 130.6, 130.8, 132.6, 133.1, 133.3, 159.2, 163.6. ESI-
HRMS: Calculated for C42H64N2S2 [M] 643.3175, observed:
643.3175.
Sn-NDI: A mixture of the Br-NDI (3.0 g, 4.65 mmol),
Bis(tributyltin) (4.71 g, 8.135 mmol, 3 equiv.) in dry toluene in
the presence of Pd2(dba)3 (15 mol%) and P (o-tol)3 (0.848, 2.79
mmol, 0.6 equiv.) under argon atmosphere was refluxed at 120 º
C for 24 h. After cooling to room temperature, the solvent was
concentrated in vacuo and purified by silica gel chromatography
using 1:1 DCM and Hexane. Obtained pure Sn-NDI as a yellow
semi-solid (1.5 g, 41.2 % yield). 1H NMR (300 MHz, CDCl3) δ:
8.98 (s, 1H), 8.73 - 8.72 (d, J = 3 Hz, 2H), 4.24 - 4.19 (t, J = 9 Hz,
4H), 1.75 - 1.72 (m, 4H), 1.57 - 1.25 (m, 38H), 0.93 - 0.85 (m,
15H); 13C NMR (75 MHz, CDCl3) δ: 11.6, 13.7, 14.0, 22.6, 27.0,
27.1, 27.4, 28.0, 29.1, 29.2, 29.3, 31.8, 40.9, 41.0, 123.6, 125.9,
126.7, 130.1, 130.2, 131.6, 138.6, 156.0, 163.0, 163.1, 163.6,
164.9; ESI-HRMS: Calculated for C42H64N2O4Sn [M+H]
781.3961, observed: 781.3970.
QDM 3: The synthetic procedure for compound 2 was adopted
to prepare the thiophene analog; but, the compound decomposes
during workup.
Acknowledgments
BTDI: A mixture of Sn-NDI (1.64 mmol, 1.28 g, 1 equiv.) and
dibromo biphenyl (1.37 mmol, 423 mg, 0.83 equiv.) was added to
round bottom flask which contains dry toluene (10 ml), and to this
solution, Pd(PPh3)4 (159 mg, 0.137 mmol) and CuI (52 mg, 0.275
mmol) were added under Argonne medium then refluxed at 140
NK is thankful for the generous support as Postdoctoral
Fellowship from the Center for Interdisciplinary Scientific
Computation (CISC) at Illinois Tech. AYR thanks the Wrangler
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[11] D. Veldman, S. M. A. Chopin, S. C. J. Meskers, R. A. J. Janssen, J. Phys.
Chem. A 2008, 112, 8617–8632.
Institute for Sustainable Energy (WISER) at Illinois Tech fort he
generous support. This material is also based upon work
supported by the National Science Foundation under a CAREER
grant no. 1753012 Awarded to AJA.
[12] M. Abe, Chem. Rev. 2013, 113, 7011–7088.
[13] S. Shokri, M. K. Manna, G. P. Wiederrecht, D. J. Gosztola, S. Jockusch,
A. Y. Rogachev, A. J.-L. Ayitou, J. Org. Chem. 2017, 82, 10167–10173.
[14] S. Shokri, G. P. Wiederrecht, D. J. Gosztola, A. J.-L. Ayitou, J. Phys.
Chem. C 2017, 121, 23377–23382.
Keywords: Quinoidal Acenes • Aromaticity • Anti-Aromaticity
[15] C. Rémy, C. Allain, I. Leray, Photochem. Photobiol. Sci. 2017, 16, 539–
546.
[1]
[2]
M. A. Kobaisi, S. V. Bhosale, K. Latham, A. M. Raynor, S. V. Bhosale,
Chem. Rev. 2016, 116, 11685–11796.
[16] X. Cui, C. Xiao, T. Winands, T. Koch, Y. Li, L. Zhang, N. L. Doltsinis, Z.
Wang, J. Am. Chem. Soc. 2018, 140, 12175–12180.
X. Zhan, T. J. Marks, M. A. Ratner, A. Facchetti, M. W. Advanced, S.
Barlow, 2011, T. J. Marks, M. A. Ratner, M. R. Wasielewski, et al., Adv.
Mater. Weinheim 2011, 23, 268–284.
[17] K. Nagarajan, A. R. Mallia, K. Muraleedharan, M. Hariharan, Chem. Sci.
2017, 8, 1776–1782.
[18] C. Li, C. Xiao, Y. Li, Z. Wang, Org. Lett. 2013, 15, 682–685.
[19] W. Yue, A. Lv, J. Gao, W. Jiang, L. Hao, C. Li, Y. Li, L. E. Polander, S.
[3]
W. B. Davis, W. B. Davis, W. A. Svec, W. A. Svec, M. A. Ratner, M. A.
Ratner, M. R. Wasielewski, M. W. Nature, 1998, Nature 1998, 396, 60–
63.
Barlow, W. Hu, et al., J. Am. Chem. Soc. 2012, 134, 5770–5773.
[20] a) J. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1996, 77, 3865–
[4]
[5]
A. A. Rachford, S. Goeb, F. N. Castellano, J. Am. Chem. Soc. 2008, 130,
2766–2767.
3868. b) D. Geuenich, K. Hess, F. Kohler, R. Herges, Chem. Rev.,
2005, 105, 3758–3772.
X. Chen, C. Xu, T. Wang, C. Zhou, J. Du, Z. Wang, H. Xu, T. Xie, G. Bi,
J. Jiang, et al., Angew. Chem. 2016, 128, 10026–10030.
S. Guo, W. Wu, H. Guo, J. Zhao, J. Org. Chem. 2012, 77, 3933–3943.
O. Yushchenko, G. Licari, S. Mosquera-Vazquez, N. Sakai, S. Matile, E.
Vauthey, J. Phys. Chem. Lett. 2015, 6, 2096–2100.
S. Wu, F. Zhong, J. Zhao, S. Guo, W. Yang, T. Fyles, J. Phys. Chem. A
2015, 119, 4787–4799.
[21] J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1997, 78, 1396–
1396.
[6]
[7]
[22] P. V. R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao, N. J. R. V. E.
Hommes, J. Am. Chem. Soc. 1996, 118, 6317–6318.
[23] Z. Chen, C. S. Wannere, C. Corminboeuf, R. Puchta, P. von Ragué
Schleyer, Chem. Rev. 2005, 105, 3842–3888.
[24] N. C. Baird, J. Am. Chem. Soc. 1972, 94, 4941–4948.
.
[8]
[9]
S. Guo, J. Sun, L. Ma, W. You, P. Yang, J. Zhao, Dyes and Pigments
2013, 96, 449–458.
[10] C. Kaiser, A. Schmiedel, M. Holzapfel, C. Lambert, J. Phys. Chem. C
2012, 116, 15265–15280.
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Entry for the Table of Contents
COMMUNICATION
Quinoidal Acenes*
Nareshbabu Kamatham , Jingbai Li ,
Siamak Shokri , Guang Yang , Steffen
Jockusch, Andrey Y. Rogachev * and A.
Jean-Luc Ayitou *
R
N
R
S
S
O
O
N
O
O
R
N
S
Lawesson's
reagent
O
P
S
π
Ar
π
H
Page No. – Page No.
N
R
N
R
Quinoidization of -Expanded
p
via
Aromatic Diimides: Photophysics,
Aromaticity, and Stability of the Novel
Quinoidal Acenes
Lawesson reagent mediating quinoidization of polyaromatic acenes to afford novel quinoidal triplet chromophores
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