Solvatochromism of dyes inspired in Effenberger's probe

Article abstract of DOI:10.1016/j.dyepig.2020.108757

Solvatochromic dyes have been utilized in recent decades as probes to measure the polarity of the medium. An interesting example is the Effenberger's dye (ED), which exhibits a very pronounced positive solvatochromism, being considered a dye that probes p

Full text of DOI:10.1016/j.dyepig.2020.108757

Dyes and Pigments 184 (2021) 108757
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Solvatochromism of dyes inspired in Effenberger’s probe
a
b
b
a,*
´
Carlos E.A. de Melo , Moises Domínguez , Marcos C. Rezende , Vanderlei G. Machado
a
´
Departamento de Química, Universidade Federal de Santa Catarina, UFSC, Florianopolis, SC, 88040–900, Brazil
b Facultad de Química y Biología, Universidad de Santiago, Av. B. O’Higgins, 3363, Santiago, Chile
A R T I C L E I N F O
A B S T R A C T
Keywords:
Solvatochromic dyes have been utilized in recent decades as probes to measure the polarity of the medium. An
interesting example is the Effenberger’s dye (ED), which exhibits a very pronounced positive solvatochromism,
being considered a dye that probes practically only the polarizability and dipolarity of the medium. This com-
pound is difficult to be accessed and, in addition, the synthesis of dyes capable to probe the polarizability of the
medium is a subject of interest. In view of this, six imine probes inspired in the molecular structure of ED were
synthesized and characterized. Two compounds were solvatochromic and exhibit different colors in various
solvents, while the other dyes exhibit a weak solvatochromism. Three probes present a behavior very similar to
ED, showing a positive solvatochromic behavior. The application of multiparametric equations shows that
polarizability is the most influential solvent parameter in the solvation of the dyes studied. Theoretical calcu-
lations were performed with a dye in ten different solvents, employing a continuum model to mimic solvent
effects and TD/DFT calculations with two functionals exhibiting a different degree of Hartree–Fock exchange to
estimate transition energy (ET) values. A HOMO–LUMO transition involving an internal charge transfer from the
N,N–dimethylaminophenyl electron–donor to the nitrothienyl electron–acceptor moieties of the dye was iden-
tified as the origin of the solvatochromic band. The calculated ET values reproduce qualitatively the positive
solvatochromism of the dye. The results obtained show that the easy synthesis of solvatochromic compounds,
inspired in the ED, represents an interesting possibility in the research for novel polarizability probes.
Solvatochromism
Reverse solvatochromism
Solvation
Solvatochromic dyes
Positive solvatochromism
Dipolarity/polarizability
1. Introduction
medium, being considered a dye that probes practically only the
polarizability and dipolarity of the solvent [6–11].
Solvatochromic compounds exhibit absorption bands in the visible
(vis) region and their position and/or intensity is dependent on the
nature of the solvent [1–3]. These dyes have been utilized in recent
decades as probes to measure the polarity of the medium. An impressive
For some families of solvatochromic dyes, the occurrence of negative
solvatochromism from the most polar solvents to the solvents of inter-
mediate polarity is initially verified. A reversal in the solvatochromism,
from negative to positive, is then observed with a further reduction in
the polarity of the solvent. This phenomenon, named as reverse sol-
vatochromism, is subtly verified in the classical Brooker’s merocyanine
(dye 3) [12,13], being a subject of much controversy during the last
decades [14–19]. This is because the change in the type of sol-
vatochromism occurs only in the region of low polarity solvents. Com-
pound 4 is another example of dye exhibiting reverse solvatochromism
[20].
example of
a
solvatochromic dye is the Reichardt pyr-
idinium–N–phenolate betaine 1 (Fig. 1), whose negative solvatochromic
behavior is the basis for the development of the largely known ET (30)
empirical polarity solvent scale [1,3–5]. The increase in the polarity of
the medium causes a displacement of the solvatochromic band of dye 1
toward a lower maximum wavelength (λmax) values.
The opposite behavior is found for dye 2, introduced by Effenberger
et al. [6,7]._ENREF_4 This probe exhibits a very pronounced positive
solvatochromism, with its solvatochromic band in the vis region being
More recently, a particular family of dyes of general structures 5 and
6 has been studied [21–27], with a phenolate electron–donor conju-
gated with a polynitroaryl acceptor moiety. These dyes are readily
accessible and are soluble in polar and nonpolar solvents, exhibiting a
reversal in their solvatochromism in solvents of intermediate polarity.
shifted to increasing λ
values as a response to the increase in the
polarity of the solvent. mInaxaddition to positive solvatochromism, dye 2 is
a compound that practically does not interact in a specific way with the
* Corresponding author.
E-mail address: vanderlei.machado@ufsc.br (V.G. Machado).
https://doi.org/10.1016/j.dyepig.2020.108757
Received 7 May 2020; Received in revised form 22 July 2020; Accepted 3 August 2020
Available online 11 August 2020
0143-7208/© 2020 Elsevier Ltd. All rights reserved.

C.E.A. de Melo et al.
Dyes and Pigments 184 (2021) 108757
exhibited by dye 2. The influence of the 5–nitro–2–thiophenyl or
5–nitro–2–furanyl electron–acceptors and of the dimethylamino,
methoxy, or methylthio electron–donor groups on the solvatochromism
of the systems was verified. In addition, theoretical calculations were
performed with dye 7 in ten different solvents to understand the nature
of the transition responsible for the solvatochromism of the dye and to
reproduce qualitatively its positive solvatochromism.
2. Experimental section
2.1. Materials and methods
All reagents and solvents were analytically pure and were obtained
from commercial sources (Sigma–Aldrich and Vetec). The solvents
(HPLC grade) were purified following the methodology described in the
literature [34,35]. Water used for all measurements was deionized,
boiled, and bubbled with nitrogen and kept in a nitrogen atmosphere to
avoid the presence of carbon dioxide.
NMR spectra were recorded with 200 MHz Bruker AC–200 F and
with 400 MHz Bruker Avance 400 spectrometers. Chemical shifts were
recorded in ppm with the solvent resonance as the internal standard and
data are reported as follows: chemical shift, multiplicity (s = singlet, d =
doublet, dd = double doublet), coupling constants (Hz), and integration.
IR spectra were obtained with an FT Varian 3100 spectrometer, by using
KBr pellets. High–resolution mass spectra were obtained with a Bruker
OTOF–Q II 10243 electrospray ionization–quadrupole time–of–flight
mass spectrometer (HR ESI–MS QTOF). The melting points were deter-
mined by means of DSC analysis, by using a Shimadzu DSC–50 appa-
ratus. UV–vis spectra were obtained with an Agilent Technologies Cary
60 spectrometer.
Fig. 1. Molecular structures of dyes 1–6 (TBA+ = tetra–n–butylammonium).
Compounds exhibiting a reversal in their solvatochromism, like the
compounds with the general molecular structure 5 or 6, should belong to
another category, such as class III dyes [27].
2.2. Synthesis
An analysis of the molecular structure of compounds 6 shows that the
electron–acceptor moiety of the compounds, a heteroaromatic thio-
phenyl or furanyl group, is analogous to that in compound 2. In addition,
a study made with compound 4 and related dyes [20] shows that a
change in the electron–donor group from phenolate (as in the case of
compounds 5) to N,N–dimethylaminophenyl changes their behavior
with respect to their interaction with the medium. Although a reverse
solvatochromism is verified for dye 4, it is capable of acting predomi-
nantly as probe for the polarizability of the medium, with very little
interference of specific interactions due to the hydrogen bonding of the
solvent [20]. In addition, compounds analogous to compounds 6, but
with N,N–dimethylaminophenyl groups in their molecular structure,
should be in principle easily obtained by simple condensation reactions,
different to compound 2, which is more difficult to synthesize [6,7]. It is
also important to remark that the design of compounds capable to probe
the polarizability of the medium is a subject of current interest [11,
28–33].
4–Amino–N,N–dimethylaniline was synthesized exactly as described
in literature [20]. The other amines used in the syntheses were obtained
from commercial sources. Compounds 7–12 were synthesized according
to the adapted methodology previously described [25]. The aldehyde
(0.7 mmol), the amine (1 equiv), ethanol (3 mL) previously dried with
molecular sieves (4 Å), and glacial acetic acid (2 drops) were mixed in a
round–bottomed flask. The reaction mixtures were maintained under
reflux at 78 ◦C for 1 h. After this period, the solid products obtained were
filtered off, washed with ice–cold ethanol, dried under vacuum, and
stored in vacuum desiccator over P4O10
.
N,N–Dimethyl–N’–[(1E)–(5–nitro–2–thienyl)methylene]benze-
ne–1,4–diamine (7). Compound synthesized from 5–nitro–2–thiophe
necarboxaldehyde and 4–amino–N,N–dimethylaniline. Dark red solid
(yield: 73%). M. p.: 199.2 ◦C. IR (KBr) νmax/cmꢀ 1: 3428 (intramolecular
–
hydrogen bond of the N from the C N); 2898 (C–H); 1560 and 1493
–
1
–
–
(N O); 1323 (CH ); 1162 (C–S). H NMR (200 MHz, DMSO–d ) δ/ppm:
8.84 (s, 1H); 8.033(d, 1H, J = 4.3 Hz); 7.52 (d, 1H, J = 4.3 Hz); 7.37 (d,
2H, J = 8.9 Hz); 6.78 (d, 2H, J = 8.9 Hz); 3.01 (s, 6H). 13C NMR (50 MHz,
DMSO–d6) δ/ppm: 151.0; 150.6; 150.4; 146.3; 137.3; 130.6; 129.6;
123.5; 112.3. HRMS (ESI, TOF) m/z: 276.0804 [M+H]+, calculated for
6
In view of this, herein we report the synthesis and characterization of
novel imines 7–12 (Fig. 2), inspired in the molecular structure of probe
2. The solvatochromism of the compounds was compared with that
C13H13N3O2S, 276.0801.
N,N–Dimethyl–N’–[(1E)–(5–nitro–2–furanyl)methylene]benze-
ne–1,4–diamine (8). Compound synthesized from 5–nitro–2–fural
dehyde and 4–amino–N,N–dimethylaniline. Dark red solid (yield: 75%).
M. p.: 180.0 ◦C. IR (KBr) νmax/cmꢀ 1: 3428 (intramolecular hydrogen
–
–
–
–
bond of the N from the C N); 2900 (C–H); 1619 (C N); 1507 and 1472
(N O); 1352 (CH ); 1256 (C–O). 1H NMR (200 MHz, acetone–d6)
–
–
3
δ/ppm: 8.58 (s, 1H); 7.62 (d, 1H, J = 3.8 Hz); 7.40 (d, 2H, J = 8.9 Hz);
7.21 (d, 1H, J = 3.8 Hz); 6.78 (d, 2H, J = 8.9 Hz); 3.02 (s, 6H). 13C NMR
(50 MHz, DMSO–d6) δ/ppm: 166.2; 153.9; 150.0; 140.3; 137.4; 128.9;
122.9; 115.1; 114.3; 111.4. HRMS (ESI, TOF) m/z: 260.1033 [M+H]+,
calculated for C13H13N3O3, 260.1030.
Fig. 2. Molecular structures of dyes 7–12.
4–Methoxy–N–[(1E)–(5–nitro–2–thienyl)methylene]aniline (9).
2

C.E.A. de Melo et al.
Dyes and Pigments 184 (2021) 108757
Compound synthesized from 5–nitro–2–thiophenecarboxaldehyde and
all constants were obtained through fitting of least–square curves using
the program ORIGIN 8.5.
◦
p–anisidine. Bright red–orange solid (yield: 87%). M. p.: 155.6 C. IR
(KBr) νmax/cmꢀ 1: 3422 (intramolecular hydrogen bond of the N from the
All theoretical calculations were performed with the ORCA 4.2.1
software [36].
–
–
–
C
N); 3096 (C–H); 1609 (C N); 1535 and 1493 (N–O); 1329 (CH );
3
–
1289 and 1244 (C–O); 1191 (C–S). 1H NMR (200 MHz, DMSO–d6)
δ/ppm: 8.71 (s, 1H); 7.96 (d, 1H, J = 4.3 Hz); 7.47 (d, 1H, J = 4.3 Hz);
7.34 (d, 2H, J = 9.0 Hz); 6.99 (d, 2H, J = 9.0 Hz); 3.82 (s, 1H). 13C NMR
(50 MHz, DMSO–d6) δ/ppm: 159.1; 150.5; 149.3; 141.9; 131.0; 130.5;
123.3; 114.6; 55.4; 18.5. HRMS (ESI, TOF) m/z: 263.0487 [M+H]+,
calculated for C12H10N2O3S, 263.0485.
The
geometry
of
dye
7
was
optimized
at
the
Tao–Perdew–Staroverov–Scuseria (TPSS) density–functional level [37],
employing the triple–ξ Karlsruhe basis set (def2–TZVP) [38]. Dispersion
forces were accounted for with Grimme’s D3 correction [39]. Fre-
quencies were calculated for all molecules to ensure energy minima.
Solvent effects were mimicked with the conductor–like polarizable
continuum model (CPCM) approach [40]. Transition energies in each
solvent were then obtained from time–dependent density functional
theory (TD/DFT) calculations on the optimized geometries at the same
level of theory, with the pure functional (PBE) [41], the range–separated
4–Methoxy–N–[(1E)–(5–nitro–2–furanyl)methylene]aniline
(10). Compound synthesized from 5–nitro–2–furaldehyde and
p–anisidine. Bright yellow solid (yield: 80%). M. p.: 123.2 ◦C. IR (KBr)
νmax/cmꢀ 1: 3424 (intramolecular hydrogen bond of the N from the
–
–
–
–
C
N); 3157 (C–H); 1619 (C N); 1529 and 1501 (N–O); 1354 (CH );
hybrid functional ω–B97X–D3 [42], and the def2–TZVP basis set [38].
1297 and 1244 (C–O). 1H NMR (200 MHz, DMSO–d6) δ/ppm: 8.64 3(s,
1H); 7.81 (d, 1H, J = 3.9 Hz); 7.42 (d, 2H, J = 8.8 Hz); 7.35 (d, 1H, J =
3.9 Hz); 7.01 (d, 2H, J = 8.8 Hz); 3.79 (s, 1H). 13C NMR (50 MHz,
DMSO–d6) δ/ppm: 159.2; 153.3; 152.1; 145.0; 142.4; 123.2; 116.9;
114.6; 114.3; 55.4. HRMS (ESI, TOF) m/z: 247.0710 [M+H]+, calcu-
lated for C12H10N2O4, 247.0713.
4. Results and discussion
4.1. Synthesis and characterization
Compounds 7–12 were synthesized following the methodology
adapted from de Melo et al. 25. The corresponding Schiff bases were
obtained through the condensation reaction of the corresponding amine
with 5–nitro–2–thiophenecarboxaldehyde or 5–nitro–2–furaldehyde in
the presence of dry ethanol and glacial acetic acid, with the consequent
elimination of water (Scheme 1). Novel compounds 7–12 were fully
characterized using IR, 1H NMR, 13C NMR, HRMS, and DSC techniques
(Figs. S2–S31) and the products were obtained with yields ranging from
73 to 87%. The results show that all compounds were obtained with the
required purity for the UV–vis spectrophotometric studies to be carried
out.
4–Methylthio–N–[(1E)–(5–nitro–2–thienyl)methylene]aniline
(11). Compound synthesized from 5–nitro–2–thiophenecarboxaldehyde
and 4–(methylthio)aniline. Bright red solid (yield: 77%). M. p.: 116.7
◦C. IR (KBr) νmax/cmꢀ 1: 3424 (intramolecular hydrogen bond of the N
–
–
–
from the C N); 1605 (C N); 1537 e 1509 (N–O); 1336 (CH ); 1195
–
(C–S). 1H NMR (400 MHz, CDCl3) δ/ppm: 8.55 (s, 1H); 7.90 (d,31H, J =
4.2 Hz); 7.35 (d, 1H, J = 4.2 Hz); 7.28 (dd, 2H, J1 = 2.0 Hz e J2 = 8.7 Hz);
7.23 (dd, 2H, J1 = 2.2 Hz e J2 = 8.7 Hz); 2.51 (s, 3H). 13C NMR (50 MHz,
DMSO–d6) δ/ppm: 152.2; 148.8; 145.9; 138.0; 131.6; 130.4; 126.5;
122.3; 14.7. HRMS (ESI, TOF) m/z: 279.0259 [M+H]+, calculated for
C12H10N2O2S2, 279.0256.
4–Methylthio–N–[(1E)–(5–nitro–2–furanyl)methylene]aniline
(12). Compound synthesized from 5–nitro–2–furaldehyde and 4–
(methylthio)aniline. Orange solid (yield: 75%). M. p.: 102.0 ◦C. IR (KBr)
νmax/cmꢀ 1: 3424 (intramolecular hydrogen bond of the N from the
4.2. Solvatochromic studies
Fig. 3 shows solutions and UV–vis spectra for compounds 7 (A) and 8
(B) in solvents of different polarities, which show that these dyes are
solvatochromic, presenting different solution colors in solvents with
different polarity. By comparison, compounds 9–12 exhibit a weaker
solvatochromism (Figs. S32 and S33). The solvatochromic bands
observed in the visible region of the spectrum of compounds 7–12 are
–
–
–
–
C
N); 3073 (C–H); 1619 (C N); 1515 and 1493 (N–O); 1352 (CH );
1258 (C–S). 1H NMR (400 MHz, CDCl3) δ/ppm: 8.41 (s, 1H); 7.42 (d, 13H,
J = 3.8 Hz); 7.28 (d, 2H, J = 9.1 Hz); 7.22 (d, 2H, J = 9.1 Hz); 7.18 (d,
1H, J = 3.8 Hz); 2.51 (s, 3H). 13C NMR (50 MHz, DMSO–d6) δ/ppm:
153.0; 152.2; 146.6; 146.4; 138.1; 126.6; 122.2; 117.6; 114.6; 14.7.
HRMS (ESI, TOF) m/z: 263.0483 [M+H]+, calculated for C12H10N2O3S,
263.0485.
the result of electronic transitions of the
π
–
π
* type, with a charge
transfer from the electron–donor moiety (N,N–dimethylamino, methoxy
or
methylthio
groups)
to
the
electron–acceptor moiety
(2–nitrothiophenyl or 2–nitrofuranyl). Taking compound 7 as an
example, the λmax of the solvatochromic band measured in n–hexane
2.3. UV–vis measurements
appears at 464 nm, while in diethyl ether, the band is displaced at λ
max
= 476 nm (Δλmax = +12 nm). In ethanol and DMSO, the λmax is verified
A stock solution with concentration of 7.0 × 10ꢀ 3 mol Lꢀ 1 for each
at 487 nm and 511 nm, respectively (Δλ
= +24 nm). Compounds 8
and 11 show similar behavior, while themoatxher compounds show only a
very small variation in maximum absorption wavelengths in solvents
with different polarities.
compound was prepared in acetone. 24 μL of this stock solution were
transferred to 5 mL volumetric flasks and after the evaporation of
acetone the compound was dissolved in pure solvents. The final con-
centration of the resulting solutions was 4.0 × 10ꢀ 3 mol Lꢀ 1. Then, the
UV–vis spectra were collected at 25 ◦C. The maxima of the UV–vis
spectra were calculated from the first derivative of the absorption
spectrum, with a precision of ±0.5 nm, and the reproducibility was
verified through the determination of two spectra for each dye in each
pure solvent. The maximum wavelength (λmax) values thus obtained
were used to determine the ET (dye) values in each solvent, given with a
precision of ±0.1 kcal molꢀ 1, through Eq. (1) [1,5].
The UV–vis spectra for each compound in various solvents were used
to obtain, through the first derivative, the λmax values of the sol-
vatochromic bands, which were used to calculate the corresponding ET
(dye) values in kcal molꢀ 1, using Eq. (1) (Table 1).
Fig. 4 shows the plots of the ET (dye) obtained for compounds 7–12 in
each of the solvents studied, as a function of ET (30). Compounds 7, 8,
and 11 exhibit a positive solvatochromic behavior. Taking compound 7
as an example, the solvatochromic band has a maximum at 464 nm [ET
(7) = 61.6 kcal molꢀ 1] in n–hexane, while in DMSO the λmax = 511 nm
[ET (7) = 56.0 kcal molꢀ 1]. Thus, a reduction in the ET (7) value by 5.6
kcal molꢀ 1 occurs following an increase in the polarity of the medium,
leading to a bathochromic change of Δλmax = +47 nm, which is char-
acteristic of positive solvatochromism. For compound 8, considering the
λmax values in n–hexane (444 nm) and in benzyl alcohol (496 nm), a
Δλmax = +52 nm was verified.
ET (dye) / (kcal m olꢀ 1) = 28590/λm ax (nm )
(1)
3. Calculation methods
For the regression analyses of the experimental transition energies,
3

C.E.A. de Melo et al.
Dyes and Pigments 184 (2021) 108757
Scheme 1. Route for the synthesis of compounds 7–12 (see Fig. 2).
Fig. 3. Solutions and UV–vis spectra of dyes 7 (A) and 8 (B) in (a) n–hexane, (b) diethyl ether, (c) ethanol, and (d) DMSO.
It was also verified that in water, compounds 7 and 8 exhibit an
anomalous behavior (red squares in Fig. 4), which does not follow the
pattern presented in the other solvents. Therefore, the later studies using
these compounds were carried out disregarding water. Probes 9, 10, and
12 exhibited a peculiar solvatochromism, because their experimental
data ploted as a function of ET (30) did not show any relationship.
Dye 2 is considerably more solvatochromic than compounds 7–12,
exhibiting a Δλmax = +97 nm between the solvents DMSO and n–hexane.
When considering formamide, which is a solvent that was not used in the
that of probe 2.
ET (dye) = m + n ET (2)
(2)
Data show that the ET values for dyes 7, 8, and 11 match reasonably
well with those of standard 2 (r2 > 0.78), while the other dyes provide r2
< 0.62 (Table S1). Positive values of m (>28) are obtained for the dyes
studied, indicating that the solvatochromic band of these probes is
hypsochromically shifted in comparison with the vis band of standard
probe 2. The analysis of n values show that all dyes studied are sol-
vatochromically less sensitive than dye 2, with the best results being
verified for dyes 7 (n = 0.50), 8 (n = 0.58), and 11 (n = 0.44).
study of compounds 7–12, the variation becomes even larger (Δλ
=
max
+111 nm). The most solvatochromic of compounds 7–12 is dye 8, with a
52 nm variation between the extremes (longer wavelength – shorter
wavelength).
4.3. Multiparametric analysis
Despite the difference in the extent of solvatochromism, when
considering the same solvents, the plots of ET (dye) as a function of ET
(30) for compounds 7 and 8 are very similar to dye 2 (Fig. S34), with
emphasis for dye 7, which has the same electron–acceptor
(5–nitro–2–thiophenyl) and electron–donor (dimethylamino) moieties.
This fact shows that the structural similarities between the compounds
are reflected in their interactions with the medium.
The experimental ET (dye) values for compounds 7–12 in pure sol-
vents were analyzed using the Kamlet–Abboud–Taft (KAT) [43,44] and
´
Catalan [30] multiparametric equations. The KAT approach uses Eq. (3),
where α, β, and π* are parameters that represent the solvent hydro-
gen–bond donor (HBD) acidity, hydrogen–bond acceptor (HBA) basic-
ity, and solvent dipolarity/polarizability, respectively, while δ is a
Fig. 5 shows plots of ET values for dyes 7–12 as a function of ET (2).
This type of plot is used to verify the similarities of the probes studied
with respect to the given standard probe 2 [24–27]. Data were treated
using Eq. (2), where m measures the average shift of the λmax value for a
solvatochromic dye with respect to standard 2 while n compares the
solvatochromic sensitivity of the dye to solvent polarity changes with
´
polarizability correction term for the solvent. The Catalan approach [30]
requires the use of Eq. (4), where specific solvent parameters SA and SB
represent the solvent HBD acidity and HBA basicity, respectively, while
SP and SdP are the nonspecific solvent parameters polarizability and
dipolarity, respectively. In these equations, ET (dye)0 represents the ET
(dye) value in the gas phase and a, b, c, d, and s are regression
4

C.E.A. de Melo et al.
Dyes and Pigments 184 (2021) 108757
Table 1
ET (30) and ET (dye) values given in kcal molꢀ 1 for compounds 2 and 7–12 for 29 solvents.
Solvent
ET (30)a
2b
7
8
9
10
11
12
Cyclohexane
n–Hexane
30.9
31.0
33.9
34.5
37.4
38.1
38.2
39.1
40.6
40.7
41.3
42.2
42.9
43.2
43.3
45.1
45.6
47.1
47.7
48.1
48.4
49.1
49.7
50.4
50.7
51.9
55.4
56.3
63.1
60.6
61.3
56.3
57.6
54.9
60.7
61.6
58.6
60.1
57.9
58.8
58.5
57.4
56.1
57.3
57.2
58.1
56.6
56.7
59.0
56.0
58.2
58.6
58.5
58.7
58.7
58.5
58.3
56.1
58.3
58.7
58.6
56.6
62.3
63.5
64.5
61.4
63.2
61.3
62.3
61.9
59.2
58.3
59.1
59.1
61.4
59.2
59.4
62.1
58.1
61.0
61.4
61.4
61.2
61.8
61.1
57.7
61.1
61.5
61.5
61.5
58.8
63.9
69.9
70.1
68.7
70.1
69.2
70.1
69.4
69.1
69.2
68.7
68.7
69.9
68.4
68.6
70.1
67.9
69.9
69.7
69.4
69.2
69.9
69.2
69.9
68.2
69.7
69.7
70.1
69.9
70.6
73.3
73.7
73.1
73.1
72.4
72.9
72.8
71.7
70.9
71.3
71.1
72.9
71.3
70.9
72.8
70.6
72.8
72.8
72.6
72.4
72.9
72.8
72.8
70.6
72.8
72.9
73.1
72.2
72.9
71.5
71.8
67.6
69.4
68.4
69.7
70.8
71.5
70.2
72.2
71.7
72.4
Toluene
Diethyl ether
THF
Ethyl acetate
1,2–Dimethoxyethane
Trichloromethane
Acetophenone
Dichloromethane
1,2–Dichloroethane
Acetone
55.7
c
68.7
71.7
d
d
53.9
c
67.3
67.8
67.4
68.9
67.6
67.4
69.2
66.8
68.9
68.6
68.2
68.1
68.9
68.6
68.4
67.0
68.7
69.1
69.4
67.8
66.5
70.4
70.1
69.9
72.0
70.2
70.2
71.5
69.4
71.7
71.5
70.8
70.8
71.7
71.5
71.1
68.9
71.5
71.7
71.8
70.9
71.5
53.4
53.3
54.1
c
DMA
DMF
52.1
55.7
50.6
2–Methylpropan–2–ol
DMSO
Acetonitrile
Butan–2–ol
Decan–1–ol
Octan–1–ol
Propan–2–ol
Pentan–1–ol
Butan–1–ol
Benzyl alcohol
Propan–1–ol
Ethanol
53.6
c
c
c
55.4
c
55.3
c
c
55.0
Methanol
54.5
c
Ethane–1,2–diol
c
Water
a
b
c
Values obtained from Reichardt [1].
Values obtained from Effenberger et al. [6,7].
Value not found.
d
Insoluble.
Fig. 4. ET (dye) value as a function of ET (30) for dyes 7–12.
coefficients that reflect the relative importance of the solvent parame-
Tables 2 and Table S2 show the contributions of solvent properties to
´
ters in terms of ET (dye).
the ET (dye) values for compounds 7–12, using the Catalan and KAT
equations, respectively. Table 2 also shows the results obtained when
ET (dye) = ET (dye)0 + a
α
+ bβ + s (
π* + dδ)
(3)
(4)
applying Eq. (4) to the literature data referring to dyes 2 [6,7], 13, and
´
14 (Fig. 6). Compound 13 was proposed by Catalan as a probe for the
ET (dye) = ET (dye)0 + aSA + bSB + cSP + dSdP
polarizability of the medium, being used as the descriptor of Eq. (4)
5

C.E.A. de Melo et al.
Dyes and Pigments 184 (2021) 108757
Fig. 5. Comparison between ET (dye) and ET (2) for compounds 7–12.
Table 2
´
Regression coefficients a, b, c, and d obtained from the Catalan multiparametric analysis through the treatment of ET (dye) values for dyes 1, 2, and 7–14 in pure
solvents.
Dye
ET (dye)0
a
b
c
d
N
r
S.D.
1a,b
30.3
70.1
68.8
74.5
74.7
79.8
78.6
78.2
68.5
70.3
24.0
4.14
1.12
9.44
28
18
28
28
28
28
28
28
38
38
0.97
0.99
0.99
0.98
0.86
0.93
0.93
0.89
1.00
0.98
1.61
0.32
0.15
0.30
0.34
0.35
0.48
0.43
0.002
0.10
2b
0.01
0.06
ꢀ 14.6
ꢀ 12.1
ꢀ 16.5
ꢀ 7.14
ꢀ 9.40
ꢀ 11.8
ꢀ 10.5
ꢀ 10.1
ꢀ 11.1
ꢀ 7.32
ꢀ 2.89
ꢀ 3.06
ꢀ 0.22
ꢀ 1.22
ꢀ 1.61
ꢀ 0.29
0.001
ꢀ 0.03
7c
ꢀ 0.03
ꢀ 1.04
0.74
ꢀ 0.35
0.34
8c
9c
ꢀ 0.41
ꢀ 0.25
ꢀ 1.21
0.15
10c
11c
12c
13d
14e
0.61
0.26
ꢀ 0.38
ꢀ 0.005
0.17
0.002
ꢀ 0.007
a
b
c
Using ET (30) values from Table 1 [1].
Using ET (2) values from Table 1 [6,7].
Excluding water.
d
e
´
Using data from Catalan, 2009 [30].
Using data from El Seoud et al., 2013 [31].
[30]. Later, El Seoud et al. proposed the use of β–carotene (14) to
neglected [33].
determine the polarizability of the medium due to the structural simi-
Eq. (4) is better applied than Eq. (3) to the studied compounds, since
´
larity of the latter with probe 13 [31,32]. Catalan argued that the sol-
provided higher correlation coefficients (r) and lower values of standard
deviation (S.D.). The analysis of the data obtained with both equations
show that the polarizability represents the most influential solvent
descriptor in the solvation of dyes 7–12, given the larger magnitude of
vatochromism of β–carotene is governed predominantly by the
polarizability of the medium, but the contribution of other sol-
ute/solvent interactions, such as acidity and dipolarity cannot be
6

C.E.A. de Melo et al.
Dyes and Pigments 184 (2021) 108757
and the highest standard deviations are obtained.
The results also show that for compounds 7–12 the solvent’s dipo-
larity parameter is the second most important factor for the solvation of
compounds, since the correlation coefficients have a small decrease
when this parameter is disregarded in the application of Eq. (4). When
dealing with compound 12 (Table S3), the results obtained from
applying Eq. (4), excluding one parameter at a time, confirm that we are
indeed facing a solvatochromic dye that probes mainly the polarizability
of the medium, considering that the correlation coefficient is not
affected when the other parameters are disregarded in the regression
analysis. In addition, the ET (12) values match reasonably well with SP,
with r2 > 0.779 (Fig. S35; Table S4), which is a value close to that ob-
tained when all parameters of Eq. (4) are utilized (r2 > 0.89). This result
is interesting because it points to the possibility of designing easily
accessible polarizability probes with an entirely different skeleton from
other polarizability probes, such as the polyenes 13 and 14.
Fig. 6. Molecular structures of compounds 13 and 14.
their correlation coefficients when Eq. (4) is applied.
Considering the data generated with Eq. (4), it is also important to
note that, in general, the other solvent parameters have only little in-
fluence on the dye solvation and that, although small, they should have
similar importance, considering that the magnitude of all values ob-
tained is quite similar and does not follow a pattern for each regression
coefficient, considering different dyes. An exception is the sensitivity of
compound 12, showing that the regression coefficients related to HBD
acidity, HBA basicity, and dipolarity are close to zero and can be
neglected. Thus, dye 12 probes practically only the polarizability of the
medium.
In general, probes 7–12 are poorly sensitive to the medium acidity
and basicity and much more sensitive to the medium dipolarity and
polarizability, being more sensitive to solvent polarizability. In partic-
ular, compounds 7 and 12 are practically not sensitive to the HBD
acidity and HBA basicity of the medium, both compounds being very
sensible to the polarizability in comparison with the dipolarity of the
medium: the c/d ratios are 4.2 and 32.4 for dyes 7 and 12, respectively.
The results shown here also illustrate the importance of electron donor
groups to tailor the level of interaction of the probes with the medium.
The combination of electron donating capacity and greater polariz-
ability of the N,N–dimethylamino and methylthio groups, in comparison
with the methoxy group, seems to be a determining factor to explain the
extent of solvatochromism exhibited by the probes.
Data obtained from applying Eq. (4) show that dye 2 is also sensitive
to the HBD acidity of the medium, but its sensitivity is low. Therefore, it
is possible to say that dye 2 interacts in a specific way with the medium,
but with little intensity [6,7]. Furthermore, when comparing the values
of the regression coefficients generated for dyes 2, 7, and 8, it is found
that their interactions with the medium are quite similar, but com-
pounds 7 and 8 interact less strongly with the HBD acidity and the HBA
basicity of the solvents, considering that the magnitude of the regression
coefficient related to these parameters is lower, especially for dye 7.
Regarding the signs obtained for each regression coefficient, all or
almost all values are negative for compounds 2, 7, 8, and 11. This is an
intrinsic characteristic for results of applying Eq. (4) for compounds that
exhibit positive solvatochromic behavior. For compounds 9 and 10, the
regression coefficients a, related to HBD acidity, have a positive value
whereas the others have a negative value. However, the values of co-
efficients a are very low, which does not constitute a reverse sol-
vatochromism, but a positive solvatochromism. Compound 12 has
almost all negative signs, only the coefficient b related to HBA basicity
being positive.
4.4. Theoretical calculations
In search of theoretical support to the spectral data obtained for
solvatochromic dyes 7–11, compound 7 was chosen for theoretical
studies because of its analogy with reference compound 2, evident from
the good correlation of its solvatochromic ET (7) values with those of
reference 2 (Fig. 5). Our theoretical experience with Effenberger’s dye 2,
which shows a positive solvatochromism that could be qualitatively
reproduced with the aid of implicit solvation models coupled with TD/
DFT methods [11], led us to employ the same methodology for the
calculation of the absorption energies of the solvatochromic band of 7.
Structure 7 was first optimized in ten different solvents, employing a
DFT/TPSS/def2–TZVP method [38] and the CPCM approach [40] as an
implicit model to mimic solvent effects.
In order to confirm that the polarizability/dipolarity of the solvents
is the predominant factor in the solvation of the dyes, Eq. (4) was
applied excluding one parameter at a time. The results obtained for
compounds 1, 2, 7, and 8 are compiled in Table 3 and for compounds
9–12 are listed in Table S3. These data confirm that the solvent’s
polarizability is the most influential parameter for the solvation of
compounds 7–12, since by excluding it from the calculation with the
Fig. 7 reproduces its HOMO and LUMO densities calculated in
DMSO. The solvatochromic band of the dye is associated with an in-
ternal charge–transfer transition from the electron–donor N,
N–dimethylaminophenyl to the electron–acceptor 5–nitrothienyl group
through an imino bridge. This transition is solvent–dependent, as can be
seen by the values of ET (7) calculated in ten different solvents of
´
Catalan multiparametric equation, the lowest correlation coefficients
Table 3
increasing dielectric permittivity (
ε), listed in Table 4. ET (7) values were
´
Influence of each solvent parameter in the Catalan multiparametric analysis on
obtained by TD/DFT calculations on the optimized structures in each
the fitting of data for dyes 1, 2, 7, and 8 (excluding water).
solvent, employing two different functionals, PBE [41] and ω–B97X–D3
Dye
ET (dye)0
a
b
c
d
N
r
S.D.
[42]. For the sake of comparison, experimental ET (7) values in the same
solvents are also reproduced in Table 4.
1
30.3
29.1
26.8
24.0
–
25.9
4.14
10.7
6.94
1.12
0.81
12.3
9.40
12.2
–
28
28
28
0.97
0.74
0.91
1.61
4.82
2.85
TD/DFT calculations offer the advantage of being rather inexpensive
and providing transition energies with reasonable errors [45]. A major
shortcoming of this rather popular method is its poor ability to repro-
duce accurate charge–transfer transitions. In addition, errors vary
widely, depending on the functional employed in the calculation. This
had been observed by us in a recent paper, where the effectiveness of
continuum models to mimic solvent effects was evaluated for three dyes
with a solvatochromic behavior that was strongly, or solely dependent
on the medium polarizability and dipolarity [11].
2
7
8
70.1
60.1
77.0
0.01
0.06
ꢀ 14.6
–
ꢀ 28.4
ꢀ 7.32
ꢀ 8.98
–
18
18
18
0.99
0.94
0.75
0.32
0.97
1.89
2.26
ꢀ 1.50
ꢀ 4.03
ꢀ 3.36
68.8
64.4
69.9
ꢀ 0.03
ꢀ 0.01
ꢀ 0.61
ꢀ 0.35
0.80
ꢀ 12.1
ꢀ 2.90
ꢀ 4.03
–
28
28
28
0.99
0.75
0.84
0.15
0.87
0.84
–
ꢀ 1.20
ꢀ 15.5
74.5
63.0
75.6
ꢀ 1.04
ꢀ 1.01
ꢀ 1.67
0.34
16.5
–
ꢀ 20.1
ꢀ 3.06
ꢀ 4.62
–
28
28
28
0.98
0.73
0.88
0.30
1.21
0.83
1.92
Traditionally regarded as non–specific solvent properties, the vari-
ation of the medium polarizability and dipolarity should be adequately
ꢀ 0.56
7

C.E.A. de Melo et al.
Dyes and Pigments 184 (2021) 108757
100% long–range HF exchange [42]. The results of the present study
reinforce our observations that functionals with little or no HF exchange
are less effective in reproducing the positive solvatochromism of dipolar
and polarizable dyes.
5. Conclusions
Dyes 7–11 were synthesized and characterized. Compounds 7 and 8
are solvatochromic and therefore exhibit different colors in various
solvents, while in comparison dyes 9–12 exhibit only a weak sol-
vatochromism. Probes 7, 8, and 11 present a behavior very similar to
Effenberger’s dye (2), showing a positive solvatochromic behavior. The
application of multiparametric equations shows that polarizability is the
most influential solvent parameter in the solvation of the dyes studied.
´
In addition, the multiparametric analysis utilizing the Catalan approach
confirms the similarity of dyes 7, 8, and 11 with dye 2 concerning the
interactions that the dyes experience with the medium. In addition, dye
12 is an excellent probe for the polarizability of the medium since it is
not sensitive to any other parameter of the solvent. Theoretical calcu-
lations were performed with dye 7 in ten different solvents, employing a
continuum model to mimic solvent effects and TD/DFT calculations
with two functionals exhibiting a different degree of Hartree–Fock
Fig. 7. Frontier molecular orbitals of dye 7 obtained with a DFT/
def2–TZVP method (CPCM = DMSO).
ω–B97X–D3/
described by a continuum model. Calculations with a TD/DFT method in
ten solvents and employing eleven different functionals showed that this
is not true. Depending on the employed functional, the calculated
transition energies do not only depart from the experimental values,
when employing a continuum model, but also yield opposite sol-
vatochromic trends. The use of molecular simulations with the intro-
duction of explicit solvent molecules in the calculations yields
significantly better results [11].
The results of the present study confirm these findings. Table 4 shows
that the differences between the calculated and experimental ET (7)
values in the ten solvents were in the range of 0.24–0.37 eV, with an
average value of 0.26 eV. This average value is thus within the range of
0.2–0.4 eV reported by Jacquemin et al. for errors by TD/DFT calcula-
tions [45]. In addition, the two methods yield opposite predictions
regarding the solvatochromism of 7. This is readily seen by inspection of
Fig. 8, where calculations employing the
ω–B97X–D3/def2–TZVP
method yield a positive solvatochromism for dye 7, in agreement with
its behavior and with that of its analog 2. An opposite trend is predicted
by the PBE/def2–TZVP method, which thus departs also qualitatively
from the behavior of dye 7.
Fig. 8. Transition energies of dye 7 in ten different solvents, plotted against the
experimental transition energies of reference dye 2 [6,7]. Experimental ET (7)
values (black circles) are compared with calculated ET (7) values by the
Following our previous conclusions [11], the different performance
of the two methods can be attributed to the different degrees of long-
–range Hartree–Fock (HF) exchange present in the calculations. PBE is a
method completely devoid of HF exchange [41], whereas the
PBE/def2–TZVP (red circles) and the
ω–B97X–D3/def2–TZVP (green circles)
methods. (For interpretation of the references to color in this figure legend, the
reader is referred to the Web version of this article.)
ω
–B97X–D3/def2–TZVP method comprises nearly 20% short–range and
Table 4
Solvent–dependent transition energies of dye 7, calculated by CPCM in ten solvents of increasing dielectric permittivity (
ε
), with two different TD/DFT methods,
employing the PBE/def2–TZVP and the
Solvent (
ω
–B97X–D3/def2–TZVP functionals.
Calculated ET (7) valueb
PBE
a
b,c
ε
)
Exp. ET (7) valueb
ΔET
ω
–B97X–D3
Cyclohexane (2.02)
Toluene (2.38)
66.18 (2.87)
65.86 (2.86)
66.64 (2.89)
66.96 (2.90)
66.96 (2.90)
67.59 (2.93)
67.43 (2.92)
67.59 (2.93)
67.59 (2.93)
66.96 (2.90)
68.73 (2.98)
67.11 (2.91)
64.83 (2.81)
64.10 (2.78)
63.53 (2.76)
62.97 (2.73)
62.84 (2.72)
62.84 (2.72)
62.56 (2.71)
61.62 (2.67)
60.7 (2.63)
58.6 (2.54)
57.4 (2.49)
57.9 (2.51)
57.3 (2.48)
58.1 (2.52)
58.7 (2.55)
58.6 (2.54)
58.2 (2.53)
56.0 (2.43)
8.03 (0.35)
8.52 (0.37)
7.42 (0.32)
6.23 (0.27)
6.24 (0.28)
4.86 (0.21)
4.13 (0.17)
4.25 (0.18)
4.33 (0.18)
5.67 (0.24)
Trichloromethane (4.81)
THF (7.25)
Dichloromethane (9.08)
Acetone (20.49)
Ethanol (24.3)
Methanol (32.63)
Acetonitrile (36.6)
DMSO (47.0)
a
b
c
Permittivity constants used in the calculations are given between brackets.
In kcal molꢀ 1 and, between brackets, in eV.
Error difference between calculated (
ω
–B97X–D3/def2–TZVP) and experimental values. Conversion factors: 1 kcal molꢀ 1 = 4.2 kJ molꢀ 1; 1 eV = 96 kJ molꢀ 1
8

C.E.A. de Melo et al.
Dyes and Pigments 184 (2021) 108757
[11] Mera–Adasme R, Rezende MC, Dominguez M. On the physical–chemical nature of
solvent polarizability and dipolarity. Spectrochim Acta, Part A 2020;229. https://
doi.org/10.1016/j.saa.2019.118008. 118008.
exchange to estimate transition energies. A HOMO–LUMO transition
involving
an
internal
charge
transfer
from
the
N,
N–dimethylaminophenyl electron–donor to the nitrothienyl electro-
n–acceptor group was identified as the origin of the solvatochromic
band of 7. Although with an average error of 0.26 eV from the experi-
mental transition energies, the calculated ET (7) values reproduce
qualitatively the positive solvatochromism of this dye in ten solvents.
Thus, the study reported here illustrates the potential of new sol-
vatochromic compounds inspired in the Effenberger’s dye, with easy
synthetic access, for probing the polarizability of microenvironments.
[12] Brooker LGS, Keyes GH, Heseltine DW. Color and constitution. XI.1 Anhydronium
bases of p–hydroxystyryl dyes as solvent polarity indicators. J Am Chem Soc 1951;
73:5350–6. https://doi.org/10.1021/ja01155a097.
[13] Brooker LGS, Keyes GH, Sprague RH, VanDyke RH, VanLare E, VanZandt G, et al.
Studies in the cyanine dye series. XI.1 the merocyanines. J Am Chem Soc 1951;73:
5326–32. https://doi.org/10.1021/ja01155a097.
[14] Benson HG, Murrell JN. Some studies of benzenoid–quinonoid resonance .2. Effect
of solvent polarity on structure and properties of merocyanine dyes. J Chem Soc
Faraday Trans II 1972;68:137–43. https://doi.org/10.1039/f29726800137.
[15] Botrel A, le Beuze A, Jacques P, Strub H. Solvatochromism of a typical
merocyanine dye. A theoretical investigation through the CNDO/SCI method
including solvation. J Chem Soc, Faraday Trans 2 1984;80:1235–52. https://doi.
org/10.1039/f29848001235.
Author contribution statement
[16] Jacques P. On the relative contributions of nonspecific and specific interactions to
the unusual solvatochromism of a typical merocyanine dye. J Phys Chem 1986;90:
5535–9. https://doi.org/10.1021/j100280a012.
Carlos E. A. de Melo: methodology, investigation, writing – original
´
draft; Moises Domínguez: conceptualization, methodology, investiga-
[17] Cavalli V, da Silva DC, Machado C, Machado VG, Soldi V. The
fluorosolvatochromism of Brooker’s merocyanine in pure and in mixed solvents.
J Fluoresc 2006;16:77–86. https://doi.org/10.1007/s10895–005–0053–9.
[18] Murugan NA, Kongsted J, Rinkevicius Z, Agren H. Demystifying the
solvatochromic reversal in Brooker’s merocyanine dye. Phys Chem Chem Phys
2011;13:1290–2. https://doi.org/10.1039/c0cp01014f.
tion, writing–original draft; Marcos C. Rezende: conceptualization,
methodology, writing–original draft; Vanderlei G. Machado: conceptu-
alization, methodology, supervision, funding acquisition, project
administration, writing–original draft, and writing–review & editing.
[19] Silva DL, Murugan NA, Kongsted J, Agren H, Canuto S. Self–aggregation and
optical absorption of stilbazolium merocyanine in chloroform. J Phys Chem B
2014;118:1715–25. https://doi.org/10.1021/jp411178h.
Declaration of competing interest
[20] de Melo CEA, Nandi LG, Domínguez M, Rezende MC, Machado VG. Solvatochromic
behavior of dyes with dimethylamino electron–donor and nitro electron–acceptor
groups in their molecular structure. J Phys Org Chem 2015;28:250–60. https://doi.
org/10.1002/poc.3402.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[21] Nandi LG, Facin F, Marini VG, Zimmermann LM, Giusti LA, Silva R, et al.
Nitro–substituted 4–[(phenylmethylene)imino]phenolates: solvatochromism and
their use as solvatochromic switches and as probes for the investigation of
preferential solvation in solvent mixtures. J Org Chem 2012;77:10668–79. https://
doi.org/10.1021/jo301890r.
Acknowledgements
[22] Stock RI, Nandi LG, Nicoleti CR, Schramm ADS, Meller SL, Heying RS, et al.
Synthesis and solvatochromism of substituted 4–(nitrostyryl)phenolate dyes. J Org
Chem 2015;80:7971–83. https://doi.org/10.1021/acs.joc.5b00983.
[23] Stock RI, Schramm ADS, Rezende MC, Machado VG. Reverse solvatochromism in
solvent binary mixtures: a case study using a 4–(nitrostyryl)phenolate as a probe.
Phys Chem Chem Phys 2016;18:20266–9. https://doi.org/10.1039/c6cp03875a.
[24] Stock RI, de Melo CEA, Schramm ADS, Nicoleti CR, Bortoluzzi AJ, Heying RS, et al.
Structure–behavior study of a family of "hybrid cyanine" dyes which exhibit
inverted solvatochromism. Phys Chem Chem Phys 2016;18:32256–65. https://doi.
org/10.1039/c6cp06708e.
The financial support of the Brazilian Conselho Nacional de Desen-
´
˜
volvimento Científico e Tecnologico (CNPq), Coordenaçao de Aperfei-
çoamento de Pessoal de Nível Superior (CAPES – Finance code 001),
˜
`
˜
Fundaçao de Amparo a Pesquisa e Inovaçao do Estado de Santa Catarina
´
(FAPESC), Laboratorio Central de Biologia Molecular (CEBIME/UFSC),
and UFSC is gratefully acknowledged. Thanks are also due to Fondecyt
project 1190045.
[25] deMelo CEA, Nicoleti CR, Rezende MC, Bortoluzzi AJ, Heying RdaS, Oliboni RdaS,
et al. Reverse solvatochromism of imine dyes comprised of 5–nitrofuran–2–yl or
5–nitrothiophen–2–yl as electron acceptor and phenolate as electron donor. Chem
Eur J 2018;24:9364–76. https://doi.org/10.1002/chem.201800613.
[26] Stock RI, Sandri C, Rezende MC, Machado VG. Solvatochromic behavior of
substituted 4–(nitrostyryl)phenolate dyes in pure solvents and in binary solvent
mixtures composed of water and alcohols. J Mol Liq 2018;264:327–36. https://doi.
org/10.1016/j.molliq.2018.05.042.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.dyepig.2020.108757.
References
[27] de Melo CEA, Nicoleti CR, Nandi LG, Schneider FSS, Oliboni RD, Caramori GF,
et al. Solvatochromism of new substituted 4–(E)–(4–nitrophenyl)diazenyl
phenolate dyes. J Mol Liq 2020;301:12. https://doi.org/10.1016/j.
molliq.2019.112330.
[1] Reichardt C. Solvatochromic dyes as solvent polarity indicators. Chem Rev 1994;
94:2319–58. https://doi.org/10.1021/cr00032a005.
[2] Suppan P, Ghoneim N. Solvatochromism. Cambridge, UK: Royal Society of
Chemistry; 1997.
´
[28] Catalan J, Hopf H. Empirical treatment of the inductive and dispersive components
of solute–solvent interactions: the solvent polarizability (SP) scale. Eur J Org Chem
2004:4694–702. https://doi.org/10.1002/ejoc.200400311.
[3] Reichardt C, Welton T. Solvents and solvent effects in organic chemistry. fourth ed.
Weinheim, Germany: Wiley–VCH; 2011.
´
[29] Catalan J, Hopf H, Mlynek C, Klein D, Kilickiran P. Electronic energy levels in
[4] Dimroth K, Reichardt C, Siepmann T, Bohlmann F. Über
Pyridinium–N–phenol–betaine und ihre Verwendung zur Charakterisierung der
all–trans long linear polyenes: the case of the 3,20–di(tert–butyl)–
2,2,21,21–tetramethyl–all–trans–3,5,7,9,11,13,15,17, 19–docosanonaen (ttbp9)
conforming to Kasha’s rule. Chem Eur J 2005;11:3915–20. https://doi.org/
10.1002/chem.200401093.
¨
¨
Polaritat von Losungsmitteln. Justus Liebigs Ann Chem 1963;661:1–37. https://
doi.org/10.1002/jlac.19636610102.
[5] Machado VG, Stock RI, Reichardt C. Pyridinium N–phenolate betaine dyes. Chem
Rev 2014;114:10429–75. https://doi.org/10.1021/cr5001157.
´
[30] Catalan J. Toward a generalized treatment of the solvent effect based on four
empirical scales: dipolarity (SdP, a new scale), polarizability (SP), acidity (SA), and
basicity (SB) of the medium. J Phys Chem B 2009;113:5951–60. https://doi.org/
10.1021/jp8095727.
[6] Effenberger F, Würthner F. 5–Dimethylamino–5′–nitro–2, 2′–bithiophene – a new
dye with pronounced positive Solvatochromie. Angew Chem Int Ed 1993;32:
719–21. https://doi.org/10.1002/anie.199307191.
[31] Loffredo C, Pires PAR, Imran M, El Seoud OA. β–Carotene: a green, inexpensive,
and convenient solvatochromic probe for the determination of solvent
polarizability. Dyes Pigments 2013;96:16–24. https://doi.org/10.1016/j.
dyepig.2012.07.017.
¨
5–Dimethylamino–5’–nitro–2,2’–bithiophen – ein neuer Farbstoff mit ausgepragter
positiver solvatochromie. Angew Chem 1993;105:742–4, 10.1002/
ange.19931050515.
[7] Effenberger F, Würthner F, Steybe F. Synthesis and solvatochromic properties of
donor–acceptor–substituted oligothiophenes. J Org Chem 1995;60:2082–91.
https://doi.org/10.1021/jo00112a032.
[32] Pires PAR, Imran M, Loffredo C, Donate PM, Previdi D, El Seoud OA.
Solvatochromism of 2–(N,N–dimethylamino)–7–nitrofluorene and the natural dye
β–carotene: application for the determination of solvent dipolarity and
polarizability. J Phys Org Chem 2013;26:280–5. https://doi.org/10.1002/
poc.3083.
[8] Ramirez CB, Carrasco N, Rezende MC. Halochromism and solvatochromism of a π*
probe in binary solvent mixtures. J Chem Soc, Faraday Trans 1995;91:3839–42.
https://doi.org/10.1039/ft9959103839.
´
[33] Catalan J. On the use of β–carotene as a probe for solvent polarizability. J Phys Org
[9] Dominguez ME, Rezende MC, Marquez S. Theoretical study of the solvatochromism
of a donor–acceptor bithiophene. J Mol Model 2013;19:689–96. https://doi.org/
10.1007/s00894–012–1593–y.
Chem 2013;26:948–52. https://doi.org/10.1002/poc.3201.
[34] Vogel AI, Tatchell AR, Furniss BS, Hannaford AJ, Smith PWG. Vogel’s textbook of
practical organic chemistry. fifth ed. Prentice Hall; 1996.
[10] Dominguez M, Mera–Adasme R, Rezende MC. Insights into the halochromism of a
bithiophene π* probe. Spectrochim Acta, Part A 2019;222. https://doi.org/
10.1016/j.saa.2019.117264. 117264.
9

C.E.A. de Melo et al.
Dyes and Pigments 184 (2021) 108757
[35] Bradley D, Williams G, Lawton M. Drying of organic solvents: quantitative
evaluation of the efficiency of several desiccants. J Org Chem 2010;75:8351–4.
https://doi.org/10.1021/jo101589h.
[41] Perdew JP, Burke K, Ernzerhof M. Generalized gradient approximation made
simple. Phys Rev Lett 1996;77:3865–8. https://doi.org/10.1103/
PhysRevLett.77.3865.
[36] Neese F. Software update: the ORCA program system, version 4.0. WIREs Comput
Mol Sci 2018;8:e1327. https://doi.org/10.1002/wcms.1327.
[42] Lin YS, Li GD, Mao SP, Chai JD. Long–range corrected hybrid density functionals
with improved dispersion corrections. J Chem Theor Comput 2013;9:263–72.
https://doi.org/10.1021/ct300715s.
[37] Tao JM, Perdew JP, Staroverov VN, Scuseria GE. Climbing the density functional
ladder: nonempirical meta–generalized gradient approximation designed for
molecules and solids. Phys Rev Lett 2003;91. https://doi.org/10.1103/
PhysRevLett.91.146401. 146401.
[43] Kamlet MJ, Taft RW. The solvatochromic comparison method. I. The β–scale of
solvent hydrogen–bond acceptor (HBA) basicities. J Am Chem Soc 1976;98:
377–83. https://doi.org/10.1021/ja00418a009.
[38] Weigend F, Ahlrichs R. Balanced basis sets of split valence, triple zeta valence and
quadruple zeta valence quality for H to Rn: design and assessment of accuracy.
Phys Chem Chem Phys 2005;7:3297–305. https://doi.org/10.1039/b508541a.
[39] Grimme S, Antony J, Ehrlich S, Krieg H. A consistent and accurate ab initio
parametrization of density functional dispersion correction (DFT–D) for the 94
elements H–Pu. J Chem Phys 2010;132. https://doi.org/10.1063/1.3382344.
154104.
[44] Kamlet MJ, Abboud JLM, Abraham MH, Taft RW. Linear solvation energy
relationships. 23. A comprehensive collection of the solvatochromic parameters,
π
*, α, and β, and some methods for simplifying the generalized solvatochromic
equation. J Org Chem 1983;48:2877–87. https://doi.org/10.1021/jo00165a018.
[45] Loos P-F, Scemama A, Jacquemin D. The quest for highly accurate excitation
energies: a computational perspective. J Phys Chem Lett 2020;11:2374–83.
https://doi.org/10.1021/acs.jpclett.0c00014.
[40] Barone V, Cossi M. Quantum calculation of molecular energies and energy
gradients in solution by a conductor solvent model. J Phys Chem A 1998;102:
1995–2001. https://doi.org/10.1021/jp9716997.
10