Colorless to All-Black Full-NIR High-Contrast Switching in Solid Electrochromic Films Prepared with Organic Mixed Valence Systems Based on Dibenzofulvene Derivatives

Article abstract of DOI:10.1021/acs.chemmater.8b01665

Functional electrochromic materials that allow energy modulation both in the visible and in the near-infrared (NIR) spectral ranges are attracting increasing interest both for the fundamental scientific aspects related to their spectroelectrochemistry and

Full text of DOI:10.1021/acs.chemmater.8b01665

Subscriber access provided by UNIV OF DURHAM
Article
Colorless to All-Black Full-NIR High-Contrast Switching in
Solid Electrochromic Films Prepared with Organic Mixed
Valence Systems Based on Dibenzofulvene Derivatives
Giuseppina Anna Corrente, Eduardo Fabiano, Francesca Manni, Giuseppe
Chidichimo, Giuseppe Gigli, Amerigo Beneduci, and Agostina-Lina Capodilupo
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b01665 • Publication Date (Web): 30 Jul 2018
Downloaded from http://pubs.acs.org on July 31, 2018
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 14
Chemistry of Materials
1
2
3
4
5
6
7
8
9
Colorless to All-Black Full-NIR High-Contrast Switching in
Solid Electrochromic Films Prepared with Organic Mixed Va-
lence Systems Based on Dibenzofulvene Derivatives
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Giuseppina Anna Corrente,† Eduardo Fabiano,§,∥ Francesca Manni,‡,⊥ Giuseppe Chidichimo,†
Giuseppe Gigli,‡ Amerigo Beneduci,†* and Agostina-Lina Capodilupo.‡,*
† Department of Chemistry and Chemical Technologies, University of Calabria, Via P. Bucci, Cubo 15D, 87036 Arca-
vacata di Rende (CS), Italy
§ Institute for Microelectronics and Microsystems (CNR-IMM), Via Monteroni, Campus Unisalento, 73100 Lecce,
Italy
∥ Centre for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia (IIT), Via Barsanti, 73010
Arnesano, Lecce, Italy
‡ CNR NANOTEC, Institute of Nanotechnology, c/o Campus Ecotekne, University of Salento, via Monteroni, 73100
Lecce, Italy
⊥ Dipartimento di Ingegneria dell'Innovazione, Università del Salento, via Monteroni, 73100 Lecce, Italy
ABSTRACT: Functional electrochromic materials which allow energy modulation both in the visible and in the near in-
frared (NIR) spectral ranges are attracting increasing interest both for the fundamental scientific aspects related to their
spectroelectrochemistry and for their technological applications. Vis-NIR dimmable windows based on these materials
are very promising for tunable shading, thus allowing lighting and heat energy use saving. Organic mixed valence com-
pounds (MVs) are an interesting class of small molecules with NIR electrochromism arising from optically induced inter-
valence charge transfer transitions (IVCT). Here we report the synthesis and Vis-NIR electrochromic properties of new
organic mixed valence systems, with two and three amino redox centers bridged by a dibenzofulvene (DBF) unit. We
studied the neutral and charged state characteristics of these MVs in solution by spectroelectrochemical experiments,
theoretical TD-DFT investigations and, in the solid state, through electrochromic devices (ECDs). We show that a fine-
tuning of the electrooptical properties of these MVs can be obtained by different functionalization on the exocyclic ful-
vene bond of the DBF moiety, including the introduction of a third redox centre, leading to compounds where all the
three redox centers participate in the electron transfer processes as a function of the applied voltage. As a proof-of-
concept, the above MVs were used to form solid thermoplastic laminable films in order to fabricate transmissive-to-black
switching electrochromic devices, with intermediate colour switching characteristics, enabling us to cover all the color
palette. Beyond this important exploitability in the Vis region, useful in many applications, the most important character-
istic of these devices is their absorption in almost the whole NIR range (800-2200 nm) through the excitation of highly
charged radical species which show intense IVCTs. Importantly, all the devices show high optical contrast, response times
of a few seconds and excellent switching stability over 10000 cycles.
related to optically-induced intervalence charge transfer
INTRODUCTION
transitions (IVCTs) in systems with a mixed redox state,14
to energy/charge internal electronic transitions15 and to
electrochemical doping in conjugated polymers.16-20 Or-
ganic mixed valence compounds (MVs) with arylamine
redox centers, are an interesting class of small molecules
with NIR electrochromism.21,22 They include two or more
redox centers linked with a saturated or unsaturated
bridge, which plays a crucial role for exploiting intramo
Near-infrared electrochromic (NIR-EC) materials are
very useful in many technological fields such as smart
windows, electronic displays, optical communications,
dynamic camouflage, information storage and thermal
control.1-4 However, compared to the electrochromism in
the visible region, electrochromic materials and films
showing distinct spectral changes in the NIR region are
less known. Common NIR-EC materials include several
transition metal oxides,5-7 inorganic coordination com-
plexes,8,9 conjugated polymers,10,11 and small organic mol-
ecules.12,13 The electrochromic functionality is generally
ACS Paragon Plus Environment

Chemistry of Materials
Page 2 of 14
1
2
Scheme 1
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
lecular electron transfer (ET) processes.23 According to
the strength of the electronic coupling between donor
and acceptor, Robin and Day24 classified MV systems into
three classes. Class I refers to the systems in which the
electronic coupling is zero and no ET occurs; class II in-
cludes the charge-localized systems with weak electronic
coupling, such that the charge can be transferred from
one redox center to the other; class III compounds corre-
spond to those with strong electronic coupling, where the
charge is essentially delocalized. The IVCT band associat-
ed to the ET process, is of significant importance since it
can extend the absorption to almost the whole NIR
range.22 Small MV molecules can switch from almost col-
orless to colored states, including the NIR range, thus
leading to a dual EC response which can be exploited for
the control of both the visible light and the thermal radia-
tion. Therefore, they are a good alternative to polymers
with comparable performances. In addition, these com-
pounds can be obtained at low cost, and their electronic
properties can be fine-tuned via easy structure modifica-
tions. In our previous work, we demonstrated the good
synthetic versatility of the dibenzofulvene (DBF) bridge as
building block for the design of arylamine MVs, since it
can be functionalized at different positions on the ben-
zene rings as well as on the exocyclic fulvene bond, thus
allowing the design of multicenter MVs.25 Specifically, we
showed the possibility to activate orthogonal electron
coupling pathways in symmetric MVs having four identi-
cal redox centers. Here we show new DBF-MVs with the
same substitution pattern on the benzene rings but with
different substitutions on the exocyclic fulvene bond, in
order to highlight the importance of such a functionaliza-
tion. Specifically, we studied 2-centers DBF-MV com-
pounds in which this position has been substituted by ei-
ther a simple linear alkyl chain or a phenyl substituent
(AN2 and PN2 in Scheme 1), and asymmetric 3-centers
DBF-MVs where a third diarylamine redox center has
been connected to the exocyclic fulvene bond through an
aromatic ring (PN3 and TN3 in Scheme 1). This leads to
an interesting tuning of the electrooptical properties of
these MVs as a function of either a simple structural func-
tionalization or as a consequence of the introduction of a
third redox center on the DBF bridge, giving rise to com-
pounds where the electron transfer process occurs among
all the three redox centers as a function of the applied
voltage. To disclose their potential applicability, extensive
electrochemical and spectroelectrochemical studies were
performed, both in solution and in solid device. Very
promising results were obtained from the developed elec-
trochromic devices, enabling us to cover all the color pal-
ette by electrochromic switching. Although no specific
optimization has been carried out, all the devices exhibit
trasmissive-to-black switching electrochromic behaviour
with high optical contrast, fast response time and excel-
ACS Paragon Plus Environment

Page 3 of 14
Chemistry of Materials
sponds to a HOMO→LUMO+1 transition in all molecules
lent switching stability over 10000 cycles. Even more sig-
1
2
3
4
5
6
7
8
nificantly, the ECDs show an intense absorption in the
near infrared region, which is an important characteristic
for energy saving, inasmuch as, Vis-NIR dimmable win-
dows based on these materials can be used for tunable
shading. Indeed, modulation of transmitted light and so-
lar heat through the use of these “smart windows” would
allow for decreasing both lighting and cooling energy use.
All these results show that the strategy here proposed for
the development of new organic MV compounds is a
promising way to realize efficient EC devices with high
performance and low cost.
(the other one corresponds instead to a transi tion from
the HOMO-1 to a high-lying virtual orbital). Different fea-
tures are instead observed for the low energy part of the
spectrum of the different compounds. For PN2 and AN2
the absorption spectra show a weak absorption at 502 and
460 nm, respectively. This is characterized by a
HOMO→LUMO single-particle transition and corre-
sponds to a moderate charge transfer (CT) from the dia-
rylamines to the DBF and its functionalizing moiety. On
the other hand, for TN3 and PN3 more intense absorption
peaks are observed at 475 and 424 nm, respectively. These
are excitations characterized by a HOMO-1→LUMO sin-
gle-particle transition that has a partial charge-transfer
character involving the third redox center and the DBF
bridge.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
RESULTS AND DISCUSSION
Design and Synthesis. Four mixed-valence systems were
synthesized; they consist of two and three redox centers
linked to the DBF bridge (Scheme 1). Arylamines were se-
lected as the redox sites for constructing organic MV sys-
tems due to the well defined N•+/0 process in a relatively
low potential region and to a high extinction coefficient
of IVCT. In addition, arylamine derivatives are known as
good hole transporter materials in optoelectronic devices
26-30
DBF was selected as the conjugated bridge due to its
known properties of electron delocalization that allow a
good charge transfer.31-33 Moreover, DBF shows a good
synthetic versatility to obtain various compounds, func-
tionalizing different positions on the benzene rings (such
as 2,7 or 3,6 positions) and the exocyclic fulvene bond.
The synthesis of the DBF-arylamino derivatives employed
extensive use of condensation reactions and palladium-
catalyzed amination reactions. All compounds were syn-
thesized in two steps (Scheme 1). First, commercially
available 2,7 dibromofluorene (1) was condensed with n-
Figure 1. Absorption spectra of AN2, PN2, PN3 and TN3 in
CH2Cl2 solution.
butyraldehyde,
4-methylbenzaldehyde,
4-
bromobenzaldehyde
and 5-bromothiophene-2-
carbaldehyde by Knoevenagel reaction, to give the com-
pounds 2, 3, 4, and 5 respectively. These reactions were
ultrasonically assisted and the products were obtained
with high yields and short times of reactions. For 2 the
reaction was carried out in toluene and potassium t-
butoxide with ratio of 2,7-dibromofluorene/ n-
butyraldehyde 1:1.2 equivalents, respectively; the other
products, 3 and 4, on the other hand, were prepared in
ethanol and potassium t-butoxide maintaining the same
ratio between the reagents. Then, the compounds ob-
tained by the previous reactions were reacted with bis(4-
methoxyphenyl)amine by Buchwald-Hartwig cross cou-
pling reaction, microwave assisted, yielding the desired
aminated products AN2, PN2, PN3 and TN3.
Neutral state absorption properties. The UV-Vis ab-
sorption spectra (Figure 1) were recorded in CH2Cl2 solu-
tion and the characteristic data are showed in Table S1.
All compounds display two distinct bands in the UV re-
gion in agreement with a π-π* transition localized on the
arylamine and the DBF moieties.34 Time-dependent den-
sity functional theory (TD-DFT) calculations confirm this
assignment (see Table S1 and Figure 2) showing, in par-
ticular, that the shorter wavelength of these bands corre-
ACS Paragon Plus Environment

Chemistry of Materials
Page 4 of 14
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. Isodensity plots of the most relevant molecular orbitals of the neutral compounds.
Electrochemical properties. Cyclic voltammograms
Notably, in contrast to previous reports on other 3-
show reversible oxidations in the potential window be-
tween +0.3 and 1.2 V vs. AgCl/Ag (Figure 3). Specifically,
two reversible one-electron oxidations are observed for
the 2-center arylamine compounds AN2 and PN2 (Figure
3), separated by a large potential electrochemical splitting
(Table 1), which is mainly due to a strong resonance con-
tribution (electron coupling) but also to a large coloum-
bic one, as determined by cyclic voltammetry experiments
performed in media of different polarity (Supporting in-
fo).35-38
center MV systems39-43 the CVs of compounds PN3 and
TN3 show three distinguishable redox processes (Figure
3). Assignment of the redox processes to each of the redox
centers is not straightforward. The first half wave poten-
tial (E1/2(1)) of these 3-center MVs is very similar to that of
the other 2-center systems, suggesting that the first oxida-
tion occurs on one of the redox centers directly connected
to the DBF (A or A’ in Scheme 2, Scheme S1). This is sup-
ported by the electrostatic potential plots of the radical
cation species of PN3 and TN3 showing that the positive
charge is distributed over the entire molecules, indicating
the occurrence of the electronic coupling among the three
redox centers, but it is mainly concentrated on the A, A’
ones (Figure S1). On the other hand, the potential plots of
the dication species suggest that the second electron
could be extracted from the redox center B since most of
the positive charge density is distributed between the
centers A (A’) and B (Figure S1). This hypothesis seems to
agree with the much lower second half wave potential of
TN3 than that of PN3 and of the other 2-center MVs (Ta-
ble 1), which could rely on the strong electron-donating
effect of the thiophene unit on the B center of TN3
(Scheme 2). Moreover, the third oxidation process occurs
at almost the same potential in both systems (Table 1) and
it could be assigned to the other center directly bonded to
the DBF. The significant negative shift of E1/2(1) and E1/2(2)
in TN3 (due to the action of the thiophene) (Table 1),
leads to different electrochemical splitting values between
the 3-center MV systems, especially on ΔE2. Indeed, while
in PN3 the third redox wave is heavily overlapped with
the second one, giving rise to a second potential splitting
of 87 mV, in TN3 the last two waves are separated by a
Figure 3. Cyclic voltammetry of AN2 (100 mV/s); PN2 (50
mV/s); PN3 (30 mV/s) and TN3 (30 mV/s), at 10−3 mol/L in
CH2Cl2/TBAPF6 (0.1 M) vs. AgCl/Ag.
ACS Paragon Plus Environment

Page 5 of 14
1
Chemistry of Materials
Table 1 Optical, Electrochemical Properties and Corresponding Energy Levels of the dibenzofulvene derivatives
2
3
4
5
6
7
8
9
optical
aE1/2(1)
(mV)
-35
aE1/2(2)
(mV)
255
aE1/2(3)
(mV)
/
bΔE1
(mV)
290
271
cΔE2
(mV)
/
dEHOMO
(eV)
eELUMO
(eV)
fEg,opt
(eV)
2.34
2.13
λ (nm) (εx103M-1cm-1)
AN2 377 (65.9) 460 (3.2)
PN2 380 (34.4) 502 (1.8)
PN3 384 (39.7) 426 (1.7)
TN3 382 (41.5) 475 (2.0)
-5.13
-2.79
-3.01
-42
229
/
/
-5.12
-25
233
320
349
258
213
87
-5.14
-2.67
-2.80
2.47
2.28
-76
147
202
-5.08
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
b
aHalf-wave potentials calculated from the CVs of Figure3 and referenced to the Fc+/Fc couple (E1/2= 493 mV); ΔE1 = E1/2(2) −
E1/2(1); cΔE2 = E1/2(3) − E1/2(2) calculated for PN3 after multiple peaks fitting; dEHOMO = −(Eonset(ox1) + 5.16) (eV)44-46. eELUMO = Eg,opt
-EHOMO. fThe bandgap, Eg,opt was determined from onset of absorption spectrum.
This spectroelectrochemical trend indicates the involve-
ment of all the three redox centers in the electron cou-
pling, as already highlighted in the electrochemical analy-
structure-property relationships acquired from the elec-
potential difference as high as 200 mV. Highlighting the
sis, with the possibility to excite multiple IVCTs arising
from the A-A’ and A (A’)-B electron transfer pathways. In
summary, the nature of the substituent in position 10 of
trochemical analysis, we can say that, in each homologous
class (2-center and 3-center), the more is the electron-
donating effect of the substituent on the exocyclic fulvene
the DBF bridge strongly affects the electrochromism of
bond the more negative are the first two oxidation poten-
these systems. Indeed, we showed that we can afford sys-
tials (Table 1 and Ref. 25).
tems which are almost uncoloured in the neutral state
(AN2, with alkyl chains substitution) and can be switched
to different colored state upon oxidation, or systems that
can be switched between two or more colored states (ar-
omatic substitution). Molecules such as AN2, could be
exploited in some applications which require a switching
from an uncoloured (off-state) to a colored state (on-
state), such as smart windows and e-papers. The other
systems could find applications in displays, camouflage
materials and optical switching devices. In the NIR, sub-
stitution on the exocyclic fulvene bond acts to modulate
the electronic coupling and, in the 3-center systems, it
allows the excitation of the IVCT bands at oxidative po-
tentials where monocation and dication radical species
coexist, giving rise to a whole NIR electrochromic re-
sponse (800-2200 nm). This condition is ideal for control-
ling the transmission of heat through windows (energy
saving). On the other hand, bleaching of the IVCT band
with the simultaneous excitation of the band at 700-1000
nm, as in the 2-center MVs, can be expoited in devices for
optical communication and data storage, as well as in
adaptive camouflage equipment.
Scheme 2. Schematic labelling of the 3 redox centers in
PN3 (Ph) and TN3 (Thio).
Spectroelectrochemical properties. Oxidation of the
compounds studied gives raise to profound changes in the
absorption spectra either in the visible or in the NIR
range (Figure 4). At increasing oxidative potentials, new
bands in the 500-700 nm range grow up for all the com-
pounds, leading to significant color changes (see the Elec-
trochromic devices section). In the NIR region, oxidation
to the radical cation (at about 0.6 V) leads to the appear-
ance of broad IVCT bands centered at about 1500 nm
(Figure 4). However, these bands start to be bleached at
higher voltages for the 2-center molecules (AN2 and
PN2), while a secondary structured band appears at 600-
1000 nm, due to the formation of the dication species
(Figure 4a,b), which overlap with the visible absorption
bands, contributing to a further color change to almost
black. In contrast, for the 3-center compounds (PN3 and
TN3) the broad IVCT bands are not bleached at higher
voltages (Figure 4c,d) when the dication species are popu-
lated, especially in TN3 (Figure 4d). Moreover, after the
first oxidation a second band appears at 700-1000 nm.
Theoretical calculation insights. TD-DFT calcula-
tions confirm the assignment of the broad and intense
absorption bands between 900 and 2200 nm of the radical
cation species of all the compounds, as IVCT excitations
(Table S5). Moreover, the higher energy NIR absorption
bands which characterize the dication radicals, are at-
tributed to N-to-bridge-charge-transfer transitions
(NBCT) in the 2-center MVs and to a combination of
NBCT and IVCT bands in the 3-center compounds (Table
S5), thus highlighting the occurrence of multiple electron
coupling pathways in the latter cases. The bandshape
analysis (Supporting info), confirms the coupling features
discussed above and indicates that all compounds belong
to class III or class II/III borderline. In particular, we
ACS Paragon Plus Environment

Chemistry of Materials
Page 6 of 14
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. Spectroelectrochemistry of AN2, PN2, PN3 and TN3 in dichloromethane solutions (0.2 mM) and TBAPF6 (0.1 M).
The potentials are referenced to the AgCl/Ag electrode. Up and down facing arrows indicate, respectively, the growth and the
bleaching
of
the
band.
found that the band shape asymmetry, i.e., the ratio be-
tween the bandwidth at half-height of the high and low-
energy side, is rather high for all the compounds (1.3-1.7)
(Table S3). Furthermore, the coupling integrals are also
rather high (even if they were calculated taking into ac-
count the geometric N-N distance between the redox cen-
ters and not the effective separation between the diabatic
states), with differences that may be attributed to the ef-
fects of the substitution on the position 10 of the bridge
(Table S3). Specifically, AN2 displays a markedly larger
coupling than PN2 (1603 cm-1 vs. 1090 cm-1). This is in
bridge in TN3, respect to the phenyl moiety in PN3. In the
previous section we have seen that the IVCT band of PN2
and AN2 is bleached upon dication formation, while in
TN3 and PN3 is not. This traces back to the fact that in
the 2-center systems the strong coupling between the two
redox centers causes a delocalization of the electron den-
sity. Thus, both the HOMO and HOMO-1 molecular or-
bitals are delocalized on both centers (Figure 2). As a con-
sequence, the AN2 and PN2 dication ground states can
have a singlet or a triplet character, depending on wheth-
er the second oxidation electron is removed from one or-
bital (HOMO-1) or the other (HOMO). In turn, this will
have influence on the optical spectra because different
occupied and virtual orbitals are involved in the two cases
(for the triplet HOMO-> virtual excitations are still possi-
ble, whereas in the singlet what is labeled here as HOMO
is a virtual (empty) orbital). We have not yet experimen-
tally determined the character of the dications ground
states (further work in this direction will be planned).
Nevertheless, some hints can be obtained by inspection of
TD-DFT results (Table S4). The latter indicate in fact, that
the experimental spectrum of AN2 and PN2 is well de-
scribed only by a superposition of the excitations from
both the singlet and the triplet dication ground states,
whereas none of them, taken alone, is able to reproduce
agreement with the larger ε of the IVCT band of AN2 than
PN2 (Figure 4) and is due to the involvement of the phe-
nyl moiety in PN2 on the electron delocalization through
the DBF bridge, which leads to a reduction of the elec-
tronic coupling between the two redox centers. This be-
havior can be observed qualitatively considering the elec-
trostatic potential of the two molecules (Figure S2). Con-
cerning the 3-center TN3 and PN3 compounds, the IVCT
analysis returns a higher value of the coupling integral for
PN3 than TN3 (1058 cm-1 and 775 cm-1, respectively). This
difference can be once more rationalized in terms of elec-
tron density effect. The thiophene unit has higher elec-
tron density compared to the phenyl moiety, thus it pro-
motes a stronger coupling of the B center to the DBF
ACS Paragon Plus Environment

Page 7 of 14
Chemistry of Materials
oxidized states (Figure 4), the deep black state is obtained
all the observed features. This suggests the coexistence of
1
2
3
4
5
6
7
8
both singlet and triplet dications. This hypothesis is also
in agreement with the fact that for both AN2 and PN2 the
singlet and triplet dications ground states are almost
isoenergetic, displaying energy separations of about 0.02
eV. On the other hand, in the 3-center MVs, the dication
has always/mainly a triplet ground state, since for these
systems DFT calculations yield triplet dication ground
states lying about 0.25 eV below the singlet ones. Thus,
since the triplet state involves as frontier orbitals both the
HOMO, which is localized on the redox centers A and A’,
and the HOMO-1, which is localized on the B redox cen-
ter, IVCT excitations are possible also for the dication and
they involve the B redox center.
with the contribution of the typical absorption bands of
the viologen (500-750 nm) to the overall visible absorp-
tion of the electrochromic film in the devices (Figure S3).
Besides this great exploitability in the Vis range, one of
the most important characteristics of these devices is
their absorption in the near infrared region. Potential
switching values as low as 0.9 V are sufficient to excite the
IVCT band in order to cover a wide range between 2000
and 1000 nm (Table S5). Notably, the absorption range
can be extended to almost the full NIR region (up to ∼750
nm) at intermediate switching potentials where a coexist-
ence of the radical cation and the dication species occurs
(Table 2 and Figure S3). This condition is particularly fa-
vourable when a 3-centre MV compound is incorporated
in the devices, as in PN3 and in TN3, because there is not
any appreciable loss of contrast of the IVCT band when
the dication transition is simultaneously excited at high
intensity (Table 2, Figure 6, Figure S4), in agreement with
the spectroelectrochemical behaviour in solution (Figure
4). The performances of these devices in the NIR range,
are summarized in Table 2. Figure 6 shows the transmit-
tance change of the devices based on AN2 (a) and TN3
(b), measured at ∼1500 nm and ∼900 nm as a function of
time during a sequence of consecutive switching pulses.
The voltage windows used correspond to the ranges
where the monocation or the dication species are gener-
ated and reaches their maximum intensity.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Electrochromic devices. Each of the four different
MVs described above were employed as anodic compo-
nents in the construction of the EC devices, while the
ethyl viologen diperchlorate was used as cathodic com-
plementary redox couple. As all the other components
were the same, the different performances of the devices
depend exclusively on the anodic component. The differ-
ent colouration of an EC device is a function of the ap-
plied voltage as well as of the molecular structure of the
electroactive components. As shown in Figure 4, the col-
ouration of each MV compound at the neutral state
strongly depends on the NBCT transition, at around 450
nm, as a consequence of their structural differences
(Scheme 1). The DBF-derivatives enable us to obtain elec-
trochromic films covering a wide range of off-state col-
ours, from the almost colourless AN2, through a pale pink
PN2 and a weakly orange PN3, up to an orange-red TN3.
Importantly, all the devices can be switched to black by
passing through several colours (Figure 5; Figure S3; Vid-
eo S1, Video S2 and Video S3).
Figure 6. Representative NIR switching cycles of the devices
showing the ꢀT% as a function of the potential difference
applied. The transmittance was measured at the wavelengths
labeled on each panel. The switching pulse sequence is speci-
fied as follows: Von (Time duration)/Voff (Time duration). (a)
dAN2: black line 1.4 V (25 s)/0 V (12 s), red line 1.8 V (25 s)/0
V (12 s); (b) dTN3: black line 1370 nm/1.6 V (40 s)/0 V (15 s),
blue line 1370 nm/2.4 V (40 s)/0 V (15 s), red line 910 nm /1.8
V (25 s)/0 V (10 s); and d(PN2+PN3) 1.4 V (40 s)/0 V (20 s),
red line 1.9 V (25 s)/0 V (15 s).
Figure 5. Colour switching of some of the devices studied.
Even though all the MV compounds have absorption
bands which cover almost the whole Vis range in their
ACS Paragon Plus Environment

Chemistry of Materials
Page 8 of 14
Table 2. Transmittance changes and switching times for the devices.
1
2
3
4
5
6
7
8
9
monocationic species
dicationic species
Δ%Ta ꢀꢁ
58 ± 6c
83 ± 1e
76.1 ± 2g
88 ± 1i
ꢂꢃꢄ ꢀ ꢁ (s)b
ꢂꢃꢅꢅ ꢀ ꢁ (s)b
6 ± 2
Δ%Taꢀꢁ
62 ± 2d
ꢂꢃꢄ ꢀ ꢁ (s)b
ꢂꢃꢅꢅ ꢀ ꢁ (s)b
3 ± 1
dAN2
8 ± 2
10 ± 2
f
dTN3
16.8 ± 0.4
15 ± 1
5.1 ± 0.2
3 ± 1
-
-
-
dTN3
81 ± 2h
95 ± 3l
17 ± 2
3.1 ± 0.8
12 ± 2
d(PN2+PN3)
14 ± 2
17 ± 2
6.6 ± 0.9
All the values are the mean (SD) over 15 switching cycles and three replicates devices. The cell gap was fixed to 30 µm for all the
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
b
devices. aThe transmittance contrast (Δ%T) is defined as the difference between the transmittance in the on and off states; The
switching time was defined as the time required for reaching 90% of the full change in transmittance after the switching of the
d
e
f
potential. c1.4V, λ = 1370 nm; 1.8V, λ = 910 nm; 1.6V, λ = 1370 nm; no dication band is observed for this potential difference;
g2.4V,
λ
=
1370
nm;
h2.4V,
λ
=
910
nm;
i1.4V,
λ
=
1430
nm;
l1.9V,
λ
=
920
nm.
electric field gradients applied to the cell.47 This type of
transmissive devices are particularly interesting for their
applications in dimmable windows systems in order to
control the transmission of both the visible and the ther-
mal components of the solar radiation. Obviously, anoth-
er crucial practical issue is related to their aging due to
environmental effects (UV light, humidity, oxygen, etc.).
Device aging is related to the reversibility of the device
which, ultimately, determines its cyclability. Figure 7
shows the loss of contrast of the devices dAN2 and
d(PN2+PN3) as a function of the number of switching cy-
cles. Despite these devices were fabricated under air and
were not sealed, the cyclability is very good, with a decay
of transmittance of less than 8% after 4500 cycles and of
about 25% after 11000 cycles. It can be seen also that, in
contrast to the smooth decreasing trend of the transmit-
tance change (ꢀT%) observed for the AN2 device, a drop
occurs at about 5000 cycles in the mixed device. This can
be due to a partial loss of the additive mechanism invoked
before but, as already stated, this interesting issue will be
further investigated.
They were chosen based on the switching potential val-
ues reported in Table S5 and measured by the cyclic volt-
ammograms acquired on the devices as well as by taking
into account the spectroelectrochemistry of the devices.
As the pulse is on, the device switches from a transmissive
state (almost 100% transmittance) to an opaque state
characterized by a low transmittance which value de-
pends on the duration time and voltage of the switching
pulse as well as on specific characteristics of each device.
Transmittance changes as high as 80% can be achieved at
these wavelengths by populating the radical cation and
the dication species, respectively. Generally, coloration
times of more than 10 seconds are needed to reach the full
contrast while the bleaching process is faster and occurs
in a few seconds. Obviously, the above parameters de-
pend on the film formulation (% of components, polymer,
solvent, electrolyte and type of electroactive compo-
nents), as well as on the film thickness sandwiched be-
tween the ITO electrodes. It is therefore possible to ad-
dress specific needs by changing the film formulation. For
instance, an efficient way to design an electrochromic de-
vice with high contrast in the whole NIR range is to com-
bine, in the same film, a 2-center and a 3-center arylamine
MVs with shifted redox and spectroelectrochemical be-
haviour, in order to simultaneously excite the IVCT bands
of both the compounds and the dication band of the 3-
center MV, at the same switching potential. This possibil-
ity has been explored here by preparing an EC film incor-
porating both the PN2 and PN3 compounds (Figure 5 and
Figure S3). The resulting device showed the highest con-
trasts in the NIR range among the devices studied, as can
be seen by the switching cycles reported in Figure 6c,d
and the average contrasts reported in Table 2. Based on
the observation of one isosbestic point (NIR range) in the
spectroelectrochemistry of the mixed device (Figure S3),
an additive effect seems to occur in this case, which can
be explained by assuming an electrochemical coupling
mechanism between the redox processes of the MV com-
pounds in the film. However, this issue deserves further
observations as well as the development of a theoretical
model which takes into account all the relevant reactions
occurring in the system as a function of the concentration
of all species, their diffusion coefficients as well as the
Figure 7. Cyclability of the devices dAN2 (red line) and
d(PN2+PN3) (black line) measured in terms of transmittance
change as a function of the potential difference, by respec-
tively applying the following pulse sequences: 1.1 V (10 s)/0 V
(10 s), red line 1.4 V (40 s)/0 V (20 s).
ACS Paragon Plus Environment

Page 9 of 14
Chemistry of Materials
working electrode, a Pt-wire auxiliary electrode, and an
CONCLUSION
1
Ag/AgCl non-aqueous reference electrode. Cyclic volt-
ammograms were acquired at different scan rate, from 30
to 100 mV s-1, on 1 mM dye solutions prepared in the elec-
trolyte solution, which consisted of 0.1 M tetrabu-
tylammonium hexafluorophosphate (TBAPF6) in di-
chloromethane (CH2Cl2). All the solutions were previous-
ly degassed with N2. The CV of the Ferroceni-
um/Ferrocene (Fc+/Fc) couple (0.1 mM) was also record-
ed in the same condition used for the MV compounds so-
lutions and used as external reference for potential cali-
bration. Spectroelectrochemical experiments were per-
formed with an elec electrolytic cell (BAS Inc.) composed
of a 1 mm path length cuvette, where a platinum gauze
Organic mixed valence compounds are a promising class
of molecules that could find extensive use in electro-
chromic devices for controlling both the visible and the
near infrared range. In this work, we have developed a
new sub-class of MVs based on the DBF bridge. They were
obtained in high yield, short time and low cost by a
straightforward synthetic path, using ultrasonically-
assisted and microwave-assisted reactions. The high syn-
thetic versatility of the DBF unit allows different func-
tionalization on the exocyclic fulvene bond, resulting in a
fine tuning of the electrochromic response, as well as to
introduce a third arylamine redox center on this side of
the DBF bridge. This leads to asymmetric 3-center MV
systems, where the three redox units all participate in the
electron coupling with distinguishable transfer pathways
resulting in the excitation of different IVCT transitions
spanning almost the whole NIR range. The above funda-
mental scientific aspects were investigated by a variety of
experimental and theoretical tools. On the other hand, as
a proof-of-concepts, solid thermoplastic laminable EC
films were developed by incorporating these MVs as an-
odic component. These devices show high optical con-
trasts both in the visible range and in the NIR region, low
response times and high switching stability. According to
the desired application, the EC film can be tailored by
changing the electroactive components as well as types
and percentage of the other components. We therefore
believe that the dual EC response, characteristic of this
novel compounds, have great potential for practical appli-
cations in many technological fields such as smart win-
dows, electronic displays, optical communication, infor-
mation storage and thermal control.
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
thin layer and a platinum wire were used as the working
48,49
electrode and the auxiliary electrode, respectively.
A
pseudo-reference electrode consisting of an Ag wire was
calibrated against the Fc+/Fc redox couple. The spectroe-
lectrochemical cell was filled with dichloromethane solu-
tions of each compound (0.2 mM) and TBAPF6 (0.1 M).
UV-vis-NIR spectra were recorded using a Vertex 80
(Bruker) spectrophotometer. The potential was supplied
by means of an Amel 2049 model potentiostat. Measure-
ments were performed at 25 °C.
Electrochromic Device Fabrication. AN2, PN2, PN3
and TN3 were synthesized freshly before use, with the
procedures reported below. The EC polymer gels were
prepared in a range from 4% to 10% (w/w) of the anodic,
electroactive MV compounds (specifically, 10% (w/w) of
AN2, PN2 and TN3, 4% (w/w) of PN3 and 5% (w/w) of
each MVs (PN2 and PN3), in the mixed device). The other
components of the mixtures were ethyl viologen diper-
chlorate (cathode) (Sigma-Aldrich) 2.5% (w/w),
Poly(vinyl) formate (PVF, Sigma-Aldrich) 30% (w/w) and
anhydrous N-methyl-2-pyrrolidinone, (NMP, Pancreac)
57.5/63.5% (w/w). The two electrochromic active species
were first dissolved in NMP at room temperature and
then mixed with the polymer under continuous stirring at
120 °C for 30 minute. ITO/EC gel/ITO devices were as-
sembled by drop casting of the hot EC mixture onto a
ITO-coated glass support (Visiontek Systems Ltd. with a
sheet resistance of 25 Ω sq−1 and a thickness of 1 mm) with
a second ITO electrode used to create a sandwich with
active area of about 2×2 cm2. The cell gap was controlled
by inserting cylindrical spacers with mean base diameter
of 5-30×10−6 m. The final cell gap was calculated by the
interference fringes in its absorption spectrum in the NIR
spectroscopy range (900–1500 nm). Standard cyclic volt-
ammetry of the electrochromic polymer gel (EC gel) was
performed with an Amel Instruments 7050 model poten-
tiostat on the ITO/EC gel/ITO cell in which the two ITO
plates worked as working and counter electrodes. Spec-
troelectrochemical experiments were performed, on the
two-electrode device, with the Vertex 80 (Bruker) spec-
trophotometer, as described above for studies in solution.
EXPERIMENTAL SECTION
Materials
and
Methods.
Pentanal,
4-
bis(4-
bromobenzaldehyde,
4-methylbenzaldehyde,
methoxyphenyl)amine, 2,7-dibromo-9H-fluorene were
purchased from commercial sources and used without
further purification. All solvents and reagents (analytical
grade) were used as received, unless otherwise claimed.
1
The H and 13C NMR spectra were recorded on a Bruker
AVANCE III 400 MHz instrument using the chloroform-d
(CDCl3) and dimethyl sulfoxide-d6 (DMSO-d6) as the sol-
vent, splitting patterns were described as singlet (s), dou-
blet (d), triplet (t), quartet (q), or multiplet (m). The mi-
crowave-assisted syntheses were performed with a CEM
Discover Labmate reactor. Elemental analyses were done
by a Carlo Erba CHNS-O EA1108-Elemental Analyzer. The
melting point was taken on Kleinfeld Melting Point De-
termination Apparatus APA. Mass spectroscopy was rec-
orded using a LTQ XL™ Linear Ion Trap Mass Spectrome-
ter. UV-Vis absorption spectra were recorded on a Varian-
Cary 500 spectrophotometer.
Electrochemistry. Electrochemical characterization of
dyes was carried out by cyclic voltammetry (CV) using a
AMEL s.r.l. (Mod. 7050) potentiostat. A typical three-
electrode cell was assembled with a glassy carbon disk-
Computational details. All calculations have been per-
50,51
formed using the TURBOMOLE program
using the
PBE0-1/3 functional52 and a def2-TZVP53 basis set. For the
dications we have considered the following possible
ACS Paragon Plus Environment

Chemistry of Materials
Page 10 of 14
ground states: closed-shell singlet, unrestricted open- Elemental analysis calcd (%) C 80.20, H 6.44, N 4.07;
1
2
3
4
5
6
7
8
shell triplet, and (broken-symmetry) unrestricted open-
shell singlet. Nevertheless, the latter yielded for all sys-
tems a considerably higher energy than the former two.
For these reasons it was not used for TD-DFT calcula-
tions.
found C 80.29, H 6.22, N 4.12.
2,7-Dibromo-9-(4-methylbenzylidene)-9H-fluorene (2). To
a 50 mL round–bottomed flask, 2,7-dibromo-9H-fluorene
(1.00 g, 3.1 mmol), 4-methylbenzaldehyde (0.445 g, 3.7
mmol) and potassium tert-butoxide (0.520 g, 4.65 mmol)
were dissolved in ethanol absolute (10 mL). The reaction
was carried out in a ultrasound bath for 20 min. The pre-
cipitate obtained was filtered-off and washed different
times with ethanol to remove the reagents. Was obtained
Synthesis. 2,7-Dibromo-9-pentylidene-9H-fluorene (1).
To a 50 mL two-necked flask were suspended 2,7-
dibromo-9H-fluorene (1.00 g, 3.1 mmol) and potassium
tert-butoxide (0.414 g, 3.70 mmol) in toluene dry (15 mL)
under nitrogen atmosphere. The mixture was placed in an
ultrasound bath and heated at 80°C for 5 min under stir-
ring. After the formation of orange precipitated, pentanal
(0.320 g, 3.70 mmol) was added dropwise to suspension.
The reaction mixture was heated at 80°C for 30 min,
cooled to room temperature and neutralized with concen-
trated HCl. The compound was extracted with CH2Cl2.
After concentration by rotary evaporation, the crude
product was purified by column chromatography on silica
gel (eluent 8/2 hexane/CH2Cl2) to give as an off-white sol-
9
1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2 as orange solid in 90% yield. Mp: 141-143. H-NMR (400
MHz, CDCl3) δ 7.89 (d, J = 1.5 Hz, 1H), 7.84 (d, J = 1.6 Hz,
1H), 7.68 (s, 1H), 7.55 (dd, J1 = 8.0, J2 = 1.3 Hz, 2H), 7.50-
7.47 (m, 3H), 7.44 (dd, J1 = 8.1, J2 = 1.7 Hz, 1H), 7.30 (d, J =
7.9 Hz, 2H), 2.43 (s, 3H). 13C NMR (100 MHz, CDCl3) δ
141.09, 138.86, 138.80, 137.92, 136.65, 133.65, 132.45, 131.17,
130.77, 130.15, 129.24, 129.06, 127.11, 123.36, 120.96, 120.77,
120.71, 120.55, 21.32. ESI-MS: m/z calcd for C21H14Br2:
425.94; found:425.96. Elemental analysis calcd (%) C
59.19, H 3.31; found C 59.30, H 3.27.
1
id 90% yield. Mp: 119-121. H-NMR (400 MHz, CDCl3) δ
N2,N2,N7,N7-tetrakis(4-methoxyphenyl)-9-(4-
7.96 (d, J = 1.6 Hz, 1H), 7.77 (d, J = 1.6 Hz, 1H), 7.58 (d, J =
8.1 Hz, 1H), 7.52 (d, J = 8.1 Hz, 1H), 7.50 (dd, J1 = 8.1, J2 = 1.7
Hz, 1H), 7.44 (dd, J1 = 8.1, J2 = 1.7 Hz, 1H), 6.77 (t, J = 7.4
Hz, 1H), 2.81 (q, 2H), 1.71-1.65 (m, 2H), 1.57-1.49 (m, 2H),
1.01 (t, J = 7.3 Hz, 3H); 13C-NMR (100 MHz, CDCl3) δ
140.82, 138.83, 138.43, 136.19, 134.11, 133.47, 130.45, 130.17,
127.82, 122.91, 120.96, 120.86, 120.78, 120.66, 31.37, 28.94,
22.38, 13.79. ESI-MS: m/z calcd for C18H16Br2: 391,96,
found:391,98. Elemental analysis calcd (%) C 55.13, H 4.11;
found C 55.25, H 4.03.
methylbenzylidene)-9H-fluorene-2,7-diamine (PN2). This
compound was prepared from 2,7-dibromo-9-(4-
methylbenzylidene)-9H-fluorene (0.200 g, 0.47 mmol)
and bis(4-methoxyphenyl)amine (0.237 g, 1.03 mmol) in
80% yield, using the similar procedure for the synthesis of
1
AN2. Mp: 131-133. H-NMR (400 MHz, DMSO-d6) δ 7.49
(d, J = 8.7 Hz, 1H), 7.45 (d, J = 5.8 Hz, 1H), 7.34 (d, J = 2.0
Hz, 1H), 7.18 (d, J = 8.0 Hz, 2H), 7.09 (d, J = 2.1 Hz, 1H),
6.97 (d, J = 9.1 Hz, 4H), 6.91-6.85 (m, 15H), 6.81 (dd, J1 =
8.2, J2 = 1.9 Hz, 1H), 6.76 (dd, J1 = 8.2, J2 = 2.1 Hz, 1H), 2.20
(s, 3H). 13C NMR (100 MHz, DMSO-d6) δ 155.74, 155.36,
147.23, 147.12, 141.18, 140.60, 140.41, 137.51, 137.12, 135.09,
133.57, 132.86, 132.83, 129.05, 128.94, 128.29, 126.54, 125.72,
122.74, 120.63, 119.92, 119.82, 116.35, 115.15, 115.12, 114.27,
55.49, 20.95. ESI-MS: m/z calcd for C49H42N2O4: 722.31;
found:722.32. Elemental analysis calcd (%) C 81.42, H 5.86,
N 3.88; found C 81.51, H 5.93, N 3.71.
N2,N2,N7,N7-tetrakis(4-Methoxyphenyl)-9-pentylidene-
9H-fluorene-2,7-diamine (AN2). A mixture of 1 (0.20 g, 0.51
mmol), bis(4-methoxyphenyl)amine (0.258 g, 1.12 mmol),
sodium tert-butoxide (0.122 g,1.27 mmol), was added to a
suspension of Pd(dba)2 (0.014 g, 0.025 mmol), and PtBu3
(0.060 mmol, 1M in toluene) in anhydrous and deoxygen-
ated toluene (5 mL), previous degassed under argon for 20
minutes. The resulting solution was heated under micro-
wave irradiation at a constant temperature of 110°C for 50
min. The solvent was removed, and the residue was dis-
solved in dichloromethane and filtered on a short celite
column. After concentration by rotary evaporation, the
crude product was purified by column chromatography
on silica gel (eluent 8/2 hexane/CH2Cl2) to give a violet
solid in 70% yield. Mp: 109-111. 1H-NMR (400 MHz,
DMSO-d6) δ 7.49 (d, J = 8.3 Hz, 1H), 7.46 (d, J = 8.2 Hz,
1H), 7.21 (d, J = 2.0 Hz, 1H), 7.14 (d, J = 2.0 Hz, 1H), 7.03 (d,
J = 9.0 Hz, 4H), 6.94 (d, J = 9.0 Hz, 4H), 6.89 (d, J = 9.0
Hz, 4H), 6.86 (d, J = 9.0 Hz, 4H), 6.08 (dd, J1 = 8.3, J2 = 2.1
Hz, 1H), 6.76 (dd, J1 = 8.2, J2 = 2.1 Hz, 1H), 6.51 (t, J = 7.9
Hz, 1H), 3.73 (s, 6H), 3.72 (s, 6H), 2.32-2.26 (q, 2H) 1.35-
1.27 (m, 2H), 1.14-1.03 (m, 2H), 0.71 (t, J = 7.3 Hz, 3H). 13C
NMR (100 MHz, DMSO-d6) δ 155.89, 155.39, 147.54, 147.08,
141.16, 140.69, 140.09, 138.02, 135.04, 133.20, 132.33, 126.66,
125.80, 125.80, 121.95, 119.98, 119.92, 119.77, 118.32, 116.95,
115.18, 115.11, 114.82, 55.51, 55.49, 30.62, 28.52, 22.27, 13.72.
ESI-MS: m/z calcd for C46H44N2O2: 688.33; found:688.36.
2,7-dibromo-9-(4-bromobenzylidene)-9H-fluorene (3).This
compound was prepared from 2,7-dibromo-9H-fluorene
(0.500 g, 1.54 mmol) and 4-bromobenzaldehyde (0.342 g,
1.85 mmol) in 92% yield, using the similar procedure for
the synthesis of 3. Mp: 131-133. 1H-NMR (400 MHz, CDCl3)
δ 7.88 (s, 1H), 7.70 (s, 1H), 7.63 (d, J = 7.6 Hz, 2H), 6.55 (d,
J = 7.6 Hz, 2H) 7.57-7.44 (m, 7H). 13C NMR (100 MHz,
CDCl3) δ 140.71, 139.04, 137.54, 136.35, 131.81, 131.62, 131.22,
130.63, 128.15, 127.11, 123.53, 122.82, 121.13, 120.93, 120.81,
120.69. ES-MSI: m/z calcd for C20H11Br3: 489.84;
found:489.85. Elemental analysis calcd (%) C 48.92, H
2.26; found C 48.88, H 2.33.
9-(4-(Bis(4-methoxyphenyl)amino)benzylidene)-
N2,N2,N7,N7-tetrakis(4-methoxyphenyl)-9H-fluorene-2,7-
diamine (PN3). A mixture of 1 (0.30 g, 0.61 mmol), bis(4-
methoxyphenyl)amine (0.503 g, 2.2 mmol), sodium tert-
butoxide (0.211 g, 2.2 mmol), was added to a suspension of
Pd(dba)2 (0.021 g, 0.037 mmol), and PtBu3 (0.074 mmol,
1M in toluene) in anhydrous and deoxygenated toluene
(10 mL), previous degassed under argon for 20 minutes.
ACS Paragon Plus Environment

Page 11 of 14
Chemistry of Materials
117.04, 114.55, 114.53, 114.43, 113.37, 113.11, 54.73, 54.64, 54.68.
The resulting solution was heated under microwave irra-
1
2
3
4
5
6
7
8
diation at a constant temperature of 110°C for 60 min. The
solvent was removed, and the residue was dissolved in
dichloromethane and filtered on a short celite column.
After concentration by rotary evaporation, the crude
product was purified by column chromatography on silica
gel (eluent 6/4 hexane/CH2Cl2) to give a red solid in 78%
ESI-MS: m/z calcd for C60H51N3O6S: 941.35; found:941.35.
Elemental analysis calcd (%) C 76.49, H 5.46, N 4.46; S
3.40; found C 76.40, H 5.55, N 4.41, S 3.34.
1
yield. Mp: 120-122. H-NMR (400 MHz, DMSO-d6) δ 7.50
ASSOCIATED CONTENT
(d, J = 8.1 Hz, 2H), 7.48 (s, 1H), 7.33 (dd, J1 = 8.4 Hz, J2 = 1.9
Hz, 2H), 7.19 (d, J =8.7 Hz, 2H), 6.97-6.90 (m, 16H), 6.87
(d, J = 8.9 Hz, 4H), 6.79 (d, J = 9.1 Hz, 4H), 6.51 (d, J = 8.7
Hz, 4H), 3.74 (s, 6H), 3.71 (s, 6H), 3.59 (s, 6H). 13C NMR
(100 MHz, DMSO-d6) δ 156.16, 155.44, 155.36, 148.55, 147.13,
146.95, 141.20, 140.89, 140.85, 140.00, 137.16, 134.03, 133.25,
132.41, 130.63, 128.43, 127.17, 126.88, 125.85, 125.68, 122.42,
121.58, 120.00, 119.88, 119.21, 117.44, 115.23, 115.14, 115.03,
114.00, 55.53, 55.49, 55.41. ESI-MS: m/z calcd for
C62H53N3O6: 935.39; found:935.38. Elemental analysis calcd
(%) C 79.55, H 5.71, N 4.49; found C 79.61, H 5.88, N 4.33.
Supporting Information. Additional experimental proce-
dures, figures, tables, and NMR spectra This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
AUTHOR INFORMATION
Corresponding Author
* agostina.capodilupo@nanotec.cnr.it (A.-L. C.)
* amerigo.beneduci@unical.it (A.B.)
2-Bromo-5-((2,7-dibromo-9H-fluoren-9-
ylidene)methyl)thiophene (4). This compound was pre-
pared from 2,7-dibromo-9H-fluorene (0.500 g, 1.54 mmol)
and 5-bromothiophene-2-carbaldehyde (0.353 g, 1.85
mmol) in 85% yield, using the similar procedure for the
ORCID
Agostina-Lina Capodilupo: 0000-0003-4755-4011
Amerigo Beneduci: 0000-0003-1185-9470
1
synthesis of 2.Mp: 168-170. H-NMR (400 MHz, CDCl3) δ
8.29 (d, J = 1.6 Hz, 1H), 7.83 (d, J = 1.5 Hz, 1H), 7.56 (d, J =
8.1 Hz, 1H), 7.51 (dd, J1 = 3.5, J2 = 1.7, 1H), 7.48 (dd, J1 = 3.5,
J2 = 1.7 Hz, 1H), 7.44 (d, J =1.0 Hz, 1H), 7.23 (dd, J1 = 3.8, J2 =
1.1 Hz, 1H), 7.15 (d, J = 3.8 Hz, 1H). 13C NMR (100 MHz,
CDCl3) δ 140.83, 139.56, 138.97, 137.20, 136.50, 134.26, 131.74,
131.22, 130.58, 130.41, 127.02, 123.40, 121.12, 120.98, 120.89,
120.84, 120.07, 115.41. ESI-MS: m/z calcd for C18H9Br3S:
495.79; found:495.79. Elemental analysis calcd (%) C
43.50, H 1.83, S 6.45; found C 43.38, H 1.88, S 6.51.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
The authors are grateful to the Ministero dell’Istruzione
dell’Universita e della Ricerca Italiano (MIUR) and the Uni-
versity of Calabria for supporting this project in the frame-
work of the ex 60% budget grant. In addition, the authors
gratefully acknowledge the project PERSEO-“PERrovskite-
based Solar cells: towards high Efficiency and lOng-term sta-
bility” (Bando PRIN 2015-Italian Ministry of University and
Scientific Research (MIUR) Decreto Direttoriale 4 novembre
2015 n. 2488, project number 20155LECAJ) and the research
project “TECNOMED - Research Centre for the application of
Nanotechnology and Photonics to Precision Medicine” for
funding.
9-((5-(Bis(4-methoxyphenyl)amino)thiophen-2-
yl)methylene)-N2,N2,N7,N7-tetrakis(4-methoxyphenyl)-
9H-fluorene-2,7-diamine (TN3). A mixture of 3 (0.20 g,
0.40 mmol), bis(4-methoxyphenyl)amine (0.330 g, 1.44
mmol), sodium tert-butoxide (0.140 g,1.44 mmol), was
added to a suspension of Pd2(dba)3CHCl3 (0.012 g, 0.012
mmol), and PtBu3 (0.048 mmol, 1M in toluene) in anhy-
drous and deoxygenated toluene (10 mL), previous de-
gassed under argon for 20 minutes. The resulting solution
was heated under microwave irradiation at a constant
temperature of 110°C for 60 min. The solvent was re-
moved, and the residue was dissolved in dichloromethane
and filtered on a short celite column. After concentration
by rotary evaporation, the crude product was purified by
column chromatography on silica gel (eluent 1/1 hex-
ane/CH2Cl2) to give a violet solid in 65% yield. Mp: 125-
REFERENCES
(1) Beaujuge, P. M.; Reynolds, J. R., Color Control in π-
Conjugated Organic Polymers for Use in Electrochromic Devic-
es. Chem. Rev. 2010, 110, 268-320.
(2) Beaupré, S.; Breton, A.-C.; Dumas, J.; Leclerc, M., Multicol-
ored Electrochromic Cells Based On Poly(2,7-Carbazole) Deriva-
tives For Adaptive Camouflage. Chem. Mater. 2009, 21, 1504-1513.
(3) Yang, P.; Sun, P.; Mai, W., Electrochromic energy storage
devices. Mater. Today 2016, 19, 394-402.
(4) Conjugated conducting polymers. In Electrochromism and
Electrochromic Devices, Rosseinsky, D.; Monk, P.; Mortimer, R.,
Eds. Cambridge University Press: Cambridge, 2007; pp 312-340.
(5) Zhou, J.; Chen, M.; Xie, J.; Diao, G., Synergistically En-
hanced Electrochemical Response of Host–Guest Recognition
Based on Ternary Nanocomposites: Reduced Graphene Oxide-
Amphiphilic Pillar[5]arene-Gold Nanoparticles. ACS Appl. Mater.
Interfaces 2013, 5, 11218-11224.
1
127. H-NMR (400 MHz, Acetone-d6) δ 7.91 (d, J =2.0 Hz,
1H), 7.51 (d, J = 8.2 Hz, 1H), 7.48 (d, J = 8.2 Hz, 1H), 7.34 (d,
J = 2.0 Hz, 1H), 7.21 (s, 1H), 7.11 (d, J = 9.1 Hz, 4H), 7.02-
6.99 (m, 8 H), 6.94 (d, J = 9.1 Hz, 4H), 6.91-6.88 (m, 3H),
6.87 (d, J = 9.1 Hz, 8H), 5.97 (d, J = 4.0 Hz, 1H), 3.80 (s,
6H), 3.76 (s, 6H), 3.68 (s, 6H). 13C NMR (100 MHz, CDCl3)
δ 156.96, 156.77, 156.49, 155.66, 155.49, 147.31, 14715, 141.30,
141.07, 141.05, 140.29, 137.06, 133.74, 132.05, 129.95, 126.81,
125.94, 125.51, 125.47, 121.69, 120.83, 119.68, 119.16, 119.09,
ACS Paragon Plus Environment

Chemistry of Materials
Page 12 of 14
(6) Liu, B. J.-W.; Zheng, J.; Wang, J.-L.; Xu, J.; Li, H.-H.; Yu, S.-
mixed-valence bis(diarylamino)stilbene: crystal structure and
H., Ultrathin W18O49 Nanowire Assemblies for Electrochromic
Devices. Nano Lett. 2013, 13, 3589-3593.
comparison of electronic coupling with biphenyl and tolane ana-
logues. Chem. Commun. 2005, 6, 764-766.
(23) Heckmann, A.; Lambert, C., Organic Mixed-Valence
Compounds: A Playground for Electrons and Holes. Angew.
Chem., Int. Ed. 2012, 51, 326-392.
(24) Robin, M. B.; Day, P., Mixed-Valence Chemistry: A Survey
and Classification. Adv. Inorg. Chem. Radiochem. 1967, 10, 247-
422.
1
2
3
4
5
6
7
8
(7) Wu, W.-T.; Wu, J.-J.; Chen, J.-S., Resistive Switching Be-
havior and Multiple Transmittance States in Solution-Processed
Tungsten Oxide. ACS Appl. Mater. Interfaces 2011, 3, 2616-2621.
(8) Shankar, S.; Lahav, M.; van der Boom, M. E., Coordination-
Based Molecular Assemblies as Electrochromic Materials: Ultra-
High Switching Stability and Coloration Efficiencies. J. Am.
Chem. Soc. 2015, 137, 4050-4053.
(9) Zhong, Y.-W.; Wu, S.-H.; Burkhardt, S. E.; Yao, C.-J.;
Abruña, H. D., Mononuclear and Dinuclear Ruthenium Com-
plexes of 2,3-Di-2-pyridyl-5,6-diphenylpyrazine: Synthesis and
Spectroscopic and Electrochemical Studies. Inorg. Chem. 2011,
50, 517-524.
(10) Li, W.; Guo, Y.; Shi, J.; Yu, H.; Meng, H., Solution-
Processable Neutral Green Electrochromic Polymer Containing
Thieno[3,2-b]thiophene Derivative as Unconventional Donor
Units. Macromolecules 2016, 49, 7211-7219.
(11) Teran, N. B.; Reynolds, J. R., Discrete Donor–Acceptor
Conjugated Systems in Neutral and Oxidized States: Implica-
tions toward Molecular Design for High Contrast Electrochrom-
ics. Chem. Mater. 2017, 29, 1290-1301.
(12) Stolar, M.; Borau-Garcia, J.; Toonen, M.; Baumgartner, T.,
Synthesis and Tunability of Highly Electron-Accepting, N-
Benzylated “Phosphaviologens”. J. Am. Chem. Soc. 2015, 137,
3366-3371.
(13) Alesanco, Y.; Viñuales, A.; Palenzuela, J.; Odriozola, I.;
Cabañero, G.; Rodriguez, J.; Tena-Zaera, R., Multicolor Electro-
chromics: Rainbow-Like Devices. ACS Appl. Mater. Interfaces
2016, 8, 14795-14801.
(14) Mortimer, R. J., Electrochromic Materials. Annu. Rev. Ma-
ter. Res. 2011, 41, 241-268.
(15) Mortimer, R. J.; Varley, T. S., Electrochromic devices
based on surface-confined Prussian blue or Ruthenium purple
and aqueous solution-phase di-n-heptyl viologen. Sol. Energy
Mater. Sol. Cells 2013, 109, 275-279.
(16) Shi, P.; Amb, C. M.; Knott, E. P.; Thompson, E. J.; Liu, D.
Y.; Mei, J.; Dyer, A. L.; Reynolds, J. R., Broadly Absorbing Black
to Transmissive Switching Electrochromic Polymers. Adv. Mater
2010, 22, 4949-4953.
(17) Beaujuge, P. M.; Ellinger, S.; Reynolds, J. R., The donor–
acceptor approach allows a black-to-transmissive switching pol-
ymeric electrochrome. Nat. Mater 2008, 7, 795-799.
(18) Sassi, M.; Salamone, M. M.; Ruffo, R.; Patriarca, G. E.; Ma-
ri, C. M.; Pagani, G. A.; Posset, U.; Beverina, L., State‐of‐the‐Art
Neutral Tint Multichromophoric Polymers for High‐Contrast
See‐Through Electrochromic Devices. Adv. Funct. Mater. 2016,
26, 5240-5246.
(19) Zhang, X.; Steckler, T. T.; Dasari, R. R.; Ohira, S.;
Potscavage, W. J.; Tiwari, S. P.; Coppee, S.; Ellinger, S.; Barlow,
S.; Bredas, J.-L.; Kippelen, B.; Reynolds, J. R.; Marder, S. R.,
Dithienopyrrole-based donor-acceptor copolymers: low band-
gap materials for charge transport, photovoltaics and electro-
chromism. J. Mater. Chem. 2010, 20, 123-134.
(20) Argun, A. A.; Aubert, P.-H.; Thompson, B. C.; Schwende-
man, I.; Gaupp, C. L.; Hwang, J.; Pinto, N. J.; Tanner, D. B.; Mac-
Diarmid, A. G.; Reynolds, J. R., Multicolored Electrochromism in
Polymers: Structures and Devices. Chem. Mater. 2004, 16, 4401-
4412.
(25) Beneduci, A.; Corrente, G. A.; Fabiano, E.; Maltese, V.;
Cospito, S.; Ciccarella, G.; Chidichimo, G.; Gigli, G.; Capodilupo,
A. L., Orthogonal electronic coupling in multicentre arylamine
mixed-valence compounds based on a dibenzofulvene-thiophene
conjugated bridge. Chem. Commun. 2017, 53, 8960-8963.
(26) Liu, X.; Kong, F.; Ghadari, R.; Jin, S.; Yu, T.; Chen, W.; Liu,
G.; Tan, Z. a.; Chen, J.; Dai, S., Anthracene-arylamine hole trans-
porting materials for perovskite solar cells. Chem. Commun.
2017, 53, 9558-9561.
(27) Capodilupo, A. L.; De Marco, L.; Fabiano, E.; Giannuzzi,
R.; Scrascia, A.; Carlucci, C.; Corrente, G. A.; Cipolla, M. P.; Gigli,
G.; Ciccarella, G., New organic dyes based on a dibenzofulvene
bridge for highly efficient dye-sensitized solar cells. J. Mater.
Chem. A 2014, 2, 14181-14188.
(28) Turkoglu, G.; Cinar, M. E.; Buyruk, A.; Tekin, E.; Mucur,
S. P.; Kaya, K.; Ozturk, T., Novel organoboron compounds de-
rived from thieno[3,2-b]thiophene and triphenylamine units for
OLED devices. J. Mater. Chem. C 2016, 4, 6045-6053.
(29) Liu, B.; Yu, Z.-W.; He, D.; Zhu, Z.-L.; Zheng, J.; Yu, Y.-D.;
Xie, W.-F.; Tong, Q.-X.; Lee, C.-S., Ambipolar D-A type bifunc-
tional materials with hybridized local and charge-transfer excit-
ed state for high performance electroluminescence with EQE of
7.20% and CIEy CIEy ∼ 0.06. J. Mater. Chem. C 2017, 5, 5402-
5410.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(30) Tsuji, H.; Nakamura, E., Design and Functions of Semi-
conducting Fused Polycyclic Furans for Optoelectronic Applica-
tions. Acc. Chem. Res. 2017, 50, 396-406.
(31) Wielopolski, M.; Marszalek, M.; Brunetti, F. G.; Joly, D.;
Calbo, J.; Arago, J.; Moser, J.-E.; Humphry-Baker, R.; Zakeerud-
din, S. M.; Delgado, J. L.; Gratzel, M.; Orti, E.; Martin, N., Syn-
thesis and optoelectronic properties of chemically modified bi-
fluorenylidenes. J. Mater. Chem. C 2016, 4, 3798-3808.
(32) Baheti, A.; Justin Thomas, K. R.; Lee, C.-P.; Li, C.-T.; Ho,
K.-C., Organic dyes containing fluoren-9-ylidene chromophores
for efficient dye-sensitized solar cells. J. Mater. Chem. A 2014, 2,
5766-5779.
(33) Gopikrishna, P.; Das, D.; Adil, L. R.; Iyer, P. K., Saturated
and Stable White Electroluminescence from Linear Single Poly-
mer Systems Based on Polyfluorene and Mono-Substituted
Dibenzofulvene Derivatives. J. Phys. Chem. C 2017, 121, 18137-
18143.
(34) Corrente, G.A.; Fabiano, E.; De Marco, L.; Accorsi, G.; Gi-
annuzzi, R.; Cardone, A.; Gigli, G.; Ciccarella, G.; Capodilupo, A.-
L., Effects of donor position on dibenzofulvene-based organic
dyes for photovoltaics. J. Mater. Sci.: Mater. Electron. 2017, 28,
8694-8707.
(35) Burrezo, P. M.; Lin, N. T.; Nakabayashi, K.; Ohkoshi, S. i.;
Calzado, E. M.; Boj, P. G.; García, M. A. D.; Franco, C.; Rovira, C.;
Veciana, J.; Moos, M.; Lambert, C.; Navarrete, J. T. L.; Tsuji, H.;
Nakamura, E.; Casado, J., Bis(aminoaryl) Carbon‐Bridged Oli-
go(phenylenevinylene)s Expand the Limits of Electronic Cou-
plings. Angew. Chem., Int. Ed. 2017, 56, 2898-2902.
(21) Chuang, Y.-W.; Yen, H.-J.; Wu, J.-H.; Liou, G.-S., Colorless
Triphenylamine-Based Aliphatic Thermoset Epoxy for Multicol-
ored and Near-Infrared Electrochromic Applications. ACS Appl.
Mater. Interfaces 2014, 6, 3594-3599.
(22) Barlow, S.; Risko, C.; Coropceanu, V.; Tucker, N. M.;
Jones, S. C.; Levi, Z.; Khrustalev, V. N.; Antipin, M. Y.; Kin-
nibrugh, T. L.; Timofeeva, T.; Marder, S. R.; Bredas, J.-L., A
(36) Coropceanu, V.; Gruhn, N. E.; Barlow, S.; Lambert, C.;
Durivage, J. C.; Bill, T. G.; Nöll, G.; Marder, S. R.; Brédas, J.-L.,
Electronic Couplings in Organic Mixed-Valence Compounds:ꢁ
The Contribution of Photoelectron Spectroscopy. Journal of the
American Chemical Society 2004, 126, (9), 2727-2731.
ACS Paragon Plus Environment

Page 13 of 14
Chemistry of Materials
(37) Winter, R. F., Half-Wave Potential Splittings ΔE1/2 as a
Measure of Electronic Coupling in Mixed-Valent Systems: Tri-
umphs and Defeats. Organometallics 2014, 33, 4517-4536.
(38) Bushby, R. J.; McGill, D. R.; Ng, K. M.; Taylor, N., Disjoint
and coextensive diradical diions. J. Chem. Soc., Perkin Trans.2
1997, 2, 1405-1414.
(39) Nie, H. J.; Yao, C. J.; Shao, J. Y.; Yao, J.; Zhong, Y. W., Oli-
gotriarylamines with a Pyrene Core: A Multicenter Strategy for
Enhancing Radical Cation and Dication Stability and Tuning
Spin Distribution. Chem.-Eur. J. 2014, 20, 17454-17465.
(40) Bonvoisin, J.; Launay, J.-P.; Verbouwe, W.; Van der Au-
weraer, M.; De Schryver, F. C., Organic Mixed Valence Systems.
II. Two-Centers and Three-Centers Compounds with Meta Con-
nections around a Central Phenylene Ring. J. Phys. Chem. B 1996,
100, 17079-17082.
(41) Chang, C.-C.; Yueh, H.; Chen, C.-T., Generation and Spec-
troscopic Profiles of Stable Multiarylaminium Radical Cations
Bridged by Fluorenes. Org. Lett. 2011, 13, 2702-2705.
(42) Hankache, J.; Wenger, O. S., Organic Mixed Valence.
Chem. Rev. 2011, 111, 5138-5178.
(43) Zhang, Y.-M.; Wu, S.-H.; Yao, C.-J.; Nie, H.-J.; Zhong, Y.-
W., A Bis(terpyridine)ruthenium Complex with Three Redox-
Active Amine Sites: Electrochemical, Optical, and Computation-
al Studies. Inorg. Chem. 2012, 51, 11387-11395.
(44) Connelly, N. G.; Geiger, W. E., Chemical Redox Agents
for Organometallic Chemistry. Chem. Rev.,1996, 96, 877–910.
(45) Pavlishchuk, V. V.; Addison, A. W, Conversion constants
for redox potentials measured versus different reference elec-
trodes in acetonitrile solutions at 25°C. Inorg. Chim. Acta 2000,
298, 97-102.
(46) Tsiplakides, D.; Archonta, D.; Vayenas, C. G., Absolute
potential measurements in solid and aqueous electrochemistry
using two Kelvin probes and their implications for the electro-
chemical promotion of catalysis. Top. Catal. 2007, 44, 469-479.
(47) Chidichimo, G.; De Simone, B. C.; Imbardelli, D.; De Ben-
edittis, M.; Barberio, M.; Ricciardi, L.; Beneduci, A., Influence of
Oxygen Impurities on the Electrochromic Response of Viologen-
Based Plastic Films. J. Phys. Chem. C, 2014, 118, 13484–13492.
(48) Maltese, V.; Cospito, S.; Beneduci, A.; Simone, B. C. D.;
Russo, N.; Chidichimo, G.; Janssen, R. A. J., Electro‐optical Prop-
erties of Neutral and Radical Ion Thienosquaraines. Chem.-Eur. J.
2016, 22, 10179-10186.
(49) Cospito, S.; Beneduci, A.; Veltri, L.; Salamonczyk, M.;
Chidichimo, G., Mesomorphism and electrochemistry of thieno-
viologen liquid crystals. Phys. Chem. Chem. Phys. 2015, 17, 17670-
17678.
(50) TURBOMOLE Version 7.1. A development of University
of Karlsruhe and Forschungszentrum Karlsruhe GmbH (2012)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1989–2007,
TURBOMOLE
GmbH,
since
2007
http://www.turbomole.com
(51) Furche, F.; Ahlrichs, R.; Hättig, C.; Klopper, W.; Sierka,
M.; Weigend, F., Turbomole. Wiley Interdiscip. Rev.: Comput.
Mol. Sci. 2014, 4, 91-100.
(52) Weigend, F.; Häser, M.; Patzelt, H.; Ahlrichs, R., RI-MP2:
optimized auxiliary basis sets and demonstration of efficiency.
Chem. Phys. Lett. 1998, 294, 143-152.
(53) Guido, C. A.; Brémond, E.; Adamo, C.; Cortona, P., Com-
munication: One third: A new recipe for the PBE0 paradigm. J.
Chem. Phys. 2013, 138, 021104.
ACS Paragon Plus Environment

Chemistry of Materials
Page 14 of 14
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table of Contents graphic
14
ACS Paragon Plus Environment