Blue Highly Fluorescent Boranil Derived From Anil Ligand: Synthesis, Characterization, Experimental and Theoretical Evaluation of Solvent Effect on Structures and Photophysical Properties

Article abstract of DOI:10.1002/aoc.5764

In this study, we report the design and the synthesis of a Schiff base; Anil and its corresponding Boron Difluoride complexe; Boranil. The synthesis procedure was carried out adopting new, optimized reaction conditions. The Boranil dye presents the advantage to be emissive in solution. 1H and 19F NMR along with FTIR confirmed both compound's structure. To gain a better understanding of the solvatochromic behavior of Anil and Boranil, the dependence of the absorption spectra on the solvent's polarity was studied in depth. Thus, UV–Vis spectroscopy was performed in five selected solvents. In addition to the solvent's polarity effect, the influence of BF2 moiety introduction on the molecule's photophysical properties was also evaluated. When examining different absorption spectra, we found that the title fluorescent dye exhibited weak solvatochromic (11 nm in THF) as well as a slight redshift broader and relatively more structured absorption spectra after complexation. Besides, we investigate the obtained key structure–property relationships through DFT and TD-DFT calculations using a 6–311++ G (d, p) basis set. Quantum chemical calculations allowed confirming proposed structures and understanding their electronic structure in larger details. Theoretical results also showed good agreement with the experimental findings. Finally, the frontier molecular orbitals were investigated to illustrate the pi-conjugation and charge transfer effect.

Full text of DOI:10.1002/aoc.5764

Received: 24 January 2020
DOI: 10.1002/aoc.5764
Revised: 8 April 2020
Accepted: 10 April 2020
F U L L P A P E R
Blue Highly Fluorescent Boranil Derived From Anil Ligand:
Synthesis, Characterization, Experimental and Theoretical
Evaluation of Solvent Effect on Structures and
Photophysical Properties
1
2
3
Soumaya Agren | Marwa Chaabene | Abdul-Rahman Allouche
|
2
4,5
1
Rafik Ben Chaâbane | Mohamed Lahcinie
| Mohamed Hassen V Baouab
1
Research Unit Materials and Organic
In this study, we report the design and the synthesis of a Schiff base; Anil and
its corresponding Boron Difluoride complexe; Boranil. The synthesis procedure
was carried out adopting new, optimized reaction conditions. The Boranil dye
presents the advantage to be emissive in solution. 1H and 19F NMR along with
FTIR confirmed both compound's structure. To gain a better understanding of
the solvatochromic behavior of Anil and Boranil, the dependence of the
absorption spectra on the solvent's polarity was studied in depth. Thus, UV–
Vis spectroscopy was performed in five selected solvents. In addition to the sol-
vent's polarity effect, the influence of BF2 moiety introduction on the mole-
cule's photophysical properties was also evaluated. When examining different
absorption spectra, we found that the title fluorescent dye exhibited weak
solvatochromic (11 nm in THF) as well as a slight redshift broader and rela-
tively more structured absorption spectra after complexation. Besides, we
investigate the obtained key structure–property relationships through DFT
and TD-DFT calculations using a 6–311++ G (d, p) basis set. Quantum chemi-
cal calculations allowed confirming proposed structures and understanding
their electronic structure in larger details. Theoretical results also showed good
agreement with the experimental findings. Finally, the frontier molecular
orbitals were investigated to illustrate the pi-conjugation and charge transfer
effect.
Synthesis (UR17ES31), Preparatory
Institute for Engineering Studies of
Monastir, University of Monastir, Avenue
of the Environment, Monastir, 5000,
Tunisia
2
Laboratory of Advanced Materials and
Interfaces (LIMA), Faculty of Sciences of
Monastir, University of Monastir, Avenue
of the Environment, Monastir, 5000,
Tunisia
3
Institute of Light and Matter, UMR5306
University of Lyon 1-CNRS, University of
Lyon, cedex, Villeurbanne, 69622, France
4
Laboratory of organometallic and
macromolecular chemistry-composites
Materials, Faculty of Sciences and
Technologies, Cadi Ayyad University,
Avenue Abdelhakim Elkhattabi, BP549,
Marrakech, 40000, Morocco
5
Mohamed VI Polytechnic University, Lot
6
4
60,Hay Moulay Rachid, Ben Guerir,
3150, Morocco
Correspondence
Mohamed Hassen V Baouab, Research
Unit Materials and Organic Synthesis
(
UR17ES31), Preparatory Institute for
K E Y W O R D S
Engineering Studies of Monastir,
University of Monastir, Avenue de
l'Environnement 5019 Monastir Tunisie.
Email: hbaouab@yahoo.fr
Anil, Boranil, FTIR, HOMO-LUMO analysis, solvent effect
Funding information
Tunisia-Morocco, Grant/Award Number:
ꢀ
N 17/TM10
Appl Organomet Chem. 2020;e5764.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 15
https://doi.org/10.1002/aoc.5764

2
of 15
AGREN ET AL.
1
| INTRODUCTION
have optimized the different reaction conditions. Our
synthetic approach is based on extending the reaction
time and modifying other reaction parameters such as
the non-bulky Base and the dried Toluen solvent through
distillation. The Boranil (b) is synthesized for the first
Nowadays, organic fluorescent dyes are considered as
potential materials due to their multidisciplinary applica-
tions in different fields including Bioimagingng,
Organic light-emitting diodes (OLED),
solar cells (DSSC),
[
1,2]
[
3–5]
dye-sensitized
medicinal and
time from the unsubstituted Anil (a) known in recent
[6]
[7]
[26,27]
chemosensors,
studies as salicylidenaniline.
This compound
pharmaceutical applications such as saccharides sensi-
exhibits upon excitation an extremely ultrafast inter-
molecular proton transfer from the hydroxyl group to the
[8]
[9]
ng and explosives detection. The use of N, O, π conju-
gated ligands heterocyclic coordination center has
opened the way to obtain various new families of fluores-
cent dyes. The extent of the π-bond conjugated system of
these chromophores is responsible for their remarkable
fluorescent color. Notably, Tetracoordinate Organic
Boron Difluoride Complexes are known to be fluores-
[
26]
nitrogen atom.
This ESIPT phenomenon leads to a cis-
keto form, which is quickly converted into a photochro-
mic product. In addition to ultrafast ESIPT phenomenon,
these compounds exhibit several non-radiative
deexcitation channels competing with the mentioned
above phenomena such as twisting about CN and CC
bonds, π-π* to n-π* internal conversion and singlet-triplet
[10]
cent.
The study of different Boron Difluoride organic
[
26]
complexes has been the subject of great research
inter system crossing.
This would allow us to address
[11–16]
interest.
In this context, researchers are focusing on
one of the most important challenges regarding the
unsubstituted ligand system. A substituted Anil seems to
have better stability and easier Boron Difluoride com-
developing new materials with desired properties
through simple synthetic procedures and low cost. Partic-
ularly, Boranils show excellent properties such as essen-
[
12,26]
plexation.
BF Et O acts usually as the main source
3 2
[
11,13–16]
tially broad and structured absorption bands.
of the boron in the preparation of π conjugated boron
[
28]
These molecules can be used as potential alternative can-
didates to the most studied known fluorescent com-
complexes.
This contribution aims to develop a new improved
synthetic procedure of an unsubstituted Boranil as well
as a detailed characterization of the target compounds
[17,18]
pounds Bodipys
that have received overwhelming
interest because of their outstanding optical proper-
[
19]
1
19
ties.
Several studies highlighted their exceptional
using H and F NMR along with FTIR. We compared
the media polarity's effect on chemical stability and
photophysical properties. We have figured out that the
solvent effect can also be exploited for tuning their opti-
cal properties. DFT and TD-DFT calculations have been
carried out to elucidate the influence of the structural
modification and solvent polarity on the spectroscopic
and electronic properties as well as providing insights
into the factors controlling charge transfer phenomenon.
chemical stability and promising spectroscopic
[17–20]
features.
To date, the study of these systems has been focused
on substituted Schiff bases and their corresponding
[11,14,21–23]
Boranils due to their high stability.
Moreover,
It has been proved that the stability of the B-N and B-O
bonds is critical for maintaining desired optical proper-
[
23]
ties.
Furthermore, Rao and coworkers emphasize that
the key role of boron is stabilizing the anionic chelating
[24]
(NO) ligand.
To improve the boranil complexes’ stabil-
ity, frath and coworkers suggested a push-pull system.
The proposed system can enhance the dye's emission
without any disruption of the boron chelate ring.
2 | EXPERIMENTAL SECTION
2.1 | Materials and methods
[
22]
Additionally, Frath and co-workers outlined also their
strategy to achieve with success the synthesis of the first
series of polyanils and their corresponding luminescent
polyboranils. These polyboranils were also functionalized
by sterically hindered substituents to enhance their solid-
1
19
H and F NMR spectra were measured by Bruker
300 MHz NMR spectrometer. FTIR spectra were mea-
sured on a Perkin Elmer spectrum ranging from 350 to
8300 cm− with DTGS as a detector. UV–vis absorption
spectra were obtained on a SPECORD PLUS ranging
from 190–1100 nm.
1
[12]
state emission.
Recently, we have successfully investi-
gated the photophysical and optoelectronic properties of
Boron Difluoride fluorescent dyes and their
corresponding ligands through a completely experimen-
[25]
tal and theoretical study in DMF solvent.
Bearing in
2.2 | Quantum chemical calculation
mind all the above considerations, we have decided to
broaden our work and face all these difficulties to obtain
a Boron Difluoride complexe with a moderate yield. We
The molecular structure of the synthesized compounds in
the ground state has been optimized by the DFT method

AGREN ET AL.
3 of 15
using B3LYP functional with the empirical dispersion
chromatography (silica gel, CH Cl /Petrolum Ether,
v/v = 4/6).
2
2
[29]
correction D3 of Grimme et al.
6–311++G (d, p) basis
set with diffuse functions has been used for all calcula-
[30,31] 1
tions.
H-NMR shielding constants have been calcu-
lated by applying the gauge-invariant atomic orbital
3 | RESULTS AND DISCUSSION
3.1 | Geometric structure
[32,33]
(GIAO) method.
Frequency calculations of all com-
pounds have also been performed to confirm the location
of the optimized structures at the local minima with the
same basis in the gas phase. The energy gap (Eg) between
the highest occupied molecular orbital (HOMO) and the
lowest unoccupied molecular orbital (LUMO) has been
calculated for all compounds in different solvents. Also,
contribution percentages of the excitations were calcu-
The DFT/B3LYP-D3 optimized geometries at 6–311++G
(d, p) level of Anil (a) and Boranil (b), in THF solvent is
shown in Figure 1. We have chosen this solvent because
it gives the highest total energy compared to the other
solvents. Therefore, the two molecules (a) and (b) are
more stable in THF (see Table 4) than in other solvents.
The selected computational values of bond lengths and
bond angles are given below in Table 1. Overall, the
[34]
lated using GaussSum 3.0 program.
Besides, simulated
absorption spectra of all synthesized molecules in differ-
ent solvents have been performed at the time-dependent
density functional theory (TD-DFT) using theCAM-
generation of BF six-membered ring slightly modifies
2
[
35,36]
B3LYP level.
All optoelectronic calculations were
the geometric structure of the Anil compound and can
make a great contribution to the rigidity of the Anil
(a) structure. This improved structural rigidity is one of
the most significant reasons for its intensive fluores-
[37]
performed using theGaussian09 program and visuali-
zations were carried by the graphical interfaces
[38]
[39]
Gabedit
and Gaussview.
[
40]
cence.
Notably, both dyes have an almost planar
structure and Anil's complexation slightly affects all
common bond lengths. It also appears that the B -O
24
2.3 | Synthesis procedure
2
5
and N -B bond lengths are respectively 1.464 Å and
21
25
As summarized in Scheme 1, the Anil (a):
E)2((phenylimino)methyl) phenol has been prepared in
1.606 Å, which is in agreement with those reported for
[
21,41,42]
(
analogous six-membered ring BF complexes.
The
2
good yield by refluxing the 1:1 molecular ratio of aniline
and salicylaldehyde in absolute ethanol and in the pres-
ence of trace amounts of p-TsOH. After heating the solu-
tion at reflux for 24 hr, the Anil (a) precipitates pure out
of the reaction mixture and can be purified by filtration
after cooling the mixture to room temperature. After-
ward, obtained yellow crystals nave been collected and
air-dried. Subsequent Boron (III) complexation has been
achieved for six days in dry toluene with BF .Et O (BF )
under basic conditions and N2 atmosphere to form
Boranil (b). The desired Boranil was obtained as a brown
oil and was extracted with acetyl acetate. After solvent
removal, the crude product has been purified by column
bond angles between (C -C -C ) of the BF2
12
11 22
six-membered ring plane has a relatively considerable
twist than those of Anil (a).those changes can essentially
be in the reflection of the electronegativity of the Fluo-
[
21]
rine atoms.
3.2 | NMR Spectrum analysis
3
2
2
1
19
To confirm elemental composition and purity, H and F
NMR spectral data of both synthesized compounds
(a) and (b) have been recorded in deuteratedDMSO at
300 MHz spectrometer and room temperature.
The assignment of each proton's resonance should
be based on its integration and multiplicity pattern.
However, a detailed proton's assignment is not possible
due to the strong π electron delocalization of aromatic
protons.
Anil (a); δ = 12.12 (s, 1H, OH), 9.12 (s, 1H, CH=N),
6.98–7.38 (m, 3H), 7.07–7.44(dd, J = 2.410 Hz, 2H), 7,66
(
dd, J = 2.781 Hz, 2H), 7.52 (dd, J = 1.221 Hz, 2H).
Boranil (b); δ =8.4 (s, 1H, CH=N), 6.96–6.99 (dd,
J = 1.97, 3H), 7.07–7.44(dd, J = 1.28 Hz, 2H), 7.52 (td,
J = 2.348 Hz, 3H), 7.52 (m, 2H).
1
SCHEME 1 General scheme for the synthesis of Anil and its
The GIAO H chemical shift calculation of (a) and
corresponding Boranil
(b) are simulated at B3LYP-D3/6–311++G (d, p) and

4
of 15
AGREN ET AL.
FIGURE 1 Optimized structures of (a) and (b) calculated at B3LYP-D3/6–311++G (d, p)
TABLE 1
The calculation bond length (in Å) andbond angles
shifts among the Boranil spectrum reveals a downward
shift in all proton signals. The imine proton shifts to
lower field proving the success of B-N bond formation
and the participation of the nitrogen atom in Boron coor-
ꢀ
(
) of (a) and (b) by DFT at 6–311++G (d. p) basis set level
Parametres
(a)
(b)
Bond length (Å)
[
43]
dination.
All obtained results are in agreement with
O
24-C12
1.344
1.323
data reported for similar Schiff bases and their
C
C
C
C
C
12-C11
1.421
1.449
1.096
1.419
1.423
1.087
[
44–46]
corresponding Boranils.
Further evidence for the
11-C22
19
identity of the Boranil compound comes from F NMR
22-H26 for (a)
22-H28 for (b)
22-N21
19
spectral data. F NMR spectrum exhibits a well-resolved
doublet broad signals at δ = −148.41 and − 148.34 ppm
revealing the presence of two non-equivalent Fluorine
atoms split by a Boron atom. The absence of quartets in
1.288
1.408
1.304
1.433
1.401
1.382
1.464
1.606
N
21-C
5
19
the F NMR spectra is occasionally explained to be the
result of the fast relaxation of the quadrupolar boron
F26-B25
F27-B25
B25-O24
----
----
----
----
[
47]
nuclei.
Doušová and co-workers reported that this
behavior could be the result of an additional not observed
splitting into doublets (due to the geminal 19F–19F cou-
pling). This phenomenon can occur in the case of the
N
21-B25
ꢀ
Bond angle ( )
[
47]
O
24-C21-C11
122
121
122
121
107
----
121
non-equivalence of the fluorines at room temperature.
19
The substitution does not affect F NMR spectra and res-
onances are practically the same as mentioned in our
C
C
C
12-C11-C22
11-C22-N21
118
122
120
----
[
25]
recent work.
Slight differences between experimental
22-N21-C
25-O24-C12
25-O24-C12
22-N21-B25
21-B25-O24
5
and theoretical values are essentially due to the model
used to be taken into account of the solvent effect on the
molecule. The PCM, used here, is not able to predict the
local strong interaction between liquid and the
H
B
123
120
109
C
----
[
25]
molecule.
N
----
compared to the experimental data. As a general over-
3.3 | IR Spectrum analysis
1
19
view, H and F NMR values have been in excellent
agreement with both proposed structures (see Table 2)
and both studied compounds yield similar proton spectra
A survey of the literature reveals that the FTIR spectros-
copy has been proven useful in confirming the proposed
except for the disappearance of hydroxyl proton for
structures of Anils, Boranils and similar organic com-
1
[12,26,48,49]
(b) spectrum. H NMR spectra of (a) and (b) exhibits the
pounds.
We have performed frequency calcula-
typical aromatic protons multiple and a typical imine
proton N=CH signal. A careful examination of proton
tions using B3LYP-D3/6–311++G (d, p) basis set in the
gas phase. The simulated harmonic vibrational

AGREN ET AL.
5 of 15
TABLE 2
H and F for (b)
Experimental and theoretical calculation NMR of
vibration modes, for both molecules (a) and (b), are very
close to those resulting from our previous study where
we have investigated and discussed in detail all vibration
1
19
(
a)
δexp (ppm)
δtheo (ppm)
[
25]
modes.
Generally, the CH out of plane bending vibra-
H
H
H
H
H
H
H
H
H
H
H
7
7.07
7.79
−
1
tions in aromatic compounds occur between 700 cm
and 1000 cm
7.47
7.61
−1.[51]
8
It is well known that CH out of plane
9
7.44
7.77
deformation presenting higher frequencies has a weaker
[52]
10
17
18
19
20
23
25
26
7.52
7.69
intensity than those absorbing at lower frequencies.
Therefore, The assignments of peaks in the region of the
corresponding region were not easy and this region was
dominated by very massive bands.
6.98
7.27
7.38
7.69
7.16
7.20
In the present work, All studied compounds exhibit
relatively weak absorption peaks in the region of
7.66
7.77
−1
−1
7.47
7.55
6
90–780 cm , 675–822 cm respectively for (a) and
12.12
9.12
12.93
9.32
(b) respectively and are assigned to CH out of plane
bending vibrational modes. These results show that com-
plexation has an obvious influence on their values and
show good agreement with the theoretical results (see
Table 3).
(
b)
δ
exp (ppm)
δ
theo (ppm)
7.90
7.86
7.8
H
H
H
H
H
H
H
H
H
H
7
6.96
8
7.18
In addition, the CH in-plane deformation vibrations
for substituted benzenes are seen in the range of
9
6.99
−
1
10
17
18
19
20
23
28
7.96
8.32
7.75
8
1000–1300 cm .
Several in-plane bending vibrations of the studied
7.68
Anil (a) and its Boranil (b) are identified in the range of
6.95
1
−1
1
073–1614 cm− and 1000–1662 cm respectively. The
7.52
7.64
7.87
7.56
8.55
theoretically calculated values appear in the range of
7.49
−1
−1
1
171–1644 cm , 1025–1646 cm for (a) and (b) respec-
7.02
tively, which shows that the predicted values are coincid-
ing very well with the observed frequencies. Taking into
account the structure modification through Boron
Difluoride complexation, there is not an appreciable
influence on the in-plane bending vibrations of the stud-
ied Boranil (b).
8.4
F
F
26
27
−148.35
−148.40
----
----
Furthermore, in the context of the results of the previ-
[
25]
wavenumbers have been scaled down uniformly by a fac-
ous study, the recently studied Anil spectra display
−
1
−1
tor of 0.987 (for wavenumbers under 1800 cm ) and
peaks in the range of 1400–1660 cm
azomethine C=N peaks for studied Anils and Boranils.
due to the
−
1
0
.961 (for those over 1800 cm ), which accounts for sys-
tematic errors caused by basis set incompleteness, neglect
of vibrational anharmonicity and electron correlation.
The computed values of these compounds are observed at
1471, 1586 and 1610 cm for (a) which implies good
[
50]
−1
The observed wavenumbers computed unscaled and
scaled frequencies of all studied compounds are listed in
Table 3. The experimental and computed FTIR of the title
compounds are presented in Figure 2.
agreement with the experimental findings. Peaks
corresponding to C=N stretching vibrations in the inves-
tigated Boranil (b) shift to higher wavenumber which
indicates that the coordination takes place through nitro-
[
25]
Both studied compounds have been characterized by
infrared spectroscopy where they exhibit typical peaks
with the appropriate shifts resulting from bonds forma-
tion. Organoboron Difluoride complex is compared to its
Anil ligand in order to investigate the coordination possi-
ble sites that could be involved in chelation. Depending
on their molecular structure, both studied compounds
display C-H and C=C stretching and bending vibrations.
Those vibrations are extremely informative and are very
gen atoms of azomethine groups.
The ring stretching
vibrations are extreme characteristics of the aromatic
[
48]
[53]
rings and their derivatives.
Most of the aromatic compounds undergo coupled
[
48]
vibrations called skeletal vibrations in the region of
1100–1600 cm
peaks.
−1
due to C-C and C=C stretching
In the same line of thought and in the presence
[
25]
[
25]
of the findings of an earlier study,
(a) and (b) exhibit
C-C and C=C stretching peaks (see Table 3) which are
very well within the cited literature range and show that
[12]
convenient for characterization purposes.
All obtained

6
of 15
AGREN ET AL.

AGREN ET AL.
7 of 15
FIGURE 2 Comparison of experimental and theoretical FT-IR spectra for (a) and (b)
the ring skeletal vibrations remain independent of other
As shown in Table 3, the comparison of the scaled
calculated frequencies gives reasonable deviations from
the experimental values.
[53]
vibration in the molecule.
It is important to emphasize that the complexation
−1
upfield CO stretching vibrations from 1453 cm for
−
1
(
a) to 1460 cm for (b). This trend is observed in our
[
25]
recent study.
We note also the appearance of novel
3.4 | Photophysical properties
−
1
peaks in the range of 822–1662 cm for (b). Those results
are similar to those obtained for a similar molecule in
3.4.1 | Frontier molecular orbital analysis
−1 [25]
our recent study (883–1093 cm ) corresponding for B-
N, B-O and B-F bending peaks. These results strongly
support the formation of foregoing Organoboron
The electronic and quantum chemical properties of the
optimized structure of (a) and (b) in different solvents are
listed in Table 4. The energy gap between HOMO and
[
11]
Difluoride Complexes.
reported by 14,
According to a detailed study
[14]
the appearance of a strong stretching
vibration above 1060 cm may be essentially due to B-N
LUMO is a critical parameter property for quantum
−
1
[54]
chemistry.
It determines the chemical activity and the
[
55]
vibration mode. Moreover, peaks in the region of
kinetic stability of the molecules
based on DFT calcu-
8
80 cm−
1[25]
were attributed to B-F stretching vibrations.
lations. From the results shown in Table 4, we can
deduce that the energy band gap of (a) has decreased
after the complexation with BF2 in all solvents. The com-
pounds (a) and (b) in the gas and the cyclohexane solvent
have the lowest gap energy compared to other solvents.
The electronic chemical potential (μ) is a chemical prop-
erty that describes the ability of an atom or a functional
group to attract electrons or electron density towards
Also, The existence of B-O bond is proven by the disap-
[25]
pearance of O-H bond.
For aromatic rings, CH stretching vibrations are
−
1
expected to occur above 3000 cm . Peaks observed in
−
1
−1
the range of 2823–3040 cm and 2823–3501 cm are
respectively assigned for CH stretching vibrations of
(a) and (b). In the light of these results, we clearly notice
[
56]
that complexation using BF , Et2O upfield CH stretching
itself.
The chemical hardness (η) measures both the
3
[
25]
[57]
vibrations. For the hydroxyl group, all the preceding
and actual spectra prove that OH stretching vibrations
are sensitive to hydrogen bonding
stability and the reactivity of a molecule.
The global
softness (σ) describes the capacity of an atom or group of
atoms to receive electrons. The values of (μ) and (σ) have
increased after the complexation with BF2 whereas the
values of (η) are decreased after the addition of BF2 as
shown in Table 4.
To establish a logical correlation, we may conclude
that the addition of BF2 makes the molecule (b) more
conductive and more polarizable (with lower molecular
[52]
and are predicted in
−
1
the range of 3500 cm .For the title compound (a), a
weak and broad peak appears in the range of
2
828–3070 cm− and is interpreted to be a sign of the for-
1
[45]
mation of hydrogen bonding.
This peak disappears in
organoboron difluoride complexe spectra indicting
deprotonation of ligands through Boron coordination.

8
of 15
AGREN ET AL.
TABLE 4
d, p)
The calculatedelectronic and quantum chemicalparameters for (a) and (b) different solventsat DFT/B3LYP-D3/6–311++ G
(
1
solvents
Chloroform
Cyclohexan
THF
HOMO
−6.296
−6.261
−6.311
−6.269
−6.232
−6.752
−6.724
−6.764
−6.730
−6.703
LUMO
−2.119
−2.096
−2.129
−2.100
−2.086
−2.775
−2.782
−2.773
−2.780
−2.798
Eg
μ (eV)
4.208
4.179
4.220
4.184
4.159
4.763
4.753
4.768
4.755
4.751
η (eV)
2.089
2.082
2.091
2.084
2.073
1.989
1.971
1.996
1.975
1.953
σ (eV−
0.479
0.480
0.478
0.480
0.482
0.503
0.507
0.501
0.506
0.512
)
μ
D
(D)
T
E (a.u)
(
a)
4.177
4.165
4.182
4.169
4.146
3.977
3.942
3.991
3.950
3.905
3.089
2.722
3.227
2.803
2.346
7.899
6.974
8.245
7.179
6.011
−632.179222
−632.176845
−632.180062
−632.177386
−632.174162
−856.381410
−856.376055
−856.383294
−856.377281
−856.369890
Toluen
Gas
(
b)
Chloroform
Cyclohexan
THF
Toluen
Gas
Eg≈ELUMO −EHOMO
μ = −½EHOMO + ELUMOꢁ=2
η = ½ELUMO −EHOMOꢁ=2
σ = 1=η
stability and high reactivity in chemical reactions) com-
pared to its Anil (a) especially in the gas phase and the
cyclohexane solvent. However, (a) and (b) are harder and
more stabilized using THF and chloroform solvents than
in other solvents.
color and the negative one is in green. It can be
deduced from this figure that the electron density of
HOMO is mostly identically localized on both phenyl
rings and azomethine moiety of (a) and their π -
bonding orbitals. Similarly, we get analogous results
for (b). Whereas, The LUMO electronic distribution
mainly populate on one phenyl ring than another espe-
cially after complexation and also their π*-bonding
orbitals. Owing to the extent of π conjugation after the
introduction of BF2 moiety, these results suggest that
structural modification has a significant effect on the
The contour plots of HOMO and LUMO investi-
gated at the DFT/B3LYP-D3/6–311++G (d, p) level of
all compounds are shown in Figure 3 in cyclohexane
solvent. The electronic absorption properties are
explained from the frontier molecular orbitals (HOMO
[58]
and LUMO).
The positive phase is presented in red
FIGURE 3 The frontier
molecular orbitals of (a) and (b)

AGREN ET AL.
9 of 15
electronic density distribution. These differences can
explain the different observed emission behavior.
effect on the short wavelengths absorption band's
intensity Long wavelengths absorption bands seem to
be dependent on the dipole moment of the solvent and
their intensities vary according to solvent polarity after
complexation as shown in Figure 4.Therefore, the short
wavelengths will not be taken as references for the
Anil and Boranil spectra analysis. An increase in sol-
3.4.2 | Electronic absorption spectra
In order to investigate the photophysical properties of the
studied anil and its Boron Difluoride Complexe; Boranil.
UV–vis absorption measurements are carried out experi-
mentally as well as theoretically using four different sol-
vents at room temperature: non-polar aprotic solvents
[
61]
vent polarity causes a bathochromic shift for Anil
spectra in the long-wavelength absorption bands. This
assumption demonstrates that the media polarity
affects essentially the keto forms rather than the enol
ones; it destabilizes the singlet excited state and/or sta-
(cyclohexan, toluen and chloroform). Polar aprotic sol-
[
62]
vent (THF) is selected and the concentration of each solu-
tion sample is maintained to be 10–4 M. TD-DFT
calculations on electronic absorption spectra in the previ-
ous solvents and in the gas phase were performed. The
calculations have been carried out using the CAM-
B3LYP/6–311++G (d, p) method. The absorption wave-
lengths (λ max), oscillator strengths (f) and major and
minor contributions (%) of (a) and (b) for solvents and
gas phase are illustrated in Table 5.
As a general observation, Boron Difluoride complexe:
Boranil shows good solubility and has a blue light emis-
sion under UV light in all tested organic media such as
Cyclohexane, toluene, chloroform, and THF. By testing,
no observable color and fluorescence fading has been
noticed over months.
bilizes the ground state of the keto forms.
Thus, Sta-
bilizing the ground state is a direct cause of the non-
fluorescence of (a).
Figure 4 represents comparative experimental and
theoretical absorption spectra of the studied Anil (a) in
different solvents. As a general trend, all Anil absorption
spectra display generally almost similar absorption spec-
tra; a large, unstructured absorption band located around
300–490 nm. The absence of structuration of the absorp-
tion bands is probably related to free rotations occurring
[
63]
in solution as reported in a previous study.
Bands
observed at short wavelengths may be attributed to elec-
tronic transitions from low lying molecular orbitals to the
LUMO. This phenomenon could also be caused by the
limited donor acceptor charge transfer due to the small
[
5]
It is apparent that there is a qualitative correlation
between the optical properties and the molecular struc-
tures. The combined effect of solvent polarity and com-
extent of the conjugation in (a) whereas bands observed
at higher energies are attributed to the π − π* presenting
an important percentage around 68%transitions of the
phenyl rings which is consistent for polyaromatic dyes
[16,59]
plexation is evident and has been widely studied.
[
12]
Solvent effects can be explained with the capacity of
hydrogen bonding both as proton donors and as proton
acceptors, thus permitting the proton transfers that result
in the formation of the keto form of the studied Anil (a).
The solvent interacts with the non-bonding electron pair
(see Table 5).
It is worth mentioning that the spectrum
superposition shows several absorption peaks for non-
polar aprotic solvents with additional shoulders. While, If
we see the absorption spectrum of both studied com-
pounds (a) and (b) recorded in THF (Polar Solvent), a red
shif is observed after complexation and the absorption
spectra shows a more structured spectra presenting three
relatively obvious absorption peaks (λabs = 301 nm,
369 nm and 488 nm). This is expected due to enhanced
[45]
of the azomethine nitrogen.
As a result, specific
solute-solvent interactions can lead to a qualitative and
quantitative change in the Anil spectra (Figure 4).
According to literature, Solvent effects are relevant in
Anils tautomers stability phenomena, since polarity dif-
ferences among tautomers can induce significant changes
[
64]
rigid structure.
After the blockage of the ESIPT core of (a) through
Boron Difluoride complexation, a different scenario of
absorption is observed. BF2 moiety introduction makes
all absorption spectra broader. A gradual increase of red-
shift is concomitantly observed for (b) from non-polar(-
Cyclohexan and Toluen) to polar solvent (THF). The
redshift is spanned in the range of 473 to 485 nm, 467 to
483 nm and 475 to 488 nm respectively for the experi-
mental spectra recorded in Cyclohexan, Toluen, and THF
and in the range of 461 to 484 nm (f = 0,68), 462 to
484 nm (f = 0,69) and 460 to 479 nm (f = 0.68) respec-
tively for the theoretical spectra. Bathochromically
[60]
in their relative energies in solution.
Besides, the
excited state of any donor-acceptor compound such as
Boranil gets strongly affected by solvents polarity due to
its stabilization through dipole–dipole, hydrogen bonding
[61]
and solvation interactions.
Both studied compounds have shown remarkable
[20]
solvatochromism behavior.
Using different solvents
has an obvious effect on the intensity and the broad-
ness of studied Anil and Boranil spectra. A direct com-
parison of the photophysical properties reveals that an
increase in solvent polarity doesn't have a relative

10 of 15
AGREN ET AL.

AGREN ET AL.
11 of 15

12 of 15
AGREN ET AL.
FIGURE 4 Observed and calculated UV–vis spectra of (a) and (b) in different solvents
shifted spectra have proven that both of the molecules
are stabilized in each excited state. Hence it can be
predicted that the studied compound is behaving like
donor-acceptor compounds while the excited state of
these compounds is highly stabilized in these solvents as
Fluorescent emissive in all studied solvents. Experimen-
tal Spectra of both studied compounds (a) and
(b) recorded in Chloroform are superimposable. A very
weak blue shift of 8 nm spanning in the range of
485–477 nm is observed in the experimental spectrum.
The respective calculated spectra feature a similar blue
shift of 10 nm(f = 0.68); this means that the absorption
occurs without differences in the spatial conformation of
[65]
compared to its ground state.
Moreover, red shifted
bands are directly related to larger electronic delocaliza-
[59]
tion.
It is obvious that there is a significant agreement
[
66]
between experimental and theoretical absorption
maxima.
the molecules.
The maximum absorption wavelength
corresponds to the electronic transition from the HOMO
to LUMO with a contribution of about 68–69% for both
studied compounds (a) and (b) while the short wave-
lengths correspond to an electronic transfer between
HOMO-1, HOMO-2, HOMO-3, … to highly excited states
LUMO+1, LUMO+4orbitals with moderate contributing
coefficients.
To find an account, on one side, using Chloroform as
a solvent gives us the predicted blue shift; on the other
side spectra recorded quality is unsatisfying and not
It is apparent, The introduction of BF2 moiety pre-
vents unsystematic rotations around single bonds, rigid-
ifies the structure in addition to helping the radiative
[
66]
process to control the non-radiative deexcitations.
The
formation of the B N dative bond via the donation of
lone-pair of the N atom to the B atom lowers the energy
gap between π* and π, which can decrease the loss of
energy via vibrational motions and increases the emis-
[11]
sion efficiency.
Thus, the synthesized Boranil is Blue

AGREN ET AL.
13 of 15
structured in comparison with calculated spectra. From
the point of view of spectra quality, peaks with several
shoulders have shown a better relative response using
THF. Therefore, the polarity of the solvent may be impor-
tant in enhancing photophysical properties of (a) and
media polarities. Current studies on the modification of
conjugated Fluorescent systems and emission properties
are in progress.
ACKNOWLEDGMENTS
(
b) and this observation is in agreement with several
The authors greatly acknowledge financial support
between cooperation Tunisia-Morocco for funding the
work through the research program N 17/TM10.
[67]
recent studies.
ꢀ
It is clear from this investigation that the obtained
experimental and theoretical spectra are in good agree-
ment. According to Chandreskaran, the small deviation
between both spectra may have resulted from the solvent
effect. The solvent causes the complexation of the chemi-
CONFLICT OF INTEREST
The authors declare that they have no conflict of interest.
[48]
cal molecular environment.
The interaction between
ORCID
different solvents and both studied Anil and Boranil can
also explain the slight fluctuations in the calculated
absorption wavelength maxima.
Abdul-Rahman Allouche https://orcid.org/0000-0003-
0725-4057
Mohamed Hassen V Baouab https://orcid.org/0000-
[68]
0003-2069-7151
4
| CONCLUSION
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How to cite this article: Agren S, Chaabene M,
Allouche A-R, Ben Chaâbane R, Lahcinie M,
Baouab MHV. Blue Highly Fluorescent Boranil
Derived From Anil Ligand: Synthesis,
Characterization, Experimental and Theoretical
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[
2020;e5764. https://doi.org/10.1002/aoc.5764