Electro-optical Properties of Neutral and Radical Ion Thienosquaraines

Article abstract of DOI:10.1002/chem.201601281

Thienosquaraines are an interesting class of electroactive dyes that are useful for applications in organic electronics. Herein, the redox chemistry and electrochromic response of a few newly synthesized thienosquaraines are presented. These properties are compared to those of the commercial 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]squaraine. The stability of the radical ions formed in electrochemical processes strongly affects these properties, as shown by cyclic voltammetry, in situ spectroelectrochemistry, and quantum chemical calculations. Furthermore, all of the dyes show aggregation tendency resulting in panchromatic absorption covering the whole UV/Vis spectral range.

Full text of DOI:10.1002/chem.201601281

DOI: 10.1002/chem.201601281
Full Paper
&
Squaraine Dyes
Electro-optical Properties of Neutral and Radical Ion
Thienosquaraines
Vito Maltese,*[a, b] Sante Cospito,[a] Amerigo Beneduci,*[a] Bruna Clara De Simone,[a]
Nino Russo,[a] Giuseppe Chidichimo,[a] and Renꢀ A. J. Janssen[b]
Abstract: Thienosquaraines are an interesting class of elec-
troactive dyes that are useful for applications in organic elec-
tronics. Herein, the redox chemistry and electrochromic re-
sponse of a few newly synthesized thienosquaraines are pre-
sented. These properties are compared to those of the com-
nyl]squaraine. The stability of the radical ions formed in
electrochemical processes strongly affects these properties,
as shown by cyclic voltammetry, in situ spectroelectrochem-
istry, and quantum chemical calculations. Furthermore, all of
the dyes show aggregation tendency resulting in panchro-
matic absorption covering the whole UV/Vis spectral range.
mercial
2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphe-
Introduction
ty to commercial 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxy-
phenyl]squaraine (DIBSQ). Moreover, the optical, redox, and
spectroelectrochemical properties of thienosquaraines were
fully investigated and compared with those of DIBSQ, chosen
as reference compound due to its wide usage in materials
chemistry.[12i–j,20]
Squaraines (SQs) are the products of the dicondensation of
electron-rich compounds with squaric acid,[1] which affords
donor–acceptor–donor (D–A–D) molecular wires that are inter-
esting for a broad range of applications in biomedicine[1d,2–4]
and optoelectronics.[1e,2f,5–15] SQs containing thiophenes as
electron-donor moiety are in principle very intriguing. Indeed,
thiophenes are widely used as backbones in conjugated poly-
mers[16] and as conjugated moieties in several small-molecule
functional materials.[17]
Notably, the different relative stabilities of the radical ions
between thienosquaraines and DIBSQ lead to opposite electro-
chromic behavior. The low oxidation potentials and the small
energy gaps combined with a panchromatic absorption due to
strong intermolecular aggregation make these dyes potential
candidates for a wide range of optoelectronics applications.
Despite the wide range of squaraine dyes now known, with
the exception of some hydroxyl-substituted 1-benzothio-
phenes[18] and 2-dialkylamino-substituted thiophenes,[2e,19] no
other thiophene-containing squaraine derivatives, known as Results and Discussion
thienosquaraines, have been disclosed. In this work, we ex-
Synthesis and characterization
tended the reactivity by changing the nitrogen-containing
groups from linear alkyl secondary amines (2b,c) to cyclic sec-
ondary amines (2a,d). For compounds 2c,d, we also inserted
one hydroxyl group on the carbon chain linked to the nitrogen
atom. Compound 2b proved to have the best solubility of
these compounds in all organic solvents, and superior solubili-
First, the N,N-disubstituted 2-aminothiophene derivatives 1a–d
were synthesized, in order to test their reactivity in squaraine
condensation. Their preparation, according to the literature, is
reported in the Supporting Information (Scheme S1 and
Table S1). Condensation of N,N-disubstituted 2-aminothio-
phenes 1a–d with squaric acid leads to the formation of the
desired thienosquaraines 2a–d. The squaraine condensation
reaction is known to be acid-catalyzed by the squaric acid
itself, which in most cases is strong enough to self-catalyze its
own reaction.[5i] This is an exceptional feature of SQ dyes com-
pared with other class of optoelectronic materials, especially
organic semiconductor materials, which are often prepared by
metal-catalyzed reactions. The above method is a green syn-
thesis strategy that avoids the employment of transition metal
catalysts to carry out dehydrogenative condensation. Although
DIBSQ is commercially available, we synthesized it by follow-
ing well-known procedures (see the Supporting Information).
The structural formulas of all the dyes in this work are shown
in Figure 1. All compounds were fully characterized by FTIR
[a] Dr. V. Maltese, Dr. S. Cospito, Dr. A. Beneduci, Dr. B. C. De Simone,
Prof. N. Russo, Prof. G. Chidichimo
Department of Chemistry and Chemical Technologies
University of Calabria
Via P. Bucci, Arcavacata di Rende (CS) 87036 (Italy)
E-mail: vito.maltese@unical.it
amerigo.beneduci@unical.it
[b] Dr. V. Maltese, Prof. R. A. J. Janssen
Molecular Materials and Nanosystems
Institute for Complex Molecular Systems
Eindhoven University of Technology
P. O. Box 513, 5600 MB Eindhoven (The Netherlands)
Supporting information for this article and ORCID for some of the authors
are available on the WWW under
http://dx.doi.org/10.1002/chem.201601281.
Chem. Eur. J. 2016, 22, 1 – 9
1
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
and NMR spectroscopy, MALDI-TOF mass spectrometry, and
thermogravimetric analysis/differential thermal analysis (TG/
DTA; see Experimental Section and Supporting Information).
TGA was performed to test whether thienosquaraines could be
directly sublimed to form thin films for device fabrication. Un-
fortunately, as shown in Figure S2 of the Supporting Informa-
tion, they decompose above about 2808C. However, they are
solution-processable thanks to their rather good solubility in
several common organic solvents.
Information, Figure S3). It originates from the transfer of
charge from the olate donors to the other two carbon atoms
of the central cyclobutenediylium fragment and the thienyl
substituents. The sharpness of this band usually is an indica-
tion of the rigidity of the p system with very little structural
change on photoexcitation. This is consistent with localization
of the excitation on the central C4O2 unit. Consequently, the ar-
omatic substituents do not have a strong influence on lmax, al-
though the more electron rich thiophenes induce a bathochro-
mic shift compared to DIBSQ, which confirms the
ICT character. The absorption spectra show a should-
er at lower wavelengths, which is common to SQ
dyes and originates from vibronic coupling.[21] The
vibronic coupling of about 1300 cmꢀ1 corresponds
to that of a C=C stretching vibration.[22] The maxi-
mum absorption wavelengths lmax and the molar ex-
tinction coefficients emax calculated at lmax of the
dyes are listed in Table 1. The lmax values of the thie-
nosquaraines were slightly redshifted relative to
DIBSQ. SQ absorption bands generally become
rather broad in the solid state as a consequence of
strong charge-transfer interactions and tendency to
aggregation.[2b] The spectra of 2a–d change dramati-
cally in more concentrated solutions, where a broad-
ening of the ICT band occurs due to formation of
aggregates (Figure 3 and Supporting Information,
Figure S4). Interestingly, a panchromatic absorption
Figure 1. Structural formulas of DIBSQ and thienosquaraines 2a–d.
spectrum extending into the NIR region was ob-
served for these dyes (Supporting Information, Fig-
Optical properties
ure S4). Aggregation is also characteristic of the solid state.
Owing to the strong ICT interactions, the absorption spectra of
thin solid films become very broad and redshifted compared
to those in dilute solution (Figure 3 and Supporting Informa-
tion, Figure S4). However, the most important spectral changes
are the new bands appearing at higher or lower wavelengths.
All of the four new compounds exhibit a clear peak in the NIR
region (ꢁ830 nm) when the film is annealed at 708C, which is
very similar to that observed in the DIBSQ film. Similar behav-
ior was also observed in concentrated solutions of 2a,b (Sup-
porting Information, Figure S5), which indicates that these
dyes easily form aggregates both in solution and in the solid
state.
Figure 2 shows the absorption spectra of 2a–d and DIBSQ in
N-methylpyrrolidinone (NMP) solution, all of which exhibited
a sharp and highly intense band in the range 600–700 nm with
a maximum around 650 nm, except for DIBSQ, the maximum
of which was blueshifted by about 20 nm. These values were
typical of squaraine dyes.[19]
This intramolecular charge-transfer (ICT) absorption band
corresponds to the HOMO–LUMO transition, as inferred by
time-dependent density functional theory (TDDFT; Supporting
DFT and TDDFT were used to better understand the aggre-
gation properties of SQ dyes; 2b and DIBSQ were chosen as
model compounds (Supporting Information, Table S2). Analysis
of the calculated excitation energies evidenced that all the
three employed exchange-correlation functionals give results
in good agreement with the experimental counterparts. The
major deviation between calculated and measured transitions
concerns the neutral species (Supporting Information,
Table S2). A similar deviation was found for a prototypical indo-
lenine-based squaraine dye.[21] To verify the possible influence
of aggregation on the electronic transitions, we considered for
2b two molecules interacting in parallel and orthogonal
modes (Supporting Information, Figure S6). In the parallel
stacking mode, a staggered arrangement of the two chromo-
phores in the dimer (J-aggregate) is favored over the parallel
Figure 2. Normalized UV/Vis spectra of DIBSQ (black curve), 2a (red curve),
2b (blue curve), 2c (green curve), and 2d (pink curve) in NMP solution
(1ꢂ10ꢀ6 m).
&
&
Chem. Eur. J. 2016, 22, 1 – 9
www.chemeurj.org
2
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
Table 1. Optical and electrochemical properties of DIBSQ and thienosquaraines 2a–d.[a]
SQ
lmax [nm]
emax ꢂ105 [Lmolꢀ1 cmꢀ1
]
Egopt [eV]
EgCV [eV]
Eox1 [V]
Ered [V]
EHOMO [eV]
ELUMO [eV]
dil
conc
DIBSQ
2a
2b
2c
2d
652
668
671
668
663
3.9
4.1
1.3
0.84
8.0
1.80
1.79
1.75
1.79
1.79
1.72
1.37
1.40
n.d.
n.d.
1.66
1.16
1.24
0.95
1.13
0.46
ꢀ1.20
ꢀ1.28
ꢀ1.35
ꢀ1.0
ꢀ5.26
ꢀ4.68
ꢀ4.69
ꢀ4.75
ꢀ4.68
ꢀ3.48
ꢀ3.52
ꢀ3.45
ꢀ3.80
ꢀ3.56
ꢀ0.12
ꢀ0.11
ꢀ0.05
ꢀ0.12
ꢀ1.24
[a] Egopt was calculated from the onset of the absorption spectra in a 1ꢂ10ꢀ6 m (dil) and a 1ꢂ10ꢀ3 m (conc) CH2Cl2solution; n.d.: not determined due to low
solubility. For 2c,d, Eox and Ered were measured from the onset of the first oxidation and reduction peak, respectively. All samples were measured in a 0.1m
TBAPF6/CH2Cl2 solution with a dye concentration of 1ꢂ10ꢀ3 m, at 258C. The electrochemical potential of Fc/Fc+ was set at 4.8 V versus vacuum.
Figure 3. Absorption spectra of 1ꢂ10ꢀ6 m DIBSQ and 2b in CH2Cl2 (blue curves), films (black curves), and films from CB solution, annealed at 708C, for 10 min
(red curves).
and orthogonal cofacial dimers (Supporting Information, Fig-
ure S6). In the J-dimer, the positively charged NBu2 moiety in-
teracts with the negatively charged squaraine C=O group, and
the distance between the two layers was found to be 3.64 ꢃ.
Excitation of this dimer, calculated at the M06 level of theory,
redshifts the ICT band by 11 nm.
Electrochemistry
To better characterize the optical properties of this class of
compounds, we calculated the absolute energy of the HOMO
and LUMO levels. This could be done from the electrochemical
data only for concentrated solutions, for which good cyclic vol-
tammograms (CVs) were measured (Figure 4).
The onset of the first oxidation potential versus the ferro-
cene/ferrocenium couple (Fc+/Fc) of DIBSQ and 2a–d deter-
mined by CV was used to estimate the HOMO (EHOMO) and
LUMO (ELUMO) levels, by assuming that the energy level of
Fc+/Fc is 4.8 eV below the vacuum level,[17c,23] and by using
the empirical Equations (1) and (2).[24]
EHOMO ¼ ꢀ½EonsetðoxÞꢀEonsetðFcþÞꢂꢀ4:8 eV
ELUMO ¼ ꢀ½EonsetðredÞꢀEonsetðFcþÞꢂꢀ4:8 eV
ð1Þ
ð2Þ
The energy gap Eg was then calculated by Equation (3).
Figure 4. Energy levels (a) and CVs (b) of DIBSQ and 2b (1ꢂ10ꢀ3 m) in an
electrolyte solution (CH2Cl2/0.1m TBAPF6).
Eg ¼ ELUMOꢀEHOMO
ð3Þ
Chem. Eur. J. 2016, 22, 1 – 9
www.chemeurj.org
3
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
For comparison, the optical band gap Egopt in solution
(Table 1) was evaluated from lonset of the absorption spectrum.
Compounds 2a,b and DIBSQ showed similar oxidation prop-
erties in dichloromethane solution with two reversible oxida-
tion waves close to that of the Fc/Fc+ couple, whereas 2c,d
have only one oxidation peak (Figure 4 and Supporting Infor-
mation, Figure S6). In the negative scan, one reversible reduc-
tion peak was observed for 2b, whereas for the other squar-
aine derivatives the reduction wave was almost irreversible
(Figure 4 and Supporting Information, Figure S7).
bonding reduces the overall energy in the squaraine core
through participation of conjugated structures.[14a,25]
The electron-transfer processes of 2b and DIBSQ were in-
vestigated by TDDFT (Supporting Information, Table S2). Ac-
cording to the experimental CVs (Figure 4), when a potential is
applied to 2b, reversible two-step one-electron oxidation (2b+
and 2b2+) and reduction to 2bꢀ are possible. For DIBSQ, only
the DIBSQ+ and DIBSQꢀ species can be formed. In both redox
processes, the radical ion is stabilized by distribution of the
charge over the entire p-conjugated system, as highlighted by
the calculated charge distribution (Figure 5). In particular, for
both compounds, the nitrogen spin density is higher in the
radical cation species, whereas a higher spin density is found
in the cyclobutadienyl moiety of the radical anion. The calcu-
lated charge distributions reported in Figure 5 show that in
DIBSQ+ the positive charge is not evenly distributed over the
entire system, but is more localized on the cyclobutadienyl
ring and on the peripheral parts of the molecule. In the radical
anion (DIBSQꢀ), the negative charge is essentially delocalized
over the core with full involvement of the phenyl rings. In con-
trast, greater delocalization of the positive charge is found in
the radical cation of 2b, in which the positive charge is more
homogeneously distributed around the terminal nitrogen moi-
eties. This leads to better stabilization of the radical cation, in
accordance with the lower oxidation potential of 2b compared
to DIBSQ (Table 1). On the other hand, the negative charge in
the radical anion of 2b is more concentrated on the cyclobuta-
dienyl ring with less involvement of the thiophenes units. This
implies worse stabilization of the radical anion of 2b compared
to that of DIBSQ. The difference in the relative stabilities of the
radical species of the two compounds is further evidenced by
the lower ionization potential of 2b (4.53 eV) compared to
The almost equal oxidation potentials of all four dyes indi-
cated only minor contributions of the peripheral substituents
on the nitrogen atom to formation of the radical cation (Sup-
porting Information Figure S3). Indeed, the positive charge is
mainly localized on the D moieties of the chromophore
(Figure 5). The results are summarized in Table 1.
From the electrochemical data in concentrated solution, we
observed that all the thienosquaraine dyes (2a–d) showed
high-lying HOMOs (a spread of about 0.6 eV) and the same
LUMOs with respect to DIBSQ. The thienosquaraines therefore
have smaller energy gaps than DIBSQ. This result seems to be
confirmed by the Egopt data calculated in concentrated solutions
for 2a,b. In contrast, the optical bandgap in dilute solution
does not change among the series of SQs and is identical to
that of DIBSQ. This difference can be explained by considering
that aggregation probably lowers the LUMO level due to the
favorable intermolecular interaction between the electron-rich
and electron-deficient moieties in the dimer (Supporting Infor-
mation, Figure S6), but has no significant effect on the HOMO
level. On the other hand, in DIBSQ and similar dyes, the
HOMO is lowered as the number of OH groups on the phenyl
rings increases, which suggests that intramolecular hydrogen
Figure 5. DFT calculated charge distribution in 2b and DIBSQ.
&
&
Chem. Eur. J. 2016, 22, 1 – 9
www.chemeurj.org
4
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
DIBSQ (5.03 eV) and the higher electron affinity of DIBSQ
(ꢀ2.85 eV) compared to 2b (ꢀ2.57 eV), calculated by DFT.
bands (Supporting Information, Figure S8), which indicates par-
tial loss of the charge-transfer characteristics in the conjugated
D–A–D array of the SQs on electron addition.[14d]
Notably, the differences discussed above in the stability of
the radical species are reflected in an opposite electrochromic
response of DIBSQ with respect to the thienosquaraines. In
this case, a drastic spectral change was observed on reduction
(Figure 7), whereas only minor changes occurred on oxidation
(Supporting Information, Figure S9). On reduction, the original
ICT band was totally bleached and an intense absorption band
centered at about 560 nm arose (Figure 7). No other bands
could be found in the UV and NIR regions. In contrast, the for-
mation of the radical cation of DIBSQ leads to a partial bleach-
ing of the ICT band (Supporting Information, Figure S9).
Spectroelectrochemistry
To gain further insight into the electronic structure on oxida-
tion and reduction of the compounds, we performed spectroe-
lectrochemical experiments in the UV/Vis/NIR region to charac-
terize the electrochemically formed redox species. The electro-
chromic behavior of the thienosquaraines was compared to
that of DIBSQ, for which such a study has never been per-
formed. The electronic spectra of 2b on oxidation are shown
in Figure 6. At the first oxidation potential the ICT band is
gradually bleached and a structured, less-intense absorption
band at 600 nm grows in (Figure 6).
Figure 7. Vis/NIR spectroelectrochemistry of DIBSQ (1ꢂ10ꢀ3 m) in NMP/0.1m
TBAPF6. Potentials versus Ag/Ag+.
Figure 6. Vis/NIR spectroelectrochemistry of 2b (1ꢂ10ꢀ3 m) in NMP/0.1m
TBAPF6. Potentials versus Ag/Ag+.
The opposite behavior of the two SQ systems could only be
explained by considering the relative stability of the radical
species formed in the redox processes. Whereas in the thienos-
quaraines the radical cation is better stabilized by the strong
electron-donating character of the thiophene ring, in the di-
phenylsquaraine this effect is less pronounced due to the elec-
tron-withdrawing OH groups.
The behavior of the other SQs in the series on formation of
the radical cation is analogous to that shown for 2b. The most
important difference is the appearance of a small band at
lower energy (840 nm; Figure 6). The calculated excitation en-
ergies for the radical cation of 2b are in good agreement with
the experimental observation (Supporting Information,
Table S2). The band at 600 nm arises from a HOMO–LUMO
transition involving charge transfer from the olate to the nitro-
gen atoms, as in the case of the neutral species (Supporting In-
formation, Figure S3 and Table S2). However, this process in-
volves only half of the molecule, and leads to a high-energy
transition. On further oxidation of 2a,b beyond the second oxi-
dation potential, almost complete bleaching of the ICT bands
is observed, while another band centered at 400 nm rises
(Figure 6), which could be attributed to the dicationic species,
as predicted by quantum chemical calculations (Table S2). The
complete bleaching of the ICT bands is a result of the loss of
the charge-transfer processes in the original, highly conjugated
D–A–D motif. Similar absorption patterns were already ob-
served for the excited states and the oxidized forms of other
squaraine dyes.[14b]
Conclusion
We have studied the electrochemical and spectroelectrochemi-
cal properties of newly synthesized thienosquaraine derivatives
2a–d and compared them with those of a well-known com-
mercial squaraine (DIBSQ). The experimental study, supported
by TDDFT calculations, of the electrochemical behavior of the
above compounds highlighted the significant role played by
the aromatic substituent attached to the squaric acid on the
stability of the radical species formed during redox processes.
The better stability of the radical cation of the thienosquar-
aines results in lower oxidation potentials and smaller energy
gaps compared to DIBSQ. The extensive delocalization of the
charge over the entire conjugated core of the thienosquar-
aines also leads to a clear electrochromic response on oxida-
tion. In contrast, the opposite electrochromic behavior of
Reduction of dyes 2a–d caused only slight bleaching of the
main absorption peak but without the appearance of other
Chem. Eur. J. 2016, 22, 1 – 9
www.chemeurj.org
5
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
DIBSQ is mainly due to the formation of a more stable radical
anion.
Electrochemistry
The electrochemical behavior of squaraine derivatives (0.1 mm)
was investigated by cyclic voltammetry in NMP for solution pro-
cesses and water as nonsolvent for thin-film degassed solutions
containing TBAPF6 and 0.1m LiClO4, respectively, as electrolytes.
The measurements were done at a glassy-carbon disk working
electrode in a three-electrode cell with a platinum auxiliary elec-
trode, an Ag/AgCl reference electrode, and a potentiostat configu-
ration from AMEL s.r.l. (Mod. 7050). All potentials were calibrated
against the Fc/Fc+ couple (0.1 mm).
The investigation of the optical properties of the neutral
species showed the aggregation tendency of these dyes in
concentrated solution or solid-state thin films. Indeed, in these
cases, the absorption spectrum covered almost the whole visi-
ble range, and this makes them suitable as panchromatic dyes
for organic electronics.
Spectroelectrochemistry
Experimental Section
Spectroelectrochemical experiments were performed in an electro-
lytic cell (BAS Inc.) composed of a 1 mm cuvette in which a plati-
num-gauze thin layer and a platinum wire were used as the work-
ing electrode and the auxiliary electrode, respectively. A pseudore-
ference electrode consisting of an Ag wire was calibrated against
the Fc+/Fc redox couple. The spectroelectrochemical cell was filled
with a solution containing 1 mm of squaraine derivative and
TBAPF6 (0.1m) dissolved in NMP. UV/Vis/NIR spectra were recorded
with a Vertex 80 (Bruker) spectrophotometer. The potential was
supplied by means of an Amel 2049 model potentiostat. Measure-
ments were performed at 258C.
Materials
Squaric acid, 2-bromothiophene, copper, copper(I) iodide, piperi-
dine, di-n-butylamine, 2-(ethylamino)ethanol, 4-hydroxypiperidine,
tetrabutylammonium hexafluorophosphate (TBAPF6), lithium per-
chlorate, n-butanol, dichloromethane, DMF, o-chlorobenzene (CB),
toluene, N-methylpyrrolidin-2-one (NMP), and propylene carbonate
(PC) were supplied by Sigma-Aldrich. All reactions were performed
under a nitrogen atmosphere. Commercial solvents and reactants
were used as received unless stated otherwise. The syntheses of 2-
piperidinothiophene (1a), 2-N,N-dibutylaminothiophene (1b), 2-
(ethylthiophen-2-yl-amino)ethanol (1c), 2-(4-hydroxypiperidino)-
thiophene (1d),[26] 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxy-
phenyl]squaraine (DIBSQ),[27] and 1,3-bis(5-piperidin-1-yl-thiophen-
2-yl)squarene (2a)[19] were previously described in the literature,
and their characterization is reported in the Supporting Informa-
tion.
Computational details
For all the species the geometry optimizations in dichloromethane
solvent were performed by employing the hybrid B3LYP[28] ex-
change-correlation functional coupled with the 6-31G* all-electron
basis set. These geometries were used for TDDFT[29] calculations
employing the B3LYP, M06,[30] and range-separated hybrid
wB97XD[31] exchange-correlation functionals coupled with the
more extended 6-31+G* basis sets. The radical species with sin-
glet spin state were treated with the restricted Kohn–Sham formal-
ism. No spin contamination was found for the open-shell system;
the hS2 i value was 0.77. The lowest twenty vertical excitation ener-
gies were calculated by TDDFT. Although previous studies have
demonstrated the reliability of the 6-31+G* basis set for reproduc-
tion of the excitation energies,[32] we redid the computations for
2b employing the more extended 6-311+G** triple-zeta basis
sets. The obtained excitation energies, in all cases, differ by few
nanometers with respect to the 6-31+G* counterpart. Solvent ef-
fects were evaluated by using the non-equilibrium implementa-
tion[33] of the polarizable continuum model[34] with dichlorome-
thane solvent (e=8.93), with which the experimental UV/Vis spec-
tra have been recorded. All calculations were carried out with the
Gaussian 09 code.[35]
Characterization
All spectroscopic measurements and chromatography were per-
formed at room temperature unless stated otherwise. Melting
points were determined with a Buchi B-540 melting point device
and measurements were performed in duplo. 1H and 13C NMR
spectra were recorded with a Varian Mercury Vx 400 MHz (100 MHz
for 13C), a Varian 400 MR 400 MHz (100 MHz for 13C), a Varian
Gemini 300 MHz (75 MHz for 13C), or a Varian Mercury Plus
200 MHz (50 MHz for 13C) NMR spectrometer. 1H chemical shifts
were determined with tetramethylsilane as internal standard
(0 ppm). 13C chemical shifts were determined from the deuterated
solvent CDCl3 (77.16 ppm) or tetramethylsilane (0 ppm) as internal
standard. Matrix-assisted laser desorption ionization time-of-flight
(MALDI-TOF) mass spectra were recorded with a PerSeptive Biosys-
tems Voyager-DEPRO spectrometer by using a-cyano-4-hydroxycin-
namic acid (CHCA) and/or trans-2-[3-(4-tert-butylphenyl)-2-methyl-
2-propenylidene]malononitrile (DCTB) as matrix. IR spectra were re-
corded in the solid state with a PerkinElmer Spectrum One 1600
FTIR spectrometer, equipped with a PerkinElmer Universal ATR
Sampler Accessory. UV/Vis spectra were recorded with a PerkinElm-
er Lambda 40 UV/Vis spectrometer in 1 cm quartz cuvette was
used for the measurements.
Preparation of 1,3-bis-(5-(dibutylamino)thiophen-2-yl)-squar-
ene (2b)
In a three-neck flask equipped with a Dean–Stark trap to remove
water, squaric acid (114 mg, 1 mmol) was dissolved in a mixture of
n-butanol (10 mL) and toluene (30 mL) at reflux. N,N-Di-n-butylami-
nothiophene (422.7 mg, 2 mmol) was dissolved in a mixture of n-
butanol (2.5 mL) and toluene (7.5 mL) and the solution added
dropwise to the above mixture, which was heated to reflux and
monitored by Vis spectroscopy until no enhancement of the ab-
sorptivity at about 700 nm could be observed (5 h). After cooling,
the precipitate was collected by filtration and washed with diethyl
ether and then several times with n-hexane (3ꢂ20 mL). The de-
sired product did not need further purification (Table 1, entry 2).
Thermal analysis
The thermal stability of dyes 2b,d was investigated with a Shimad-
zu DTG-60 simultaneous DTA/TG instrument. The measurements
were carried out from room temperature to 6008C in air flow at
a heating rate of 108Cminꢀ1
.
&
&
Chem. Eur. J. 2016, 22, 1 – 9
www.chemeurj.org
6
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
Green solid (200 mg, 40%); m.p. >300 (degradation); 1H NMR
(200 MHz, CDCl3, 258C, TMS): d=7.94 (d, J(H,H)=4.7 Hz, 2H, H-3),
59.44, H 5.44, N 6.30, S 14.43; found: C 59.38, H 5.45, N 6.28, S
14.47.
3
6.20 (d, 3J(H,H)=4.8 Hz, 2H, H-4), 3.42 (t, 3J(H,H)=7.4 Hz, 8H,
NCH2CH2CH2CH3), 1.78–1.62 (m, 8H, NCH2CH2CH2CH3), 1.43–1.31 (m,
8H, NCH2CH2CH2CH3) 0.97 ppm (t, 3J(H,H)=7.2 Hz, 12H,
NCH2CH2CH2CH3); IR (film): n˜ =2958 (m), 2937 (m), 2872 (w), 1611
(m), 1543 (w), 1417 (s), 1341 (s), 1296 (m), 1269 (m), 1104 (m), 1064
(s), 910 (m), 808 (w), 522 cmꢀ1 (w); UV/Vis (chlorobenzene): lmax
(e)=671 nm (5.133ꢂ104 molꢀ1 dm3 cmꢀ1); MS (MALDI-TOF): m/z
(%): 500.26 (100) [M+]; elemental analysis calcd (%) for
C28H40N2O2S2:C 67.16, H 8.05, N 5.59, S 12.81; found: C 67.26, H
8.01, N 5.58, S 12.84.
Acknowledgements
The authors thank the University of Calabria and Dr. Enrico Cat-
izzone (University of Calabria) for the thermal measurements.
The postdoctoral fellowship of S.C. and V.M. was co-funded by
the European Commission, the European Social Fund, and by
the Regione Calabria in the framework of ARUE project. The
authors are the uniquely responsible of this work and both the
European Commission and the Regione Calabria refuse any re-
sponsibility on the use of the information reported here.
Preparation of 1,3-bis{5-[ethyl(2-hydroxyethyl)amino]thio-
phen-2-yl}squarene (2c)
In a three-neck flask equipped with a Dean–Stark trap to remove
water, squaric acid (114 mg, 1 mmol) was dissolved in a mixture of
n-butanol (10 mL) and toluene (30 mL) at reflux. 2-(Ethylthiophen-
2-ylamino)ethanol (342.5 mg, 2 mmol) was dissolved in a mixture
of n-butanol (2.5 mL) and toluene (7.5 mL) and the solution added
dropwise to the mixture, which was heated to reflux for 5 h. The
solution was then concentrated to approximately half volume
(25 mL) and diluted with a similar amount of n-hexane. After stand-
ing at room temperature for 15 h, the precipitate formed was col-
lected by filtration and washed with diethyl ether and hexane (3ꢂ
20 mL) to afford the desired product without any other purification
(Table 1, entry 3). Dark green solid (215 mg, 51%); m.p. >300 (deg-
radation); 1H NMR (200 MHz, [D6]DMSO, 258C, TMS): d=7.71 (d,
Keywords: aggregation · density functional calculations ·
electrochemistry · radical ions · squaraines
[1] a) A. Treibs, K. Jacob, Angew. Chem. Int. Ed. Engl. 1965, 4, 694; Angew.
Chem. 1965, 77, 680; b) A. H. Schmidt, in Oxocarbons, (West, Robert),
1980, 185–231; c) J. D. Park, S. Cohen, J. R. Lacher, J. Am. Chem. Soc.
1962, 84, 2919–2922; d) A. Ajayaghosh, Acc. Chem. Res. 2005, 38, 449–
459; e) S. Sreejith, P. Carol, P. Chithra, A. Ajayaghosh, J. Mater. Chem.
2008, 18, 264–274.
[2] a) A. C. Tam, Appl. Phys. Lett. 1980, 37, 978; b) K.-Y. Law, Chem. Rev.
1993, 93, 449; c) S. J. Chung, S. J. Zheng, T. Odani, L. Beverina, J. Fu,
L. A. Padilha, A. Biesso, J. M. Hales, X. W. Zhan, K. Schmidt, A. J. Ye, E.
Zojer, S. Barlow, D. J. Hagan, E. W. Van Stryland, Y. P. Yi, Z. G. Shuai, G. A.
Pagani, J. L. Bredas, J. W. Perry, S. R. Marder, J. Am. Chem. Soc. 2006, 128,
14444–14445; d) S. Jisha, K. T. Arun, M. Hariharan, D. Ramaiah, J. Am.
Chem. Soc. 2006, 128, 6024–6025; e) S. Ohira, I. Rudra, K. Schmidt, S.
Barlow, S. J. Chung, Q. Zhang, J. Matichak, S. R. Marder, J. L. Bredas,
Chem. Eur. J. 2008, 14, 11082–11091.
[3] a) J. V. Ros-Lis, R. Martınez-MꢄÇez, J. Soto, Chem. Commun. 2002, 2248–
2249; b) J. V. Ros-Lis, B. Garcia, D. Jimenez, R. Martınez-Manez, F. Sance-
non, J. Soto, F. Gonzalvo, M. C. Valldecabres, J. Am. Chem. Soc. 2004,
126, 4064–4065; c) B. J. Wallace, M. Gray, Z. Zhong, V. M. Lynch, E. V.
Anslyn, Dalton Trans. 2005, 2436–2441; d) T. Snee, R. C. Somers, G. Nair,
J. P. Zimmer, M. G. Bawendi, D. G. Nocera, J. Am. Chem. Soc. 2006, 128,
13320–13321; e) J. Thomas, D. B. Sherman, T. J. Amiss, S. A. Andaluz,
J. B. Pitner, Bioconjugate Chem. 2007, 18, 1841–1846; f) R. J. T. Houk,
K. J. Wallace, H. S. Hewage, E. V. Anslyn, Tetrahedron 2008, 64, 8271–
8278.
3
3J(H,H)=4.7 Hz, 2H, H-3), 6.56 (d, J(H,H)=4.7 Hz, 2H, H-4), 3.65 (t,
3J(H,H)=5.5 Hz, 4H, NCH2CH2OH), 3.60–3.55 (m, 8H, NCH2CH2OH+
3
NCH2CH3), 1.20 ppm (t, J(H,H)=7.1 Hz, 6H, NCH2CH3); IR (film): n˜ =
3366 (m, br), 2974 (m), 2939 (m), 2869 (w), 1596 (m), 1547 (w),
1419 (s), 1373 (m), 1347 (s), 1285 (s), 1110 (s), 1057 (s), 989 (s), 910
(m), 848 (w), 743 (m), 677 (m), 544 (w), 507 (w), 463 cmꢀ1 (m); UV/
Vis (chlorobenzene): lmax (e)=668 nm (9.192ꢂ103 molꢀ1 dm3 cmꢀ1);
MS (MALDI-TOF): m/z (%): 420.12 (100) [M+]; elemental analysis
calcd (%) for C20H24N2O4S2:C 57.12, H 5.75, N 6.66, S 15.25; found: C
57.20, H 5.76, N 6.64, S 15.23.
Preparation of 1,3-bis(5-(4-hydroxypiperidin-1-yl)thiophen-
2-yl)squarene (2d)
[4] a) R. Bonnett in Chemical Aspects of Photodynamic Therapy, (Gordon and
Breach), Amsterdam, 2000; b) D. Ramaiah, I. Eckert, K. T. Arun, L. Wei-
denfeller, B. Epe, Photochem. Photobiol. 2002, 76, 672; Photochem. Pho-
tobiol. 2004, 79, 99; c) A. D. Quartarolo, E. Sicilia, N. Russo, J. Chem.
Theory Comput. 2009, 5, 1849–1857; d) V. Rapozzi, L. Beverina, P. Salice,
G. A. Pagani, M. Camerin, L. E. Xodo, J. Med. Chem. 2010, 53, 2188–
2196; e) R. R. Avirah, D. T. Jayaram, N. Adarsh, D. Ramaiah, Org. Biomol.
Chem. 2012, 10, 911; f) M. S. Soumyaa, K. M. Shafeekh, S. Dasb, A. Abra-
ham, Chemico-Biological Interactions 2014, 222, 44–49.
[5] a) A. Ajayaghosh, Chem. Soc. Rev. 2003, 32, 181–191; b) B. Halton,
Chem. N. Z. 2008, 72, 57–62; c) J. J. Gassensmith, J. M. Baumes, B. D.
Smith, Chem. Commun. 2009, 6329–6338; e) L. Beverina, P. Salice, Eur. J.
Org. Chem. 2010, 1207–1225; f) L. Hu, Z. Yan, H. Xu, RSC Adv. 2013, 3,
7667; g) L. Beverina, M. Sassi, Synlett 2014, 25, 477–490; h) J.-Q. Jiang,
C.-L. Sun, Z.-F. Shi, H.-L. Zhang, RSC Adv. 2014, 4, 32987–32996; i) D. E.
Lynch, Metals-Open Access Metallurgy Journal 2015, 5, 1349–1370; j) G.
Chen, H. Sasabe, T. Igarashi, Z. Hong, J. Kido, J. Mater. Chem. A 2015, 3,
14517.
In a three-neck flask equipped with a Dean–Stark trap to remove
water, squaric acid (114 mg, 1 mmol) was dissolved in a mixture of
n-butanol (15 mL) and toluene (15 mL) at reflux. 1-Thiophen-2-yl-
piperidin-4-ol (366.5 mg, 2 mmol) was dissolved in a mixture of n-
butanol (5 mL) and toluene (5 mL) and the solution added drop-
wise to the mixture, which was heated to reflux for 0.5 h. The solu-
tion was then concentrated to approximately half volume (20 mL)
and diluted with a similar amount of n-hexane. After standing at
room temperature for 15 h, the precipitate formed was collected
by filtration and washed with diethyl ether and hexane (3ꢂ20 mL),
to afford the desired product without any other purification
(Table 1, entry 4). Bright green solid (133 mg, 30%); m.p. >300
(degradation); 1H NMR (200 MHz, [D6]DMSO, 258C, TMS): d=7.73
(d, 3J(H,H)=4.7 Hz, 2H, H-3), 6.72 (d, 3J(H,H)=4.7 Hz, 2H, H-4),
3.80–3.72 (m, 2H, CHOH), 1.93–1.49 (m, 8H, NCH2), 1.39–0.8 ppm
(m, 8H, NCH2CH2CH); IR (film): n˜ =3347 (m, br), 2957 (m), 2930 (m),
2871 (w), 1793 (w), 1670 (m), 1563 (s), 1476 (m), 1427 (s), 1368 (m),
1350 (m), 1277 (m), 1120 (w), 1070 (s), 1010 (m), 872 (w), 795 (w),
681 (w), 603 (w), 504 cmꢀ1 (w); UV/Vis (chlorobenzene): lmax (e)=
663 nm (7.223ꢂ102 molꢀ1 dm3 cmꢀ1); MS (MALDI-TOF): m/z (%):
444.13 (100) [M+]; elemental analysis calcd (%) for C22H24N2O4S2:C
[6] a) R. S. Stoll, N. Severin, J. P. Rabe, S. Hecht, Adv. Mater. 2006, 18, 1271–
1275; b) S.-Y. Hsueh, C.-C. Lai, Y.-H. Liu, S.-M. Peng, S.-H. Chiu, Angew.
Chem. Int. Ed. 2007, 46, 2013–2017; Angew. Chem. 2007, 119, 2059–
2063; c) A. Ajayaghosh, P. Chithra, R. Varghese, K. P. Divya, Chem.
Commun. 2008, 969–971; d) J. J. McEwen, K. J. Wallace, Chem. Commun.
2009, 6339–6351.
Chem. Eur. J. 2016, 22, 1 – 9
www.chemeurj.org
7
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
[7] a) J. R. Cox, P. Muller, T. M. Swager, J. Am. Chem. Soc. 2011, 133, 12910–
12913.
[17] a) A. Beneduci, S. Cospito, A. Crispini, B. Gabriele, F. P. Nicoletta, L. Veltri,
G. Chidichimo, J. Mater. Chem. C 2013, 1, 2233; b) A. Beneduci, S. Cospi-
to, M. La Deda, L. Veltri, G. Chidichimo, Nat. Commun. 2014, 5:3105 DOI
10.1038/ncomms4105; c) S. Cospito, A. Beneduci, L. Veltri, M. Salamonc-
zykc, G. Chidichimo, Phys. Chem. Chem. Phys. 2015, 17, 17670; d) M. Fu-
nahashi, T. Kato, Liq. Cryst. 2015, 42, 909–917.
[18] H. H. Sprenger, W. Ziegenbein, Angew. Chem. 1968, 80, 541.
[19] a) D. Keil, H. Hartmann, T. Moschny, Dyes Pigm. 1991, 17, 19–27; b) D.
Keil, H. Hartmann, Dyes Pigm. 2001, 49, 161–179; c) X. Song, J. W. Foley,
WO 2010054183; d) W. Liu, E. M. Peck, K. D. Hendzel, B. D. Smith, Org.
Lett. 2015, 17, 5268–5271; e) E. M. Peck, W. Liu, G. T. Spence, S. K. Shaw,
A. P. Davis, H. Destecroix, B. D. Smith, J. Am. Chem. Soc. 2015, 137,
8668–8671.
[20] a) J.-H. Yum, P. Walter, S. Huber, D. Rentsch, T. Geiger, F. Nꢆesch, F.
De Angelis, M. Grꢅtzel, M. K. Nazeeruddin, J. Am. Chem. Soc. 2007, 129,
10320–10321; b) S. Wang, E. I. Mayo, M. D. Perez, L. Griffe, G. Wei, P. I.
Djurovich, S. R. Forrest, M. E. Thompson, Appl. Phys. Lett. 2009, 94,
233304; c) S. Wang, M. E. Thompson, K. V. B. Josyula, Material Matters
2012, 7, 9; d) G. Chen, D. Yokoyama, H. Sasabe, Z. Hong, Y. Yang, J.
Kido, Appl. Phys. Lett. 2012, 101, 083904; e) Q. An, F. Zhang, L. Li, J.
Wang, J. Zhang, L. Zhou, W. Tang, ACS Appl. Mater. Interfaces 2014, 6,
6537–6544.
[8] a) C. W. Dirk, W. C. Herndon, F. Cervantes-Lee, H. Selnau, S. Martinez, P.
Kalamegham, A. Tan, G. Campos, M. Velez, I. Zyss, I. Ledoux, L.-T. Cheng,
J. Am. Chem. Soc. 1995, 117, 2214–2225; b) G. J. Ashwell, G. Jefferies,
D. G. Hamilton, D. E. Lynch, M. P. S. Roberts, B. S. Bahra, C. R. Brown,
Nature 1995, 375, 385; c) M. Furuki, L. S. Pu, F. Sasaki, S. Kobayashi, T.
Tani, Appl. Phys. Lett. 1998, 72, 2648.
[9] a) F. Silvestri, M. D. Irwin, L. Beverina, A. Facchetti, G. A. Pagani, T. J.
Marks, J. Am. Chem. Soc. 2008, 130, 17640–17641; b) C. Zhang, X.
Zhang, X. Zhang, X. Ou, W. Zhang, J. Jie, J. C. Chang, C. S. Lee, S. T. Lee,
Adv. Mater. 2009, 21, 4172–4175; c) Y. Zhang, W. Deng, X. Zhang, X.
Zhang, X. Zhang, Y. Xing, J. Jie, ACS Appl. Mater. Interfaces 2013, 5,
12288–12294; d) M. Gsꢅnger, E. Kirchner, M. Stolte, C. Burschka, V. Ste-
panenko, J. Pflaum, F. Wꢆrthner, J. Am. Chem. Soc. 2014, 136, 2351–
2362.
[10] a) M. Binda, T. Agostinelli, M. Caironi, D. Natali, M. Sampietro, L. Beveri-
na, R. Ruffo, F. Silvestri, Org. Electron. 2009, 10, 1314–1319; b) U. Mayer-
hçffer, B. Fimmel, F. Wurthner, Angew. Chem. Int. Ed. 2012, 51, 168–171;
Angew. Chem. 2012, 124, 172–176; c) U. Mayerhçffer, B. Fimmel, F.
Wurthner, Angew. Chem. Int. Ed. 2012, 51, 164–167; Angew. Chem.
2012, 124, 168–171.
[21] R. Borrelli, S. Ellena, C. Barolo, Phys. Chem. Chem. Phys. 2014, 16, 2390.
[22] a) S. Spencer, H. Hu, Q. Li, H.-Y. Ahn, M. Qaddoura, S. Yao, A. Ioannidis,
K. Belfield, C. J. Collison, Prog. Photovolt. Res. Appl. 2014, 22, 488–493;
b) V. V. Kurdyukova, A. I. Tolmacheva, M. L. Dekhtyar, Y. G. Vlasenkoa,
A. N. Chernega, J. Phys. Org. Chem. 2015, 28, 452–459.
[23] M. Helbig, H.-H. Horhold, Macromol. Chem. 1993, 194, 1607.
[24] I. Seguy, P. Jolinat, P. Destruel, J. Farenc, J. Appl. Phys. 2001, 89, 5442.
[25] G. Chen, H. Sasabe, Y. Sasaki, H. Katagiri, X.-F. Wang, T. Sano, Z. Hong, Y.
Yang, J. Kido, Chem. Mater. 2014, 26, 1356–1364.
[26] Z. Lu, R. J. Twieg, Tetrahedron 2005, 61, 903–918.
[27] M. Tian, M. Furuki, I. Iwasa, Y. Sato, L. S. Pu, S. Tatsuura, J. Phys. Chem. B
2002, 106, 4370–4376.
[28] a) A. D. Becke, Phys. Rev. A 1988, 38, 3098–3100; A. D. Becke, J. Chem.
Phys. 1993, 98, 5648–5652; b) C. Lee, W. Yang, R. G. Parr, Phys. Rev. B
1988, 37, 785–789.
[29] M. E. Casida in: Recent advances in density functional methods Part I.
(Word Scientific, Ed: D. P. Chong), Singapore, 1995.
[30] Y. Zhao, D. G. Truhlar, Theor. Chem. Acc. 2008, 120, 215–241.
[31] J. D. Chai, M. Head-Gordon, Phys. Chem. Chem. Phys. 2008, 10, 6615–
6620; J. D. Chai, M. Head-Gordon, Phys. Chem. Chem. Phys. 2008, 128,
84106–84155.
[32] a) M. E. Alberto, B. C. De Simone, G. Mazzone, T. Marino, N. Russo, Dyes
Pigm. 2015, 120, 335–339; b) J. Pirillo, B. C. De Simone, N. Russo, Theor.
Chem. Acc. 2016, 135, 8.
[11] a) K. Y. Law, F. C. Bailey, J. Imaging Sci. 1987, 31, 172–177; b) K. Y. Law,
J. S. Facci, F. C. Bailey, J. F. Yanus, J. Imaging Sci. 1990, 34, 31–38; c) K. Y.
Law, Chem. Mater. 1992, 4, 605–611; d) S. H. Hwang, N. K. Kim, K. N.
Koh, S. H. Kim, Dyes Pigm. 1998, 39, 359–369.
[12] a) V. Y. Merritt, H. J. Hovel, Appl. Phys. Lett. 1976, 29, 414; b) D. L. Morel,
A. K. Ghosh, T. Feng, E. L. Stogryn, P. E. Purwin, R. F. Shaw, C. Fishman,
Appl. Phys. Lett. 1978, 32, 495; c) M. Iwamoto, S. Shidoh, Jpn. J. Appl.
Phys. 1990, 29, 2031; d) U. Mayerhçffer, K. Deing, K. Gruß, H. Braunsch-
weig, K. Meerholz, F. Wurthner, Angew. Chem. Int. Ed. 2009, 48, 8776–
8779; Angew. Chem. 2009, 121, 8934–8937; e) S. F. Vçlker, S. Uemura, M.
Limpinsel, M. Mingebach, C. Deibel, V. Dyakonov, C. Lambert, Macromol.
Chem. Phys. 2010, 211, 1098–1108; f) D. Bagnis, L. Beverina, H. Huang,
F. Silvestri, Y. Yao, H. Yan, G. A. Pagani, T. J. Marks, A. Facchetti, J. Am.
Chem. Soc. 2010, 132, 4074–4075; g) G. Wei, S. Wang, K. Sun, M. E.
Thompson, S. R. Forrest, Adv. Energy Mater. 2011, 1, 184–187; h) Y. R.
Shi, R. B. M. Hill, J. H. Yum, A. Dualeh, S. Barlow, M. Graetzel, S. R.
Marder, M. K. Nazeeruddin, Angew. Chem. Int. Ed. 2011, 50, 6619–6621;
Angew. Chem. 2011, 123, 6749–6751; i) G. Chen, H. Sasabe, Z. Wang, X.-
F. Wang, Z. Hong, Y. Yang, J. Kido, Adv. Mater. 2012, 24, 2768–2773; j) G.
Wei, X. Xiao, S. Wang, K. Sun, K. J. Bergemann, M. E. Thompson, S. R.
Forrest, ACS Nano 2012, 6, 972–978; k) K. C. Deing, U. Mayerhoffer, F.
Wurthner, K. Meerholz, Phys. Chem. Chem. Phys. 2012, 14, 8328–8334;
l) B. Stender, S. F. Volker, C. Lambert, J. Pflaum, Adv. Mater. 2013, 25,
2943–2947.
[33] M. Cossi, V. Barone, J. Chem. Phys. 2000, 112, 2427–2435.
[34] J. Tomasi, B. Mennucci, R. Cammi, Chem. Rev. 2005, 105, 2999–3093.
[35] Gaussian 09, Revision E.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Men-
nucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian,
A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, 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. Ko-
bayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyen-
gar, 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, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cio-
slowski, D. J. Fox, Gaussian (Inc, Wallingford CT), 2009.
[13] E. C. P. Smits, S. Setayesh, T. D. Anthopoulos, M. Buechel, W. Nijssen, R.
Coehoorn, P. W. M. Blom, B. de Boer, D. M. de Leeuw, Adv. Mater. 2007,
19, 734–738.
[14] a) G. Sauve, P. V. Kamat, K. G. Thomas, K. J. Thomas, S. Das, M. V. George,
J. Phys. Chem. 1996, 100, 2117–2124; b) M. Bꢆschel, A. Ajayaghosh, E.
Arunkumar, J. Daub, Org. Lett. 2003, 5, 2975–2978; c) S. F. Vçlker, M.
Renz, M. Kaupp, C. Lambert, Chem. Eur. J. 2011, 17, 14147–14163; d) J.
Chen, R. F. Winter, Chem. Eur. J. 2012, 18, 10733–10741.
[15] a) A. A. Argun, P.-H. Aubert, B. C. Thompson, I. Schwendeman, C. L.
Gaupp, J. Hwang, N. J. Pinto, D. B. Tanner, A. G. MacDiarmid, J. R. Rey-
nolds, Chem. Mater. 2004, 16, 4401–4412; b) R. J. Mortimer, D. R. Ros-
seinsky, P. M. S. Monk, Electrochromic Materials and Devices 2015 Wiley-
VCH Verlag GmbH & Co. KGaA.
[16] a) I. F. Perepichka, D. F. Perepichka, Front Matter, in Handbook of Thio-
phene-Based Materials: Applications in Organic Electronics and Photonics
2009, John Wiley & Sons, Ltd, Chichester, UK; b) P. M. Beaujuge, J. R.
Reynolds, Chem. Rev. 2010, 110, 268–320; c) L. Beverina, G. A. Pagani,
M. Sassi, Chem. Commun. 2014, 50, 5413; d) A. L. Kanibolotsky, N. J. Fin-
dlay, P. J. Skabara, Beilstein J. Org. Chem. 2015, 11, 1749–1766.
Received: March 17, 2016
Published online on && &&, 0000
&
&
Chem. Eur. J. 2016, 22, 1 – 9
www.chemeurj.org
8
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
Panchromatic squaraines: The redox
chemistry and electrochromic (see
&
Squaraine Dyes
V. Maltese,* S. Cospito, A. Beneduci,*
B. C. De Simone, N. Russo, G. Chidichimo,
R. A. J. Janssen
figure) response of a few newly synthe-
sized thienosquaraines are presented
and compared to those of a commercial
squaraine dye (see figure). These prop-
erties are strongly affected by the stabil-
ity of the radical ions formed in electro-
chemical processes. Furthermore, all of
the dyes show aggregation tendency re-
sulting in panchromatic absorption cov-
ering the whole UV/Vis spectral range.
&& – &&
Electro-optical Properties of Neutral
and Radical Ion Thienosquaraines
Chem. Eur. J. 2016, 22, 1 – 9
www.chemeurj.org
9
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ