Benzo[e]pyrene skeleton dipyrylium dication with a strong donor-acceptor-donor interaction, and its two-electron reduced molecule

Article abstract of DOI:10.1002/chem.201101708

The donor-acceptor-donor (D-A-D) conjugated molecules 1,4- bis(diarylaminophenylethynyl)anthraquinone (1,4-Am₂Aq) and 1,4-bis(ferrocenylethynyl)anthraquinone (1,4-Fc₂Aq), undergo a double proton cyclization reaction with bis(trifluoromethanesulfone)imide acid (TFSIH) to yield 1,4-bis(diarylaminophenyl or ferrocenyl) dipyrylium salts [1,4-R ₂Pyl₂](TFSI)₂ (R=Am or Fc) with novel planar pentacyclic structures similar to the aromatic benzo[e]pyrene-type skeleton. [1,4-Am₂Pyl₂](TFSI)₂ could be reduced to give the neutral molecule [1,4-Am₂Pyl₂]⁰, which is stable and maintains the benzo[e]pyrene-type skeleton.

Full text of DOI:10.1002/chem.201101708

DOI: 10.1002/chem.201101708
Benzo[e]pyrene Skeleton Dipyrylium Dication with a Strong Donor–
Acceptor–Donor Interaction, and Its Two-Electron Reduced Molecule
Koya Prabhakara Rao,[a] Mio Kondo,[a] Ryota Sakamoto,[a] Tetsuro Kusamoto,[a]
Michihiro Nishikawa,[a] Shoko Kume,[a] Masayuki Nihei,[b] Hiroki Oshio,[b] and
Hiroshi Nishihara*[a]
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FULL PAPER
Abstract: The donor–acceptor–donor
(D–A–D) conjugated molecules 1,4-
bis(diarylaminophenylethynyl)anthra-
quinone (1,4-Am2Aq) and 1,4-bis(fer-
tacyclic structures similar to the aro-
matic benzo[e]pyrene-type skeleton.
[1,4-Am2Pyl2]ACTHNUGTRNE(NUG TFSI)2 could be reduced
tains the benzo[e]pyrene-type skeleton.
To the best of our knowledge, this is
the first oxygen-atom-containing poly-
cyclic aromatic hydrocarbon with 22
(4n+2) p-electrons. The obtained con-
densed-ring benzo[e]pyrene-type skele-
ton compounds show physical and
chemical properties that are significant-
ly different from those of [1,5-
to give the neutral molecule [1,4-
rocenylethynyl)anthraquinone
(1,4-
Am2Pyl2]0, which is stable and main-
Fc2Aq), undergo a double proton cycli-
zation reaction with bis(trifluorometha-
nesulfone)imide acid (TFSIH) to yield
1,4-bis(diarylaminophenyl or ferrocen-
Keywords: donor–acceptor
sys-
tems · pi interactions · protonation-
induced cyclization · redox chemis-
try · valence tautomerization
yl) dipyrylium salts [1,4-R2Pyl2]
N
Am2Pyl2]ACHTUNGTRNE(NUNG TFSI)2, which has a pery-
(R=Am or Fc) with novel planar pen-
lene-type skeleton.
Introduction
tomers[11] are generated. The electronic structure of D–A
and D–A–D molecules directly influences the molecular
physical properties by controlling the electronic communica-
tion between two redox active centers in the presence of ex-
ternal stimuli[12–14] such as protons, photons, magnetic fields,
or electrons, to produce molecular devices.[15]
Polycyclic aromatic hydrocarbons (PAHs) are subunits of
graphene, and they have been exploited in a variety of or-
ganic electronic devices[1] including field-effect transistors,
injection layers, and solar cells. The electronic structure of
PAHs has been of fundamental interest in theoretical
chemistry for decades, and may be treated by the Clar
sextet theory[2] and others.[3] PAHs containing neutral or
positively charged heteroatoms (e.g., nitrogen, oxygen, or
sulfur) in the aromatic framework exhibit unprecedented
chemical and physical properties.[4] Heteroatom-containing
PAHs, particularly six-membered ring structures with
oxygen, are scarce[5] because of their instability. In our
recent studies, we have developed a new class[6–10] of donor–
acceptor (D–A) and D–A–D molecules, in which D (ferro-
cenyl (Fc), diarylaminophenyl (Am), phenyldithiolene (Pdt),
phenyl, m-tolyl, or p-tolyl) and A (ethynylanthraquinone
(Aq)) undergo mono and double intramolecular cyclization,
respectively, to give pyrylium cations. The monoprotonated
pyrylium cation [1-RPyl]+ has a tetracyclic structure in
which oxygen is in cationic form in the p-conjugated aro-
matic six-membered ring. This phenomenon can be used to
lower the energy of the lowest unoccupied molecular orbital
(LUMO) to allow intramolecular electron transfer. When R
is a strong donor such as Fc, Am, or Pdt, a strong and broad
band ascribed to charge transfer (CT) between R and Pyl+
appears in the Vis/NIR region,[6–10] and thereby valence tau-
We recently described a D–A–D molecule, 1,5-bis(diaryl-
AHCTUNGTRENNUNG
aminoarylethynyl)anthraquinone, 1,5-Am2Aq,[10a] which un-
dergoes a novel double proton cyclization reaction to yield a
1,5-bis(diarylaminoarylethynyl)dipyrylium salt [1,5-
Am2Pyl2](TFSI)2 (TFSI=bis(trifluoromethanesulfone)-
AHCTUNGTREGiNNNU mide) with a new type of pentacyclic structure, which is
AHCTUNGTRENNUNG
similar to the perylene-type skeleton and has the same
number of p-electrons (4n=4ꢁ5=20). Apparently, one of
the isomers of the pentacyclic perylene is benzo[e]pyrene,
which presents good stability[2,3] and physical properties that
are completely different from those of the other isomers. It
is in this context that we considered the synthesis of the D–
A–D molecules 1,4-bis(diarylaminophenyl or ferrocenyl)an-
thraquinone, 1,4-R2Aq (R=Am or Fc), which can undergo
double proton cyclization reactions to yield 1,4-bis(diaryla-
minophenyl or ferrocenyl)dipyrylium ions, [1,4-R2Pyl2]2+
(R=Am or Fc). The goal of this effort was to produce a
new type of pentacyclic structure similar to that of the tar-
geted benzo[e]pyrene-type skeleton, which is supposed to
have better stability than [1,5-Am2Pyl2]2+, as predicted by
Clarꢂs sextet electron resonance structures (Scheme 1).[2]
In the present study, we report the synthesis and charac-
terization of the new D–A–D molecules 1,4-R2Aq (R=Am
or Fc) and their double protonation-induced intramolecular
cyclization reactions with TFSIH to yield [1,4-R2Pyl2]-
[a] Dr. K. P. Rao, Dr. M. Kondo, Dr. R. Sakamoto, Dr. T. Kusamoto,
M. Nishikawa, Dr. S. Kume, Prof. H. Nishihara
Department of Chemistry, School of Science
The University of Tokyo
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan)
Fax : (+81)3-5841-8063
E-mail: nisihara@chem.s.u-tokyo.ac.jp
reduced to give the neutral molecule [1,4-Am2Pyl2]0, which
maintained the benzo[e]pyrene-type skeleton. The obtained
neutral molecule [1,4-Am2Pyl2]0 was stable. To the best of
our knowledge, this is the first oxygen-atom-containing
PAH with 22 (4n+2) p-electrons. The obtained condensed-
ring benzo[e]pyrene-type skeleton compounds showed phys-
ical and chemical properties that were significantly different
[b] Dr. M. Nihei, Prof. Dr. H. Oshio
Department of Chemistry
Graduate School of Pure and Applied Sciences
University of Tsukuba
Tennodai 1-1-1, Tsukuba 305-8571 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101708.
from those of [1,5-Am2Pyl2]ACHTNUTRGNENUG(TFSI)2, which has a perylene-
Chem. Eur. J. 2011, 17, 14010 – 14019
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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14011

H. Nishihara et al.
infra). Subsequently, the band
characteristic of the pyrylium
ring at 540 nm decreased slight-
ly with a shift in lmax to 535 nm,
and the broadness and intensity
of the CT band increased fur-
ther over the range 660–
1560 nm along with a shift in
lmax to 960 nm. The 1,4-Am2Aq
Scheme 1. Clarꢂs sextet resonance structures of pentacycles.
solution turned from yellow to
violet after the addition of two
equivalents of TFSIH. This
type skeleton.[10a] The synthesis and characterization of the
1,4-bis(diarylaminophenyl)anthraquinone, and the synthesis,
X-ray structures, and chemical and physical properties of
the protonated products [1,4-bis(diarylaminophenyl or ferro-
cenyl) dipyrylium salts] are described in this paper.
UV/Vis/NIR absorption spectrum differed from that corre-
sponding to the double protonation of [1,5-Am2Pyl2]-
AHCTUNGTRENNUNG
(TFSI)2.[10a] The band characteristic of the pyrylium ring de-
creased slightly for the second protonation of 1,4-Am2Aq,
[10a]
which was in contrast with [1,5-Am2Pyl2]2+
.
The UV/Vis/
NIR absorption spectra of the proton-induced cyclization re-
action of 1,4-Fc2Aq was similar to that of 1,4-Am2Aq, al-
though the CT band at lmax =1000 nm was broader (see Fig-
ure S3 in the Supporting Information).
Results and Discussion
Synthesis and characterization of 1,4-Am2Aq: 1,4-Am2Aq
was synthesized by the Sonogashira cross-coupling of 1-ethy-
nyltriarylamine with 1,4-dibromoanthraquinone, and was
The cyclization products [1,4-R2Pyl2]ACHTNUTRGNEU(GN TFSI)2 (R=Am or
Fc) were synthesized under an argon atmosphere by the ad-
dition of four and six equivalents of TFSIH in dichlorome-
thane, giving yields of 86% and 70%, respectively. The for-
mation of a pentacyclic compound was suggested by single-
1
characterized by ESI mass spectrometry, H and 13C NMR
(see Figures S1 and S2 in the Supporting Information), and
elemental analysis. The synthesis and X-ray crystal struc-
tures involving guest-induced and reversible crystal-to-crys-
tal transformations of 1,4-Fc2Aq[16] have been reported pre-
viously by our group, but the protonation reaction and phys-
ical properties were previously unknown.
crystal X-ray crystallography of [1,4-Am2Pyl2]ACTHUNTRGEN(UNG TFSI)2, al-
though this analysis was insufficient because of the poor
quality of the single crystals obtained (see Figure S4 and the
Supporting Information for details). Similarly, single crystals
of [1,4-Fc2Pyl2]ACTHNUTRGEN(NUG TFSI)2 suitable for X-ray analysis were not
Double protonation of 1,4-Am2Aq and 1,4-Fc2Aq and prop-
erties of the products: The protonation-induced cyclization
reaction of 1,4-Am2Aq with TFSIH in dichloromethane was
monitored by UV/Vis/NIR absorption spectroscopy. As
shown in Figure 1, the spectrum changed in two steps, indi-
cating that two protonation reactions occurred sequentially.
First, the band corresponding to the anthraquinone moiety
at 455 nm decreased, and the band characteristic of the
pyrylium ring at 540 nm grew along with a broad donor–ac-
ceptor CT band[6–10] at 650–1450 nm with lmax =850 nm (vide
obtained. However, the anion TFSIꢀ was exchanged with
ꢀ
BF4 , leading to good single-crystal X-ray data for [1,4-
Fc2Pyl2]ACTHNUTRGNEUNG
(BF4)2 (Table S1, Supporting Information).[17]
Figure 2 shows an ORTEP diagram of [1,4-Fc2Pyl2]2+ and its
3D packing structure. The pentacyclic structure of the mole-
cule was determined, and was found to be similar to the aro-
matic benzo[e]pyrene-type skeleton with the same number
of p-electrons. The high planarity of the pentacyclic ring was
consistent with an expansion of the p-conjugated system
ꢀ
upon cyclization. The C C bond lengths in the pentacyclic
ꢀ
moiety were in the range 1.35(1)–1.44(1) ꢃ, and the C O
bond lengths were in the range 1.365(9)–1.378(9) ꢃ, suggest-
ing an additional expansion of the p-conjugated system
upon cyclization. The donor (Fc) and pentacyclic benzo[e]-
pyrene-type skeleton moieties were organized in a “wave-
like” structure, as viewed along the c-axis. We can conclude
that the double protonation of the ethynyl moieties of 1,4-
R2Aq induced intramolecular cyclization by annelation of
the carbonyl and ethynylene groups to give the first example
of a pentacyclic dipyrylium salt of [1,4-R2Pyl2]ACTHUNTRGEN(UNG TFSI)2 con-
sisting of a benzo[e]pyrene-type skeleton (Scheme 2).
The results of cyclic voltammetry (CV) of 1,4-Am2Aq and
[1,4-Am2Pyl2]ACTHUNGTREN(UGN TFSI)2 in 0.1m Bu4NClO4-CH2Cl2 are shown
in Figure 3a, and the numerical data are summarized in
Table 1. The CV of 1,4-Am2Aq revealed one reversible and
one subsequent irreversible one-electron reduction step. The
Figure 1. UV/Vis/NIR absorption spectra of 1,4-Am2Aq in dichlorome-
thane after each addition of TFSIH (bottom).
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Benzo[e]pyrene Skeleton Dipyrylium Dication
FULL PAPER
moiety.[20] On the other hand, in
the case of the latter, the
second oxidation may be ascrib-
able to the p-methoxyphenyl
rings. In agreement with the
UV/Vis/NIR absorption meas-
urements, the HOMO–LUMO
gap estimated from the differ-
ence between the first oxidation
potential and the first reduction
potential, DE0’, decreased with
increasing p-conjugation. The
DE0’ value for [1,4-Am2Pyl2]-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
was reduced by 1.04 V upon
cyclization.
The protonated product [1,4-
Am2Pyl2]ACTHNUGTRNEU(GN TFSI)2 was found to
be NMR-active (see Figur-
es S5–S7 in the Supporting In-
formation), supporting the con-
clusion of
a benzo[e]pyrene-
type skeleton. This structure
contrasted with the structures
of [1,5-R2Pyl2]ACTHNUGTRENUNG(TFSI)2 (R=Am
or Fc), which were NMR-
silent.[10] This result indicated
that the majority of molecules
in equilibrium between the va-
lence tautomers, as shown in
Scheme 2, were present in the
diamagnetic form. Therefore,
DFT calculations were per-
Figure 2. ORTEP diagrams (50% probability, hydrogen atoms omitted for clarity) of [1,4-Fc2Pyl2]ACHTNURGTNE(UNG BF4)2 (top),
and its three-dimensional packing structure viewed along the c axis (bottom).
Table 1. Electrochemical data of 1,4-Am2Aq and [1,4-Am2Pyl2]ACHTUNGTRENNUNG
(TFSI)2.[a]
redox behavior of the second step of quinones reflects the
effective electronic environments in some systems, and is
generally irreversible because of the slow electron transfer
by electronic mediation among the radical anion species.[18]
On the other hand, the CV of [1,4-Am2Pyl2]2+ revealed two
reversible one-electron reduction steps, which were substan-
tially shifted to the positive direction compared to those of
1,4-Am2Aq, indicating a lowering of the LUMO energy. As
for the oxidation, both the nonprotonated form 1,4-Am2Aq
Compound
Oxidation
Reduction
E0’ (ox1)
E0’ (red1)
E0’ (red2)
1,4-Am2Aq
[1,4-Am2Pyl2]ACHTNURGTNEUNG(TFSI)2
0.31
0.62
ꢀ1.39
ꢀ0.04
ꢀ1.95[b]
ꢀ0.36
[a] V versus ferrocenium/ferrocene. [b] Cathodic peak potential, Ep,c
.
formed for [1,4-Am2Pyl2]2+, and indicated that the diamag-
netic species were slightly energetically more favorable than
the triplet paramagnetic species (0.2 eV). This result is in
contrast with that for [1,5-Am2Pyl2]2+, where the triplet par-
amagnetic species were energetically favored.[10a] These cal-
culation data were consistent with the fact that DE0’ of [1,4-
and the protonated form [1,4-Am2Pyl2]ACHTNUGTRNEUNG(TFSI)2 exhibited
one reversible oxidation wave, attributable to the oxidation
of the two triarylamine moieties. This positive E0’ shift,
caused by protonation, was probably due to the stronger
electron-withdrawing ability of the dicationic dipyrylium
moiety compared to that of the neutral diethynylanthraqui-
none moiety. We note that a further oxidation wave was ob-
served in both 1,4-Am2Aq (irreversible, anodic peak poten-
Am2Pyl2]
(TFSI)2, and thus, the electron-transfer efficiency in [1,4-
Am2Pyl2](TFSI)2 was lower than in [1,5-Am2Pyl2](TFSI)2.
ACHTUNGTRNE(NUNG TFSI)2 was larger than that of [1,5-Am2Pyl2]-
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
tial, Ep,a =0.97 V) and [1,4-Am2Pyl2]
N
Preparation of the neutral form [1,4-Am2Pyl2]0 by reduction
of [1,4-Am2Pyl2](TFSI)2: Recently, we reported the synthe-
sis and X-ray crystal structure of the first neutral compound
[1,5-Am2Pyl2]0 by reduction of [1,5-Am2Pyl2]
E
p,a =0.89 V). As to the former, this wave may be attributa-
ACHTUNGTRENNUNG
ble either to the oxidation of the p-methoxyphenyl rings on
the triarylamines[19] or to that of the anthraquinone
ACHTUNGTRENNUNG
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H. Nishihara et al.
Scheme 2. Reaction pathways of 1,4-R2Aq and [1,4-Am2Pyl2]2+
.
Am2Pyl2]0 was highly unstable, and an X-ray crystal struc-
ture was not obtained. The protonated product discussed
here, [1,4-Am2Pyl2]ACHTUNGTRENNUNG(TFSI)2, had a benzo[e]pyrene-type skel-
ponents of the flat extended p-conjugated six-membered
ꢀ
ꢀ
ring with 22 p-electrons in total. The C C and C O bond
lengths in the tetracyclic moiety were in the range 1.348(4)–
1.443(4) ꢃ and 1.378(4)–1.393(4) ꢃ, respectively, and the ex-
panded p-conjugated system was maintained upon reduc-
eton that provided additional stability due to Clarꢂs sextet
electron resonance structures (Scheme 1).[2] In this context,
we attempted to synthesize the neutral compound by chemi-
cal reduction.
ꢀ
tion. The C40 C41 bond length was 1.420(4) ꢃ, which was
longer than that in the dicationic form (1.345(5) ꢃ). The
The neutral compound [1,4-Am2Pyl2]0 was prepared by
C41 C42 and C39 C40 lengths of 1.381(4) and 1.384(4) ꢃ,
respectively, were shorter than those in the cationic form
(1.459(5) and 1.435(5) ꢃ, Figure S10). This was consistent
with the theoretical calculations described below.
ꢀ
ꢀ
treating [1,4-Am2Pyl2]
ACHTUNGTNER(NUNG TFSI)2 with lithium tetracyanoquino-
dimethane (Li[TCNQ]) to give a yield of 40%. The com-
ACHTUNGTRENNUNG
1
pound was characterized by ESI mass spectrometry, H and
13C NMR (Figures S8 and S9), XRD measurements, and ele-
mental analysis, which indicated that this compound was
more stable than [1,5-Am2Pyl2]0.
The FTIR spectra of 1,4-R2Aq (R=Am or Fc) indicated
that the CꢁC stretching vibration of the acetylene moiety
at 2183 or 2194 cmꢀ1 and the C=O vibration of the quinone
moiety at 1672 or 1669 cmꢀ1 are observed, but these peaks
disappeared completely in their protonated products, [1,4-
Single crystals of [1,4-Am2Pyl2]0 suitable for X-ray analy-
sis were obtained by recrystallization from dichloromethane/
hexane at 293 K in the absence of light (see Table S1 in the
Supporting Information).[17] An ORTEP diagram and the
3D packing structure of [1,4-Am2Pyl2]0 are shown in
Figure 4. The pentacyclic structure of the molecule was
found to maintain the planar pentacyclic backbone of the di-
cation, similar to that of the aromatic benzo[e]pyrene-type
skeleton. It should be noted that this is the second example
of a neutral compound in which the oxygen atoms are com-
R2Pyl2]ACHTNUTRGENNG(U TFSI)2 (see Figure S11 in the Supporting Informa-
tion). These spectral changes indicated that both ethyne
moieties reacted with the proton, and a cyclocondensation
reaction proceeded. The vibrations of the TFSIꢀ ion were
observed at 1355, 1191, 738, and 572 cmꢀ1, and the C=O vi-
brations of the pyrylium moieties were observed at 1609,
1529, and 1505 cmꢀ1 for [1,4-Am2Pyl2]
tions appeared in the spectrum of [1,4-Fc2Pyl2]
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
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Benzo[e]pyrene Skeleton Dipyrylium Dication
FULL PAPER
form, in which the orbital was the HOMO, as determined by
X-ray crystallographic analysis (vide supra). It should be
noted that the LUMO (227) was uniformly delocalized over
[10a]
the entire pentacyclic perylene ring in [1,5-Am2Pyl2]2+
,
unlike the LUMO in [1,4-Am2Pyl2]2+. This finding was in
agreement with the UV/Vis/NIR absorption spectra and
redox properties, as noted above. Time-dependent DFT
(TDDFT) calculations were performed for the diprotonated
product [1,4-R2Pyl2]2+ (R=Am or Fc), and the energies as-
sociated with excitation to the lowest excited states were es-
timated (see Tables S2 and S3 in the Supporting Informa-
tion). The excitation energies to the lowest excited state
found experimentally matched the calculated ones. The cal-
culations indicated that the absorption peaks at 530 nm for
[1,4-Am2Pyl2]
(221)–LUMO
transitions. The CT band was ascribed to HOMO
arylamine)–LUMO(227) (pyrylium) transitions.
ACHTUNGTRENNUNG
G
E
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
Reversible alcohol and acid reaction of [1,4-Am2Pyl2]-
(TFSI)2: As previously reported,[10a] [1,5-Am2Pyl2]
(TFSI)2
did not react with alcohol and acid. In contrast, [1,4-
Am2Pyl2](TFSI)2 reacted readily with two molecules of
NaOMe in methanol to afford the neutral acetal compound
1,4-Am2A(Pyl-OMe)2 (Scheme 2), similar to the monopyryli-
um cations[10a,21] [1-AmPyl]+ and [1-FcPyl]+. The reaction of
[1,4-Am2Pyl2](TFSI)2 with methanol was monitored by UV/
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
CTHUNGTRENNUNG
AHCTUNGTRENNUNG
Vis/NIR absorption spectroscopy (see Figure S15 in the Sup-
porting Information), which indicated that the formation of
the acetal derivative occurred in a single step with two me-
thoxy groups. The characteristic UV/Vis/NIR absorption
bands at 535 and 960 nm disappeared upon formation of
Figure 3. a) Cyclic voltammograms of 1,4-Am2Aq (red line), and [1,4-
Am2Pyl2]
ACHTUNGTRENNUNG
at 0.1 Vsꢀ1. The inset shows a voltammogram of [1,4-Am2Pyl2]
AHCTUNGTRENNUNG
cusing on the first and second oxidations. b) Energies are shown with ref-
erence to the Fc+/Fc redox reaction. Schematic energy diagrams for 1,4-
Am2Aq and [1,4ꢀAm2Pyl2]2+ are estimated from the redox potentials
measured by cyclic voltammetry.
1,4-Am
2ACHTUNGTRENN(UNG Pyl-OMe)2, but these bands were recovered upon
addition of TFSIH, indicative of the recovery of [1,4-
Am2Pyl2]ACTHNUGTRENNG(U TFSI)2. These spectral results indicated that a qua-
These results also supported the conclusion that the dipyry-
lium salts have benzo[e]pyrene-type pentacyclic structures
formed by the two-step cyclocondensation reaction of the
acetylene moiety and the carbonyl group of the quinone
moiety. The CV of [1,4-Am2Pyl2]0 in 0.1m Bu4NClO4-CH2Cl2
showed two reversible one-electron reduction steps at ꢀ0.05
and ꢀ0.27 V versus Fc+/Fc, which are ascribed to the Pyl2
moiety (see Figure S12 in the Supporting Information). One
irreversible oxidation wave appeared at Ep,a =0.68 V, which
sireversible reaction with OMeꢀ and H+ led to structural
changes that produced nearly quantitative on–off switching
and the appearance of the CT band. Although some un-
known intermediates were generated during the reaction be-
cause of the CT nature of [1,4-Am2Pyl2]ACHTNUGTRNEUNG(TFSI)2 under ambi-
ent conditions, the HRMS ESI-TOF spectrum of the prod-
uct of the reaction with NaOMe clearly showed a peak at
m/z 926.3331 (calcd M+ 926.3567) corresponding to 1,4-
Am
acetal derivative, 1,4-Am
for further characterization. The differences in reactivity of
[1,4-Am2Pyl2](TFSI)2 and [1,5-Am2Pyl2](TFSI)2 toward
NaOMe may be due to the higher fraction of paramagnetic
tautomers (30%) in [1,5-Am2Pyl2](TFSI)2 compared with
[1,4-Am2Pyl2](TFSI)2 (only a minute fraction in solution). In
(Pyl-OMe)2. However, isolation of the pure form of this
is not consistent with the reduction wave of [1,4-Am2Pyl2]2+
the reason for this is not clear at this stage.
;
CHTUNGTRENNUNG
The geometries of 1,4-Am2Aq, [1,4-Am2Pyl2]2+
,
[1,4-
A
ACHTUNGTRENNUNG
Am2Pyl2]0, and [1,4-Fc2Pyl2]2+ were fully optimized by using
density functional theory (DFT) methods (molecular orbital
diagrams are shown in Figures 5 and S13, and energy dia-
grams are shown in Figure S14 in the Supporting Informa-
tion). The LUMO (227) of [1,4-Am2Pyl2]2+ was mainly lo-
calized on the pyrene ring and partially on three adjacent
benzene rings, and, as expected, had a similar shape to that
of the HOMO (227) of [1,4-Am2Pyl2]0. The LUMO of the
dicationic form had a nodal plane between C24 and C25,
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
the paramagnetic form, the positive charge is not localized
on the central polyaromatic rings (Scheme 2). These results
also demonstrate that the D–A–D conjugated molecules
show unique chemical and physical properties depending on
the aromatic framework of the acceptor moiety.
ꢀ
consistent with the C40 C41 bond elongation in the neutral
Chem. Eur. J. 2011, 17, 14010 – 14019
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H. Nishihara et al.
Conclusion
We have described the double
protonation-induced cyclization
reaction of the new D–A–D
conjugated molecules 1,4-R2Aq
(R=Am or Fc) to yield dipyry-
lium salts [1,4-R2Pyl2]ACHTUNGTRENNUNG(TFSI)2
(R=Am or Fc) with a novel
planar pentacyclic structure of
a benzo[e]pyrene-type skeleton.
[1,4-Am2Pyl2]ACTHNUGTRNENUG(TFSI)2 could be
reduced to give the neutral
molecule [1,4-Am2Pyl2]0, which
was stable and maintained the
planarity of the rings. An im-
portant finding was that the ob-
tained condensed-ring benzo[e]-
pyrene-type
skeleton
com-
pounds showed different opti-
cal, electrochemical, and mag-
netic properties to those of the
previously
reported
[1,5-
Am2Pyl2](TFSI)2, which had a
AHCTUNGTRENNUNG
perylene-type skeleton. These
facts should be useful in design-
ing novel heteroatom-contain-
ing PAH molecular systems, as
well as for the synthesis,
through protonation reactions,
of novel molecular structures
displaying unusual physical and
Figure 4. ORTEP diagram (50% probability, hydrogen atoms omitted for clarity) (top) and the three-dimen- chemical properties.
sional packing structure of [1,4-Am2Pyl2]0 viewed along the a axis (middle) and along the b axis (bottom).
Figure 5. Molecular orbitals of 1,4-Am2Aq (left), [1,4-Am2Pyl2]2+ (middle), and [1,4-Am2Pyl2]0 (right) calculated by the DFT method.
14016
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14010 – 14019

Benzo[e]pyrene Skeleton Dipyrylium Dication
FULL PAPER
(w), 909 (w), 853 (w), 837 (w), 788 (w), 739 (w), 719 (w), 679 (w), 651
(w), 599 (m), 570 (m), 509 cmꢀ1 (m).
Experimental Section
Synthesis of [1,4-Am2Pyl2]0: Under N2, [1,4-Am2Pyl2]
ACHTNUTRGNE(UNG TFSI)2 (0.100 g,
General method: Solvents and reagents were used as received from com-
mercial sources. 4-ethynyl N,N-bis(4-methoxyphenyl)aniline was pre-
pared by a procedure described in the literature.[22] Anhydrous solvents
were obtained as guaranteed grade from Kanto Chemicals Ltd. and used
after a freeze-pump-thaw cycle unless otherwise noted. Triethylamine
was dried by reflux over KOH, distilled under nitrogen, and degassed
with a freeze-pump-thaw cycle. Hexane and dichloromethane were dis-
tilled from CaH2 under nitrogen, and degassed with a freeze-pump-thaw
cycle. All syntheses were performed under an atmosphere of dry nitrogen
or dry argon unless otherwise indicated.
0.07 mmol) was dissolved in CH2Cl2/DMF (5 mL/10 mL) and stirred with-
out exposure to light. LiTCNQ (0.030 g, 0.14 mmol) was added to this re-
action mixture. The color of the solution changed from dark violet to red-
dish violet. After being stirred for 1 h, the solvent was removed under
vacuum. The reddish violet product was purified by column chromatogra-
phy on an Al2O3 (II-III) column eluted with CH2Cl2:hexane=1:1. The
first violet fraction was collected and the solvent was evaporated. The
product was recrystallized with CH2Cl2/hexane. This compound was sen-
sitive to light; purification was performed without exposure to light. [1,4-
Am2Pyl2]0 was obtained in 40% yield. HRMS (ESI-TOF): m/z: 864.3167
(calcd [M+] 864.3199); H NMR ([D7]DMF, 400 MHz): d=3.84 (s, 12H),
Synthesis of 1,4-Am2Aq: Under N2, a mixture of 1,4-dibromo anthraqui-
none (0.330 g, 0.91 mmol), 4-ethynyl N,N-bis(4-methoxyphenyl)aniline
(0.599 g, 1.82 mmol), bis(triphenylphosphine)palladium(II) dichloride
(0.127 g, 0.18 mmol), and cuprous iodide (0.069 g, 0.36 mmol) in triethyla-
mine (80 mL) solvent was heated under reflux at 708C for 3 h. The color
of the reaction mixture changed from orange to dark red. After being
cooled to room temperature, the solvent was removed under vacuum.
The residue was dissolved in CH2Cl2 and washed with water, then dried
with Na2SO4. The product was purified by column chromatography on an
Al2O3 (II-III) column eluted with CH2Cl2:hexane=(1:1!1:0). 1,4-
Am2Aq was obtained in 40% yield. Elemental analysis calcd (%) for
C58H42N2O6·1.7H2O: C 77.96, H 5.12, N 3.13; found: C 77.96, H 5.08, N
3.25; MS (ESI-TOF): m/z: 862.42 (calcd [M+] 862.30); 1H NMR (CDCl3
500 MHz): d=3.82 (s, 12H), 6.88 (m, 12H), 7.09 (dd, 8H, J=9.0 Hz, J=
2.0 Hz), 7.51 (d, 4H, J=8.8 Hz), 7.76 (dd, 2H, J=5.7 Hz, 3.4 Hz), 7.81 (s,
2H), 8.30 ppm (dd, 2H, J=5.7 Hz, 3.2 Hz); 13C NMR (CDCl3 125 MHz):
d=55.6, 89.4, 99.0, 113.7, 114.9, 119.1, 123.5, 127.2. 127.4, 133.4, 133.6,
133.9, 134.0, 138.4, 140.1, 149.6, 156.6, 182.2 ppm; IR (KBr): n˜ =3037 (w),
1
6.21 (s, 2H), 6.42 (s, 2H), 6.88 (d, 4H, J=9.2 Hz), 7.03 (d, 8H, J=
8.8 Hz), 7.19 (d, 8H, J=8.8 Hz), 7.49 (m, 2H), 7.76 (d, 4H, J=9.2 Hz),
8.14 ppm (m, 2H); 13C NMR ([D7]DMF 125 MHz): d=55.8, 115.7, 128.3
(not all peaks were observed because of the low concentration); IR (in-
frared microscope): n˜ =3049 (m), 3012 (m), 2931 (m), 2907 (m), 2836
(m), 1651 (m), 1613 (s), 1602 (s), 1570 (w), 1502 (s), 1461 (m), 1440 (w),
1403 (w), 1374 (m), 1323 (s), 1294 (s), 1240 (s), 1169 (s), 1112 (m), 1089
(m), 1036 (s), 997 (w), 928 (w), 825 (s), 753 (w), 732 (w), 684 (w), 644
(w), 576 (w), 566 (w), 523 (w), 507 cmꢀ1 (w).
NMR measurements, mass spectrometry, and IR spectra: 1H, 1H 2D
COSY, and 13C NMR spectra of samples in CDCl3, [D7]DMF, and
CD2Cl2 were collected using AL-400 (JEOL), ECX-400 (JEOL), and
DRX500 (Bruker) NMR spectrometers. ESI-TOF mass spectra were re-
corded with an LCT time-of-flight mass spectrometer (Micromass). IR
transmission spectra were recorded with an FT/IR-620 (JASCO) spec-
trometer and an FT/IR-420 (JASCO) spectrometer equipped with an
Irtron IRT-30 infrared microscope (JASCO). The IR spectra of all sam-
ples except [1,4-Am2Pyl2]0 were measured as KBr pellets. The IR spec-
trum of [1,4-Am2Pyl2]0 was measured as a powder.
ꢁ
2995 (w), 2948 (w), 2930 (w), 2903 (w), 2832 (w), 2175 (m, C C), 1675
(m, CO), 1598 (s), 1504 (s), 1463 (w), 1441 (w), 1387 (w), 1319 (m), 1288
(s), 1241 (s), 1159 (m), 1105 (w), 1034 (m), 869 (w), 827 (m), 781 (w), 725
(m), 642 (w), 624 (w), 599 (w), 578 (m), 530 cmꢀ1 (w).
UV/Vis/NIR spectroscopy in solution: Samples for UV/Vis/NIR spectros-
copy in solution were prepared under an argon atmosphere. UV/Vis/NIR
spectra were recorded with a V-570 spectrometer (JASCO). Quartz cells
with a path length of 1 cm were used to observe absorption in the UV
region.
Synthesis of [1,4-Am2Pyl2]ACTHNUTRGNE(NUG TFSI)2: Under Ar, 1,4-Am2Aq (0.200 g,
0.23 mmol) was dissolved in CH2Cl2 (15 mL) and stirred. Bis(trifluorome-
thanesulfone)imide (0.261 g, 0.93 mmol) in CH2Cl2 (5 mL) was added to
this reaction mixture. The color of the solution changed from red to
violet. After being stirred for 30 min, hexane (30 mL) was added. The
whole mixture was allowed to crystallize overnight. The dark violet pre-
cipitate was filtered off using a membrane filter and washed with hexane.
Single-crystal X-ray analysis: Single crystals of [1,4-Fc2Pyl2]ACHTUNGTRENNUNG(BF4)2 and
[1,4-Am2Pyl2]0 were mounted on a loop, and data were collected with a
Rigaku AFC10 diffractometer with the Rigaku Saturn CCD system
equipped with a rotating-anode X-ray generator that emits graphite-mon-
ochromated MoKa radiation (l=0.7107 ꢃ). An empirical absorption cor-
rection using equivalent reflections and Lorentzian polarization correc-
tion were performed with the program Crystal Clear 1.3.6. The structures
were solved with the program SHELXS-97[23] and refined against F2
using SHELXL-97.[24]
[1,4-Am2Pyl2]ACHTUNGTRENNUNG(TFSI)2 was obtained in 86% yield. Elemental analysis
calcd (%) for C62H44N4F12O14S4·3.5H2O: C 50.03, H 3.45, N 3.76; found:
C 50.02, H 3.73, N 3.40; MS (ESI-TOF): m/z: 864.35 (calcd [M+] 864.32);
1H NMR (CD2Cl2 500 MHz 235 K): d=3.83 (s, 12H), 6.99 (d, J=8.9,
8H+2H), 7.11 (d, J=7.9, 2H), 7.23 (d, J=8.7, 8H), 7.97 (s, 2H), 8.06 (d,
J=9.1, 2H), 8.19 (dd, J=6.2, 3.3, 2H), 8.29 (s, 2H), 8.37 (d, J=9.0, 2H),
8.81 ppm (dd, J=6.4, 3.2, 2H); 1H NMR (CD2Cl2 500 MHz 295 K): d=
3.87 (s, 12H), 7.02 (d, 8H, J=9.1 Hz), 7.09 (d, 4H, J=9.6 Hz), 7.26 (d,
8H, J=9.1 Hz), 7.98 (2H), 8.2–8.3 (8H), 8.83 ppm (2H); 13C NMR
(CD2Cl2 100 MHz 295 K): d=56.1, 115.8, 118.5, 119.4, 121.7, 124.5, 124.9,
128.6, 133.8, 136.5, 159.9 ppm; IR (KBr): n˜ =3186 (w), 3075 (w), 2937
(w), 2902 (w), 2839(w), 1600 (s, Pyrylium), 1598 (s, Pyrylium), 1528 (m),
1487 (s), 1465 (w), 1434 (s), 1355 (s), 1301 (w), 1249 (m), 1190 (s), 1161
(s), 1057 (w), 1030 (w), 1008 (w), 948 (w), 850 (w), 833 (w), 799 (w), 740
(w), 683 (w), 652 (w), 615 (w), 598 (w), 572 (w), 536 (w), 511 cmꢀ1 (w).
Cyclic voltammetry: A glassy carbon (GC) rod (outer diameter 3 mm,
Tokai GC-20) was embedded in Pyrex glass, and the cross-section was
used as the working electrode (polished with Al2O3 fine particles (0.3 mm
diameter) and washed with purified water and acetone with ultrasonica-
tion prior to use). Cyclic voltammetry was carried out under an argon at-
mosphere using a platinum wire counter electrode and an Ag+/Ag refer-
ence electrode (10 mm AgClO4 and 0.1m Bu4NClO4-CH3CN solution; E0’
of ferrocenium/ferrocene is 0.20 V under our conditions) and an ALS-
650B voltammetric analyzer.
DFT calculations: The geometries of 1,4-R2Aq (R=Am or Fc), [1,4-
R2Pyl2]2+, and [1,4-Am2Pyl2]0 were fully optimized using the DFT meth-
ods. The three-parameterized Becke-Lee–Yang–Parr (B3LYP) hybrid ex-
change-correlation functional was employed. The LanL2DZ (Hay–Wadt
ECP) basis set was used for the Fe atom, and the 6–31G** basis set was
used for all other atoms. On the basis of the optimized structure, the
TDDFT method was applied to calculate the excited states relevant to
the absorption spectra of each compound. The solvent effect (CH2Cl2)
was considered using the PCM model. The present calculations were im-
plemented using the Gaussian03 program package.[25] For [1,4-Am2Pyl2]2+
, optimization using the unrestricted method (uB3LYP) was also per-
formed assuming the triplet state. In the triplet state, one spin was
Synthesis of [1,4-Fc2Pyl2]ACTHNUTRGNE(NUG TFSI)2: Under Ar, 1,4-Fc2Aq (0.016 g,
0.026 mmol) was dissolved in CH2Cl2 (5 mL) and stirred. Bis(trifluorome-
thanesulfone)imide (0.042 g, 0.15 mmol) in CH2Cl2 (3 mL) was added to
this reaction mixture. The color of the solution changed from dark brown
to a dark color. After being stirred for 10 min, the solution was allowed
to stand for 20 min, and dark red crystals were formed. [1,4-Fc2Pyl2]-
ACHTUNGTRENNUNG(TFSI)2 was obtained in 70% yield. Elemental analysis calcd (%) for
C42H26N2F12O10S4: C 42.51, H 2.21, N 2.36; found: C 42.65, H 2.49, N
2.59; HRMS (ESI-TOF): m/z: 626.0627 (calcd M+ 626.0633); NMR:
silent; IR (KBr): n˜ =3094 (w), 1613 (m, Pyrylium), 1587, 1535 (s), 1508
(s), 1491 (s), 1415 (w), 1347 (s), 1322 (s), 1187 (s), 1134 (s), 1052 (s), 958
Chem. Eur. J. 2011, 17, 14010 – 14019
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14017

H. Nishihara et al.
mainly centered on the triarylamine moieties, and the other was located
on the pentacyclic skeleton.
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ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
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MeOH was added stepwise to this solution (20 mL in each step, 160 mL in
total) and the absorption spectra were recorded [Figure S15 (top)]. A
quasireversible UV/Vis/NIR absorption spectral change was obtained by
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ˇ
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[1,4-Am2Pyl2](TFSI)2 (0.020 g, 0.014 mmol) was added to NaOMe
ACHTUNGTRENNUNG
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(0.003 g, 0.056 mmol) in MeOH (10 mL) and stirred for 1 h without expo-
sure to light. The color of the solution changed from violet to dark green.
The reaction mixture was filtered in order to remove the counter anion
TFSIꢀ as an inorganic NaTFSI salt. A 1H NMR study indicated that iso-
lation of pure form of the acetal derivative 1,4-Am2ACTHNUTRGNE(UGN Pyl-OMe)2 could not
be achieved. Our efforts to separate the products by column chromatog-
raphy were also unsuccessful. However, the HRMS ESI-TOF spectrum
of the reaction product indicated a peak at m/z 926.3331 (calcd [M+]
926.3567), corresponding to 1,4-Am2ACTHNUTRGNEU(GN Pyl-OMe)2.
Acknowledgements
This work was supported by Grants-in-Aid from MEXT of Japan [Nos.
20245013 and 21108002, area 2107 (Coordination Programming)], and
the Global COE Program for Chemistry Innovation.
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Received: June 5, 2011
Revised: August 25, 2011
Published online: November 14, 2011
Chem. Eur. J. 2011, 17, 14010 – 14019
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