Synthesis, characterization and photophysical-theoretical analysis of compounds A-π-D. 1. Effect of alkyl-phenyl substituted amines in photophysical properties

Article abstract of DOI:10.1016/j.molstruc.2017.04.019

The study of new dipolar A-π-D molecules, which have an acceptor (A) and donor (D) charge joined by a conjugate bridge, have been an attention focus in the recent years due their different properties. In the current work, a molecular system has been modified in order to compare the effect on properties, such as quantum yield. Thus, two series were generated (alkyl- and alkoxy-substituted) to determine if molecules with tertiary asymmetric amines change their optical properties and whether quantum yield is affected. The different products have been characterized by several techniques such as UV–Vis spectrophotometry, elemental analysis, NMR, FT-IR, mass spectroscopy and fluorescence spectroscopy. Furthermore, their behavior in eight organic solvents, dichloromethane, tetrahydrofuran, ethyl acetate, 1,4-dioxane, acetone, acetonitrile, dimethylformamide and dimethylsulfoxide were experimentally and theoretically studied. The quantum yields were higher for the alkyl-substituted series. Theoretically, the dihedral angles formed between the tertiary amine and carbonyl group moieties have a correlation with quantum yield values, helping to explain why they are higher in non-polar solvents. Consequently, the maximum quantum yield was obtained with (E)-2-cyano-3-(5-((E)-2-(9,9-diethyl-7-(methyl(phenyl)amino)-9H-fluoren-2-yl) vinyl)thiophen-2-yl)acrylic acid (M8-1) in 1,4-dioxane, reaching 98.8%.

Full text of DOI:10.1016/j.molstruc.2017.04.019

Accepted Manuscript
Synthesis, characterization and photophysical-theoretical analysis of compounds A-π-
D. 1. Effect of alkyl-phenyl substituted amines in photophysical properties
E. Ortega, R. Montecinos, L. Cattin, F.R. Díaz, M.A. del Valle, J.C. Bernède
PII:
S0022-2860(17)30450-7
10.1016/j.molstruc.2017.04.019
MOLSTR 23641
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 24 January 2017
Revised Date: 6 April 2017
Accepted Date: 6 April 2017
Please cite this article as: E. Ortega, R. Montecinos, L. Cattin, F.R. Díaz, M.A. del Valle, J.C. Bernède,
Synthesis, characterization and photophysical-theoretical analysis of compounds A-π-D. 1. Effect of
alkyl-phenyl substituted amines in photophysical properties, Journal of Molecular Structure (2017), doi:
10.1016/j.molstruc.2017.04.019.
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ACCEPTED MANUSCRIPT
M8-1, 2
M8-O1,O2
40
60
M8-2
M8-2
M8-1
35
M8-1
polar solvent
50
30
25
20
15
10
5
0
Non-polar solvent
40
M8-2
M8-2
M8-1
M8-1
Ar-CO
Al-CO
Ar-CO
Al-CO
30
Φ ∝ Dihedral angle
F
20
M8-02
M8-O2
M8-O1
150
M8-01
25
M8-01
150
M8-O1
10
25
50
75
100
125
175
50
75
100
125
175
Average diedral angle (°)
Average diedral angle (°)

ACCEPTED MANUSCRIPT
Synthesis, characterization and photophysical-theoretical analysis of compounds A-π-D. 1.
Effect of alkyl-phenyl substituted amines in photophysical properties
a
a
b
c*
a
d*
E. Ortega , R. Montecinos , L. Cattin , F. R. Díaz , M. A. del Valle , J. C. Bernède
a
Pontificia Universidad Católica de Chile, Av.V. Mackenna 4860-Macul, BP 7820436, Santiago,
Chile.
b
Institut des Matériaux Jean Rouxel (IMN), CNRS, UMR 6502, 2 rue de la Houssinière, BP 32229,
4322 Nantes cedex 3, France.
4
c
Departamento de Química y Biología, Facultad de Ciencias Naturales, Universidad de Atacama,
Copayapu 485, Copiapó, Chile.
d
MOLTECH-Anjou, CNRS, UMR 6200, Université de Nantes, 2 rue de la Houssinière, BP 92208,
Nantes, F-44000 France.
Abstract
The study of new dipolar A-π-D molecules, which have an acceptor (A) and donor (D) charge joined
by a conjugate bridge, have been an attention focus in the recent years due their different properties.
In the current work, some molecular systems have been modified in order to rationalize changes,
aimed at preparing products of high quantum yield, is reported. a molecular system has been
modified in order to compare the effect on properties, such as quantum yield. Thus, two series were
generated (alkyl- and alkoxy-substituted) to determine if molecules with tertiary asymmetric amines
change their optical properties and whether quantum yield is affected. To this end, the synthesis and
characterization of four new dyes using UV-Vis spectrophotometry, elemental analysis, NMR, FT-IR,
mass spectroscopy and fluorescence spectroscopy was performed. The different products have been
characterized by several techniques such as UV-Vis spectrophotometry, elemental analysis, NMR,
FT-IR, mass spectroscopy and fluorescence spectroscopy. Furthermore, their behavior in eight
organic solvents, dichloromethane, tetrahydrofuran, ethyl acetate, 1,4-dioxane, acetone, acetonitrile,
dimethylformamide and dimethylsulfoxide were experimentally and theoretically studied. The
quantum yields were higher for the alkyl-substituted series. Moreover, theoretically, the dihedral
angles formed between the tertiary amine and carbonyl group moieties helps to explain yields, that
are higher in non-polar solvents. Theoretically, the dihedral angles formed between the tertiary amine
and carbonyl group moieties have a correlation with quantum yield values, helping to explain why
they are higher in non-polar solvents. Consequently, the maximum quantum yield was obtained with
1

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(E)-2-cyano-3-(5-((E)-2-(9,9-diethyl-7-(methyl(phenyl)amino)-9H-fluoren-2-yl)
vinyl)thiophen-2-
yl)acrylic acid (M8-1) in 1,4-dioxane, reaching 98.8%.
Corresponding authors: Fernando Díaz, fdiaz@uc.cl and Christian Bernède, jean-
christian.bernede@univ-nantes.fr
Keywords: dye, dipole, quantum yield, dipolar moment, dihedral angle effect.
1. Introduction
In recent years, research dedicated to organic electronic has attracted considerable interest [1].
Nowadays organic devices such as thin film transistors [2], organic light emitting devices (OLED) [3]
and even organic and hybrid photovoltaic cells [4] are available in the market. The interest to organic
devices is due to their flexibility, lightness, low price, ease of realization and great diversity of
properties [5]. Nevertheless, if compared with similar inorganic devices, the performances of organic
devices are lower [6,7]. Therefore, the future development of organic devices depends, among other
things, on the improvement of the properties of organics materials. The chemical tailoring allows to
attain the variety of properties required for the particular technology [8-10]. This means targeting the
incorporation of various molecular units, each enriching the final material with specific properties. In
this context, the aim of this article is to propose new molecules based on small molecular structures
combining structural versatility, simplicity and low molecular weight, features that are generally
associated with higher overall chemical yield, lower environmental impact and easier up-scaling of the
synthesis. It is hoped that emphasis on such structures will stimulate further synthetic chemistry
oriented towards the reduction of the cost and environmental impact of active materials and thus
contribute to a future industrial development of photovoltaic cells. Considering all the above, it is
possible to determine that, structurally, compounds as fluorene, aniline and thiophene, not only
display photophysical properties in their derivatives and polymers but also excellent charge transfer
and electrochemical properties, most of them being used in photovoltaic systems [11-15]. In the
current work, the synthesis is carried out and the subsequent characterization is accomplished by
UV-Vis, FT-IR, mass, fluorescence and NMR spectroscopy and elemental analysis of 4 dyes, M8-1,
M8-2, M8-O1 and M8-O2 (Fig. 1, Table 1). Dyes molecular characteristics were compared by
grouping them into two families (alkyl- or alkoxy-substituted), in order to characterize their behavior
and establish whichmodification is the most appropriate. As for the chemical structures, the
synthesized products are based on "molecule 4" skeleton reported by Chih-Hsin Chen et al. [16],
2

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which was subjected to modifications, mainly in the areas close to the only existing nitrogen of the
molecule, in order to determine how the photophysical behavior is modified. Both the experimental
and theoretical photophysical studies were conductedusing 8 solvents, sorted in ascending order
according to their polarity index: dichloromethane (DCM), tetrahydrofuran (THF), ethyl acetate (ETA),
1,4-dioxane (DIO), acetone (ACT), acetonitrile (ACN), dimethylformamide (DMF) and
dimethylsulfoxide (DMSO). It is noteworthy that in DCM and ACN, studies were just qualitative as the
dyes were not fully soluble.
2. Material and Methods
The molecules indicated previously are shown below,
All solvents used in both syntheses and subsequent analyses were high purity anhydrous, and
purchased from Aldrich. Synthesis methods are shown at the end in "dyes synthesis" section, where
both the synthesis itself and the results of the characterization of each of the new prepared products
are detailed. NMR spectra were recorded on a Bruker 400 MHz Spectrometer (Spectra available on
the supplementary material). Subsequently, measurements of solutions of each dye, concentrations
-
1
between 0.5 and 3 µmol L , were used for quantum yield determinations. UV-Vis spectra were
recorded on an Agilent spectrophotometer and fluorescence on a HORIBA Scientific Fluoromax-
4spectrofluorometer. FT-IR spectra were recorded on
a
Bruker, VECTOR 22 model
spectrophotometer (Spectra available on the supplementary material). The samples have been
-
1
prepared with KBr (for solid ones), and KBr liquid film (for oils), the resolution used is 16 cm with 32
-
1
scans and a range of measurement of 600-4500cm .
For mass spectrometry, a Triple Quad, 4500 AB SCIEXmass spectrometerwas employed.
.
Theoretical calculations were performed with the Gaussian 09 program, utilizing the density functional
theory (DFT), specifically, the B3LYP method and 6-31g(d) basis set for optimizations. As for photo-
physical, calculations were performed using time dependent methods, TD-DFT, to obtain three of the
most important dyes intensities [16].
3

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3. Results and Discussion
The most relevant results of this systematic study, grouped according to the type of study, i.e.
synthesis (3.1), photo-physical (3.2) and theoretical (3.3), are described and discussed below.
3.1 Synthesis and characterization of dyes
The synthesis route consists of several steps, based mainly on ref. 16, however, some modifications,
detailed at the end of the corresponding section, have been carried out to improve purity and yield.
The synthesized products are donor-π-acceptor (D-π-A) type and The molecules studied here have
three distinct parts: the charge donor centered on the nitrogen, the spacer chain (or bridge) is the
moiety that includes fluoren-vinyl thiophene structure and finally, the acceptor is the acrylic acid,
which acts as anchor group in the chemical adsorption on the TiO surface. As for the The synthetic
2
method has many steps (Fig.2), and they were carried out by: 1) a SN2 reaction wherein the
hydrogens at the thiophene sp3 carbon act as acid compared to KOH (M1) [17]; 2) an addition-
elimination reaction (M2); 3) a reduction with NaBH4 (M4); 4) alcohol reaction with
triphenylphosphoniumbromide forming the phosphonium salt (M5), and 5) formation of a pair of E/Z
isomers using the Wittig reaction (M6) [16]. Purification of the mixture is conducted by exposure to I2
(Fig. 3). An important detail that should be emphasized in this reaction is that whenever the solution is
diluted, the corresponding stereomutation of the Z compound is brought about, however, when
dealing with concentrate solutions, a different process occurs, which produces a solid with other
properties, different to the goal of the synthesis proposed herein. This is explained considering that
the stereomutation mechanism possesses a cationic intermediate [18] that produces an attack on the
double bond of another neighboring molecule, yielding other structures. NMR spectrum of the mixture
exhibits a pair of double signals for Z isomer, chemical shift of 6.72 and 6.63 ppm and coupling
constant 11.9 Hz (in chloroform-D), which disappears after exposure to I . Continuing with the
2
synthetic pathway (Fig. 4) in 6), a PdCl
2
catalyzed Buchwald-Hartwig coupling reaction of C-N, using
(
t-Bu) PHBF , was performed. This ligand is deprotonated in solution, by complexing with the metal,
3
4
which catalyzes the reaction. This compound was selected because it is more environmentally stable
and improves yields (M6) [19-21]; in 7) an addition-elimination reaction in the α-hydrogen of the
thiophene fraction (M7) occurs. Subsequently, a condensation reaction between the aldehyde and
cyanoacetic acid (M8) [16, 22] takes place in 8). Thus, the four compounds, all solid, dark red,
partially soluble in DCM and ACN and completely soluble in THF, DMSO, DIO, ETA, DMF and ACT,
were produced.
4

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3.2 Photophysical properties of synthesized dyes
3.2.1 UV-Vis spectrometry
In general, the dyes exhibit two absorption bands in the UV-Vis range (example for M8-1 in all
solvents in Fig. S1), the highest wavelength at 300 nm (band I) and the lowest, at about 450 nm
(band II). Band I is ascribed to n-π*-type localized transitions of high energy [16]. This band tends to
move to the low wavelength zone, being confused in the experimental noise Band II, also
corresponds to a n-π*-type transition, as demonstrated by the hypsochromic shift (Table S1) of the
visible band of the dyes in the tested solvents [23]. Furthermore, this shift evidences a charge transfer
mechanism, which, as usually, occurs in the amino-benzene derivatives [23]. It should be noted that
the compounds have average solubility in DCM and ACN, but studies were conducted all the same,
because these solvents are classic in this kind of study. In solvents where the compounds are
solubles, the molar extinction coefficients, ε (Table S1) was determined. In each case, in the different
0
studied solvents, a large value of ε was found indicating that these molecules have high absorption
0
at its λmax compared with other chromophores [24, 25]. Therefore, it is noteworthy that low
-
1
concentrations of these substances (in the order of µmol L ), enable the measurement of the optical
characteristics. Furthermore, in all cases, using between 1 to 3 mg in 50 mL of the corresponding
solvent, saturate any optical instrument, consequently 25 to 100-fold dilution will be required in order
to satisfactorily conduct each measurement. Thus, concentrations for measuring ranged between 0.5
-
1
and 3 µmol L .
3
.2.2 Fluorescence spectrometry of synthesized dyes
.2.2.1 Solvent effect on emission patterns
3
Spectra of each dye showed different patterns, from which 1 to 4 bands were found. Consequently,
two patterns for two different wavelengths were obtained. Each maximum were analysed using
gaussian functions (Fig. S2), to separate and obtain those values exactly . The first, λ is the
1,
maximum absortion wavelength. The second, λ , is the wavelength at which the absortion spectra of
2
both, the sample and the standard, are intersected. Thus, this wavelength will be use for quantum
yield calculations later in this paper. The different bands are related to different excited states, each
5

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1 2 3 4
one was labeled (ordered from lowest to highest energy), S , S , S and S . The shown bold number
corresponds to the intensity of each one, 1 being the highest and 4 being the lowest. When excited at
a wavelength corresponding to λmax (Fig. 5[a, b] for M8-1 and Figs. S3, S4, S5 [a, b]), a shouldered
band is usually observed. When excited at a wavelength different from λmax (Fig. 5[c, d] for M8-1 and
Figs. S3, S4, S5 [c, d]), a separation of the previous pattern is observed, in two or more bands,
depending on the solvent. In summary, it is possible to observe, in general, that the energy absorbed
at λmax, is subsequently emitted in two different ways: S and S to S . On the other hand, when
1
2
0
excited at a wavelength different from λmax, energy is emitted through S , S , S S to S .
1
2
3
4
0
Table 2 (and Table S2, S3, S4) summarizes maximum emission wavelenghts for all the samples
emission figures summary). As mentioned above, these bands are assigned to the four singlet
states, S at ca. 640 nm, S at 600 nm, S at 500 nm and S at 450 nm (approximately). In general,
(
1
2
3
4
ACT quenches the first state S
1
. An explanation for this would be that in acetone some form of
"quenching" is favored, such as in the most classic in the case of donor-acceptor dipolar molecules
namely, the Forster resonance energy transfer (FRET) effect, where charge transfer from donor to
acceptor occurs, decreasing the fluorescence intensity [28]. In this particular case, the A-π-D
molecules are dipolar, which would explain that, when excited at the maximum absorbance
wavelength, the first state intensity be lower than the second. Another explanation would be that
acetone quenches the intensity of the first state due to some effect on the of the excited-state
complex, also possible in this case [29].
3.2.2.2 Stokes shift of the studied dyes
The difference between each maximum, the so-called "Stokes shift" (Table S5), is useful to determine
differences in dipole moment of the molecules under survey, between their ground and excited states,
after light absorption [30]. In this instance, a polarity decrease occurs for all products, because n-π*
transitions depolarize the chemical system, as usually happens in the anilines [31, 32] and, therefore,
the ground state is more polar than the excited state.
6

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3.2.2.3 Lippert equation and calculation of polarity difference in ground and excited state of
the synthesized dyes
To determine the value of the difference in the dipole moments of the compounds, the Lippert
equation (Eq. 1) was utilized:
(1)
-
1
Where "Stokes shift" or ∆ν, corresponds to the difference between the frequencies (cm ) of the
absorption and emission maxima. The polarity difference (µ -µ ) is the difference between the excited
and ground state dipole moment, respectively. C is the light speed (approximately 3·10 ms ). h is
e
g
8
-1
-
34
3
Planck's constant (6.63·10 J s). a is the volume of solvent box around the fluorophore. ε is the
dielectric constant of the solvent and η it’s the refractive index, whose mathematical relationship
corresponds to the solvent dipolar factor.
Thus, by plotting the "Stokes shift" value in all studied solvents vs. the dipolar solvent facto, known as
Lippert-Mataga plot, the difference in dipole moments for each dye can be obtained from the
respective slope [33, 34]. Thus, the absolute value of the difference between absorption and emission
-
1
maxima, in frequency units (cm ), vs. solvent dipolar factor was plotted (Fig. 6). A large slope, as
inferred from Eq. 2, indicates that the dye presents a greater difference between its ground and
excited state, meaning that donation of the nitrogen non-bonding electron pair is highly shared with
the rest of the molecule. On the other hand, for the polarity estimation of the excited state, the
Onsager radius (a), is assessed as the ninth of the distance between the carbonfrom the carbonyl
and nitrogen [34], i.e. 17.87Å. The difference of dipole moment in this case corresponds to the
difference between the ground and the excited state. Due to the type of transition occurring in this
kind of molecules, the ground state is more polar than the excited one [35]. On relation with the
graphics, the points tend to diverge, moreover in many cases they do not follow exactly the straight
line. However, this is not an isolated fact. Many compounds π conjugated have been studied resulting
in different behaviours. For example, there are compounds that follow the linearity (with some
divergences) [36-43], others have different tendencies inside one plot [44-47] and an asymmetric
amine [48], which has a close behaviour with the type of compound reported here. In addition,
compounds like ketocoumarins [49] shown this behaviour. In general, the aim is to compare, then this
plot has been made to obtain some information related with substituents (qualitative information).
7

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Values for ground states were estimated by performing theoretical calculations using the Gaussian 09
program and optimizing the chemical structures [16, 50]. This way, comparing the values of the
difference of dyes dipole moment (Table 3) the greater difference corresponded to M8-2. Ethyl group
has a greater effect on the transition than the methyl group and this is evident when comparing M8-1
with 2. Nevertheless, the inverse effect it has been seen for M8-O1 compared with O2. As for the
comparison of M8-2 with M8-1 and O1 with O2, in the former the methoxyl group decreases the
difference of the dipole moment, whereas in the second, ethoxyl decreases even more this difference.
F
3.2.2.4 Dyes quantum yield (Φ )
A comparative method reported by Williams et al. [51,52], employing standard zinc phthalocyanine
(ZnPc) in 1% pyridine in toluene, was used for determining the quantum yields according to Eq. 2:
(2)
X
where Φ stands for quantum yield of the sample and ΦST for the quantum yield of the reference, in
this case 0.30. Grad is the slope of integrated emission intensity vs. sample absorbance plot and
x
GradST is the standard slope. η and η are the refractive indexes of sample and standard solvents,
X
ST
respectively. For solvents wherein the solubility is not complete, as DCM and ACN, the above method
was employed but as an equation with unknowns, not as an equation derived from a plot, according
to Eq. 3:
(
3)
stand for sample and reference quantum yields. Area
emission intensity for sample and reference, respectively. Abs and Abs
sample absorbance. η and η are, respectively, the refractive indexes of sample and reference
where Φ
S
and Φ
R
S
R
and Area are the integrated
R
S
correspond to reference and
S
R
solvents,
As for the quantum yields values (Table 4), no linear relationship with the polarity of the solvent was
found, but some trends are likely to be observed. Taking into account the main factors affecting
fluorescence, e.g. chemical structure, structural stiffness, temperature, solvent, pH and concentration
effect. For the measurements, parameters such as temperature (ambient), structural rigidity, pH (not
applicable) and low concentrations (less than 0.1 absorbance units) were kept constant. The
8

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chemical structure changes and the modifications were mentioned in the Introduction. The solvent
was changed, in order to observe the different responses. Comparison of M8-1 and 2 yields with M8-
O1 and O2 yields demonstrated that the latter are largely overcome, i.e. the solely nitrogen alkyl
modification increases the quantum yield, but not the alkoxy modification. As for the length chain, in
most solvents, M8-2 exhibits higher yield consequently, the substituent length affects it proportionally.
In the alkoxy-substituted series, the opposite is true, i.e. an inverse proportional relationship is found.
Another important point is that, on average, yields are higher in nonpolar solvents DCM, THF, ETA
and DIO vs. polar solvents ACT, ACN, DMF and DMSO (Table 5), which will be discussed in the
"theoretical approximation of the molecular properties" section. It is noteworthy that the yields are
particularly low for ACT and ACN. In the former, this is due to the total quenching of the S state,
1
discussed in emissions section. In contrast, in ACN, is due only to the general quenching of the
signals and the intensity is only partly diminished. On the other hand, in DIO yields are high, since in
most dyes the appearance of the contribution of the four states is observed and all display high
intensity. In addition, it can be seen that, on average (Table 4), "low" viscosities (ACT) negatively
affect yields; the same also occurs for "high" viscosities (DMSO). Then, intermediate viscosities as
DIO particularly favor this property.
Another important point is the relationship with the "Stokes shift": in this case, M8-2 has a value
greater than that of M8-1 and, therefore, yields are higher for M8-2. As for M8-O1 and O2, yields are
higher for the former, but in general tend to the same value. Consequently, a large difference in
polarity between ground and excited state leads to an increase of quantum yield.
3.3 Theoretical approach to molecular properties of dyes
In the search for answers to the observed phenomena, theoretical calculations were conducted to
determine whether there is any relationship between molecules geometry and experimental changes.
3.3.1 Dihedral angles and their relationship to the quantum yield
Another way to find an answer for Φ values is to compare the values of the dihedral angles. In this
F
respect, the angle formed between the carbonyl acceptor and the amine donor is compared, as an
9

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approximation to the lining up of these two groups (Fig. 7). This takes place because both LUMO and
HOMO orbitals settle around these functional groups (Fig. S6 [a, b, c. d])
In this comparison, two angles are possible: Ar-CO (aryl to carbonyl), which refers to that formed
between ring-nitrogen and carbonyl, and the other, Al-CO (alkyl to carbonyl), to that formed between
aliphatic chain-nitrogen and carbonyl. The π-bridge is considered as linear and it does not show any
important change on these values.
3.3.1.1 M8-n vs. M8-On series
It can be verified (Table S6) that the Ar-CO angle is less for M8-n, in turn, the Al-CO angle is less for
M8-On. This allows explaining that a high quantum yield is associated with lower values of Ar-CO and
higher values of Al-CO, as in the M8-n series (Table 5). The alkyl group also has the function of
orienting the aromatic ring with the remainder of the conjugated chain. In addition, both angles are
inversely proportional for both families. Comparing the effect of the substituent length, firstly between
M8-1 and 2, both possess similar yields, M8-1 being greater, on average, by only 0.1%. This relates
to the fact that the Ar-CO dihedral angle is always greater and Al-CO lower for M8-1. Besides,
between M8-O1 and O2 they also exhibited similar yields, M8-O1 being higher, on average, by 0.2 %.
Opposite to the previous series, in this case Ar-CO is lower and Al-CO higher for M8-O1. In summary,
the alkoxy group distorts the geometry of the molecule so that to maintain the quantum yield trend in
its series, but decreasing it by 77.0% on average. In Table 4, difference in yields measured in
nonpolar and polar solvents is observed; their relationship with the geometry of the molecules will be
discussed later.
3.3.1.2 Effect of nonpolar solvents
In this respect, it is possible to appreciate (Table S6 and S7) that in series M8-n the Ar-CO angle
increases and Al-CO decreases with polarity. Furthermore, Ar-CO values are always higher for M8-1
(
Table 6) and Al-CO is always greater for M8-2. Relating this to quantum yields in nonpolar solvents
Table S4), a greater Ar-CO angle favors higher values of the quantum yield. Although yield (Table 4)
(
is proportional to the Ar-CO angle for M8-1, this is not true for M8-2 wherein the trend between DCM-
ETA and THF-DIO is perceived. In the M8-On series Ar-CO decreases and Al-CO increases with
polarity. In addition, Ar-CO values are always higher for M8-O2 (Table 6) and Al-CO is always greater
for M8-O1. Relating this to quantum yields in nonpolar solvents, an Ar-CO lower angle favors higher
1
0

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quantum yield values. In this case, the yield (Table 4) is inversely proportional to Ar-CO angle for both
dyes,
but
the
trend
between
DCM-ETA
and
THF-DIO
do
exists
3.3.1.3 Effect of polar solvents
Table S7, shows that in the M8-n series the Ar-CO angle decreases or remains constant and Al-CO
increases with polarity. Furthermore, Ar-CO values are always higher for M8-1 (Table 6) and Al-CO is
always greater for M8-2, ascribing this to quantum yields, in polar solvents (Table 5), a lower Ar-CO
angle favors higher values of quantum yield. The yields (Table 4) cannot be explained hereby the
dihedral angles, as they remain relatively constant, however, between ACT-DMF and ACN-DMSO, a
slight angle decrease is observed, which allows inferring that the yield is influenced by these
geometrical changes. In the M8-series, Ar-CO increases and Al-CO slightly decreases or remains
constant with polarity. In addition, Ar-CO values are always higher for M8-O2 (Table 6) and Al-CO is
always greater for M8-O1. Relating this to quantum yields in nonpolar solvents, a greater Ar-CO
angle favors higher values of quantum yield. In this respect, the yield (Table 4) increases linearly
between ACT-DMF and ACN-DMSO, which is consistent with the fact that the Ar-CO angle increases
between these solvents, i.e. the quantum yield is affected by geometric changes
In summary, Table 4 shows that quantum efficiencies are greater in nonpolar solvents than in polar
solvents. In the case of M8-1 and 2 molecules, because the ring is more aligned with the acceptor,
which would favor conjugation from the benzene ring, participating thus in the fluorescence. On the
other hand, fluorescence is affected in M8-O1 and O2, where the ring, because of the alkyl group,
cannot achieve this structure and, consequently, the fluorescence becomes diminished. Finally, for
M8-1 and 2 in polar solvents, the Ar-CO angle decreases and the Al-CO increases and, on the other
hand, for M8-O1 and O2, the Ar-CO angle increases and Al-CO decreases, corroborating that the
structure where the acceptor is flatter with the substituent ring, favors fluorescence in the first family.
3.3.2 Theoretical photophysics, assignments comparison
To corroborate assignments patterns in the fluorescence spectra, theoretical calculations were made,
as mentioned in experimental section. Most transitions occur between the frontier orbital and other
close orbitals. HOMO (H), the orbital before HOMO (H-1) and that prior to this (H-2) appear in this
case. As for LUMO (L), the following to LUMO (L + 1) and the next to this (L + 2) also appear. Both
HOMO and LUMO orbitals, for both families, are depicted in Fig. 4. The other orbitals are observed in
Fig. S6 and S7. In general, "Stokes shifts" are explained by the Franck-Condon principle, which also
1
1

ACCEPTED MANUSCRIPT
explains that at two different excitation lengths (λ and λ ), where the former has lower energy than
1
2
the second, some or all excited states are displayed [39]. In general in all studied molecules, the
theoretical approximation (Tables S8 and S9) is accurate enough to predict the first excited state
(maximum error near to 6.7% from the real value). The second and third states are predicted but not
accurate. The fourth excited state is not predicted by this method in any case.
Summarizing, these results would validate the TD-DFT calculations, even though it is true that predict
only 3 of the 4 states, the most likely state is always predicted with fairly good accuracy. As for the
Stokes Shift, M8-2 presents the largest difference between the ground and excited state, which is
directly related to the fact that this molecule possesses the largest quantum efficiency in most of the
studied solvents. Thus, this systematic study, both experimental and theoretical, will enable
adequately design the use of the best dyes for assembling solar cells, to corroborate its usefulness in
the development of these devices, to be investigated in the near future.
Conclusions
The synthesis and characterization of four A-π-D-type dyes, in two series: alkyl- and alkoxy-
substituted, M8-n and M8-On, were respectively completed. Total obtained The reaction yields are
1
0.0% (M8-1), 7.8% (M8-2), 7.4% (M8-O1) and 8.8% (M8-O2). Two absorption bands, at 300 nm and
50 nm range, were observed. As for the fluorescence, Four different states have been found, S1
4
2 3 4 1
(640 nm), S (600 nm), S (500 nm) and S (450 nm). State S is usually moderately quenched by the
dipolar effect of this typeof molecule FRET effect. TD-DFT calculations predict only 3 of 4 states. The
first is more precisely predicted, at 650 nm, while the state S at 600 nm, is not predicted. As for the
2
Stokes Shift, M8-2 has the largest difference between the ground state and excited state, which is
directly related to the fact that this molecule shows the highest quantum yield in many solvents.
Quantum yields are higher for the M8-n series in all solvents. However, the yields are always higher
in non-polar solvents due In non-polar solvents (DCM, THF, ETA, DIO) to planarity of the aromatic
ring (amine) respect to the acceptor carbonyl moiety has to be more planar with respect to the
acceptor carbonyl, alkyl group for M8-n and M8-On. In polar solvents, the alkyl group must be planar.
for M8-n and the aromatic ring for M8-On. Consequently, having the most planar ring with the
carbonyl acceptor, strongand definitely favors fluorescence. Maximum yield was achieved with (E)-2-
cyano-3-(5-((E)-2-(9,9-diethyl-7-(methyl(phenyl)amino)-9H-fluoren-2-yl)vinyl)thiophen-2-yl)acrylic acid
in 1,4-dioxane, reaching a yield of 98.8%, that allows projecting the utility of this dye in the fabrication
of photovoltaic cells. Products reported here in will shortly be tested to corroborate these results in
practice.
1
2

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Acknowledgements
This work was made possible thanks to the contribution of Fondecyt1141158 and Ecos-Conicyt
C14E05 grants.
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[
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π
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[
1
5

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Figure index
Figure 1. Synthesized products: (a) alkyl-substituted series, M8-n; (b) alkoxy-sustituted series, M8-
On. n = 1(Me), 2(Et).
3 2
Figure 2.Synthetic route to “M5” compound: i) KOH, KI, CH CH Br, DMSO; ii) n-BuLi, DMF, THF,
-
78ºC; iii) NaBH , MeOH, THF; iv) PHPh Br, CHCl , reflux; v) thiophen-2-carbaldehyde, t-BuOK,
4
3
3
reflux, toluene.
Figure 3.Z to E isomer stereomutation reaction.
Figure 4.Synthetic route to“M5” final products: vi) secondary amine, PdCl , (t-bu) PHBF , t-BuOK,
2
3
4
toluene; vii) n-BuLi, DMF, THF, -78ºC; viii) cyanoacetic acid, ammonium acetate, acetic acid, 120 ºC.
Figure 5.M8-1 emission spectra in the solvents indicated in the insets, exciting at: (a) and (b) λmax; (c)
and (d) λ ≠ λmax
Figure 6.Dyes Lippert-Matagaplots: (a) M8-1. (b) M8-2. (c) M8-O1. (d) M8-O2.
Figure 7. Approximate structures for the determination of dihedral angles of: a) M8-1 and M8-2. b)
M8-O1 and M8-O2.
Table index
Table 1. Synthesized dyes nomenclature.
Table 2. M8-1λem excited at λmax andλ ≠ λmax. The numbers indicated are related to intensity.
Table 3. Dipole moment from Lippert plots.
Table 4. Dyes quantum yield in different solvents.
Table 5. Average quantum yield in polar and non-polar solvents.
Table 6. Angles grouped according nonpolar and polar solvents.
1
6

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Table 1. Synthesizeddyesnomenclature.
Dye IUPAC name
E)-2-cyano-3-(5-((E)-2-(9,9-diethyl-7-(methyl(phenyl)amino)-9H-fluoren-2-
Codenumber
M8-1
(
yl)vinyl)thiophen-2-yl)acrylic acid
(
E)-2-cyano-3-(5-((E)-2-(9,9-diethyl-7-(ethyl(phenyl)amino)-9H-fluoren-2-
M8-2
M8-O1
M8-O2
yl)vinyl)thiophen-2-yl)acrylic acid
(
9
E)-2-cyano-3-(5-((E)-2-(9,9-diethyl-7-((4-methoxyphenyl)(methyl)amino)-
H-fluoren-2-yl)vinyl)thiophen-2-yl)acrylic acid
(
E)-2-cyano-3-(5-((E)-2-(7-((4-ethoxyphenyl)(ethyl)amino)-9,9-diethyl-9H-
fluoren-2-yl)vinyl)thiophen-2-yl)acrylic acid

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Table 2. M8-1λemexcitedatλmax andλ ≠ λmax. The numbers indicated are related to intensity.
Solvent
λmax
λem(nm)
λ ≠
λem(nm)
(
nm)
Estado
481.0
464.0
460.0
λmax(nm)
S1
S2
Estado
387.0
S1
S2
S3
S4
DCM
THF
ETA
636 (2)
638 (2)
621 (1)
606 (1)
639 (2)
639(2)
631 (3)
638 (3)
621 (1)
600 (1)
384.0
474 (3)
637 (2)
639 (2)
638 (2)
641 (1)
599 (1)
616 (1)
627 (1)
627 (2)
383.7
391.8
390.8
387.0
569 (1)
586 (2)
598 (2)
617 (2)
474 (2)
542 (1)
495 (1)
DIO
466.0
463.0
439.0
444 (4)
443 (3)
ACT
ACN
653(1)
635 (2)
638 (3)
DMF
432.0
430.0
639 (2)
643 (1)
612 (1)
629 (2)
385.6
381.0
610(1)
513 (3)
515 (1)
DMSO
625 (2)

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Table 3.Dipole momentfrom Lippert plots.
Dipolemomento
difference(D)
Ground state dipole
moment (D)
Excited state dipole
moment (D)
Dye
Slope
M8-1
M8-2
24162.04
21356.95
17790.75
12774.43
3.69
3.47
3.17
2.69
11.47
14.24
11.40
9.93
7.778
10.767
8.236
7.246
M8-O1
M8-O2

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Table 4. Dyes quantum yield in different solvents.
Solvent
DCM
3.1
THF
4.0
ETA
4.4
DIO
4.8
ACT
5.1
ACN
5.8
DMF
6.4
DMSO
7.2
Polarity
index
Viscosity
0.40
0.51
0.41
1.15
0.31
0.37
0.77
2.13
Dye
M8-1
20.5
18.4
19.5
0.9
32.7
47.1
39.9
16.2
10.6
13.4
61.4
34.2
47.8
7.4
98.8
62.5
80.7
34.5
33.9
34.2
10.9
26.3
18.6
1.4
8.2
25.5
16.9
1.2
56.1
60.2
58.2
7.1
17.6
31.7
24.7
2.7
M8-2
Average
M8-O1
M8-O2
Average
5.2
5.8
0.8
1.0
7.1
5.1
3.1
6.6
1.1
1.1
7.1
3.9

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Table 5. Average quantum yield in polar and non-polar solvents.
Non-polar
solventsaverage solventsaverage
Polar
General
average
Dye
M8-1
53.4
40.6
14.8
13.9
23.2
35.9
3.1
38.3
38.2
8.9
M8-2
M8-O1
M8-O2
3.5
8.7

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Table 6. Angles grouped according nonpolar and polar solvents.
Averageinnonpolarsolvents
Average in polar solvents
Dye/Angle
M8-1
An-CO
45.5
Al-CO
122.7
170.0
127.0
90.1
An-CO
44.1
Al-CO
124.8
171.5
126.3
88.3
M8-2
21.3
19.7
M8-O1
M8-O2
38.3
39.3
62.9
64.8

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Figure 1.

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Figure 2.

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Br
Br
I /CH Cl
2
2 2
S
Darkness
S
M5 (Z isomer)
M5 (E isomer)
Figure 3.

ACCEPTED MANUSCRIPT
Figure 4.

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DCM
THF
ETA
DIO
(a)
6
4
3
2
1
x10
6
x10
6
x10
6
x10
0
500
600
700
800
900
(nm)
λ
Figure 5 a.

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ACT
6
6
6
6
6
(b)
5x10
4x10
3x10
2x10
1x10
ACN
DMF
DMSO
0
4
00
500
600
700
800
900
λ (nm)
Figure 5 b.