Meso Alkynylated Tetraphenylethylene (TPE) and 2,3,3-Triphenylacrylonitrile (TPAN) Substituted BODIPYs

Article abstract of DOI:10.1021/acs.joc.5b01117

The tetraphenylethylene (TPE) substituted BODIPY 2a, and 2,3,3-triphenylacrylonitrile (TPAN) substituted BODIPYs 2b and 2c were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. Their photophysical and electrochemical prope

Full text of DOI:10.1021/acs.joc.5b01117

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Meso alkynylated tetraphenylethylene (TPE) and 2,3,3ꢀtriphenylacrylonitrile
(TPAN) substituted BODIPYs
Bhausaheb Dhokale, Thaksen Jadhav, Shaikh M. Mobin, and Rajneesh Misra*
Eꢀmail: rajneeshmisra@iiti.ac.in
*
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Department of Chemistry, Indian Institute of Technology Indore,
Indoreꢀ 452 017, India.
Cl
5
N
F
N
F
CN
B
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4
3
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1
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NC
CN
N
F
N
F
B
2
c
N
F
N
F
B
2b
N
F
N
B
F
3
N
F
N
F
B
2
a
500
550
600
650
700
750
Wavelength (nm)
Abstract
The tetraphenylethylene (TPE) substituted BODIPY 2a, and 2,3,3ꢀtriphenylacrylonitrile
(TPAN) substituted BODIPYs 2b and 2c were designed and synthesized by the Pdꢀcatalyzed
Sonogashira crossꢀcoupling reaction. Their photophysical, and electrochemical properties were
investigated. The BODIPY 2a exhibits strong DꢀA interaction with poor fluorescence quantum
yield. The BODIPYs 2b and 2c show red shifted absorption and emission with higher
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fluorescence quantum yield compared to BODIPY 2a. The photonic properties of BODIPYs 2a –
2c were compared with 4ꢀethynylbenzonitrile substituted BODIPY 3 and phenylacetylene
substituted BODIPY 4. The results reveal that the electron donating group at the meso position of
BODIPY blue shifts the absorption and emission with decreased fluorescence quantum yield,
whereas the electron withdrawing group at the meso position of BODIPY red shifts the
absorption and emission with enhanced quantum yields. The single crystal structures of
BODIPYs 2a and 2b reflect the planar orientation of meso substituent and the BODIPY core,
which leads to close πꢀπ stacking. The extensive πꢀπ stacking and strong donor–acceptor (DꢀA)
interaction makes these BODIPYs AIE inactive. The experimental observations were supported
by DFT calculation.
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Introduction
The BODIPY fluorophores are known for their strong absorption and emission with
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excellent fluorescence quantum yield. Their unique photonic properties make them attractive
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candidate for wide range of applications. The spectral properties of the BODIPY fluorophore
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can be tuned by introducing different functionalities at α, β and meso positions. The BODIPYs
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are strong acceptor owing to their electron deficient nature. Recently we have shown that the
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electron deficiency of 8ꢀchloro BODIPY is sufficient to oxidize aliphatic tertꢀamines. A variety
of donor groups were introduced at the meso position of the BODIPY through alkyne linkage,
which resulted in strong donorꢀacceptor (DꢀA) systems. Introduction of alkyne linkage at the
meso position induces planarity between the meso substituent and the BODIPY, which improves
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the electronic communication. The donor group at the meso position of the BODIPY leads to
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blue shifted absorption with poor quantum yield. To the best of our knowledge the effect of
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acceptor group on the photonic properties of meso alkynylated BODIPYs has not been explored
yet.
The conventional fluorophores suffer from aggregation caused quenching (ACQ), which
quenching of fluorescent in solid state. This problem was overcome by introducing the concept
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AIE. The AIE active molecules are poorly emissive in solutions at the same time highly
emissive in solid state. Tetraphenylethylene (TPE) and 2,3,3ꢀtriphenylacrylonitrile (TPAN) are
propeller shaped molecules, known for their unique ability to promote aggregation induced
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emission (AIE) in different fluorophores. The electronegative groups like (ꢀCN, ꢀF) are known
1
0
to induce the aggregation induced enhanced emission (AIEE). We have chosen the TPE and
TPAN functionalities and coupled them with the BODIPY through alkyne linkage at the meso
position to study their effect on the photonic properties of BODIPYs.
Herein, we report the design and synthesis of meso alkynylated TPE substituted BODIPY
2a, and TPAN substituted BODIPYs 2b, and 2c by Sonogashira crossꢀcoupling reaction. Their
photonic properties were studied and compared with 4ꢀethynylbenzonitrile substituted BODIPYs
3
and phenylacetylene substituted BODIPYs 4 (Chart 1). The planar orientation of meso
substituent and the BODIPY ensures the strong electronic communication between them. The
photonic properties were strongly influenced by the nature of substituents and the πꢀπ stacking
interaction.
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Results and Discussion
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Chart 1. The TPE substituted BODIPY 2a, TPAN substituted BODIPYs 2b, 2c and BODIPYs 3
and 4.
The TPE substituted BODIPY 2a, TPAN substituted BODIPYs 2b, 2c, BODIPYs 3 and
4
were synthesized by the Pdꢀcatalyzed Sonogashira crossꢀcoupling reaction of 8ꢀchloro
BODIPY 1 with the respective alkynes (Scheme 1). The precursor 8ꢀchloro BODIPY 1 was
synthesized by the reaction of dipyrrylketone with POCl followed by in situ deprotonation by
3
1
1
the base triethylamine and complexation with BF .etherate.
3
R1
R
R2
R1
R2
R
PdCl (PPh ) ,CuI,
Cl
2
3 2
PdCl (PPh ) ,CuI,
2 3 2
THF:TEA (10:1)
0 °C
THF:TEA (10:1)
0 °C
N
F
N
F
N
F
N
F
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N
F
B
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3
ꢀ 4
1
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R
BODIPY
Alkyne R1 R2 BODIPY
CN
H
3
4
a
b
c
Ph Ph
CN Ph
Ph CN
2a
2b
2c
Scheme 1. Synthesis of TPE substituted BODIPY 2a, TPAN substituted BODIPYs 2b, 2c and
BODIPYs 3 and 4.
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The TPEꢀalkyne a was synthesized using reported procedure from bromoꢀTPE (Scheme
1
2
S1, ESI). The TPANꢀalkyne b was synthesized by the Sonogashira crossꢀcoupling reaction of
bromoꢀTPAN with TMSꢀacetylene, followed by deprotection of TMS group by K CO in overall
2
3
1
3
69 % yield (Scheme 2). The TPANꢀalkyne c was synthesized by the condensation reaction of
ꢀbromo benzophenone with benzyl nitrile in the presence of base NaH, followed by the
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Sonogashira crossꢀcoupling reaction with TMSꢀacetylene and deprotection of TMS group by
K CO in overall 29 % yield (Scheme 3).
2
3
Si
Pd(PPh ) Cl , CuI,
K CO
3
NC
2
NC
NC
3
2
2
MeOH: Et O
2
THF:TEA
Br
e
Si
d
b
Scheme 2. Synthesis of 2ꢀ(4ꢀethynylꢀphenyl)ꢀ3,3ꢀdiphenylacrylonitrile (TPANꢀalkyne b).
The Sonogashira crossꢀcoupling reaction of 8ꢀchloro BODIPY 1 with alkynes a, b and c
at 0 °C resulted TPE substituted BODIPY 2a, and TPAN substituted BODIPYs 2b, and 2c in 70
, 74 % and 72 % yields respectively (Scheme1). The TPAN substituted BODIPY 2c is mixture
%
of cis and trans isomers. Its purification by repeated column chromatography and
recrystallization was unsuccessful (Figure S1; ESI), and reported as 1:1 mixture. The BODIPYs
3
and 4 were synthesized by the Sonogashira crossꢀcoupling reaction of 8ꢀchloro BODIPY 1
with 4ꢀethynylbenzonitrile and phenylacetylene in 52 % and 76 % yields respectively (Scheme
).
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Pd(PPh ) Cl , CuI,
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CN
CN
K CO
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MeOH: Et O
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c
f
Scheme 3. Synthesis of 2,3ꢀdiphenylꢀ3ꢀ(4ꢀethynylphenyl)ꢀacrylonitrile (TPANꢀalkyne c).
1
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The BODIPYs were well characterized by H NMR, C NMR, B NMR and HRMS
techniques. The BODIPYs 2a, and 2b were also characterized by single crystal Xꢀray
crystallography.
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The H NMR spectra of BODIPYs 2a – 2c, 3 and 4 shows the α, β and βʹ protons, at ~
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.8, 6.5 and 7.3 δ ppm respectively. The meso phenyl protons of BODIPY, 3 and 4 behave in
unusual manner. In BODIPY 4 the five phenyl protons appear as multiplets in two sets at δ =
7.65 and δ = 7.45, whereas in BODIPY 3 the four phenyl protons appear as singlet at δ = 7.75
(
Figure S2; ESI). This indicates that the cyano group in BODIPY 3 minimizes the dipole
moment (µ = 1.24) compared to BODIPY 4 (µ = 6.82) making the four phenyl protons
equivalent.
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Photophysical Properties
The electronic absorption spectra of BODIPYs 1, 2a – 2c and 3 were recorded in THF
Figure 1), and the corresponding data are shown in Table 1. The TPE substituted BODIPY 2a
(
absorbs at 543 nm and the TPAN substituted BODIPYs 2b, and 2c absorb at 546 nm. Compared
to the 8ꢀchloro BODIPY 1, the BODIPY 2a exhibits red shift of 41 nm, whereas the BODIPYs
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2b and 2c exhibit red shift of 44 nm. The red shift in the absorption is attributed to the extension
of πꢀconjugation. The higher red shift of the TPAN substituted BODIPYs 2b and 2c, than TPE
substituted BODIPY 2a is attributed to the stabilization of LUMO due to the acceptor group (ꢀ
1
4
CN) at the meso position. The effect of (ꢀCN) acceptor cyano on the red shift in absorption is
also evidenced from the absorption of BODIPY 3 at 552 nm, which is highly red shifted than
BODIPY4 and BODIPYs 2a – 2c. The BODIPYs (2a, 2b, 2c, 3 and 4) exhibit negative
solvatochromism with increasing solvent polarity (Figure S3ꢀS7; ESI).
The TDꢀDFT calculation was performed on TPAN substituted BODIPY 2b to understand
the origin of absorption bands. The TDꢀDFT calculation was performed by using two different
methods B3LYP and CAM B3LYP at 6ꢀ31G(d) level in THF solvent using the IEFPCM
formulation for solvent effects. The calculation performed by B3LYP method show more close
resemblance with the experimental data (Figure S17). The oscillator strengths and configurations
of vertical transitions are shown in Table S4 and the molecular orbitals involved in the
transitions are displayed in Figure S18 (ESI). The TD DFT calculations reveals that the main
absorption band at ~585 nm is contributed by the transitions from HOMO, HOMOꢀ1 and
HOMOꢀ2 to LUMO, whereas the band at ~380 nm is contributed by the transitions from
HOMOꢀ2 and HOMOꢀ3 to LUMO; and from HOMO and HOMOꢀ1 to LUMO+1.
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Wavelength (nm)
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Wavelength (nm)
Figure 1. Normalized electronic absorption spectra of BODIPYs 1, 2a – 2c and 3 in THF.
The emission studies of BODIPYs 1, 2a – 2c and 3 were performed in THF (Figure 2);
and the corresponding data are shown in Table 1. The red shift in the emission spectra follows
the order 3>2c=2b>2a>4>1. The TPE substituted BODIPY 2a exhibits dual emission from
locally excited (LE) state at 561 nm, and from charge transfer state at 731 nm with poor quantum
yield (ɸ = 0.02), whereas the TPAN substituted BODIPYs 2b and 2c emit only from the LE
F
state at 564 nm with higher fluorescence quantum yield (ɸ = 0.41 and 0.43 respectively).
F
The BODIPY 3 exhibits red shifted emission at 571 nm, whereas the BODIPY 4 emits at
5
56 nm. The cyano group in BODIPY 3, red shifts the absorption and emission, but decreases
the fluorescence quantum yield Compared to BODIPY 4. The fluorescence quantum yield of
BODIPYs 1 – 4 follows the order 1>4>2c>2b>3>2a.
The TPE substituted BODIPY 2a and TPAN substituted BODIPYs 2b and 2c are AIE
inactive. This suggests that fluorescence of TPE substituted BODIPY 2a in solution is quenched
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due to the charge transfer from donor TPE to the acceptor BODIPY moiety, whereas in TPAN
substituted BODIPYs 2b and 2c the charge transfer is minimized, which leads to the increased
fluorescence quantum yield.
Table 1. Photophysical properties of BODIPYs 1, 2a – 2c, 3 and 4 in THF.
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b
c
BODIPY λmax
ɛ/10
λem
Stokes shift ɸF
HOMOꢀLUMO gap (eV)
ꢀ1
ꢀ1
a
ꢀ1
d
(nm) (M .cm ) (nm)
(cm )
(Theoretical)
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503
468
543
435
10.2
2.7
515
561
731
564
463
0.72
ꢀ
2
a
4676
0.019
2.63
2
b
585
585
0.409
0.428
2.72
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46
428
46
3.0
2c
3
564
2.71 (cis)
2.70 (trans)
2.66
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3.1
4.4
4.3
552
543
571
556
601
431
0.440
0.632
1
6
4
2.78
a
b
c
Recorded at λmax, Excited at λmax, Determined by using Rhodamine B as standard (ɸ = 0.50, in ethanol),
d
From DFT calculation.
In order to evaluate the effect of cyano (ꢀCN) acceptor at the meso position of BODIPY,
the quantum yield of BODIPYs 3 and 4 were compared. The cyano group in BODIPY 3
decreases the fluorescence quantum yield compared to the BODIPY 4. This indicates that the
acceptor at the meso position of BODIPY increases the quantum yield only upto certain limit
2a>2b>2a as it minimizes the chargeꢀtransfer interaction. However after certain limit the
acceptor at the meso position quenches the fluorescence, which may be through the oxidative
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charge transfer from BODIPY, leading to poor quantum yield of BODIPY 3 than 4. This is in
1
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accordance with the work by Nagano et al. Similar trend in photophysical properties was
observed in different solvents (Figure S3ꢀS7 and Table S1).
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Wavelength (nm)
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a
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c
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Wavelength (nm)
Figure 2. Emission spectra of BODIPYs 1, 2a – 2c and 3 (inset shows enlarged view of emission
spectra of BODIPY 2a) in THF.
The TPE substituted fluorophores are poorly emissive in solutions due to the molecular
rotations of phenyl rings, and exhibit higher fluorescence quantum yield in aggregate state due to
restricted molecular rotation. The AIE properties of TPE substituted BODIPY 2a, and TPAN
substituted BODIPYs 2b and 2c were studied by fluorescence spectroscopy in THFꢀwater
mixture with varying amount of water fraction. The BODIPYs 2a – 2c are readily soluble in
tetrahydrofuran (THF) and insoluble in water, by increasing the water fraction in the THFꢀwater
mixture, the dissolved solute molecules transform into the aggregated particles. The study
reveals that the BODIPYs 2a – 2c are AIE inactive, and show aggregation caused fluorescence
quenching (ACQ) (Figure S8ꢀS9; ESI). The fluorescence intensity of BODIPYs 2a – 2c in pure
THF solution decreases with increasing water fraction. Thus the alkynylated TPE and TPAN
moieties are unable to induce AIE in BODIPYs like the previously reported TPE substituted
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BODIPYs. The alkyne linkage increases the distance between TPE and BODIPY, which gives
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sufficient space for planarization and πꢀπ stacking. This favors the aggregation caused
fluorescence quenching and makes these BODIPYs AIE inactive. The previously reported TPE
substituted BODIPYs were AIE active as there was no scope for πꢀπ stacking interactions and
aggregation caused fluorescence quenching.
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60
Electrochemical Properties
Table 2. The electrochemical properties of BODIPYs 2a – 2c, 3 and 4.
3
2
1
1
2
3
E
E
E
E
E
E
BODIPY
2a
b
b
b
b
b
b
Oxid
Oxid
1.16
1.36
1.45
1.27
1.33
Oxid
0.97
1.11
1.17
1.18
1.18
Red
Red
Red
1.81
ꢀ0.96
ꢀ0.96
ꢀ0.90
ꢀ0.90
ꢀ0.99
ꢀ1.25
ꢀ1.27
ꢀ1.20
ꢀ1.22
ꢀ1.28
ꢀ1.36
ꢀ1.39
ꢀ1.31
ꢀ1.36
ꢀ1.40
2
2
3
4
b
c
ꢀ
ꢀ
ꢀ
ꢀ
a
The electrochemical analysis was performed in a 0.1 M solution of Bu NPF in dichloromethane at
4
6
−
1
+ b
1
00mV s scan rate, versus Fc/Fc . Irreversible wave.
The electrochemical properties of the BODIPYs 2a – 2c, 3 and 4 were investigated by
cyclic and differential pulse voltammetric (CV and DPV) techniques (Figure 3 and S10 – S13)
and the corresponding data are displayed in Table 2. The First reduction potential of TPE
substituted BODIPY 2a, TPAN substituted BODIPYs 2b, 2c and BODIPYs 3 and 4 follows the
order 4~2a~2b>2c~3, which indicates that, compared to BODIPYs 2a and 4, the of cyano group
in 2b does not perturbs the LUMO energy level (similar reduction potential) but in 2c and 3 it
stabilizes the LUMO energy level significantly (easier reduction). The first oxidation potential
values follow the order 4~3~2c>2b>2a, which indicates that the meso substituents has negligible
effect on the HOMO energy level in BODIPYs 2b, 2c, 3 and 4 but in BODIPY 2a the meso
substituted alkynylated TPE unit destabilizes the HOMO slightly.
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1
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
4
0.0ꢁ
0.0ꢁ
CV
DPV
2
0.0
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
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9
0
1
2
3
4
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
ꢀ
20.0ꢁ
40.0ꢁ
ꢀ
ꢀ60.0ꢁ
ꢀ80.0ꢁ
ꢀ
2.5
ꢀ2.0
ꢀ1.5
ꢀ1.0
ꢀ0.5
0.0 +
0.5
1.0
1.5
Potential Vs Fc/Fc (V)
Figure 3. Overlaid CV and DPV plots of TPE substituted BODIPY 2a in 0.1 M TBAF solution
6
in dichloromethane.
DFT Calculation
The Density functional theory (DFT) calculation was performed to understand the
electronic structure of the BODIPYs 2 – 4 at B3LYP/6ꢀ31G** level. The comparison of
geometry optimized structure and crystal structure is shown in Figure S14 (ESI). The crystal
structure closely resembles with the energy optimized structure. The energy optimized structures
show highly symmetrical BODIPY framework, whereas in crystal structures two pyrrolic rings
of BODIPY framework show slight variations in the bond lengths due to the close solid state
packing.
The frontier molecular orbital (FMO) plots of BODIPYs 2a – 2c, 3 and 4 are displayed in
Figure 4. The frontier molecular orbital plots of BODIPY 2a reveals that the HOMO is localized
on the TPE moiety, whereas the LUMO is localized on BODIPY moiety. This supports strong Dꢀ
A interaction and charge transfer from TPE to BODIPY unit. In case of BODIPYs 2b, 2c, 3 and
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4 the HOMO is localized on the BODIPY moiety and the LUMO is distributed over the entire
molecule.
CN
NC
CN
CN
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
BODIPY
N
F
N
F
N
F
N
F
N
F
N
F
N
F
N
F
N
F
N
N
F
N
F
B
B
B
B
B
B
F
2
a
2b
2c (cis)
2c (trans)
3
4
LUMO
HOMO
Figure 4. Frontier molecular orbital plots of the BODIPYs 2a, 2b, 2c (cis),2c (trans), 3 and 4
estimated by DFT calculation at B3LYP/6ꢀ31G** level.
Crystal Structure
The crystals of BODIPYs 2a and 2b for xꢀray analysis were grown by slow evaporation
of their dichloromethane:hexane solution. The BODIPYs 2a and 2b crystalize in triclinic Pꢀ1
space group (Figure 5). The crystal structure, and data refinement parameters are given in Table
S2. The crystal structures of TPE substituted BODIPY 2a, and TPAN substituted BODIPY 2b
reflect planar BODIPY framework with fluorine atoms projecting above and below the average
plane. The distances, and angles of intermolecular interactions are shown in Table S3 (ESI).
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1
1
1
1
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1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
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5
5
5
5
5
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0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 5. Single crystal structures of TPE substituted BODIPY 2a and TPAN substituted
BODIPY 2b.
Crystal structure packing
The single crystal structure reveals, extensive hydrogen bonding and close πꢀπ stacking
interactions (Figure 6 and 7). In the crystal packing of TPE substituted BODIPY 2a, the two
hydrogen bonding interactions C(13)ꢀH(13)ꢀꢀꢀF(1) and C(17)ꢀH(17)ꢀꢀꢀF(2) and CꢀHꢀꢀꢀπ
interactions C(33)ꢀH(33)ꢀꢀꢀπ C(21) (TPE Phenyl) and C(16)ꢀH(16)ꢀꢀꢀπ C(34) (TPE Phenyl) and
the extensive πꢀπ stacking interaction between BODIPY moieties form a staircase shaped 2D
framework. This further leads to complex 3D structural arrangement through CꢀHꢀꢀꢀπ
interactions C(7)ꢀH(7)ꢀꢀꢀπ C(34, 35) (TPE Phenyl) and C(36)ꢀH(36)ꢀꢀꢀπ C(17) (Phenyl centroid)
(
Figure 6).
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33
34
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 6. Crystal packing of TPE substituted BODIPY 2a showing hydrogen bonded πꢀπ
stacked staircase shaped 2D network.
The crystal structure packing of TPAN substituted BODIPY 2b reveals that, the
hydrogen bonding interaction B(1)ꢀF(1)ꢀꢀꢀπ C(19)( Cyano) and πꢀπ stacking between phenyl ring
and the BODIPY central core forms a dimeric framework. These dimers connect to one another
via two mutual C(7)ꢀH(7)ꢀꢀꢀF(2) interactions and πꢀπ stacking interaction between two pyrrolic
rings to form a sheet. Such sheets are connected to one another via C(24)ꢀH(24)ꢀꢀꢀF(2) and
C(26)ꢀH(26)ꢀꢀꢀπ C(8) (Pyrrolic centroid) and C(2)ꢀH(2)ꢀꢀꢀF(2) interactions leading to 3D
framework. The 3D framework is also stabilized by interaction C(17)ꢀH(17)ꢀꢀꢀπ C(24) (TPE
Phenyl) (Figure 7).
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7
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9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
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5
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5
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5
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0
1
2
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4
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1
2
3
4
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6
7
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0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 7. Crystal packing of TPAN substituted BODIPY 2b showing hydrogen bonded πꢀπ
stacked 2D framework.
Conclusions
In summary, The tetraphenylethylene (TPE) substituted BODIPY 2a, and 2,3,3ꢀ
triphenylacrylonitrile (TPAN) substituted BODIPYs 2b, 2c and 4ꢀethynylbenzonitrile substituted
BODIPYs 3 and phenylacetylene substituted BODIPYs 4 were designed and synthesized by Pdꢀ
catalyzed Sonogashira crossꢀcoupling reaction. The planarization induced extensive πꢀπ stacking
and strong DꢀA interaction makes these BODIPY AIE inactive. The introduction of donor group
at the meso position of BODIPY induces the blue shift in absorption and emission spectra,
whereas the electron withdrawing group induces the red shift. The fluorescence quantum yields
of TPAN substituted BODIPYs 2b and 2c are higher than the TPE substituted BODIPY 2a,
which indicates that, the introduction of cyano group minimizes the CT interaction and increases
the fluorescence quantum yield. But this is not true in case of 4ꢀethynylbenzonitrile substituted
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BODIPYs 3 and phenylacetylene substituted BODIPYs 4, where the introduction of cyano group
decreases the fluorescence quantum yields, may be due to the oxidative charge transfer from
BODIPY moiety. The detailed photonic applications of these molecules are ongoing in our
laboratory.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
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41
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49
50
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EXPERIMENTAL SECTION
General methods. Chemicals were used as received unless otherwise indicated. All oxygen or
moisture sensitive reactions were performed under nitrogen/argon atmosphere using standard
schlenk method. Triethylamine (TEA) was received from commercial source and distilled on
1
13
11
19
KOH prior to use. H NMR (400 MHz), C NMR (100MHz), B NMR (128.37MHz), and F
NMR (376.49MHz) spectra were recorded on 400 MHz instrument by using CDCl as solvent.
3
1
H NMR chemical shifts are reported in parts per million (ppm) relative to the solvent residual
peak (CDCl , 7.26 ppm). Multiplicities are given as: s (singlet), d (doublet), t (triplet), q
3
(quartet), dd (doublet of doublets), m (multiplets), and the coupling constants, J, are given in Hz.
13
C NMR chemical shifts are reported relative to the solvent residual peak (CDCl , 77.36 ppm).
3
HRMS were recorded on mass spectrometer. UVꢀvisible absorption spectra of all compounds
were recorded on a UV/Vis Spectrophotometer. Fluorescence spectra of all the compounds were
recorded on emission spectrophotometer. The voltammograms were recorded in dichloromethane
solvent and 0.1 M TBAF as supporting electrolyte. The electrodes used were glassy carbon as
6
working electrode, Pt wire as counter electrode and the saturated calomel electrode as reference
+
20
electrode. The potentials were referenced against Fc/Fc as per IUPAC guidelines.
Generalized synthetic procedure for the BODIPYs 2a, 2b, 3a and 3b
8
ꢀchloro BODIPY 1 (100 mg, 0.44 mmol), and corresponding TPE alkynes (a/b/c) (0.66
mmol) were dissolved in THF:triethylamine (10:1,v/v; 15 ml), and the mixture was cooled to 0
C using an ice bath. The reaction mixture was purged with argon, and Pd(PPh ) Cl (15 mg, 5
°
3
2
2
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1
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
mol %), and CuI (8.3 mg, 10 mol %) were added, followed by stirring at 0 – 10 °C for 2 hrs.
After complete conversion of starting aryl alkyne a/b, the reaction mixture was evaporated to
dryness, and the crude product was dissolved in CH Cl , chromatographed on ~ 70 cm long
2
2
silica bed using dichloromethane as eluent to get 2 and 3. The isolated products from column
were recrystallized from chloroform: hexane (1:3) mixture as crystalline solid.
Characterization Data
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
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1
2
3
4
5
6
7
8
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0
1
2
3
4
5
6
7
8
9
0
TPE substituted BODIPY 2a: Red crystalline solid. Yield: 70% (170 mg); mp 193 – 194 °C.
1
H NMR (CDCl 400 MHz, ppm): δ 7.81 (s, 2H), 7.41ꢀ7.39 (m, 2H), 7.36 (d, J = 4 Hz; 2H),
3
,
13
7
.17ꢀ7.10 (m, 11H), 7.07ꢀ7.02 (m, 6H), 7.52 (d, J = 4 Hz; 2H); C NMR (CDCl 100 MHz,
3,
ppm): 147.4, 143.5, 143.2, 143.0, 139.8, 136.6, 132.3, 132.0, 131.5, 131.4, 129.0, 128.12,
11
1
28.07, 127.9, 127.6, 127.2, 127.0, 118.8, 118.4, 106.7, 84.8; B NMR (CDCl , 128 MHz, ppm)
3
0
.19 (t, JBꢀF = 28.16 Hz); HRMS (ESIꢀTOF) m/z = calculated for C H BF N = 569. 1977
37 25
2
2
+
+
−
1
−
1
4
[
M+Na] , measured 569.1961 [M+Na] ; UV/vis (THF) λ (ε [M cm ]) 543 (2.7 × 10 ).
max
TPAN substituted BODIPY 2b: Red crystalline solid. Yield: 74% (243 mg); mp 209 – 210
1
°C. H NMR (CDCl 400 MHz, ppm): δ 7.83 (s, 2H), 7.52ꢀ7.45 (m, 7H), 7.37ꢀ7.31 (m, 5H),
3
,
13
7
.27ꢀ7.23 (m, 2H), 7.05ꢀ7.02 (m, 2H), 6.55 (d, J = 4 Hz; 2H); C NMR (CDCl 100 MHz,
3,
ppm): 159.8, 144.0, 140.1, 138.8, 137.8, 136.7, 132.8, 130.9, 130.6, 130.3, 130.1, 129.7, 129.3,
1
1
1
28.7, 127.0, 120.8, 119.7, 118.6 (b), 110.4, 104.8, 85.2; B NMR (CDCl , 128 MHz, ppm) 0.14
3
+
(
t, JBꢀF = 29.4 Hz); HRMS (ESIꢀTOF) m/z = calculated for C H BF N = 518.1616 [M+Na] ,
32
20
2
3
+
−
1
−
1
4
measured 518.1617 [M+Na] ; UV/vis (THF) λmax (ε [M cm ]) 546 (3.0 × 10 ).
1
TPAN substituted BODIPY 2c: Red crystalline solid. Yield: 72 % (236 mg); mp 206 – 208. H
NMR (CDCl 400 MHz, ppm): 20 H δ 7.85 (d, 2H, J = 8Hz), 7.72 (d, 1H, J = 8Hz), 7.56 (d, 1H,
3,
J = 8Hz), 7.49ꢀ7.46 (m, 3H), 7.41ꢀ7.34 (m, 2H), 7.30ꢀ7.21 (m, 7H), 7.12 (d, 1H, J = 8Hz), 7.02
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1
3
(d, 1H, J = 8Hz), 6.58ꢀ6.55 (m, 2H); C NMR (CDCl 100 MHz, ppm): 156.21, 156.16, 144.1,
3,
1
42.9, 141.9, 139.7, 138.4, 136.7, 136.6, 134.4, 134.3, 132.8, 132.6, 131.4, 130.8, 130.5, 130.4,
30.0, 129.83, 129.76, 129.5, 129.3, 129.2, 129.03, 128.9, 128.8, 128.7, 128.6, 126.87, 126.76,
1
1
1
122.3, 121.4, 119.80, 119.77, 118.6, 113.1, 113.0, 104.6, 104.5, 85.4, 85.3; B NMR (CDCl ,
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
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45
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47
48
49
50
51
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59
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1
28 MHz, ppm) 0.19 (t, JBꢀF = 28.16 Hz); HRMS (ESIꢀTOF) m/z = calculated for C H BF N
32 20 2 3
+
+
−
1
−
1
=
518.1616 [M+Na] , measured 518.1622 [M+Na] ; UV/vis (THF) λ (ε [M cm ]) 546 (3.1 ×
max
4
1
0 ).
1
BODIPY 3: Red crystalline solid. Yield: 52 % (73 mg); mp 181 – 182 °C. H NMR (CDCl 400
3
,
1
3
MHz, ppm): δ 7.87 (s, 2H), 7.75 (s, 4H), 7.38 (bs, 2H), 6.58 (bs, 2H); C NMR (CDCl 100
3
,
MHz, ppm): 144.8, 136.7, 133.1, 132.5, 129.6, 125.7, 125.6, 119.0, 118.0, 114.2, 101.6, 86.8;
1
1
B NMR (CDCl , 128 MHz, ppm) 0.14 (t, J = 29.4 Hz); HRMS (ESIꢀTOF) m/z = calculated
3
BꢀF
+
+
for C H10BF N = 340.0831 [M+Na] , measured 340.0834 [M+Na] ; UV/vis (THF) λ (ε
max
1
8
2
3
−
1
−
1
4
[
M cm ]) 552 (4.4 × 10 )
1
8
The 2ꢀ(4ꢀbromophenyl)ꢀ3,3ꢀdiphenylacrylonitrile (e) was synthesized from previous report.
Synthesis of 2ꢀ(4ꢀethynyltrimethylsilylphenyl)ꢀ3,3ꢀdiphenylacrylonitrile (d): 1gm (2.78 mol)
of 2ꢀ(4ꢀbromophenyl)ꢀ3,3ꢀdiphenylacrylonitrile (e) was dissolved in 50ml dry THF and
Triethylamine 4:1 mixture. The reaction mixture was degased with argon and
trimethylsillyacetylyne (370 µL; 2.33mol), Pd(PPh ) Cl (160 mg, 0.14 mol), and CuI (53 mg,
3
2
2
0.27 mol) were added to the reaction mixture. The reaction mixture was refluxed for 24 hours.
After complete conversion the reaction mixture was evaporated to dryness and chromatographed
on silica gel column chromatography with hexane as eluent. The product was obtained as white
colored crystalline solid with 80 % yield. Characterization data: White crystalline solid. Yield:
1
80 % (840mg); H NMR (CDCl 400 MHz, ppm): δ 7.46ꢀ7.40 (m, 5H), 7.32ꢀ7.29 (m, 2H), 7.28ꢀ
3
,
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1
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1
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1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
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5
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5
5
6
1
3
7.25 (m, 1H), 7.22ꢀ7.18 (m, 4H), 7.01ꢀ6.98 (m, 2H), 0.24 (s, 9H); C NMR (CDCl 100 MHz,
3
,
ppm): 158.5, 140.30, 138.9, 135.0, 132.1, 130.8, 130.1, 130.0, 129.6, 129.3, 128.6, 128.5, 123.1,
19.9, 111.0, 104.5, 96.0, 0.28; HRMS (ESIꢀTOF) m/z = calculated for C H NSi = 400.1492
1
26
23
+
+
[M+Na] , measured 400.1498 [M+Na] .
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
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Synthesis of 2ꢀ(4ꢀethynylꢀphenyl)ꢀ3,3ꢀdiphenylacrylonitrile (TPANꢀalkyne b): The (720mg;
.9 mol) 2ꢀ(4ꢀethynyltrimethylsilylphenyl)ꢀ3,3ꢀdiphenylacrylonitrile d was dissolved in 60 ml
diethylether :methanol (1:3) mixture and was added (393mg; 2.85 mol) K CO under argon
1
2
3
atmosphere and stirred for 4 hours at room temperature. After complete conversion, the reaction
mixture was evaporated to dryness and chromatographed on silica gel column chromatography
with dichloromethane: hexane as eluent. The product was obtained as white crystalline solid in
1
8
7 % yield. Characterization data: Crystalline solid. Yield: 87 % (506 mg); H NMR (CDCl 400
3
,
MHz, ppm): δ δ 7.47ꢀ7.40 (m, 5H), 7.36ꢀ7.32 (m, 2H), 7.30ꢀ7.26 (m, 1H), 7.24ꢀ7.19 (m, 4H),
1
3
7
.02ꢀ6.99 (m, 2H), 3.11 (s, 1H); C NMR (CDCl 100 MHz, ppm): 158.7, 140.3, 138.9, 135.4,
3,
1
32.3, 130.8, 130.2, 130.0,129.7, 129.4, 128.6, 128.5, 122.2, 119.9, 110.9, 83.1, 78.7; HRMS
+
+
(ESIꢀTOF) m/z = calculated for C H N = 328.1097 [M+Na] , measured 328.1103 [M+Na] .
2
3
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Synthesis of 2,3ꢀdiphenylꢀ3ꢀ(4ꢀbromophenyl)ꢀacrylonitrile (g): 4ꢀbromobenzophenone (4.46
gm; 0.017 mol), and 60% NaH (0.47gm; 0.020 mol) were dissolved in 20 ml toluene, in threeꢀ
necked round bottom flask equipped with a condenser under argon atmosphere. The mixture was
reflux for 10 min, then benzylnitrile (2gm; 0.017 mol) in 20 ml toluene was added drop wise
over 20 min under reflux conditions. During addition reaction mixture turns pink to purple.
Evolving H was observed at the oil bubbler. The reaction mixture was stirred for 20 hours. After
2
completion of reaction, the reaction mixture was washed with water and brine. The organic phase
was then dried over anhydrous Na SO and concentrated under reduced pressure. The yellow oil
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was chromatographed on silica gel to obtain desired product as mixture of cis and trans isomers
1
in 49 % yield. Characterization data: Crystalline solid. Yield: 49 % (3 mg); H NMR (CDCl 400
3
,
MHz, ppm): δ 7.60 (d, J = 7.3 Hz, 2H), 7.40ꢀ7.35 (m, 5H), 7.33ꢀ7.27 (m, 3H), 7.16 (d, J = 7.0
13
Hz, 2H), 7.02 (d, J = 7.5 Hz 2H); C NMR (CDCl 100 MHz, ppm): 157.0, 139.0, 138.2, 133.5,
3
,
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31.81, 131.78, 131.5, 131.2, 130.6, 129.6, 128.6, 124.6, 122.8, 119.5, 110.8; HRMS (ESIꢀTOF)
+
+
m/z = calculated for C H BrN = 382.0202 [M+Na] , measured 382.0213 [M+Na] .
21 14
Synthesis of 2,3ꢀdiphenylꢀ3ꢀ(4ꢀethynyltrimethylsilylphenyl)ꢀacrylonitrile (f): 0.9 gm (2.5
mol) of 2,3ꢀdiphenylꢀ3ꢀ(4ꢀbromophenyl)ꢀacrylonitrile (g) was dissolved in 50ml dry THF and
Triethylamine 4:1 mixture. The reaction mixture was degased with argon and
trimethylsillyacetylyne (336 µL; 3 mol), Pd(PPh ) Cl (144 mg, 0.125 mol), and CuI (48 mg,
3
2
2
0.25 mol) were added. The reaction mixture was refluxed for 24 hours. After complete
conversion the reaction mixture was evaporated to dryness and chromatographed on silica gel
column chromatography with hexane as eluent. The product was obtained as mixture of cis and
trans isomers with 74 % yield. Characterization data: White, crystalline solid. Yield: 74 % (700
1
mg); H NMR (CDCl 400 MHz, ppm): δ 7.52ꢀ7.49 (m, 2H), 7.40ꢀ7.38 (m, 2H), 7.28ꢀ7.17 (m,
3
,
13
8H), 6.98ꢀ6.96 (m, 2H); C NMR (CDCl 100 MHz, ppm): 156.9, 140.4, 138.8,134.7, 132.1,
3,
1
30.9, 130.0, 129.8, 129.3, 128.6, 128.4, 124.8, 120.0, 112.0, 104.6, 96.5, 00.0; HRMS (ESIꢀ
+
+
TOF) m/z = calculated for C H NSi = 400.1492 [M+Na] , measured 400.1491 [M+Na] .
2
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Synthesis of 2,3ꢀdiphenylꢀ3ꢀ(4ꢀethynylphenyl)ꢀacrylonitrile (c): 2,3ꢀdiphenylꢀ3ꢀ(4ꢀ
ethynyltrimethylsilylphenyl)ꢀacrylonitrile (f) (600 mg; 1.59 mol) was dissolved in 60 ml
diethylether :methanol (1:3) mixture and was added (2.12 gm; 15.9 mol) K CO under argon
2
3
atmosphere and stirred for 4 hours at room temperature. After complete conversion, the reaction
mixture was evaporated to dryness and chromatographed on silica gel column chromatography
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with dichloromethane: hexane as eluent. The product was obtained as mixture of cis and trans
1
isomers in 80 % yield. Characterization data: White, crystalline solid. Yield: 80 % (388 mg); H
NMR (CDCl 400 MHz, ppm): δ 7.64 (d, J = 8Hz, 1H), 7.53 (m, 2H), 7.41ꢀ7.29 (m, 8H), 7.08
3
,
1
3
(t, J = 8Hz, 2H), 3.36ꢀ3.21 (2×s, 1H); C NMR (CDCl 100 MHz, ppm): 156.79, 156.75, 140.8,
3,
0
1
2
3
4
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0
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140.0, 139.6, 138.8, 134.65, 134.61, 132.3, 132.0, 130.9, 130.85, 130.2, 130.0, 129.8, 129.3,
128.76, 128.73, 128.68,128.63, 128.5, 123.81, 122.86, 119.97, 119.94, 112.4, 112.2, 83.2, 83.1,
+
79.1, 78.9; HRMS (ESIꢀTOF) m/z = calculated for C H N = 328.1097 [M+Na] , measured
2
3
15
+
3
28.1112 [M+Na] .
Acknowledgement
We thank DST, New Delhi for financial support. BD and TJ thank CSIR and UGC New
Delhi for their fellowships. We are thankful to Sophisticated Instrumentation Centre (SIC), IIT
Indore.
Supporting Information
1
13
11
Text, figures, tables, and CIF files giving general experimental methods, H, C, B, and
1
9
F NMR and HRMS spectra of all new compounds, crystallographic data for 2a and 2b (CCDC
numbers 1401617 and 1401616 respectively), DFT calculation data and electrochemical studies.
This material is available free of charge via the Internet at http://pubs.acs.org.
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