Colorless to purple-red switching electrochromic anthraquinone imides with broad visible/near-IR absorptions in the radical anion state: Simulation-aided molecular design

Article abstract of DOI:10.1002/asia.201300176

The large redshift of near-infrared (NIR) absorptions of nitro-substituted anthraquinone imide (Nitro-AQI) radical anions, relative to other AQI derivatives, is rationalized based on quantum chemical calculations. Calculations reveal that the delocalization effects of electronegative substitution in the radical anion states is dramatically enhanced, thus leading to a significant decrease in the HOMO-LUMO band gap in the radical anion states. Based on this understanding, an AQI derivative with an even stronger electron-withdrawing dicyanovinyl (di-CN) substituent was designed and prepared. The resulting molecule, di-CN-AQI, displays no absorption in the Vis/NIR region in the neutral state, but absorbs intensively in the range of λ=700-1000 (λ_max≈860 nm) and λ=1100-1800 nm (λ_max≈1400 nm) upon one-electron reduction; this is accompanied by a transition from a highly transmissive colorless solution to one that is purple-red. The relationship between calculated radical anionic HOMO-LUMO gaps and the electron-withdrawing capacity of the substituents is also determined by employing Hammett parameter, which could serve as a theoretical tool for further molecular design.

Full text of DOI:10.1002/asia.201300176

FULL PAPER
DOI: 10.1002/asia.201300176
Colorless to Purple–Red Switching Electrochromic Anthraquinone Imides
with Broad Visible/Near-IR Absorptions in the Radical Anion State:
Simulation-Aided Molecular Design
[
a]
[a]
[b]
[a]
Fengkun Chen, Jie Zhang, Hong Jiang, and Xinhua Wan*
Abstract: The large redshift of near-in-
frared (NIR) absorptions of nitro-sub-
stituted anthraquinone imide (Nitro-
AQI) radical anions, relative to other
AQI derivatives, is rationalized based
on quantum chemical calculations. Cal-
culations reveal that the delocalization
effects of electronegative substitution
in the radical anion states is dramati-
cally enhanced, thus leading to a signifi-
cant decrease in the HOMO–LUMO
band gap in the radical anion states.
Based on this understanding, an AQI
derivative with an even stronger elec-
tron-withdrawing dicyanovinyl (di-CN)
substituent was designed and prepared.
The resulting molecule, di-CN-AQI,
displays no absorption in the Vis/NIR
region in the neutral state, but absorbs
intensively in the range of l=700–1000
(lmax ꢀ860 nm) and l=1100–1800 nm
(lmax ꢀ1400 nm) upon one-electron re-
duction; this is accompanied by a transi-
tion from a highly transmissive color-
less solution to one that is purple–red.
The relationship between calculated
radical anionic HOMO–LUMO gaps
and the electron-withdrawing capacity
of the substituents is also determined
by employing Hammett parameter,
which could serve as a theoretical tool
for further molecular design.
Keywords: anthraquinone imides ·
density functional calculations
substituent effects molecular
near-infrared electro-
·
·
devices
·
chromism
Introduction
the low environmental stability of the reduced form and the
lack of an in-depth understanding of the structure–property
relationship for efficient molecular design, although these
materials are preferably needed to balance charge transport
and obtain a high chromatic contrast ratio in EC variable
optical attenuator (ECVOA) devices, which can be used to
modulate light transmission in telecommunication windows
Electrochromic (EC) materials operating in the near-infra-
red (NIR) region (l=780–2500 nm) have been attracting
more and more attention for their great importance in mili-
tary and civilian applications, such as telecommunications,
biomedicine, and even thermal control for buildings or
Most of the NIR EC materials, which have
been extensively explored and are currently available for
practical use, are transition-metal oxides or complexes.
Organic EC compounds with NIR absorptions are emerging
materials because they are solution processable, have a fast
[1–3]
[5]
spacecrafts.
(l=1310–1550 nm). Apart from some conjugated poly-
[4d,f]
[6]
mers,
stacked naphthalene diimides (NDIs) and conju-
[2,3]
[7]
gated diquinones, to the best of our knowledge, are the
only two known systems that display intense absorptions in
the telecommunication wavelength range with distinct NIR
absorption origins upon reduction from the excitation of p
electrons along the stacks and p*–p* transitions of delocal-
ized radical anions. Recently, we reported another kind of
cathodic NIR EC materials based on anthraquinone imide
[4]
response to stimuli, and a high color contrast ratio, but are
relatively less addressed. This is especially the case for
cathodic EC materials working in reduced states, owing to
[8]
(
AQI). AQI consists of both quinone and imide motifs in
one molecule to afford better solubility than conjugated di-
quinones and other benefits such as further functionaliza-
tion. Most of the explored AQI derivatives exhibit absorp-
tions ranging from l=700 to 1100 nm (lmax ꢀ820 nm) upon
reduction. One exception, nitro-substituted AQI (Nitro-
AQI), displays two intense NIR absorptions with maximal
peaks centered at about l=860 and 1260 nm, respectively,
[
a] Dr. F. Chen, Prof. J. Zhang, Prof. X. Wan
Beijing National Laboratory for Molecular Sciences
Key Laboratory of Polymer Chemistry and
Physics of Ministry of Education
College of Chemistry and Molecular Engineering
Peking University, Beijing 100871 (P.R. China)
Fax : (+86)10-62751708
E-mail: xhwan@pku.edu.cn
[8a]
[
b] Prof. H. Jiang
upon one-electron reduction.
However, an in-depth un-
Beijing National Laboratory for Molecular Sciences
Institute of Theoretical and Computational Chemistry
College of Chemistry and Molecular Engineering
Peking University, Beijing 100871 (P.R. China)
derstanding of the substitution effect on NIR absorption of
AQI radical anions remains unknown. The absorption range
of Nitro-AQI is also still not long enough for telecommuni-
cation windows, that is, l=1310 and 1550 nm.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201300176.
Chem. Asian J. 2013, 00, 0 – 0
1
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

www.chemasianj.org
Xinhua Wan et al.
Herein, the effect of electronegative substitution (e.g.,
nitro group) on the NIR absorption of AQI radical anions
was investigated through quantum chemical calculations. It
was revealed that the delocalization effect of electronegative
substitutions was significantly enhanced in radical anion
states relative to that in neutral states. Based on this finding,
a new AQI molecule with an even stronger electron-with-
drawing dicyanovinyl (di-CN) group was designed and pre-
pared. Compared with Nitro-AQI, the resulting di-CN-AQI
molecule exhibits much broader intense absorptions in the
Vis–NIR region, which cover the entire biomedical and tele-
communication windows, upon one-electron reduction. In-
terestingly, the transition between different redox states of
this molecule also results in a color change of the solution
from colorless to purple–red.
none segment was stretched and the adjacent CꢁC bond
was compressed. This alternation of bond-length changes
upon addition of one electron could be understood from the
distribution of the LUMO of the radical anions and indicat-
ed the bond homogenization of AQI in the radical anion
[9]
states. The frontier molecular orbitals (MOs) of the model
molecules (i.e., AQI’ and Nitro-AQI’) in the neutral and
radical anion states are presented in Figure 1. In the neutral
state, the HOMO–LUMO gap of Nitro-AQI’ is 3.94 eV,
slightly reduced (by 0.05 eV) relative to that of AQI’, which
mainly results from a slightly more stabilized LUMO level
by the electron-withdrawing substituent. This effect of elec-
tronegative substitution (i.e., halogen or cyano) is effectively
used to tune the band gaps of n-type neutral organic semi-
conductors, in addition to common strategies, such as conju-
gation length control, bond-length alternation, and donor–
[10]
acceptor charge transfer. However, the situations in the
radical anion states we disclose herein are remarkably dif-
ferent. The HOMO and LUMO of Nitro-AQI’ radical
anions are both delocalized over the whole molecular skele-
ton and their energies are significantly lower with respect to
those of the AQI’ radical anions. Even more importantly,
the LUMO level is stabilized much more strongly than the
HOMO level, thereby leading to a dramatic reduction in the
HOMO–LUMO gap by about 0.66 eV. This reduction in the
energy gap is in accordance with the large redshift observed
in the spectroelectrochemical measurements. The simulation
results clearly reveal that the delocalization effect of electro-
negative substitution is drastically enhanced in the radical
anion states. Such a delocalization effect was also achieved
by increasing conjugation, as explored in the case of helical
Results and Discussion
Quantum Chemical Calculations
The effect of electronegative substitution on the electronic
structures and corresponding NIR absorption properties of
AQIs were first investigated by quantum chemical calcula-
tions based on DFT and time-dependent DFT (TD-DFT) at
the B3LYP/6-31+G ACHUTNGRNENUG( d,p) level by using unsubstituted and
nitro-substituted AQI for comparison. To simplify the calcu-
lations, we considered model compounds obtained by re-
placing the long alkyl group in the experimentally used AQI
compounds with a methyl group. All molecules in their neu-
tral and radical anion states were fully relaxed. Adding an
electron to the molecules induced predominant bond-length
changes in both molecules (Figure S1 in the Supporting In-
formation). For example, the C=O bond of the anthraqui-
[11]
diquinones.
Figure 1. Selected frontier MOs of unsubstituted and 6-substituted AQIs in their neutral and radical anion states obtained at the UB3LYP/6-31G+(d, p)
level.
&
&
Chem. Asian J. 2013, 00, 0 – 0
2
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

www.chemasianj.org
Xinhua Wan et al.
Based on this understanding of electronegative substitu-
ent effects on AQI radical anions, we believe that the NIR
absorptions of AQI radical anions could be further redshift-
ed by a substituent with a stronger electron-withdrawing ca-
pacity, such as the di-CN group. To confirm our expecta-
tions, the electronic structures and absorptions of di-CN-
AQI, together with the precursor methyl-substituted AQI
(
Me-AQI), were simulated. As indicated in Figure 1, Me-
AQI’ and AQI’ have very similar frontier MOs in the radical
anion state, with the HOMO mainly located on the AQI
core. This is understandable when considering that the elec-
tron-donating effect of the methyl group in Me-AQI’ is neg-
ligible in electron-rich anionic states. Derivative di-CN-AQI’
also shows similar frontier MOs to those of Nitro-AQI’;
however, the HOMO–LUMO band gap of the di-CN-AQI’
radical anions is further reduced by 0.05 eV compared with
that of Nitro-AQI’ radical anions. TD-DFT calculated ab-
sorptions of di-CN-AQI’ radical anions are presented in
Figure 2. These results revealed that a further redshift of
about 100 nm relative to Nitro-AQI’ could be obtained by
incorporation of the di-CN group. Detailed transitions of
these NIR absorptions are summarized in Table S1 in the
Supporting Information; the two lowest energy transitions
for di-CN-AQI’ can be assigned to the a-HOMO!a-
LUMO and a-HOMO!a-LUMO+1 (a and b for spin up
and down, respectively) transitions, respectively. The unique
absorption at about 520 nm of di-CN-AQI radical anions
also makes it more interesting to examine this molecule ex-
perimentally.
Figure 2. Calculated absorption spectra of neutral and radical anion
states obtained by TD-DFT at the B3LYP/6-31+G (d,p) level.
stituents and were thereby fully characterized for compari-
son.
Electrochemistry
The electrochemical properties of these molecules were in-
vestigated by cyclic voltammetry (CV) in CH Cl with tetra-
2
2
butylammonium perchlorate (TBAP) as a supporting elec-
trolyte (Figure 3). As indicated in the CV curves, Me-AQI
and CHO-AQI exhibit two quasi-reversible one-electron re-
ductions, corresponding to the formation of stable radical
anions and dianions, respectively. A third reduction process
is found at a more negative potential for di-CN-AQI, and
this third process could be ascribed to the reduction of the
carbonyl group in the imide moiety as a result of the strong
Synthesis of di-CN-AQI
The synthetic route to di-CN-AQI is illustrated in Scheme 1.
The target molecule was synthesized by Knoevenagel con-
[8a]
electron-withdrawing characteristics of the di-CN group.
[12]
densation
of malononitrile with formyl-substituted AQI
The redox potentials, according to the energy level of the in-
ternal ferrocene (Fc) reference, are summarized in Table 1.
(
CHO-AQI), which was obtained by successive bromination,
hydrolysis, and oxidation of
Me-AQI (Scheme 1). Me-AQI
was facilely prepared by bis-
Diels–Alder addition reactions
of 1,4-benzoquinone, following
reported procedures with slight
[13]
modifications.
The chemical
structures of these molecules
1
were confirmed by
H
and
C NMR spectroscopy, high-
resolution mass spectrometry
HRMS), and elemental analy-
13
(
sis. Detailed synthetic proce-
dures are described in the Ex-
perimental Section. The two
important intermediates, Me-
AQI and CHO-AQI, also
served to illustrate a variation
of electron-donating/-withdraw-
ing characteristics in the sub-
Scheme 1. The synthetic route for di-CN-AQI. DDQ=2,3-dichloro-5,6-dicyanobenzoquinone, TsOH=p-tolue-
nesulfonic acid, THF=tetrahydrofuran, DMF=dimethylformamide, NBS=N-bromosuccinimide, BPO=ben-
zoyl peroxide, DMSO=dimethylsulfoxide, PCC=pyridinium chlorochromate.
Chem. Asian J. 2013, 00, 0 – 0
3
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

www.chemasianj.org
Xinhua Wan et al.
Figure 4. UV/Vis–NIR spectra of di-CN-AQI (1.0 mm containing 0.1m
Bu NClO ) in the neutral and radical anion states in CH Cl (inset: pho-
tographs of the sample solution taken in the neutral and reduced states).
Figure 3. Cyclic voltammograms recorded in CH
Bu NClO (0.10m) with a glassy carbon working electrode at a scanning
rate of 100 mVs (vs. Ag/AgCl).
2 2
Cl (1.0 mm) containing
4
4
2
2
4
4
ꢁ1
appears together with the intense NIR absorptions
in the radical anion states. This new peak in the
visible region makes di-CN-AQI unique in AQIs
and results in a color change of the solution from
colorless to purple–red upon reduction (Figure 4,
inset). Colored/black-to-transmissive switching has
been achieved in EC materials with a donor–ac-
Table 1. Electrochemical potentials, energy levels, and band gaps of the compounds in
CH Cl (c=10 molL at a scanning rate of 100 mVs vs. Ag/AgCl).
2 2
ꢁ
3
ꢁ1
ꢁ1
1
2
[a]
[b]
[c]
Compound
E
[
1/2
E
1/2
DE
Electrochemistry
LUMO
DFT calculations
HOMO
V]
[V]
[V]
LUMO
Me-AQI
CHO-AQI
di-CN-AQI
ꢁ0.90
ꢁ0.73
ꢁ0.64
ꢁ1.39
ꢁ1.23
ꢁ1.05
0.49
0.50
0.41
ꢁ3.67
ꢁ3.84
ꢁ3.93
ꢁ7.42
ꢁ7.78
ꢁ7.60
ꢁ3.67
ꢁ3.90
ꢁ4.00
1
2
[
a] DE (V)=E 1/2ꢁE 1/2. [b] LUMO (eV)=ꢁ(EredꢁEFc/Fc+ +4.8) (eV). [c] HOMO and
ceptor strategy, which can be exploited in display
LUMO values were obtained for the optimized structures at the B3LYP/6-31G+(d,p)
[15]
devices and smart windows.
However, transmis-
level.
sive-to-black/colored switching EC materials are
still limited owing to the complexity of material
[
16]
The first reduction potentials of these AQI derivatives in-
crease drastically with strengthening of the electron-with-
design.
The intense absorptions of di-CN-AQI radical
anions appearing in both visible and NIR regions also distin-
guish this molecule from other known systems, such as
donor–acceptor-based conjugated polymers, and may find
other applications in thermal control and solar cells.
drawing capacity of the substituents. For example, an in-
1
crease in DE 1 by 0.26 V is observed on going from di-CN-
/2
AQI to Me-AQI, which implies the destabilization effect of
strong electron-withdrawing substituents in the neutral
[14]
state. The LUMO energy levels measured from the first
reduction potentials and the calculated HOMO and LUMO
energy levels are also listed in Table 1. The calculated
LUMO energy levels show good agreement with the experi-
mental ones.
Hammett Parameter
Substituent effects on the electrochemical and electronic
properties were further investigated by employing the Ham-
mett parameter (s ) because it may have provided a quanti-
x
[17]
tative measure of electronic effects. Plots of the first re-
duction potentials and the calculated HOMO–LUMO gap
Spectroelectrochemical Properties
(
DE) for Me-AQI, CHO-AQI, di-CN-AQI, and other three
Of primary interest, however, are the electronic spectra of
AQIs in the radical anion states, which were investigated by
spectroelectrochemical measurements (Figure 4 for di-CN-
AQI and Figure S2 in the Supporting Information for Me-
AQI and CHO-AQI). As shown in Figure 4, when reduced
to the radical anion states, di-CN-AQI displays two broad
NIR absorptions over the ranges l=700–1000 (lmax
previously reported AQI derivatives (i.e., methoxylphenyl-
substituted (MeO-Ph-AQI), thiophene-substituted (Th-
[8a,e]
AQI), and Nitro-AQI)
versus s are depicted in Figure 5.
x
A good linear correlation between these quantities is ob-
served, which can be used as a theoretical tool for new mo-
lecular designs. The reduction potential increases together
with the electron-withdrawing capacity of the substituent be-
cause strong electron-withdrawing substituents enhance the
relative stability of the AQI radical anions. On the other
hand, the calculated HOMO–LUMO gap decreases, leading
to a bathochromic shift of the electronic spectra.
ꢀ
860 nm) and 1100–1800 nm (lmax ꢀ1400 nm), respectively,
which cover the entire biomedical and telecommunication
[8b,c]
windows. Compared with unsubstituted AQI,
strong elec-
tronegative substitution from the di-CN group results in
a redshift as large as 580 nm. Notably, nearly no absorption
beyond l=400 nm is observed for neutral di-CN-AQI in so-
lution and a new absorption in the range of l=450–600 nm
To obtain a more complete picture of substitution effects
on the NIR behavior of AQIs, optical absorption data for
several AQI radical anions with different substituents are
&
&
Chem. Asian J. 2013, 00, 0 – 0
4
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

www.chemasianj.org
Xinhua Wan et al.
substitution at the 6-position with a di-CN group. Upon
one-electron reduction, the resulting molecule, di-CN-AQI,
displayed intensive NIR absorptions in the range of l=700–
1
000 (lmax ꢀ860 nm) and 1100–1800 nm (l ꢀ1400 nm), ac-
max
companied by a colorless to purple–red color change of the
solution. The relationship between calculated radical anionic
HOMO–LUMO gaps and the electron-withdrawing capaci-
ties of the substituents was also determined by employing
the Hammett parameter, which could be used as a theoreti-
cal tool for further molecular design. We have shown that
the NIR absorption range of AQIs is readily tuned upon
variation of the electron-withdrawing capacity of the sub-
stituents. It is expected that EC AQIs that absorb at even
longer wavelengths can be obtained by taking into account
the enhanced delocalization effects of electronegative substi-
tution in the radical anion states and the tunability of the
molecular conjugation length. This contribution could also
serve as a novel molecular design strategy for other NIR
EC materials and further efforts to exploit this aspect are
underway.
Figure 5. Plots of the first reduction potentials of AQIs and the calculated
HOMO–LUMO gap (DE) versus Hammett parameters, s (obtained
from ref. [17b]). (^): Me-AQI, (&): MeO-Ph-AQI, (!): Th-AQI, (*):
CHO-AQI, (~): Nitro-AQI, (I): di-CN-AQI.
x
Experimental Section
Materials
Methyl propiolate (99%), DDQ (98%), propanedinitrile (99%), and
[
3 2 2
Pd ACHTUNGTREUNNGN( PPh ) Cl ] (98%) were purchased from J&K (Beijing, China) and
used as received. Tri-n-butyl tin hydride (99%), isoprene (96%), and
PCC (98%) were obtained from TCI and used without purification. All
solvents used for characterization were of spectrophotometric grade or
distilled prior to use.
2
,3-Dicarbomethoxy-1,3-butadiene (2)
Tri-n-butyltin hydride (1.61 mL, 6.0 mmol) was added dropwise within
2 min to a solution of methyl propiolate (0.42 g, 5.0 mmol) in THF
(15 mL) containing [PdCl ACHTNURTGNENG(U PPh ) ] (70 mg, 0.1 mmol). After addition, the
2 3 2
Figure 6. Substituent effects on the NIR absorption of AQI radical
anions in CH
2
Cl
2
(1.0 mm/0.1m TBAP).
originally light-yellow solution rapidly turned orange–brown. Stirring was
continued for about 10 min. THF was then evaporated in vacuo and the
resulting oily residue was purified by column chromatography (silica gel;
petroleum ether/dichloromethane 2:1 v/v). Pure methyl 2-(tributylstan-
collected in Figure 6. For AQIs with electron-donating sub-
stituents, such as MeO-Ph-AQI and Th-AQI, broad absorp-
tions centered at l=820 nm with a shoulder at around l=
nyl)propenoate (1) was obtained as an oil (1.50 g, 80%) after evapora-
1
tion of the solvents. H NMR (300 MHz, CDCl
3
): d=6.91 (d, J=2.4 Hz,
1
H), 5.94 (d, J=2.4 Hz, 1H), 3.74 (s, 3H), 1.54–1.25 (m, 18H), 0.91 ppm
(t, J=7.2 Hz, 9H).
The above-obtained 1 (0.75 g, 2 mmol) was added to a solution of Cu-
(NO ·H O (0.48 g, 2 mmol) in THF (2 mL). The reaction mixture was
1000 nm were observed. However, the shoulder was isolated
and bathochromically shifted in a stepwise manner with in-
creasing electronegativity of the substituent. A bathochro-
mic shift of 580 nm was achieved simply by the introduction
of the strongly electronegative di-CN group into AQI at
a particular position.
A
H
U
G
R
N
U
G
3
)
2
2
stirred for 10 min at room temperature. It was then diluted with ethyl
acetate (150 mL) and washed successively with 5% aqueous ammonia
(
100 mL), water (100 mL), and brine (100 mL). The organic layer was
dried over anhydrous magnesium sulfate. After evaporation of the sol-
vent, the crude residue was purified by column chromatography (silica
gel; petroleum ether/dichloromethane=2:1 v/v) to yield 2,3-dicarbome-
1
thoxy-1,3-butadiene (0.12 g, 68%). H NMR (300 MHz, CDCl
3
): d=6.29
Conclusion
(
s, 2H), 5.82 (s, 2H), 3.77 ppm (s, 6H).
Dimethyl-5,8-dioxo-5,8-dihydronaphthalene-2,3-dicarboxylate (NQ-
diester)
In terms of DFT and TD-DFT calculations, the remarkably
enhanced delocalization effect of electronegative substitu-
tion on AQI-containing molecules in the radical anion state
was revealed. This results in a smaller HOMO–LUMO band
gap in the radical anion state than that in the neutral state.
Based on such an understanding, even longer NIR absorp-
tions of AQI radical anions were achieved by incorporating
A solution of freshly sublimed 1,4-benzoquinone (0.54 g, 5.0 mmol) and
diester 2 (0.53 g, 3.1 mmol) in 1,4-dioxane (15 mL) was heated to 808C
under a nitrogen atmosphere in the dark for 48 h. Then, the reaction mix-
ture was cooled to room temperature and the solvent was evaporated.
The crude residue was not further purified and used directly in the next
oxidation reaction.
Chem. Asian J. 2013, 00, 0 – 0
5
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

www.chemasianj.org
Xinhua Wan et al.
TsOH·H
2
O (0.28 g, 1.65 mmol) and DDQ (1.2 g, 5.28 mmol) were added
reflux overnight. The mixture was then allowed to cool to room tempera-
ture and washed with distilled water (3ꢁ20 mL). The collected organic
layer was dried over anhydrous magnesium sulfate. After the evaporation
of the solvent, the crude residue was purified by column chromatography
to a stirred solution of the obtained residue (0.42 g) in toluene (20 mL),
and the reaction mixture was heated to reflux for 2 h. The mixture was
then cooled and filtered. The filtrate was evaporated and the residue was
dissolved in dichloromethane and washed successively with a saturated
solution of sodium carbonate and brine. The organic layer was dried over
anhydrous magnesium sulfate. After evaporation of the solvent, the
crude residue was purified by column chromatography (silica gel; petro-
(silica gel; petroleum ether/EtOAc=20:1 v/v) to give CH2Br-AQI as
1
a yellow–green solid (0.33 g, 60%). H NMR (400 MHz, CDCl
3
): d=8.76
(s, 2H), 8.37 (s, 1H), 8.35 (s, 1H), 7.91 (d, J=8.0 Hz, 1H), 4.61 (s, 2H),
4.28–4.23 (m, 1H), 2.10–2.06 (m, 2H), 1.75–1.66 (m, 2H), 1.28–1.23 (m,
leum ether/EtOAc=4:1 v/v) to give NQ-di-ester as a yellow solid (0.30 g,
16H), 0.86 ppm (t, J=6.8 Hz, 6H); HRMS (ESI): m/z calcd for
1
+
7
3
3%). H NMR (300 MHz, CDCl
.98 ppm (s, 6H).
3
): d=8.43 (s, 2H), 7.09 (s, 6H),
C
30
H
35BrNO
4
[M+H] : 552.1749; found: 552.1757.
N-(1-Hexylheptyl)-6-formylanthraquinone-2,3-dicarboxylic Imide (CHO-
AQI)
Dimethyl-6-methyl-9,10-dioxo-9,10-dihydroanthracene-2,3-dicarboxylate
Me-AQ-diester)
(
2
A suspension of CH Br-AQI (0.33 g, 0.6 mmol) in water (10 mL) and
A solution of NQ-di-ester (0.90 g, 3.3 mmol) and isoprene (0.5 mL,
.0 mmol) in 1,4-dioxane (25 mL) was heated to 808C under a nitrogen
atmosphere in the dark for 48 h. Then, the reaction mixture was cooled
to room temperature and the solvent was evaporated to obtain an oily
residue, which was used without further purification.
DMSO (30 mL) was heated at reflux with vigorous stirring for 20 h and
the mixture was then cooled to room temperature. After being poured
into water (100 mL), the mixture was extracted with dichloromethane
(3ꢁ30 mL) and the collected organic layer was washed with brine and
dried over anhydrous magnesium sulfate. The 6-hydroxymethyl-substitut-
ed AQI was obtained after evaporation of the solvent and used directly
in the next oxidation step.
5
2
DDQ (2.25 g, 1 mmol) and TsOH·H O (0.60 g, 3.16 mmol) were added to
a solution of the residue in toluene (80 mL) and the mixture was heated
to reflux for 2 h. Then, the mixture was cooled and filtered. The filtrate
was evaporated and the residue was dissolved in dichloromethane and
washed successively with a saturated solution of sodium carbonate and
brine. The organic layer was dried over anhydrous magnesium sulfate.
After evaporation of the solvent, the crude residue was purified by
column chromatography (silica gel: petroleum ether/EtOAc=4:1 v/v) to
PCC (0.16 g, 0.74 mmol) was added to a suspension of the above hydroly-
sate in dichloromethane (15 mL). The mixture was stirred at room tem-
perature for 12 h and excess PCC was removed by filtration. After evap-
oration of the solvent, the crude residue was washed with water (50 mL)
and extracted with dichloromethane (3ꢁ30 mL). The resulting organic
layer was washed with brine and dried over anhydrous magnesium sul-
fate. The solvent was removed under reduced pressure and the crude
product was purified by column chromatography (silica gel; petroleum
1
give Me-AQ-di-ester as a pale-yellow solid (0.59 g, 53%). H NMR
(
300 MHz, CDCl
3
): d=8.43 (s, 2H), 7.09 (s, 6H), 3.98 ppm (s, 6H);
H NMR (400 MHz, CDCl ): d=8.63 (s, 2H), 8.25 (d, J=8.0 Hz, 1H),
.14 (s, 1H), 7.67 (d, J=8.0 Hz, 1H), 4.00 (s, 6H), 2.56 ppm (s, 3H);
1
1
ether/EtOAc=6:1 v/v) to afford CHO-AQI (0.15 g, 51%). H NMR
3
8
3
(400 MHz, CDCl ): d=10.27 (s, 1H), 8.86 (s, 1H), 8.81 (d, J=8.0 Hz,
2H), 8.55 (d, J=8.0 Hz, 1H), 8.39 (d, J=8.0 Hz, 1H), 4.30–4.26 (m, 1H),
1
3
C NMR (100 MHz, CDCl
3
): d=181.9, 181.4, 166.6, 146.1, 136.5, 136.4,
1
2
35.5, 134.9, 134.8, 133.2, 131.1, 128.11, 128.08, 127.9, 127.8, 53.2,
2.0 ppm.
2.10–2.06 (m, 2H), 1.78–1.61 (m, 2H), 1.28–1.23 (m, 16H), 0.86 ppm (t,
1
3
J=6.4 Hz, 6H); C NMR (125 MHz, CDCl
3
): d=190.4, 181.0, 180.7,
66.7, 140.3, 137.8, 136.3, 136.0, 133.8, 129.8, 128.7, 122.7, 53.3, 32.3, 31.7,
8.9, 26.7, 22.5, 14.0 ppm; HRMS (ESI): m/z calcd for C30 34NO
5
1
2
6
-Methylanthraquinone-2,3-dicarboxylic Anhydride (3)
H
+
[
M+H] : 488. 2437; found: 488.2427; elemental analysis calcd (%) for
: C 73.90, H 6.82, N 2.87; found: C 73.59, H 6.85, N 2.83.
A 1m solution (15 mL) of sodium hydroxide in methanol was added to
a solution of Me-AQ-di-ester (0.40 g) in THF (15 mL) and the mixture
was heated at reflux for 2 h. After being cooled to room temperature, the
mixture was poured into a 2m solution of hydrochloric acid (100 mL).
The precipitate was filtered, washed with water, and dried to give a solid
30 5
C H33NO
[
(N-(1-Hexylheptyl)-6-anthraquinoneyl-2,3-dicarboxylic imide)methylene]
Malononitrile (di-CN-AQI)
A suspension of CHO-AQI (0.15 g, 0.31 mmol), malononitrile (30 mg,
(
0.31 g), which was dissolved in acetic anhydride (20 mL) and the mixture
0
.46 mmol), ammonium acetate (14 mg, 0.18 mmol), and acetic acid
was heated at reflux for 4 h. After cooling, the precipitate was collected
and dried to yield 3 (0.21 g).
(
6.7 mg) in benzene (15 mL) was heated at reflux for 24 h. After the re-
action, the mixture was washed with distilled water and brine. The organ-
ic layer was dried over anhydrous magnesium sulfate and benzene was
removed under reduced pressure. The residue was purified by column
N-(1-Hexylheptyl)-6-methylanthraquinone-2,3-dicarboxylic Imide (Me-
AQI)
chromatography (silica gel; petroleum ether/EtOAc=6:1 v/v) to afford
1
-Hexylheptylamine (0.33 g, 1.6 mmol) was added to a solution of 3
1
di-CN-AQI as a yellow solid (54 mg, 33%). H NMR (500 MHz, CDCl
3
):
(
0.36 g, 1.1 mmol) in freshly distilled DMF (20 mL) and the mixture was
d=8.79 (d, J=2.0 Hz, 2H), 8.73 (d, J=2.0 Hz, 1H), 8.55 (d, J=8.5 Hz,
heated to reflux for 4 h. Then, the mixture was allowed to cool to room
temperature, and poured into dilute hydrochloric acid (150 mL). The
solid thus precipitated was filtered and washed with methanol. After
being dried, the product was purified by column chromatography (silica
gel; petroleum ether/dichloromethane=1:2, v/v) to afford the product
Me-AQI (0.46 g, 87%) as a yellow solid. H NMR (400 MHz, CDCl
1
1
H), 8.47 (q, J
1 2
=8.5 Hz, J =2.0 Hz, 1H), 7.99 (s, 1H), 4.30–4.24 (m,
H), 2.12–2.05 (m, 2H), 1.78–1.72 (m, 2H), 1.34–1.18 (m, 16H), 0.85 ppm
13
(
3
t, J=7.0 Hz, 6H); C NMR (125 MHz, CDCl ): d=180.4, 180.3, 166.6,
1
1
57.0, 137.7, 137.6, 136.1, 136.0, 135.6, 134.3, 133.7, 130.4, 129.1, 122.7,
12.6, 111.6, 87.9, 53.4, 32.3, 31.7, 28.9, 26.6, 22.5, 14.0 ppm; HRMS
1
3
):
+
(
ESI): m/z calcd for C33
Instruments and Measurements
The CV measurements were carried out on chromatographically pure
H
34
N
3
O
4
[M+H] : 536.2549; found: 536.2544.
d=8.75 (s, 2H), 8.27 (d, J=7.6 Hz, 1H), 8.15 (s, 1H), 7.68 (d, J=7.6 Hz,
1
2
H), 4.28–4.23 (m, 1H), 2.57 (s, 3H), 2.10–2.06 (m, 2H), 1.75–1.70 (m,
1
3
H), 1.28–1.22 (m, 16H), 0.85 ppm (t, J=6.8 Hz, 6H); C NMR
): d=181.9, 181.4, 167.0, 146.3, 138.1, 138.0, 135.7,
35.5, 133.0, 130.9, 128.0, 127.9, 122.4, 53.2, 32.3, 31.7, 28.9, 26.7, 22.0,
(
125 MHz, CDCl
3
solutions in CH Cl containing 0.1m TBAP as the supporting electrolyte
2
2
1
1
+
on a CHI 840b electrochemical workstation. A three-electrode assembly
was used with glassy carbon as the working electrode, a platinum wire as
the counter electrode, and a silver wire as a pseudo-reference electrode.
All experimentally measured redox potentials were calibrated externally
4.0 ppm; HRMS (ESI): m/z calcd for C30
H
36NO
4
[M+H] : 474. 2644;
: C 76.08, H
found: 474.2628; elemental analysis calcd (%) for C30
.45, N 2.96; found: C 76.17, H 7.55, N 2.86.
H35NO
4
7
+
N-(1-Hexylheptyl)-6-bromomethylanthraquinone-2,3-dicarboxylic Imide
CH Br-AQI)
by using a 2 mm solution of ferrocene (Fc/Fc ). The solutions were de-
(
2
gassed with nitrogen prior to measurements being recorded. Spectroelec-
trochemical measurements were carried out on a Shimadzu UV 3100
A mixture of Me-AQI (0.45 g, 1.0 mmol), NBS (0.22 g, 1.2 mmol), and
benzoyl peroxide (25 mg, 0.1 mmol) in benzene (20 mL) was heated to
&
&
Chem. Asian J. 2013, 00, 0 – 0
6
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

www.chemasianj.org
Xinhua Wan et al.
UV/Vis/NIR spectrophotometer connected to a computer in an optical
transparent thin layer (OTTLE) cell.
[8] a) W. Q. Qiao, J. Zheng, Y. F. Wang, Y. J. Zheng, N. H. Song, X. H.
Wan, Z. Y. Wang, Org. Lett. 2008, 10, 641; b) Y. J. Zheng, J. Zheng,
L. T. Dou, W. Q. Qiao, X. H. Wan, J. Mater. Chem. 2009, 19, 8470;
c) Y. J. Zheng, J. X. Cui, J. Zheng, X. H. Wan, J. Mater. Chem. 2010,
Computational Methods
2
0, 5915; d) F. K. Chen, J. Zhang, X. H. Wan, Macromol. Chem.
To simplify the calculations, a methyl group was employed to replace
other alkyl groups. Molecular geometries of all AQIs in both the neutral
and radical anion states were fully optimized by using Kohn–Sham DFT
based on the Beckeꢂs three-parameter hybrid functional B3LYP with the
Phys. 2011, 212, 1836; e) F. K. Chen, J. Zhang, X. H. Wan, Chem.
Eur. J. 2012, 18, 4558; f) F. Chen, J. Zhang, X. H. Wan, Scientia
Sinica Chimica 2011, 41, 341.
[
18]
[9] a) S. E. Boesch, R. A. Wheeler, J. Phys. Chem. A 1997, 101, 8351;
b) K. M. Rosso, D. M. A. Smith, Z. M. Wang, C. C. Ainsworth, J. K.
Fredrickson, J. Phys. Chem. A 2004, 108, 3292.
6
-31 G+(d,p) basis set using the Gaussian 09 program package.
For
radical anions, the spin-unrestricted approach of the corresponding
method was used. Each optimization was verified by frequency analysis.
The frontier MO energy levels were calculated by using the optimized
structures. TD-DFT was employed to stimulate the vertical transitions of
the first 10 states by using UB3LYP/6-31+G (d,p). In all cases, solvation
effects were considered by using the polarizable continuum model
[
10] a) G. Battagliarin, Y. Zhao, C. Li, K. Mꢄllen, Org. Lett. 2011, 13,
3
399; b) A. L. Appleton, S. M. Brombosz, S. Barlow, J. S. Sears, J. L.
Bredas, S. R. Marder, U. H. F. Bunz, Nat. Commun. 2010, 1, 91;
c) M. L. Tang, J. H. Oh, A. D. Reichardt, Z. N. Bao, J. Am. Chem.
Soc. 2009, 131, 3733; d) R. Schmidt, M. M. Ling, J. H. Oh, M. Win-
kler, M. Kçnemann, Z. Bao, F. Wꢄrthner, Adv. Mater. 2007, 19,
(
PCM) with dichloromethane as the solvent.
3
692; e) B. A. Jones, M. J. Ahrens, M. H. Yoon, A. Facchetti, T. J.
Marks, M. R. Wasielewski, Angew. Chem. 2004, 116, 6523; Angew.
Chem. Int. Ed. 2004, 43, 6363; f) C. L. Wang, H. L. Dong, W. P. Hu,
Y. Q. Liu, D. B. Zhu, Chem. Rev. 2012, 112, 2208; g) C. R. Newman,
C. D. Frisbie, D. A. da Silva Filho, J.-L. Brꢅdas, P. C. Ewbank, K. R.
Mann, Chem. Mater. 2004, 16, 4436.
Acknowledgements
We are grateful for financial support from the National Natural Science
Foundation of China (no. 20834001) and the Research Fund for Doctoral
Program of Higher Education of MOE of China (no. 20060001029).
[
[
11] a) C. A. Liberko, L. L. Miller, T. J. Katz, L. B. Liu, J. Am. Chem.
Soc. 1993, 115, 2478; b) B. W. Yang, L. B. Liu, T. J. Katz, C. A. Liber-
ko, L. L. Miller, J. Am. Chem. Soc. 1991, 113, 8993.
12] J. Mirek, M. Adamczyk, M. Mokrosz, Synthesis 1980, 296.
[13] B. Tarnchompoo, C. Thebtaranonth, Y. Thebtaranonth, Tetrahedron
Lett. 1987, 28, 6671.
[
1] a) G. Qian, Z. Y. Wang, Chem. Asian J. 2010, 5, 1006; b) J. Fabian,
H. Nakazumi, M. Matsuoka, Chem. Rev. 1992, 92, 1197.
2] a) S. K. Deb, Sol. Energy Mater. Sol. Cells 2008, 92, 245; b) P. Monk,
R. J. Mortimer, D. R. Rosseinsky, Electrochromism: Fundamentals
and Applications, VCH, Weinheim, 1995; c) C. G. Granqvist, Hand-
book of Inorganic Electrochromic Materials, Elsevier, Amsterdam,
[
[14] a) T. M. Pappenfus, J. D. Raff, E. J. Hukkanen, J. R. Burney, J.
Casado, S. M. Drew, L. L. Miller, K. R. Mann, J. Org. Chem. 2002,
67, 6015; b) X. Q. Zhu, C. H. Wang, J. Org. Chem. 2010, 75, 5037.
[15] a) P. M. Beaujuge, S. Ellinger, J. R. Reynolds, Nat. Mater. 2008, 7,
795; b) P. M. Beaujuge, S. Ellinger, J. R. Reynolds, Adv. Mater. 2008,
20, 2772; c) S. V. Vasilyeva, P. M. Beaujuge, S. Wang, J. E. Babiarz,
V. W. Ballarotto, J. R. Reynolds, ACS Appl. Mater. Interfaces 2011,
3, 1022; d) C. M. Amb, J. A. Kerszulis, E. J. Thompson, A. L. Dyer,
J. R. Reynolds, Polym. Chem. 2011, 2, 812; e) A. Balan, D. Baran, L.
Toppare, J. Mater. Chem. 2010, 20, 9861.
[16] a) H. J. Yen, K. Y. Lin, G. S. Liou, J. Mater. Chem. 2011, 21, 6230;
b) M. Sassi, M. M. Salamone, R. Ruffo, C. M. Mari, G. A. Pagani, L.
Beverina, Adv. Mater. 2012, 24, 2004.
[17] a) C. Frontana, ꢆ. Vꢇzquez-Mayagoitia, J. Garza, R. Vargas, I. Gon-
zꢇlez, J. Phys. Chem. A 2006, 110, 9411; b) C. Hansch, A. Leo, R. W.
Taft, Chem. Rev. 1991, 91, 165.
[18] Gaussian 09, Revision A.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V.
Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X.
Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Son-
nenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J.
Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A.
Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, ꢈ.
Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian,
Inc., Wallingford CT, 2009.
1
995.
[
3] a) C. J. Yao, Y. W. Zhong, H. J. Nie, H. D. Abruna, J. N. Yao, J. Am.
Chem. Soc. 2011, 133, 20720; b) S. Wang, X. Li, S. Xun, X. Wan,
Z. Y. Wang, Macromolecules 2006, 39, 7502; c) J. Garcꢃa-CaÇadas,
A. P. Meacham, L. M. Peter, M. D. Ward, Angew. Chem. 2003, 115,
119; Angew. Chem. Int. Ed. 2003, 42, 3011; d) P. Deplano, M. L.
Mercuri, G. Pintus, E. F. Trogu, Comments Inorg. Chem. 2001, 22,
53; e) W. Kaim, Coord. Chem. Rev. 2011, 255, 2503; f) M. Ward, J.
3
3
Solid State Electrochem. 2005, 9, 778; g) W. R. Lin, Y. J. Zheng, J.
Zhang, X. H. Wan, Macromolecules 2011, 44, 5146.
[
4] a) H. J. Yen, H. Y. Lin, G. S. Liou, Chem. Mater. 2011, 23, 1874;
b) H.-J. Yen, G.-S. Liou, J. Mater. Chem. 2010, 20, 9886; c) P. M.
Beaujuge, J. R. Reynolds, Chem. Rev. 2010, 110, 268; d) J. H. Hou,
S. Q. Zhang, T. L. Chen, Y. Yang, Chem. Commun. 2008, 6034;
e) A. L. Dyer, C. R. G. Grenier, J. R. Reynolds, Adv. Funct. Mater.
2
007, 17, 1480; f) H. Meng, D. Tucker, S. Chaffins, Y. Chen, R. Hel-
geson, B. Dunn, F. Wudl, Adv. Mater. 2003, 15, 146; g) J. D. Tovar,
T. M. Swager, Adv. Mater. 2001, 13, 1775; h) J. Zheng, Y. J. Zheng,
X. H. Wan, Z. Y. Wang, Chin. J. Polym. Sci. 2012, 30, 328; i) J.
Zheng, Y. J. Zheng, X. H. Wan, Chin. J. Polym. Sci. 2011, 29, 117.
5] W. A. Gazotti, G. Casalbore-Miceli, A. Geri, M.-A. de Paoli, Adv.
Mater. 1998, 10, 60.
[
[
6] a) J. Zheng, W. Q. Qiao, X. H. Wan, J. P. Gao, Z. Y. Wang, Chem.
Mater. 2008, 20, 6163; b) J. F. Penneau, L. L. Miller, Angew. Chem.
1
991, 103, 1002; Angew. Chem. Int. Ed. Engl. 1991, 30, 986; c) J. F.
Penneau, B. J. Stallman, P. H. Kasai, L. L. Miller, Chem. Mater.
991, 3, 791.
7] a) S. F. Rak, T. H. Jozefiak, L. L. Miller, J. Org. Chem. 1990, 55,
794; b) J. E. Almlof, M. W. Feyereisen, T. H. Jozefiak, L. L. Miller,
1
[
4
Received: February 8, 2013
J. Am. Chem. Soc. 1990, 112, 1206; c) T. H. Jozefiak, J. E. Almlof,
M. W. Feyereisen, L. L. Miller, J. Am. Chem. Soc. 1989, 111, 4105;
d) S. Wang, E. K. Todd, M. Birau, J. Zhang, X. Wan, Z. Y. Wang,
Chem. Mater. 2005, 17, 6388.
Published online: && &&, 0000
Chem. Asian J. 2013, 00, 0 – 0
7
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

FULL PAPER
Radical Ions
All change! The delocalization effect
of electron-withdrawing substituents
on anthraquinone imide (AQI) deriva-
tives is enhanced in the radical anion
state, which leads to the design and
synthesis of a new AQI molecule (di-
CN-AQI) substituted with a strongly
electron-withdrawing dicyanovinyl sub-
stituent. Upon one-electron reduction,
this compound reveals broad absorp-
tions in the ranges of l=700–1000 and
Fengkun Chen, Jie Zhang, Hong Jiang,
Xinhua Wan*
&&&& — &&&&
Colorless to Purple–Red Switching
Electrochromic Anthraquinone Imides
with Broad Visible/Near-IR Absorp-
tions in the Radical Anion State:
Simulation-Aided Molecular Design
1
100–1800 nm together with a colorless
to purple–red transition.
&
&
Chem. Asian J. 2013, 00, 0 – 0
8
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!