Synthesis, electrochemical/photophysical properties and computational investigation of 3,5-dialkyl BODIPY fluorophores

Article abstract of DOI:10.1016/j.ica.2018.06.006

A series of 3,5 dimethyl and diethyl BODIPY with different substitutions at meso position are synthesized and characterized. Photophysical and electrochemical features of the 3,5 dialkyl BODIPY fluorophores are investigated using experimental and computational approaches. All fluorophores display absorption maxima around at 510 nm and emission maxima around at 520 nm which correspound to very narrow Stokes shift. Among the fluorophores, 3,5,8 alkylated BODIPYs are found to have high fluorescence quantum yield (1.00–0.93). 4-Bromophenyl group at meso position decreases fluorescence quantum yield of the dye while it increases with 4-methoxyphenyl group at meso position. The HOMO-LUMO energies of synthesized fluorophore compounds were calculated by B3LYP/6-31G(d,p) and B3LYP/6-311+G(d,p) levels in chloroform phase. Electron donating and accepting groups show increasing and decreasing effect on the band gaps of the fluorophores respectively.

Full text of DOI:10.1016/j.ica.2018.06.006

InorganicaChimicaActa482(2018)130–135
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Synthesis, electrochemical/photophysical properties and computational
investigation of 3,5-dialkyl BODIPY fluorophores
Yavuz Derina, Raşit Fikret Yılmaza, İbrahim Halil Baydilekb, Vildan Enisoğlu Atalayc,⁎
,
Abdil Özdemira, Ahmet Tutara,⁎
a
Sakarya University, Department of Chemistry, Faculty of Arts and Sciences, Sakarya 54187, Turkey
Department of Medical Services and Techniques, Health Services Vocational School, Iğdır University, 76000 Iğdır, Turkey
b
c
Üsküdar University, Department of Bioengineering, Istanbul 34662, Turkey
A R T I C L E I N F O
A B S T R A C T
Keywords:
BODIPY
Fluorescence quantum yield
HOMO-LUMO
DFT
A series of 3,5 dimethyl and diethyl BODIPY with different substitutions at meso position are synthesized and
characterized. Photophysical and electrochemical features of the 3,5 dialkyl BODIPY fluorophores are in-
vestigated using experimental and computational approaches. All fluorophores display absorption maxima
around at 510 nm and emission maxima around at 520 nm which correspound to very narrow Stokes shift.
Among the fluorophores, 3,5,8 alkylated BODIPYs are found to have high fluorescence quantum yield
(1.00–0.93). 4-Bromophenyl group at meso position decreases fluorescence quantum yield of the dye while it
increases with 4-methoxyphenyl group at meso position. The HOMO-LUMO energies of synthesized fluorophore
compounds were calculated by B3LYP/6-31G(d,p) and B3LYP/6-311+G(d,p) levels in chloroform phase.
Electron donating and accepting groups show increasing and decreasing effect on the band gaps of the fluor-
ophores respectively.
1. Introduction
position. Some of these dyes were reported in elsewhere nonetheless
complete study of photophysical, electrochemical and computational
Fluorescent dyes are of important place in many areas from clinical
applications to technological applications [1]. Important class of these
dyes is 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene abbreviated as
BODIPY and they have gained increasing attention, due to their ex-
cellent properties, for example chemical robustness, nearly insensitivity
to polarity of the enviroment, good solubilty, intense absorption peak
with high molar absoption coefficient in visible region, high fluores-
cence quantum yield and small Stokes shift [2–4]. In addition, these
photophysical features can be easily tailored by different synthetic
strategies on BODIPY core [5]. Thereby these dyes have many appli-
cations such as fluorescence probes [6–7], bio-labeling reagent [8],
laser dyes [9], photo sentisizer for photodynamic therapy [10,11] and
solar cell [12]. Photophysical and electrochemical behavior of BODIPY
dyes are highly dependent upon the groups substituted to the structure.
Some BODIPY derivatives such as dimethyl, tetramethyl BODIPY
compounds were synthesized and relationship between the stuructures
and properties was investigated [13,14].
investigation does not exist [14–18]. The relationship between struc-
ture and electronic properties of these fluorophores was investigated
via experimental and computational approach.
2. Results and discussion
2.1. Spectroscopic properties of 3,5-dialkyl BODIPY fluorophores
1H, 13C and 19F NMR spectroscopic methods were applied for
characterization of all compounds (Fig. 1). For the final BODIPY com-
pounds, NMR chemical shifts were computed by theoretical methods
and compared with the experimental shifts so it is revealed that com-
puted 1H and 13C chemical NMR shifts by GIAO method in CDCl3 were
best matched with the experimantal chemical shifts (Table S1). Fig. 2
shows that the absorption and emission spectra of the 3,5-dialkyl
BODIPY fluorophores in CH2Cl2. The photophysical parameters of the
fluorophores such as absorption maxima, molar extinction coefficient,
emission maxima, Stokes shift and quantum yield were summarized in
Table 1. Maximum absorption peaks of the fluorophores were located
between the range of 508 and 515 nm, as for their emission maximas,
In our present study, we carried out the synthesis of 3,5-dialkyl
BODIPY fluorophores containing different substituents including ethyl
(1), phenyl (2), 4-methoxyphenyl (3) and 4-bromophenyl (4) at meso
⁎
Corresponding authors.
E-mail addresses: vildan.enisoglu@uskudar.edu.tr (V.E. Atalay), atutar@sakarya.edu.tr (A. Tutar).
https://doi.org/10.1016/j.ica.2018.06.006
Received 5 April 2018; Received in revised form 24 May 2018; Accepted 4 June 2018
0020-1693/©2018ElsevierB.V.Allrightsreserved.

Y. Derin et al.
InorganicaChimicaActa482(2018)130–135
Fig. 1. Synthesized fluorophore molecules.
Fig. 2. The electronic absorption (A and B) and fluorescence spectra (C and D) of the 3,5-dialkyl BODIPY fluorophores 1A–4B in dilute solution in CHCl3.
they ranged between 514 and 529 nm. The fluorophores show strong
absorption peaks around at 510 nm and a shoulder located at higher
energy side (approximately 480 nm) attributed to S0-S1 and the 0–1
vibrational transitions, respectively. This peaks are similar for structu-
rally typical BODIPY fluorophores [19]. The fluorophores can be cate-
gorised into two groups according to meso position and 3,5 positions.
The dye couples having same group at meso position and methyl
(1A–4A) or ethyl (1B–4B) at 3,5 positions differ from each other only
∼1–2 nm in absorption and emission spectra. The reason for the small
difference value in absorption and emission spectra is due to similar
electronic effects of methyl and ethyl groups on the core BODIPY
structure [20].
Table 1
Photophysical properties of 3,5-dialkyl BODIPY fluorophores (1A–4B) in CHCl3
solvent.
Compound
λabs (nm)
λem (nm)
Δλ (nm)a Stokes Shift
φb
εc
1A
2A
3A
4A
1B
2B
3B
4B
508
512
511
514
509
514
512
515
514
525
522
529
515
526
523
528
6
1.00
0.36
0.45
0.24
0.93
0.37
0.51
0.25
6.8 × 104
5.7 × 104
7.1 × 104
6.6 × 104
7.3 × 104
5.8 × 104
7.0 × 104
5.6 × 104
13
11
15
6
12
11
13
a
It is obvious that the fluorophores (1A–1B) bearing alkyl group at
meso position showed the highest fluorescence quantum yield
(∼1.00–0.93) and the smallest Stokes shift. However it is worth noting
that the fluorophores bearing phenyl ring at meso position drastically
decreased the fluorescence quantum yield with respect to fully
Stokes Shift (nm).
b
c
Fluorescence quantum yield.
Molar absorption coefficient (mol·L−1·cm−1).
131

Y. Derin et al.
InorganicaChimicaActa482(2018)130–135
Fig. 3. The cyclic voltametry of the 3,5-dialkyl BODIPY fluorophores 1A–4B in dilute solution in CH3CN containing 0.1 M TBAPF6 at a scan rate of 100 mV/s.
alkylated fluorophores in the series. 4-methoxy phenyl which serves as
electron donating group resulted in somewhat higher quantum yield
and smaller Stokes shift. On the other hand 4-bromophenyl as electron
accepting group led to low quantum yield steaming from heavy atom
effect of the bromine atom [21,22] and larger Stokes shift among the
phenyl bearing fluorophores. The fluorophores with methoxy and
bromine containing phenyl ring exhibit hypsochromic and bath-
ochromic shift with respect to only phenyl possessing counterparts,
respectively.
bromophenyl groups decreased the band gap as in the fluorophores
4A–4B, 4-methoxyphenyl groups caused to the wide band gap in the
fluorophore couples 3A–3B. Although ethyl groups at meso posion
(1A–1B) are electron donating groups, considerable change was not
observed in the band gap which is found very similar to phenyl bearing
ones (2A–2B).
Finaly, theoretical HOMO-LUMO and band gap energies (in Fig. 4)
of the fluorophore 3,5 dimethylBODIPY (1A–4A) and diethylBODIPY
(1B–4B) were found to have same trend compared to the experimental
values.
2.2. Electrochemistry properties
3. Conclusions
Cyclic voltammetry (CV) is frequently utilized to measure electro-
chemical properties of the dyes from which the highest occupied mo-
lecular orbital (HOMO) and the lowest unoccupied molecular orbital
(LUMO) energy levels are predicted. The cyclic voltammograms were
recorded for the fluorophores (1A–4B) and depicted in Fig. 3.
In this study firstly, all compounds are successfully synthesized by
given methods and structurely charecterized by 1H, 13C, 19F NMR
spectroscopy methods. Our study reveals the effect of substituated
phenyl groups at meso position and alkyl groups on photophysical
properties such as fluorescence quatum yield, absorption/emission
maxima, Stokes shift, molar absorption coefficient. In this respect, The
fluorophores (1A–1B) bearing alkyl group instead of phenyl groups at
meso position are found to show highest quantum yields (1.00–0.93)
which can be good candidate for quantum yield standart. On the other
hand, the absorption and emission spectrum profiles of the fluorophores
are bearly influenced from phenyl groups but slightly effected from
alkyl group at meso position. Cyclic voltammetry in combination with
UV–vis spectrophotometry is applied to investigate electrochemical
properties of the fluorophores such as HOMO-LUMO energy levels and
band gap. Alkyl groups (methyl and ethyl) at 3,5 position lead to almost
no change on electrochemical properties which may be due to similar
electronic effect of methyl and ethyl. It is observed that band gap gets
wide introducing electron accepting group namely 4-bromophenyl to
meso position and remains nearly unchanged in ethyl, phenyl, 4-
methoxyphenyl bearing fluorophores at meso position.
The HOMO energies are directly related to the ionization potential,
LUMO energies are directly related to the electron affinity. The energy
and distribution of the HOMO-LUMO orbitals energy difference be-
tween HOMO-LUMO gap orbital are an important stability for struc-
tures [23]. Also HOMO-LUMO and band gap values of the fluorophores
calculated via experimental and theoretical methods were gathered in
Table 2. A molecule with a small gap is more polarized and is known as
soft molecule. More importantly, the HOMO orbitals are mainly loca-
lized on the nitrogen-containing five-membered ring, whereas the
LUMO orbitals are distributed over the whole molecules. This means
that pyrrole ring in 3,5-dialkyl BODIPY fluorophores (1A–4B) would be
more easily attacked. All fluorophores have similar CV profiles which
consist of an irreversible reduction and oxidation peak appeared at
around 0.9 V and 1.30 V, respectively. For all fluorophores, it appears
that HOMO energies are almost same however, the band gaps and
LUMO energies are different. It can be clearly stated that electron ac-
cepting groups lead to narrow band gap on the other hand electron
donating groups widen the band gap [24,25]. The order of stability of
the fluorophore compounds is 4B < 4A < 2B < 2A < 1A ≈ 1B <
4. Experimental and theoretical section
4.1. General methods of synthesis
3B < 3A as obtained by theoretical methods. As
a result 4-
Thin layer chromatography was carried out on Merck silica F254
0.255 mm plates, and spots were visualized by UV at 254 nm. Flash
column chromatography was performed using Merck 60 (70–230 mesh)
silica gel. Melting points were taken on a MPM-H1 capillary melting
points apparatus. Solvents were concentrated at reduced pressure. IR
spectra were recorded on a Shimadzu Prestige-21 (200 VCE) FT/IR
instrument. 1H (300 MHz), 13C (75 MHz) and 19F (282 MHz) NMR
spectra in CDCl3 were obtained on a Varian Infinity Plus spectrometer.
2-methyl-1H-pyrrole (B1) and 2-ethyl-1H-pyrrole (B2) were synthe-
sized by modification of the method given in the literature [26,27].
Table 2
Calculated (B3LYP/6-311+G(d.p)) and experimental HOMO-LUMO values
(eV) and band gaps levels in CHCl3 phase.
Compounds
Theoretical
HOMO
Experimental
LUMO
Band Gap
HOMO
LUMO
Band Gap
1A
1B
2A
2B
3A
3B
4A
4B
−5.61
−5.60
−5.64
−5.63
−5.65
−5.52
−5.70
−5.68
−2.58
−2.57
−2.67
−2.67
−2.30
−2.29
−2.75
−2.75
3.03
3.03
2.97
2.96
3.35
3.23
2.95
2.93
−5.59
−5.56
−5.56
−5.59
−5.54
−5.57
−5.59
−5.59
−3.25
−3.22
−3.22
−3.24
−3.19
−3.22
−3.28
−3.27
2.34
2.34
2.34
2.33
2.35
2.35
2.31
2.32
4.1.1. Synthesis of 2-methyl-1H-pyrrole B1
Two-necked reaction balloon (250 mL); ethyleneglycol (80 mL),
KOH (8 g, 142 mmol), hydrazinehydrate (N2H4·H2O), (6 mL,
132

Y. Derin et al.
InorganicaChimicaActa482(2018)130–135
Fig. 4. The HOMO-LUMO energies of 1A–4B and bandgaps are in eV.
collection adapter on the distillate bridge, 25 mL collection bubbles on
both ends of the adapter, and the distillate bridge connected to the
vacuum device. The system was turned on and the temperature was
raised slowly. When the temperature reached 92 °C, the reaction mix-
ture started to boil. The first distillate came to the collection balloon at
97 °C. The distillate was collected for 47 min and the temperature
slowly began to fall. Then the temperature and vacuum were turned off.
The distillate from the system was extracted with diethylether
(3 × 20 mL) and dried over Na2SO4 to remove the excess solvent under
reduced vacuum (light yellow liquid, 3.11 g, % 64), (Fig. 6). 1H NMR
(CDCl3, 300 MHz, ppm) δH 7.98 (bs, 1H, NeH), 6.82 (s, 1H, Pi-H), 6.38
(t, J = 2.8 Hz, Pi-H), 6.17 (s, 1H, Pi-H), 2.80 (q, J = 2.4 Hz, 2H, eCH2),
1.45 (t, J = 2.8 Hz 3H, eCH3). 13C NMR (CDCl3, 75 MHz, ppm) δC
134.5, 116.5, 108.4, 104.4, 21.1, 13.9. FT-IR (cm−1): 3381, 3100,
2967, 1875, 1685, 1630, 1568, 1459, 1326, 1209, 1117, 1096, 1022,
932, 883, 794, 707.
Fig. 5. Synthesis of 2-methyl-1H-pyrrole B1.
0.12 mmol) and pyrrole-2-carboxyaldehyde (1H-pyrrole-2-carbalde-
hyde) (4 g, 42 mmol) were added at room temperature under nitrogen.
The reaction balloon was placed in the jacketed heater and the tem-
perature control probe and the other neck reflux system were placed.
The temperature controller was heated for 15 min at 80 °C then brought
to 130 °C and stirred for 15 min. (After 30 min, the mixture was further
refluxed for 3 h at 180 °C) . After 3 h, the temperature was turned off
and the temperature of there action medium was reduced to 50 °C. The
reflux of there action system, which cooled to 50 °C, was removed, re-
placing the small distillate bridge and collection adapter on the dis-
tillate bridge, 25 mL collection bubbles on both ends of the adapter, and
the distillate bridge connected to the vacuum device. The system was
turned on and the temperature was raised slowly. When the tempera-
ture reached 88.4 °C, the reaction mixture started to boil. The first
distillate came to the collection balloon at 90 °C. The distillate was
collected for 35 min and the temperature slowly began to fall. Then the
temperature and vacuum were turned off. The distillate from the system
was extracted with diethylether (3 × 20 mL) and dried over Na2SO4 to
remove the excess solvent under reduced vacuum (light yellow liquid,
2.51 g, % 73), (Fig. 5). 1H NMR (CDCl3, 300 MHz, ppm) δH 7.92 (bs, 1H,
NeH), 6.69 (s, 1H, Pi-H), 6.16 (t, J = 2.6 Hz, 1H, Pi-H), 5.94 (d,
J = 2.5 Hz, 1H, Pi-H), 2.31 (s, 3H, eCH3). 13C NMR (CDCl3, 75 MHz,
ppm) δC 128.0, 116.7, 108.7, 106.1, 13.2. FT-IR (cm−1): 3376, 3097,
2916, 1684, 1571, 1457, 1412, 1269, 1117, 1094, 1025, 951, 884, 782,
707.
4.2. General procedure for 3,5-dialkyl BODIPY fluorophores (1A–4B)
To a solution of substituted pyrrole (2 eq.) in C2H4Cl2 (40 mL) was
dropwise added a solution of acylchloride (1 eq.) at room temperature
under nitrogen. After addition, the solution was stirred at 120 °C for
16 h under nitrogen. The solution was cooled to 0 °C ice-water bath,
triethylamine (5 eq.) was then added dropwise at 0 °C for 10 min, and
the mixture was stirred for 10 min (Fig. 7). The ice-water bath was
removed. After reaction mixture was reached to room temperature,
then BF3.OEt2 (10 eq.) was added, and the mixture was stirred at room
temperature for 20 h. After removal of solvent, the residue was passed
through a silica gel column using 25% CH2Cl2 in hexanes to give
BODIPY as crystalline product after removal of solvent.
4.2.1. Synthesis of 4,4-difluoro-8-ethyl-3,5-dimethyl-4-bora-3a,4a-diaza-s-
indacene (1A)
Green powder (400 mg, 28%, isolated yield); m.p = 182–184 °C; Rf
(25% Hexane/EtOAc) = 0.57. 1H NMR (CDCl3, 300 MHz, ppm) δH 7.09
(d, J = 4.1 Hz, 2H, Pi-H), 6.27 (d, J = 4.1 Hz, 2H, Pi-H), 2.83 (q,
J = 7.7 Hz, 2H, eCH2e), 2.60 (s, 6H, eCH3), 1.37 (t, J = 7.7 Hz, 3H,
eCH3). 13C NMR (CDCl3, 75 MHz, ppm) δC 158.8, 147.1, 134.5, 126.8,
4.1.2. Synthesis of 2-ethyl-1H-pyrrole B2
Two-necked reaction balloon (250 mL); ethyleneglycol (100 mL),
KOH (10 g, 177.5 mmol), hydrazinehydrate (N2H4·H2O), (8 mL,
0.16 mmol) and methyl-2-pyrrole ketone (5 g, 45 mmol) were added at
room temperature under nitrogen. The reaction balloon was placed in
the jacketed heater and the temperature control probe and the other
neck reflux system were placed. The temperature controller was heated
for 15 min at 100 °C then brought to 150 °C and stirred for 15 min. After
30 min, the temperature was further refluxed for 5 h at 200 °C. After
5 h, the temperature was turned off and the temperature of the reaction
medium was reduced to 50 °C. The reflux of the reaction system, which
cooled to 50 °C, was removed, replacing the small distillate bridge and
Fig. 6. Synthesis of 2-ethyl-1H-pyrrole B2.
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Y. Derin et al.
InorganicaChimicaActa482(2018)130–135
(d, J = 8.8 Hz, 2H, Ar-H), 7.00 (d, J = 8.8 Hz, 2H, Ar-H), 6.76 (d,
J = 4.1 Hz, 2H, Pi-H), 6.28 (d, J = 4.1 Hz, 2H, Pi-H), 3.89 (s, 3H,
eOCH3), 2.64 (s, 6H, eCH3). 13C NMR (CDCl3, 75 MHz, ppm) δC 157.2,
134.7, 132.4, 131.2, 130.5, 126.8, 119.4, 113.9, 113.7, 55.7, 15.1. 19F
NMR (CDCl3, 282 MHz, ppm) δF −147.95 (q, JBF = 33.00 Hz) FT-IR
(cm−1): 3111, 3019, 2971, 2922, 2850, 1739, 1599, 1573, 1547, 1491,
1446, 1374, 1250, 1218, 1136, 1074, 1026, 960, 882, 840, 784, 762,
739, 713, 589, 527. MALDI-TOF-MS m/z calcd. for C18H17BF2N2O
[M]+: 326.1402; found: 326.1281.
4.2.6. Synthesis of 4,4-difluoro-8-(4-methoxyphenyl)-3,5-diethyl-4-bora-
3a,4a-diaza-s-indacene (3B)
Orange-yellow
crystal
(460 mg,
25%,
isolated
yield);
m.p = 136–138 °C; Rf (50% Hexane/CHCl3) = 0.13. 1H NMR (CDCl3,
300 MHz, ppm) δH 7.47 (AA′ part of AA′BB′, 2H, Ar-OCH3), 7.01 (BB′
part of AA′BB′, 2H, Ar-OCH3), 6.78 (d, J = 3.9 Hz, 2H, Pi-H), 6.36 (d,
J = 3.9 Hz, 2H, Pi-H), 3.90 (s, 3H, eOCH3), 3.08 (q, J = 7.5 Hz, 4H,
eCH2e), 1.35 (t, J = 7.5 Hz, 6H, eCH3). 13C NMR (CDCl3, 75 MHz,
ppm) δC 163.2, 161.4, 143.2, 134.4, 132.3, 130.6, 126.9, 117.3, 113.9,
55.7, 22.2, 13.1 19F NMR (CDCl3, 282 MHz, ppm) δF −145.70 (q,
JBF = 33.50 Hz). FT-IR (cm−1): 2970, 2938, 2876, 1605, 1573, 1550,
1508, 1488, 1433, 1319, 1280, 1250, 1215, 1175, 1127, 1087, 1022,
999, 980, 882, 833, 758, 736, 706, 644, 589. MALDI-TOF-MS m/z
calcd. for C20H21BF2N2O [M]+: 354.2077; found: 354.2034.
Fig. 7. General synthesis scheme of 3,5-dialkyl BODIPY (1A–4B).
119.0, 23.9, 18.4, 15.0. 19F NMR (CDCl3, 282 MHz, ppm) δF −148.65
(q, JBF = 33.76 Hz) FT-IR (cm−1): 2967, 2922, 2858, 1727, 1572, 1493,
1456, 1373, 1286, 1241, 1146, 1097, 999, 958, 909, 784, 717, 664.
MALDI-TOF-MS m/z calcd. for C13H15BF2N2 [M]+: 248.1296; found:
248.1474.
4.2.2. Synthesis of 4,4-difluoro-8-ethyl-3,5-diethyl-4-bora-3a,4a-diaza-s-
indacene (1B)
4.2.7. Synthesis of 4,4-difluoro-8-(4-bromophenyl)-3,5-dimethyl-4-bora-
3a,4a-diaza-s-indacene (4A)
Orange powder (400 mg, 25%, isolated yield); m.p = 135–137 °C; Rf
(50% Hexane/CHCl3) = 0.18. 1H NMR (CDCl3, 300 MHz, ppm) δH 7.13
(d, J = 4.2 Hz, 2H, Pi-H), 6.34 (d, J = 4.2 Hz, 2H, Pi-H), 3.04 (q,
J = 7.6 Hz, 4H, eCH2e), 2.82 (q, J = 9.0 Hz, 2H, eCH2e), 1.35 (m,
J = 7.6 Hz, 3H, eCH3), 1.30 (t, J = 9.0 Hz, 6H, eCH3). 13C NMR
(CDCl3, 75 MHz, ppm) δC 162.8, 147.5, 134.2, 126.8, 116.9, 23.9, 22.2,
18.4, 13.0. 19F NMR (CDCl3, 282 MHz, ppm) δF −146.45 (q,
JBF = 33.81 Hz) FT-IR (cm−1): 2971, 2937, 2877, 1565, 1486, 1437,
1316, 1241, 1131, 1101, 1026, 965, 803, 736, 713. MALDI-TOF-MS m/
z calcd. for C15H19BF2N2 [M+H]+: 277.1688; found: 277.1691.
Red powder (390 mg, 21%, isolated yield); m.p = 180–182 °C; Rf
(50% Hexane/CHCl3) = 0.15. 1H NMR (300 MHz, CDCl3, ppm): δH 7.62
(AA′ part of AA′BB′, 2H, Ar-H), 7.37 (BB′ part of AA′BB′, 2H, Ar-H),
6.68 (d, J = 4.2 Hz, 2H, Pi-H), 6.28 (d, J = 4.2 Hz, 2H, Pi-H), 2.65 (s,
6H, eCH3). 13C NMR (75 MHz, CDCl3): δC 158.3, 141.1, 134.5, 133.2,
132.0, 131.8, 130.4, 124.7, 120.0, 15.2. 19F NMR (CDCl3, 282 MHz,
ppm) δF −148.05 (q, JBF = 33.94 Hz) FT-IR (cm−1): 3140, 2925, 2858,
1738, 1572, 1550, 1535, 1452, 1373, 1264, 1215, 1140, 1073, 986,
877, 828, 795, 765, 731, 652, 580. MALDI-TOF-MS m/z calcd. for
C
17H14BBrF2N2 [M+H]+: 375.0480; found: 375.0468.
4.2.3. Synthesis of 4,4-difluoro-8-phenyl-3,5-dimethyl-4-bora-3a,4a-diaza-
s-indacene (2A)
4.2.8. Synthesis of 4,4-difluoro-8-(4-bromophenyl)-3,5-diethyl-4-bora-
3a,4a-diaza-s-indacene (4B)
Bright
green
crystal
(400 mg,
28%,
isolated
yield);
m.p = 110–112 °C; Rf (50% Hexane/EtOAc) = 0.67. 1H NMR (CDCl3,
300 MHz, ppm) δH 7.49–7.46 (m, 5H, Ar-H), 6.70 (d, J = 4.1 Hz, 2H, Pi-
H), 6.26 (d, J = 4.1 Hz, 2H, Pi-H), 2.66 (s, 6H, eCH3). 13C NMR (CDCl3,
75 MHz, ppm) δC 157.8, 142.8, 134.7, 134.3, 130.7, 130.6, 130.2,
128.4, 119.6, 15.2. 19F NMR (CDCl3, 282 MHz, ppm) δF −147.95 (q,
JBF = 33.51 Hz) FT-IR (cm−1): 2975, 2850, 1738, 1576, 1538, 1493,
1437, 1395, 1260, 1218, 1135, 1064, 981, 879, 781, 717. MALDI-TOF-
MS m/z calcd. for C17H15BF2N2 [M]+: 296.1296; found: 296.1237.
Red powder (230 mg, 23%, isolated yield); m.p = 138–139 °C; Rf
(50% Hexane/CHCl3) = 0.20. 1H NMR (300 MHz, CDCl3): δH 7.68 (AA′
part of AA′BB′, 2H, Ar-H), 7.30 (BB′ part of AA′BB′, 2H, Ar-H), 6.67 (d,
J = 4.2 Hz, 2H, Pi-H), 6.34 (d, J = 4.2 Hz, 2H, Pi-H), 3.06 (q,
J = 7.6 Hz, 4H, eCH2e), 1.33 (t, J = 7.6 Hz, 6H, eCH3). 13C NMR
(75 MHz, CDCl3): δC 164.2, 141.4, 134.1, 133.2, 132.0, 131.7, 130.4,
124.7, 117.8, 22.3, 13.0. 19F NMR (CDCl3, 282 MHz, ppm) δF −145.45
(q, JBF = 33.49 Hz) FT-IR (cm−1): 3095, 2964, 2501, 2196, 2049, 1915,
1762, 1693, 1569, 1551, 1486, 1462, 1435, 1403, 1389, 1341, 1312,
1255, 1219, 1120, 1080, 1067, 1035, 1006, 978, 881, 797, 769, 757,
4.2.4. Synthesis of 4,4-difluoro-8-phenyl-3,5-diethyl-4-bora-3a,4a-diaza-s-
indacene (2B)
731, 699. MALDI-TOF-MS m/z calcd. for C19H18BBrF2N2 [M+H]+
:
Orange-green
crystal
(400 mg,
25%,
isolated
yield);
403.0793; found: 403.1129.
m.p = 155–157 °C; Rf (50% Hexane/EtOAc) = 0.71. 1H NMR (CDCl3,
300 MHz, ppm) δH 7.50–7.47 (m, 5H, Ar-H), 6.75 (d, J = 4.2 Hz, 2H, Pi-
H), 6.36 (d, J = 4.2 Hz, 2H, Pi-H), 3.10 (q, J = 7.6 Hz, 4H, eCH2e),
1.35 (t, J = 7.6 Hz, 6H, eCH3). 13C NMR (CDCl3, 75 MHz, ppm) δC
163.7, 143.1, 134.4, 130.7, 130.6, 130.2, 129.1, 128.4, 117.5, 22.3,
13.1. 19F NMR (CDCl3, 282 MHz, ppm) δF −145.45 (q, JBF = 33.64 Hz)
FT-IR (cm−1): 2971, 2922, 2850, 1735, 1550, 1489, 1429, 1369, 1312,
1282, 1128, 1090, 977, 883, 788, 720, 645, 592. MALDI-TOF-MS m/z
calcd. for C19H19BF2N2 [M]+: 324.1609; found: 324.1940.
4.3. Photophysical and electrochemical measurements
All absorption and fluorescence spectra were acquired from diluted
solution of BODIPY compunds in CH2Cl2 using Shimadzu UV-2600
UV–VIS spectrophotometer and Hitachi F-7000 Fluorescence spectro-
photometer respectively. The absorbance at excitation wavelenght was
kept below 0.1. Fluorescence quantum yields were calculated from the
equation given below [28]. Rhodamine B solution in ethanol was used
as reference dye (φr = 0.49) [29].
4.2.5. Synthesis of 4,4-difluoro-8-(4-methoxyphenyl)-3,5-dimethyl-4-bora-
3a, 4a-diaza-s-indacene (3A)
2
μsmp
μref
Ismp
Iref
Aref
Asmp
⎛
⎜
⎞
⎟
⎛
⎜
⎞
⎛
⎜
⎞
⎟
φ = φ
⎟
s
r
Red crystal (500 mg, 21%, isolated yield); m.p = 188–190 °C; Rf
⎝
⎠
⎝
⎠
⎝
⎠
(50% Hexane/EtOAC) = 0.54. 1H NMR (CDCl3, 300 MHz, ppm) δH 7.45
134

Y. Derin et al.
InorganicaChimicaActa482(2018)130–135
The subscripts ref and smp reffer to the reference and sample dyes. φ
[2] G. Ulrich, R. Ziessel, A. Harriman, Angew. Chem. Int. Ed. 47 (2008) 1184–1201.
[3] A. Louder, K. Burgess, Chem Rev. 107 (2007) 4891–4932.
[4] T.V. Goud, A. Tutar, J.F. Biellmann, Tetrahedron 62 (2006) 5084–5091.
[5] N. Boens, V. Leen, W. Dehaen, Chem. Soc. Rev. 41 (2012) 1130–1172.
[6] R. Ziessel, G. Ulrich, A. Harriman, New J. Chem. 31 (2007) 496–501.
[7] W. Qin, W. Dou, V. Leen, W. Dehaen, M.V. Auweraer, N. Boens, RSC Adv. 6 (2016)
7806–7816.
[8] S. Niu, C. Massif, G. Ulrich, P.Y. Renard, A. Romieu, R. Ziessel, Chem. Eur. J. 18
(2012) 7229–7242.
[9] T.G. Pavlopoulos, J.H. Boyer, K. Thangaraj, G. Sathyamoorthi, M.L. Soong, Appl.
Opt. 31 (1992) 7089–7094.
[10] M.J. Ortiz, A.R. Agarrabeitia, G.D. Sampedro, B.J. Prieto, T.A. Lopez, W.A. Massad,
H.A. Montejano, A.G. Norman, I.L. Arbeloa, J. Tetrahedron. 68 (4) (2012)
1153–1162.
[11] Y. Cakmak, S. Kolemen, S. Duman, Y. Dede, Y. Dolen, B. Kilic, Z. Kostereli,
L.T. Yildirim, A.L. Dogan, D. Guc, E.U. Akkaya, Angew. Chem. Int. Ed. 50 (2011)
11937–11941.
is the fluorescence quantum yield; I is the area under fluorescence
spectrum; A is the absorption of light at excitation wavelenght; μ is
refraxtive index of the solvents (Ethanol and CH2Cl2).
Cyclic voltammetric (CV) studies were carried out on Gamry
Interphase 1000 potentiostat with an electrochemical system utilizing a
three-electrode configuration consisting of a platinum electrode, pla-
tinum wire electrode and a silver/silver chloride electrode as working
electrode, counter electrode, and reference electrode, respectively. The
electrochemical behaviors of BODIPY dyes were investigated in CH3CN
containing 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6)
as supporting electrolyte at a scan rate of 100 mV/s.
HOMO is calculated via oxidation peak potential, while band gap is
calculated from absorption onset wavelenght using the given equations.
Therefore LUMO can be obtained from these two values of EHOMO and
[12] H. Klfout, A. Stewart, M. Elkhalifa, H. He, ACS Appl. Mater. Interfaces 9 (2017)
39873–39889.
[13] Y. Chen, L. Wan, D. Zhang, Y. Bian, J. Jiang, Photochem. Photobiol. Sci. 10 (2011)
1030–1038.
Eg. The potentials were calibrated with ferrocene redox couple (Fc/Fc+
)
[30,32].
[14] W. Qin, M. Baruah, M.V. Auweraer, F.C.D. Schryver, N. Boens, J. Phys. Chem. A.
109 (2005) 7371–7384.
[15] D.J. Kimball, S. Raut, P.L. Jameson, W.N. Smith, Z. Gryczynski, V.S. Dzyuba, RSC
Adv. 5 (2015) 19508–19511.
EHOMO = −(E [oxvsFc/Fc+] + 4.8)eV
Eg = 1240/λonset
[16] E. Lager, J. Liu, A. Aguilar-Aguilar, B.Z. Tang, E. Peña-Cabrera, J. Org. Chem. 74 (5)
(2009) 2053–2058.
[17] J.Y. Shin, K. Kim, J.M. Lim, T. Tanaka, D. Kim, K. Kim, H. Shinokubo, A. Osuka,
Chem. Eur. J. 20 (2014) 4574–4582.
[18] W.N. Smith, A. Alonso, C.M. Brown, V.S. Dzyuba, Biochem. Biophys. Res. Commun.
391 (2010) 1455–1458.
[19] Y. Yu, L. Jiao, J. Wang, H. Wang, C. Yu, E. Haoa, N. Boens, Chem. Commun. 53
(2017) 581.
ELUMO = EHOMO−Eg
4.4. Computational methods
[20] C. Hansch, A. Leo, R.W. Taft, Chem. Rev. 91 (1991) 165–195.
[21] L. Jiao, W. Pang, J. Zhou, Y. Wei, X. Mu, G. Bai, E. Hao, J. Org. Chem. 76 (2011)
9988–9996.
[22] S.H. Lim, C. Thivierge, P.N. Sliwinska, J. Han, H. Bergh, G. Wagnières, K. Burgess,
H.B. Lee, J. Med. Chem. 53 (2010) 2865–2874.
[23] J. Aihara, J. Phys. Chem. A 103 (1999) 7487–7495.
[24] S. Berson, S. Cecioni, M. Billon, Y. Kervella, R. Bettignies, S. Bailly, S. Guillerez, Sol.
Energy Mater. Sol. Cells 94 (2010) 699–708.
[25] P. Matlaba, T. Nyokong, Polyhedron 21 (2002) 2463–2472.
[26] T.D. Lash, D.T. Richter, C.M. Shiner, J. Org. Chem. 64 (1999) 7973–7982.
[27] M.M.C. Lo, G.C. Fu, J. Am. Chem. Soc. 124 (2002) 4572–4573.
[28] K. Rurack, M. Spieles, Anal. Chem. 83 (2011) 1232–1242.
[29] K.G. Casey, E.L. Quitevis, J. Phys. Chem. 92 (1988) 6590–6594.
[30] J. Liao, Y. Wang, Y. Xu, H. Zhao, X. Xiao, X. Yang, J. Tetrahedron 71 (2015)
5078–5084.
Conformational searches were performed for eight different com-
pounds synthesized with semi-emprical PM6 method [33,34] by using
the Spartan’16 v1.1.4 [35]. The obtained most stable conformer
structures each compound were optimized with semi-emprical PM6
method in the gas phase and Density Functional Theory (DFT) B3LYP
(Becke’s Three Parameter Hybrid Functional using the Lee, Yang and
Parr Correlation Functional) [36] with 6-31G(d,p) basis set in the gas
phase and in the dichloroethane solvent with the IEF-PCM approach. To
determine the HOMO-LUMO energies were calculated using time-de-
pendent density functional theory (TD-DFT) at the B3LYP/6-31G(d,p)
and B3LYP/6-311+G(d,p) levels in chloroform phase was done by
using the Self-Consistent Reaction Field (SCRF) method. DFT/B3LYP
has been reported as a method to calculate BODIPY’s HOMO-LUMO
orbital energies in the literature [37,38]. Chemical shifts (δ, ppm) of the
synthesized compounds (1A–4B) were computed by using DFT/B3LYP/
6-31Gdp method with the Continuous Set of Gauge Transformations
(CSGT) approach [39–41] and the Gauge-Independent Atomic Orbital
(GIAO) [42,43] method for all compounds in gas and deuterated
chloroform (CDCl3) phases. All of the visualizations and calculations
were carried out by the methods implemented in GaussView5.0 [44]
and Gaussian 09 package [45].
[31] S.P. Economopoulos, C.L. Chochos, H.A. Ioannidou, M. Neophytou, C. Charilaou,
G.A. Zissimou, J.M. Frost, T. Sachetan, M. Shahid, J. Nelson, M. Heeney,
D.D.C. Bradley, G. Itskos, P.A. Koutentis, S.A. Choulis, RSC Adv. 3 (2013)
10221–10229.
[32] A. Günsel, E. Güzel, A.T. Bilgiçli, I. Şişman, M.N. Yarasir, J. Photochem. Photobiol.
A 348 (2017) 57–67.
[33] J.J.P. Stewart, J. Mol. Model. 14 (2008) 499–535.
[34] J.J.P. Stewart, J. Mol. Model. 15 (2009) 765–805.
[35] Spartan’16. Wavefunction, Inc., Irvine, CA.
[36] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785–789.
[37] D. Hu, T. Zhang, S. Li, T. Yu, X. Zhang, R. Hu, J. Feng, S. Wang, T. Liang, J. Chen,
N.L. Sobenina, A.B. Trofimov, Y. Li, J. Ma, G. Yang, Nat. Commun. 9 (2018) 362.
[38] J. Wang, Q. Wu, Y. Xu, C. Yu, Y. Wei, X. Mu, E. Hao, L. Jiao, RSC Adv. 6 (2016)
52180–52188.
Acknowledgements
[39] T.A. Keith, R.F.W. Bader, Chem. Phys. Lett. 194 (1992) 1–8.
[40] T.A. Keith, R.F.W. Bader, Chem. Phys. Lett. 210 (1993) 223–231.
[41] J.R. Cheeseman, G.W. Trucks, T.A. Keith, M.J.J. Frisch, Chem. Phys. 104 (1996)
5497–5509.
We are grateful to İlkay Şişman for running the cyclic voltammetry.
This work was financially supported by the Scientific and Technological
Research Council of Turkey (TUBITAK) (Grant Number 114Z176).
Sakarya University Scientific Research Foundation [Project no. 2014-
02-04-010].
[42] F. London, J. Phys. Radium 8 (1937) 397–409.
[43] K. Wolinski, J.F. Hilton, P. Pulay, J. Am. Chem. Soc. 112 (1990) 8251–8260.
[44] GaussView, Version 5, Dennington R, Keith T, Millam J. Semichem Inc., Shawnee
Mission KS, 2009.
[45] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
J.A. Montgomery, J.T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian,
J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J.
Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth,
P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, A.D. Daniels, O. Farkas, A.D.
Rabuck, K. Raghavachari, J.V. Ortiz, “Gaussian 09”, Gaussian, Inc., Pittsburgh PA.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.ica.2018.06.006.
References
[1] R.M. Christie, Rev. Prog. Color. Relat. Top. 23 (1993) 1–18.
135