Meso enyne substituted BODIPYs: synthesis, structure and properties

Article abstract of DOI:10.1039/c5dt00565e

We report the synthesis of meso enyne substituted BODIPYs by the reaction of 8-chloro BODIPY with terminal alkynes under Sonogashira coupling conditions, and by Pd-Cu catalyzed hydroalkynylation reaction of terminal alkynes, across the -C≡C- bond of meso

Full text of DOI:10.1039/c5dt00565e

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: R. Misra, B.
Dhokale, T. Jadhav and M. M. Shaikh, Dalton Trans., 2015, DOI: 10.1039/C5DT00565E.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/dalton

Page 1 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
Meso enyne substituted BODIPYs: synthesis, structure and
properties
Bhausaheb Dhokale, Thaksen Jadhav, Shaikh M. Mobin and Rajneesh Misra*
Department of Chemistry, Indian Institute of Technology Indore 452 017 (India)
ABSTRACT
We report the synthesis of meso enyne substituted BODIPYs by the reaction of 8ꢀ
chloro BODIPY with terminal alkynes under Sonogashira coupling condition, and by PdꢀCu
catalyzed hydroalkynylation reaction of terminal alkynes, across the –C≡C– bond of meso
alkynylated BODIPYs. The scope of reaction was explored by reacting different meso
alkynylated BODIPYs with various terminal alkynes, which results meso enyne substituted
BODIPYs with different substituents. The meso enyne substituted BODIPYs show blue
shifted absorption and red shifted emission with large Stokes shift compared to meso
alkynylated BODIPYs. The single crystal structure of BODIPYs 2a, 3b, 4a and 2d are
reported. Their packing diagram exhibits extensive intermolecular CꢀHꢀꢀꢀπ, CꢀHꢀꢀꢀF
hydrogen bonding and πꢀꢀꢀπ staking interaction, leading to 1D supramolecular frameworks
extending into the complex 3D structural frameworks.
1

Dalton Transactions
Page 2 of 23
View Article Online
DOI: 10.1039/C5DT00565E
INTRODUCTION
The BODIPY fluorophore outdistances itself from contemporary fluorophores, due to
its unique photophysical properties such as strong absorption with high molar extinction
coefficient and high fluorescence quantum yield.1 The BODIPY dyes have been explored for
variety of applications such as ion sensing, nonꢀlinear optics, organic photovoltaics,
photodynamic therapy and bioꢀmedical imaging.2 The photonic properties of the BODIPY
fluorophore can be tuned by introducing the appropriate functionalities at α, β and meso
positions or by ringꢀfusion.3 The meso alkynylated BODIPYs exhibit red shifted absorption
than α and βꢀalkynylated BODIPYs, but their absorption is blue shifted than αꢀalkynylated
benzoꢀfused BODIPYs.4
Our group is involved in the design and synthesis of donor substituted, β and meso
functionalized BODIPYs for optoelectronic applications.5 Recently we reported the synthesis
of meso enamine substituted BODIPYs by catalyst free oxidation of tertꢀamines and cross
coupling with 8ꢀchloro BODIPY.6
Enynes are important building block in synthetic chemistry, and has been explored in
organic electronics.7 The literature reveals formation of enynes as side product in
Sonogashira coupling reaction of certain aryl halides with terminal alkynes.8 There are few
reports, where enynes were obtained as major product.9 Tremendous efforts have been
devoted for the selective synthesis of E or Z enynes by metal catalyzed alkyne dimerization.10
Herein we report the synthesis of meso enyne substituted BODIPYs by reacting
excess terminal alkynes with 8ꢀchloro BODIPY under Sonogashira coupling condition
(Method A), and by the PdꢀCu catalyzed hydroalkynylation reaction of terminal alkynes
across the –C≡C– bond of meso alkynylated BODIPY (Method B) and their structural,
photophysical and electrochemical properties. The reaction methodology furnishes, meso
enyne substituted BODIPYs in good yields with two different substituents at a time. The
2

Page 3 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
methodology involves PdꢀCu catalyzed –C≡C– bond activation and new C–C bond
formation.
Results and Discussion
The reaction of 8ꢀchloro BODIPY 1, with excess terminal alkynes a and b under
Sonogashira coupling condition resulted BODIPYs 2a and 2b as major products in 58 % and
57 % yields along with minor products 3a and 3b in 20 % and 21 % yields respectively
(Method A; Scheme 1).
Ar
Ar
Cl
Ar
Method A
+
Ar
N
F
N
F
N
F
N
F
N
F
N
F
B
B
B
PdCl2(PPh3)2,CuI,
THF:TEA (10:1)
0ꢀ10 °C
2a ꢀ 2b
3a ꢀ 3b
1
Method B
=
Ar
Ar
PdCl2(PPh3)2, CuI,
THF:TEA (10:1)
RT
b
a
Scheme 1 Synthesis of meso ethynyl and enyne substituted BODIPYs 2a, 2b and 3a, 3b.
The isolated meso alkynylated BODIPYs 2a and 2b were subjected to PdꢀCu
catalyzed hydroalkynylation reaction with alkynes a and b, which resulted meso enyne
substituted BODIPYs 3a and 3b in 60 % and 62 % yield respectively (Method B; Scheme 1).
The reaction works well in different solvents like tetrahydrofuran, toluene and
dichloromethane, but presence of both Pd(PPh3)2Cl2 and CuI catalysts are essential for the
reaction.
The scope of the reaction was explored to incorporate two different substituents into
the BODIPY. The meso alkynylated BODIPYs 2a – 2c were subjected to PdꢀCu catalyzed
hydroalkynylation reaction with ethynyl ferrocene (Scheme 2), which resulted meso enyne
substituted BODIPYs 4a, 4b and 4c in 61 %, 60 % and 58 % yields respectively.
3

Dalton Transactions
Page 4 of 23
View Article Online
DOI: 10.1039/C5DT00565E
Ar
B
Ar
Fe
PdCl2(PPh3)2,CuI,
Fe
THF:TEA (10:1)
RT
N
F
N
F
N
F
N
F
4a ꢀ 4c
B
2a ꢀ 2c
Ar
=
Fe
c (58%)
a (61%)
b (60%)
Scheme 2 Synthesis of meso ferrocenyl enyne substituted BODIPYs 4a – 4c (Isolated yields in
bracket).
The scope of the reaction was further explored for the Stille coupling. We tried the
Stille reaction of (Phenylethynyl)tributylstannane with the 8ꢀchloro BODIPY. The reaction
resulted only meso alkynylated BODIPY 2d in 80 % yield (Scheme 3). Even use of excess
(Phenylethynyl)tributylstannane in Stille reaction resulted only BODIPY 2d.11
Cl
Ph
Sn(nꢀBu)3
Pd(PPh3)4,
Toluene
110 °C
N
F
N
F
B
N
F
N
F
B
1
2d
Scheme 3 Synthesis of BODIPY 2d by Stille reaction.
The plausible mechanism for the PdꢀCu catalyzed hydroalkynylation reaction across
the –C≡C– of meso alkynylated BODIPYs is displayed in Scheme 4. The coordination of
Pd[0] species with the –C≡C– bond of meso alkynylated BODIPY results πꢀcomplex A. The
activation of the terminal alkyne by Cu results σꢀcomplex B. The combination of A and B
12
leads to the intermediate C, which further transforms into the meso alkynylated BODIPY.
4

Page 5 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
Ar
Ar
L
Pd
L
N
F
N
B
F
N
F
N
F
B
A
L
Pd[0]
Cu
L
Cu
Ar'
H
Ar'
B
Cu
Ar
H
Ar
L
H
L
Ar'
Pd
N
F
N
F
Ar'
B
N
F
N
F
B
C
Scheme 4 Plausible reaction mechanism.
The BODIPYs were well characterized by 1H NMR, 13C NMR and HRMS
techniques. The BODIPYs 2a, 3b, 4a and 2d were also characterized by single crystal Xꢀray
crystallography.
PHOTOPHYSICAL PROPERTIES
The electronic absorption and emission spectra of the BODIPYs 1 – 4 were recorded
in toluene (Fig. 1 and S1 – S3; ESI) and the corresponding data are displayed in Table 1. The
color variations in the BODIPY solution are shown in Fig. 2. The meso alkynylated
BODIPYs 2a – 2c exhibit absorption band at ~ 548 nm. The electronic absorption spectrum
of meso enyne substituted BODIPYs 3a and 3b exhibits blue shift of ~ 34 nm compared to
the meso alkynylated BODIPYs 2a – 2c due to the loss of planarity between enyne
substituent and BODIPY (torsional angle from crystal structure 50.60°).
5

Dalton Transactions
Page 6 of 23
View Article Online
DOI: 10.1039/C5DT00565E
The ferrocenyl enyne substituted BODIPYs 4a – 4c exhibit blue shift of ~ 38 nm,
which suggests that incorporation of bulkier alkyne (ethynyl ferrocene) disturbs the planarity
more than the BODIPYs 3a – 3c (torsional angle from crystal structure 58.41°).
(a) 10
(b)
1.0
0.8
0.6
0.4
0.2
0.0
8
6
4
2
0
1
1
2a
3a
4a
2a
3a
4a
400
500
600
700
800
500
550
600
650
700
750
Wavelength (nm)
Wavelength (nm)
Fig. 1 (a) Electronic absorption spectra and (b) Normalized emission spectra of BODIPYs 1,
2a, 3a and 4a in toluene at the concentration of 0.1 optical densities at λmax
.
The meso alkynylated BODIPYs 2a and 2b exhibits sharp emission band at ~ 566 nm
whereas, the meso enyne substituted BODIPYs 3a and 3b exhibit ~ 8 nm red shifted broad
emission band with lower quantum yield. (Fig. 1 (b) and S3 (ESI); Table 1). The decrease in
fluorescence quantum yield can be attributed to the dissipation of excited state energy by
increased molecular rotations.13 The BODIPYs bearing ferrocenyl unit (4a – 4c) are poorly
emissive in nature due to the fast nonꢀradiative deactivation of the exited state with
intramolecular charge transfer from the donor ferrocenyl unit to the acceptor BODIPY
moiety.14
6

Page 7 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
Fig. 2 BODIPYs 1 – 4 in Toluene at 10−4 M concentration.
The meso alkynylated BODIPYs 2a, 2b and 2c exhibit Stokes shift of 500 – 600 cmꢀ1,
whereas the meso enyne substituted BODIPYs 3a, 3b, 4a and 4b exhibit Stokes shift of ~
2000 cmꢀ1. The large Stokes shift of enyne substituted BODIPYs can be attributed to the
higher differences in the excited state dipole moment and free molecular rotations.13 The
absorption and emission spectra of the BODIPYs were recorded in different solvents. The
absorption spectra of BODIPYs 2 – 4 show blue shift in polar solvents and red shift in non
polar solvents (Fig. S4 – S9), which indicates the negative solvatochromic effect.
Table 1 Photophysical properties of BODIPYs 2 – 4.
b
λmax
(nm)
548
549
515
515
510
510
511
ɛ×104
(Mꢀ1.cmꢀ1) a
4.1
λem
Stokes shift
(cmꢀ1)
580
c
BODIPY
ɸF
(nm)
566
567
575
575
572
568
0.50
0.43
0.05
0.04
0.0001
0.0004
–
2a
2b
3a
3b
4a
4b
4c
4.2
578
3.4
2026
2026
1940
2095
–
3.6
3.4
3.5
d
3.7
–
aRecorded at λmax, bExcited at λmax, cDetermined by using Rhodamine 6G as standard (ɸ = 0.88, in ethanol),
dBODIPYs are nonꢀemissive in nature
7

Dalton Transactions
Page 8 of 23
View Article Online
DOI: 10.1039/C5DT00565E
ELECTROCHEMICAL PROPERTIES
The electrochemical properties of BODIPYs 2 – 4 were investigated by cyclic and
differential pulse voltammetric (CV and DPV) techniques in a 0.1 M solution of Bu4NPF6 in
dichloromethane at 100 mVs−1 scan rate, versus Fc/Fc+ (Fig. 3 and S10 – S13). The
electrochemical data are displayed in Table 2. The redox waves of the BODIPY origin are
irreversible, whereas the ferrocenyl oxidation waves are reversible in nature (dotted blue line;
Fig. 3).
CV
DPV
30.0µ
CV (ferrocenyl oxidation)
0.0
ꢀ30.0µ
ꢀ60.0µ
1.5
1.0
0.5
0.0
ꢀ0.5
ꢀ1.0
ꢀ1.5
ꢀ2.0
ꢀ2.5
Potential Vs Fc/Fc+ (V)
Fig. 3 Overlaid CV and DPV plots of meso enyne substituted BODIPY 4c bearing two
ferrocenyl units in different environment.
The first reduction potential follows the order 2a>3a>4a (Table 2), indicating better
delocalization of donor electrons onto the BODIPY moiety in meso enyne substituted
BODIPYs compared to meso alkynylated BODIPYs. The harder reduction of BODIPY 4
compared to BODIPY 3 indicates better electron donating ability of ferrocene than biphenyl
and naphthalene moieties.
8

Page 9 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
The BODIPY 4c exhibits two merging oxidation waves in CV and DPV at 0.08 V and
0.00 V, corresponding to the oxidation of ferrocenyl moiety attached to the triple bond and
the phenyl ring respectively.
Table 2 The electrochemical properties of the BODIPYs 2 – 4.
E2
E1
E1
Oxid
(Fc)
ꢀ
E1
Redb
(BODIPY)
ꢀ0.98
E2
Redb
(BODIPY)
ꢀ1.35
BODIPY
Oxidb
Oxidb
(BODIPY) (BODIPY)
1.35
1.28
1.41
1.33
ꢀ
1.10
1.07
1.01
0.97
1.16
1.17
2a
2b
3a
3b
4a
4b
ꢀ
ꢀ0.99
ꢀ1.04
ꢀ1.08
ꢀ1.12
ꢀ1.13
ꢀ1.28
ꢀ1.36
ꢀ1.41
ꢀ1.40
ꢀ1.43
ꢀ
ꢀ
0.10
ꢀ
0.08
0.00 (Phenyl Fc)
0.08 (Ethynyl Fc)
ꢀ
1.01
ꢀ1.14
ꢀ1.40
4c
aThe electrochemical analysis was performed in a 0.1 M solution of Bu4NPF6 in dichloromethane at
100 mVs−1 scan rate, versus Fc/Fc+. bIrreversible wave.
THEORETICAL CALCULATIONS
Computational calculation was performed using density functional theory (DFT), and
the frontier molecular orbitals (FMOs) of the BODIPYs 2 – 4 are displayed in Fig. 4 and S22
(ESI). The LUMO in BODIPYs 2a, 3a and 4a are localized on the BODIPY core, which
indicates the strong acceptor nature of BODIPY. The HOMO in 2a is distributed on BODIPY
and in 3a on BODIPY as well as on the ethynyl biphenyl moiety, indicating better electronic
distribution. The HOMO in BODIPYs 4a is localized on the ferrocenyl part only due to the
stronger electron donating ability of ethynyl ferrocene than ethynyl biphenyl. The overall
distribution of HOMO on aryl moiety and LUMO on BODIPY reflects the strong donor
acceptor interactions in meso enyne substituted BODIPYs.
9

Dalton Transactions
Page 10 of 23
View Article Online
DOI: 10.1039/C5DT00565E
Fe
BODIPY
Fe
Fe
Fe
N
F
N
F
N
F
N
F
N
F
N
F
B
N
F
N
F
N
F
N
B
N
F
N
F
B
B
B
B
F
4b
3a
3b
4c
2a
4a
LUMO
HOMO
Fig. 4 Frontier molecular orbital plots of BODIPYs 2 – 4, calculated at B3LYP/6ꢀ31G* level for C, N,
B, F, H, and Lanl2DZ level for Fe.
CRYSTAL STRUCTURE
The Single crystals of the BODIPYs 2a, 3b, 4a and 2d were obtained by slow
evaporation of their dichloromethane:hexane solution at room temperature. The BODIPY 2a
crystalizes into monoclinic C2/c space group, 3b and 4a crystallizes into triclinic Pꢀ1 space
group, whereas the BODIPY 2d crystallizes into monoclinic P21/c space group. The crystal
structure and data refinement parameters are displayed in Table S2 (ESI). The crystal
structures reveal that the meso enyne substituted BODIPYs were obtained only in (E)
conformation. The highly planar BODIPY core in meso alkynylated BODIPYs maintains
planarity in meso alkynylated BODIPYs also (Fig. 5).
10

Page 11 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
Fig. 5 Single crystal structures of BODIPYs 2a, 3b, 4a and 2d (BODIPY 2a: Only molecule
B is shown from the asymmetric unit; details in Fig. S14; ESI).
The comparison of selected bond lengths and bond angles of the crystal structure is
shown in Figure S20 and S21 (ISI) respectively. The meso substituent and BODIPY core are
planar in meso alkynylated BODIPYs, and nonꢀplanar in meso enyne substituted BODIPYs.
The higher torsional angle between BODIPY plane and meso enyne substituent in BODIPY
4a than BODIPY 3b, suggests the bulky nature of ferrocenyl moiety than naphthalene
moiety, which supports the higher blue shit in the absorption spectra of 4a and 4b than 3a and
3b.
The close packing in the crystal structures of BODIPYs 2a, 3b, 4a and 2d exhibit
marvelous supramolecular frameworks. The distances and angles of the supramolecular
interactions in the crystals are shown in Table 3.
11

Dalton Transactions
Page 12 of 23
View Article Online
DOI: 10.1039/C5DT00565E
Fig. 6 Crystal structure packing of BODIPY 2a.
The crystal structure of BODIPY 2a contains three molecules (A, B and C) in an
asymmetric unit. These three molecules slightly differ in bond lengths and angles. The C(46)ꢀ
H(46)ꢀꢀꢀπ (Phenyl) interaction connects molecule B and C whereas the (13)ꢀH(13)ꢀꢀꢀF(3) and
C(3)ꢀH(3)ꢀꢀꢀF(3) interactions connect molecules B and A. The molecules B and C form a
chain along cꢀaxis with molecule A hanging above the chain with C(32)ꢀH(32)ꢀꢀꢀF(6) and
C(32)ꢀH(32)ꢀꢀꢀF(5) interactions. The two chains are arranged in antiparallel fashion via πꢀꢀꢀπ
stacking interaction between two pyrrolic rings of molecule C. The set of two antiparallel
chains further grows into a complex 3D framework via C(1)ꢀH(1)ꢀꢀꢀF(1), C(59)ꢀH(59)ꢀꢀꢀF(4),
C(16)ꢀH(16)ꢀꢀꢀπ (Pyrrolic), C(17)ꢀH(17)ꢀꢀꢀπ (Pyrrolic) and C(31)ꢀH(31)ꢀꢀꢀπ (Pyrrolic)
interactions (Fig. 6).
12

Page 13 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
Fig. 7 Crystal structure packing of BODIPY 3b.
In the packing diagram of BODIPY 3b, the two molecules form a dimeric structure in
head to head sliding manner via two mutual C(10)ꢀH(10)ꢀꢀꢀF(2) interactions. These dimers
connect to oneꢀanother diagonally to form a 1D chain along aꢀaxis via C(31)ꢀH(31)ꢀꢀꢀF(1)
and C(1)ꢀH(1)ꢀꢀꢀF(1) interactions (Fig. 7(a)). These one dimensional chains connect to
another chains laterally via C(3)ꢀH(3)ꢀꢀꢀπ and C(28)ꢀH(28)ꢀꢀꢀπ interactions along b and c axis
respectively to form complex 3D framework (Fig. 7(b)).
Fig. 8 Crystal structure packing of BODIPY 4a.
13

Dalton Transactions
Page 14 of 23
View Article Online
DOI: 10.1039/C5DT00565E
Table 3 Distances and angles of intermolecular interactions in the crystal structures of
BODIPYs 2a, 3b, 4a and 2d.
Sr. No. Interaction
Distance (Å) Angle (°)
BODIPY 2a
C(1)ꢀH(1)ꢀꢀꢀF(1)
C(3)ꢀH(3)ꢀꢀꢀF(3)
C(13)ꢀH(13)ꢀꢀꢀF(3)
C(59)ꢀH(59)ꢀꢀꢀF(4)
C(32)ꢀH(32)ꢀꢀꢀF(5)
C(32)ꢀH(32)ꢀꢀꢀF(6)
1
2
3
4
5
6
2.504
2.588
2.527
2.402
2.413
2.597
147.10
172.52
147.56
158.47
155.87
150.25
7
8
9
10
11
C(16)ꢀH(16)ꢀꢀꢀπ (Pyrrolic) 2.481
C(17)ꢀH(17)ꢀꢀꢀπ (Pyrrolic) 3.277
C(31)ꢀH(31)ꢀꢀꢀπ (Pyrrolic) 3.093
C(25)ꢀH(25)ꢀꢀꢀπ (Pyrrolic) 2.892
C(46)ꢀH(46)ꢀꢀꢀπ (Phenyl)
3.606
BODIPY 3b
1
2
3
4
5
C(31)ꢀH(31)ꢀꢀꢀF(1)
C(1)ꢀH(1)ꢀꢀꢀF(1)
C(10)ꢀH(10)ꢀꢀꢀF(2)
C(3)ꢀH(3)ꢀꢀꢀπ (Naph)
C(28)ꢀH(28)ꢀꢀꢀπ (Naph)
2.638
2.354
2.493
3.183
2.733
145.99
164.33
165.23
BODIPY4a
1
2
3
4
5
6
7
C(9)ꢀH(9)ꢀꢀꢀF(1)
C(9)ꢀH(9)ꢀꢀꢀF(2)
2.664
2.645
2.324
3.183
3.395
3.271
2.731
161.46
147.39
153.72
C(10)ꢀH(10)ꢀꢀꢀF(2)
C(1)ꢀH(1)ꢀꢀꢀπ (Fc)
C(7)ꢀH(7)ꢀꢀꢀπ (Fc)
C(28)ꢀH(28)ꢀꢀꢀπ (Phenyl)
C(23)ꢀH(23)ꢀꢀꢀπ (Fc)
BODIPY 2d
1
2
3
4
5
C(1)ꢀH(1)ꢀꢀꢀF(1)
C(8)ꢀH(8)ꢀꢀꢀF(2)
C(17)ꢀH(17)ꢀꢀꢀF(2)
C(13)ꢀH(13)ꢀꢀꢀ π (Pyrrolic) 3.198
π (Pyrrolic)ꢀꢀꢀπ (Pyrrolic)
2.397
2.570
2.541
160.15
153.85
152.86
In the crystal structure packing of BODIPY 4a, four mutual hydrogen bonding C(9)ꢀ
H(9)ꢀꢀꢀF(1) and C(9)ꢀH(9)ꢀꢀꢀF(2) interactions form a head to head pair. This pair connects to
neighboring pair via C(7)ꢀH(7)ꢀꢀꢀπ (Fc) and C(28)ꢀH(28)ꢀꢀꢀπ (Phenyl) interactions forming a
hydrogen bonded tetramer (Fig. 8). This tetramer further grows above and below via two
mutual interactions C(10)ꢀH(10)ꢀꢀꢀF(2) to form a chain of tetramers, which further form a
thick sheet via C(23)ꢀH(23)ꢀꢀꢀπ (Fc) interaction (Fig. S19 (ESI)).
In the crystal structure packing of BODIPY 2d the head to tail πꢀꢀꢀπ staking between
two BODIPY frameworks form a dimeric structure which is stabilized by C(17)ꢀH(17)ꢀꢀꢀF(2)
14

Page 15 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
interaction. These dimeric structures extend into 1D chain via interaction C(13)ꢀH(13)ꢀꢀꢀπ (Pyrrolic).
The 1D chain further extends to complex 3D framework via interactions C(8)ꢀH(8)ꢀꢀꢀF(2) and C(1)ꢀ
H(1)ꢀꢀꢀF(1) (Fig. 9).
Fig. 9 Crystal structure packing of BODIPY 2d.
Conclusions
We have developed a straightforward route for the synthesis of meso enyne
substituted BODIPYs with two different substituents. The meso enyne substituted BODIPYs
exhibit large Stokes shift, compared to the meso alkynylated BODIPYs. The electrochemical
properties and theoretical calculations reveal strong donorꢀacceptor interactions between
enyne substituent and the BODIPY. Meso enyne substituted BODIPYs with two different
substituents are potential candidates for optoelectronic applications. This methodology would
15

Dalton Transactions
Page 16 of 23
View Article Online
DOI: 10.1039/C5DT00565E
enable rapid construction of a library of multiꢀsubstituted BODIPYs. The synthesis of new
enyne substituted BODIPYs and their optoelectronic applications are ongoing in our group.
Experimental Section
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 KOH
prior to use. 1H NMR (400 MHz), and 13C NMR (100 MHz) spectra were recorded on Bruker
1
Avance (III) 400 MHz instrument using CDCl3 as solvent. H NMR chemical shifts are
reported in parts per million (ppm) relative to the solvent residual peak (CDCl3, 7.26 ppm).
Multiplicities are given as: s (singlet), d (doublet), t (triplet), q (quartet), dd (doublet of
doublets), m (multiplet), and the coupling constants, J, are given in Hz. 13C NMR chemical
shifts are reported relative to the solvent residual peak (CDCl3, 77.36 ppm). HRMS were
recorded on BrukerꢀDaltonics micrOTOFꢀQ II mass spectrometer. UVꢀvisible absorption
spectra of all compounds were recorded on Caryꢀ100 Bio UVꢀvisible Spectrophotometer and
fluorescence spectra were recorded on Horiba Jobin Yvon Fluoromax 4P Spectrophotometers
in toluene at the concentration of 0.1 optical densities at λmax. The voltammograms were
recorded on CHI620D electrochemical analyzer in dichloromethane solvent and 0.1 M
TBAF6 as supporting electrolyte. The electrodes used were glassy carbon as working
electrode, Pt wire as counter electrode and the saturated calomel electrode as reference
electrode. The potentials were referenced against Fc/Fc+ as per IUPAC guidelines.12
Generalized synthetic procedure for BODIPYs 2a, 2b, 3a and 3b (Method A)
8ꢀChloro BODIPY 1 (100 mg, 0.44 mmol), and corresponding arylethynes (a or b) (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(PPh3)2Cl2 (15
mg, 5 mol%), and CuI (8.3 mg, 10 mol%) were added, followed by stirring at 0 °C for 30
16

Page 17 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
min. The reaction mixture was brought to the room temperature and further stirred for 4 Hrs.
After complete conversion of starting aryl alkyne a/b, the reaction mixture was evaporated to
dryness, and the crude product was dissolved in CH2Cl2, chromatographed on silica (2:1;
hexanes:CH2Cl2) to get 2a/2b and 3a/3b. The isolated products from column were
recrystallized from chloroform: hexane (1:3) mixture as crystalline solid.
Generalized synthetic procedure for BODIPYs 3a, 3b, 4a, 4b and 4c (Method B)
Meso alkynylated BODIPY (2a, 2b or 2c) (0.30 mmol) and aryl alkyne (ethynyl biphenyl,
ethynyl naphthalene or ethynyl ferrocene) (0.30 mmol) were dissolved in THF:triethylamine
(10:1,v/v; 15 ml). The reaction mixture was purged with argon, and Pd(PPh3)2Cl2 (10.0 mg, 5
mol%), and CuI (6.7 mg, 10 mol%) were added, followed by stirring at room temperature for
10 Hrs. After completion of the reaction, the reaction mixture was evaporated to dryness, and
the crude product was dissolved in CH2Cl2, chromatographed on silica (1:2; hexanes:CH2Cl2)
to get 3a, 3b, 4a, 4b or 4c. The isolated products from column chromatography were
recrystallized from chloroform: hexane (1:3) mixture as crystalline solid.
Characterization Data
3a
1
Red crystalline solid. Yield: Method Aꢀ 20% (48 mg); Method Bꢀ 60 % (89 mg); H NMR
(CDCl3, 400 MHz, ppm): δ 7.99ꢀ7.96 (m, 2H), 7.91 (bs, 2H), 7.76ꢀ7.73 (m, 2H), 7.69ꢀ7.66
(m, 2H), 7.58ꢀ7.55 (m, 2H), 7.53ꢀ7.50 (m, 3H), 7.48ꢀ7.45 (m, 4H), 7.44ꢀ7.41 (m, 2H), 7.40ꢀ
7.34 (m, 2H), 7.33ꢀ7.30 (m, 2H), 6.55ꢀ7.53 (m, 2H); 13C NMR (CDCl3, 100 MHz, ppm):
144.0, 143.1, 142.8, 142.4, 140.4, 140.38, 136.4, 134.5, 133.3, 132.6, 130.1, 129.3, 129.2,
128.3, 128.2, 127.9, 127.8, 127.5, 127.4, 127.37, 125.4, 121.1, 118.3, 100.3, 87.4; 11B NMR
(CDCl3, 128 MHz, ppm) 0.28 (t, JBꢀF = 28.7 Hz);; UV/vis (Toluene): λmax (ε [Mꢀ1cmꢀ1]) 515
(3.38× 104). HRMS (ESIꢀTOF) m/z = calculated for C37H25BF2N2 = 585.1717 [M+K]+,
measured 585.1720 [M+K]+.
17

Dalton Transactions
Page 18 of 23
View Article Online
DOI: 10.1039/C5DT00565E
4a
1
Purpleꢀred crystalline solid. Yield: 61% (96 mg);. H NMR (CDCl3, 400 MHz, ppm): δ 7.93ꢀ
7.90 (m, 4H), 7.74ꢀ7.70 (m, 2H), 7.68ꢀ7.65 (m, 2H), 7.51ꢀ7.48 (m, 2H), 7.43ꢀ7.39 (m, 4H),
6.57ꢀ6.55 (m, 2H), 4.27 (t, 2H, J = 1.76 Hz), 4.23 (t, 2H, J = 1.76 Hz), 4.08 (s, 5H); 13C NMR
(CDCl3, 100 MHz, ppm): 143.7, 143.6,142.9,140.4, 136.5, 134.9, 133.8, 130.5, 129.3, 128.2,
127.8, 127.75, 127.4, 123.7, 118.1, 101.0, 83.4, 72.1, 70.5, 70.0, 63.7; 11B NMR (CDCl3, 128
MHz, ppm) 0.29 (t, JBꢀF = 29.5 Hz); UV/vis (Toluene): λmax (ε [Mꢀ1cmꢀ1]) 510 (3.4× 104).
HRMS (ESIꢀTOF) m/z = calculated for C35H25BF2FeN2 = 578.1429 [M]+, measured
578.1425 [M]+.
3b
1
Red crystalline solid. Yield: Method Aꢀ 21% (46 mg); Method Bꢀ 62 % (89 mg); H NMR
(CDCl3, 400 MHz, ppm): δ 8.42 (s, 1H), 8.01ꢀ8.98 (m, 3H), 7.93ꢀ7.91 (m, 3H), 7.80ꢀ7.73 (m,
4H), 7.60ꢀ7.57 (m, 2H), 7.56 (s, 1H), 7.51ꢀ7.48 (m, 4H), 7.29ꢀ7.27 (m, 1H), 6.54ꢀ6.53 (m,
2H); 13C NMR (CDCl3, 100 MHz, ppm): 144.0, 143.0, 134.7, 134.6, 134.3, 133.8, 133.6,
133.5, 133.2, 132.8, 130.2, 129.1, 129.0, 128.5, 128.4, 128.3, 128.13, 128.1, 127.9, 127.7,
127.6, 127.3, 127.1, 126.1, 124.0, 119.6, 118.3, 101.0, 87.3; 11B NMR (CDCl3, 128 MHz,
ppm) 0.34 (t, JBꢀF = 29.5 Hz); UV/vis (Toluene): λmax (ε [Mꢀ1cmꢀ1]) 515 (3.6 × 104). HRMS
(ESIꢀTOF) m/z = calculated for C33H21BF2N2 = 517.1664 [M+Na]+, measured 517.1651
[M+Na]+.
4b
1
Purple crystalline solid. Yield: 60% (97 mg); H NMR (CDCl3, 400 MHz, ppm): δ 8.32 (s,
1H), 7.97ꢀ7.89 (m, 6H), 7.58ꢀ7.54 (m, 2H), 7.47 (s, 1H), 7.44 (d, 2H, J = 4 Hz), 6.57ꢀ6.56 (m,
2H), 4.30 (t, 2H, J = 1.76 Hz), 4.24 (t, 2H, J = 1.76 Hz), 4.09 (s, 5H); 13C NMR (CDCl3, 100
MHz, ppm): 143.8, 143.6, 134.9, 134.7, 134.2, 134.16, 133.5, 130.1, 129.1, 128.9, 128.1,
127.9, 127.6, 127.2, 124.3, 124.0, 118.2, 101.0, 83.39, 72.4, 70.9, 70.3, 53.8; 11B NMR
18

Page 19 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
(CDCl3, 128 MHz, ppm) 0.31 (t, JBꢀF = 28.7 Hz); UV/vis (Toluene): λmax (ε [Mꢀ1cmꢀ1]) 510
(3.5× 104). HRMS (ESIꢀTOF) m/z = calculated for C33H23BF2FeN2 = 575.1170 [M+Na]+,
measured 575.1170 [M+Na]+.
4c
1
Purple crystalline solid. Yield: 58% (84 mg); H NMR (CDCl3, 400 MHz, ppm): δ 7.92 (s,
2H), 7.78ꢀ7.75 (m, 2H), 7.58ꢀ7.56 (m, 2H), 7.44 (d, 2H, J = Hz), 7.37 (s, 1H), 6.56ꢀ6.54 (m,
2H), 4.73 (t, 2H, J = 2 Hz), 4.41 (t, 2H, J = 1.76 Hz), 4.27 (multiplate, 2H), 4.23 (t, 2H, J =
1.76 Hz), 4.09ꢀ4.08 (m, 10 H); 13C NMR (CDCl3, 100 MHz, ppm): 143.9, 143.5, 142.2,
134.9, 134.7, 134.2, 132.2, 130.0, 127.4, 126.5, 122.8, 118.0, 84.3, 83.5, 72.1, 70.5, 70.2,
70.0, 69.9, 87.1, 63.8; UV/vis (Toluene): λmax (ε [Mꢀ1cmꢀ1]) 511 (3.7× 104). HRMS (ESIꢀ
TOF) m/z = calculated for C39H29BF2Fe2N2 = 686.1093 [M]+, measured 686.1091 [M]+.
Synthesis of BODIPY 2d
8ꢀChloroꢀBODIPY 1 (100mg 0.44 mmol) was dissolved in toluene and purged with argon.
The (Phenylethynyl)tributylstannane reagent and Pd(PPh3)4 (25.5 mg, 5 mol%) were added,
followed by reflux for 20 hrs under argon atmosphere. After completion of the reaction, the
reaction mixture was evaporated to dryness, and the crude product was dissolved in CH2Cl2,
chromatographed on silica (1:2; hexanes:CH2Cl2) to get BODIPY 2d. The isolated product
from column chromatography was recrystallized by slow evaporation of dichloromethane:
hexane solution.
1
Product ꢀRed crystalline solid. Yield: 80% (104 mg); H NMR (CDCl3, 400 MHz, ppm): δ
7.84 (s, 2H), 7.67 (d, 2H, J = 6.76 Hz), 7.55ꢀ7.45 (m, 3H), 7.41 (d, J = 4 Hz, 2H), 6.55 (d, J =
4 Hz, 2H); 13C NMR (CDCl3, 100 MHz, ppm): δ 143.6, 136.6, 132.8, 131.1, 129.2, 128.9,
127.3, 120.9, 118.4, 106.0, 84.1 ppm; HRMS (ESIꢀTOF) m/z = calculated for C17H11BF2N2 =
315.0879 [M+Na]+, measured 315.0879 [M+Na]+. Data in agreement with literature.3h
ASSOCIATED CONTENT
19

Dalton Transactions
Page 20 of 23
View Article Online
DOI: 10.1039/C5DT00565E
Supporting Information
† Electronic supplementary information (ESI) available: Photophysical and electrochemical
characterization data, CCDC 1018403 – 1018405 for 2a, 3b and 4a respectively and 1041639
for 2d; copies of HRMS, 1H, 13C, 11B and 19B NMR spectra. This material is available free of
charge via the internet at DOI: 10.1039/b000000x/
AUTHOR INFORMATION
Corresponding Author
* Fax: +91 731 2361 482, Eꢀmail: rajneeshmisra@iiti.ac.in
ACKNOWLEDGMENT
We thank DST New Delhi for financial Support. BD and TJ thank CSIR and UGC New
Delhi for their fellowships. We thank SIC, IIT Indore.
REFERENCES
1 (a) H. Lu, J. Mack, Y. Yang and Z. Shen, Chem. Soc. Rev., 2014, 43, 4778–4823; (b) A. Loudet and
K. Burgess, Chem. Rev., 2007, 107
Rev., 2010, 110, 2709ꢀ2728.
, 4891–4932; (c) J. Han and K. Burgess, Chem.
2 (a) A. Hagfeldt, G. Boschloo, L. C. Sun, L. Kloo, and H. Pettersson, Chem. Rev., 2010, 110, 6595–
6663; (b) O. A. Bozdemir, R. Guliyev, O. Buyukcakir, S. Selcuk, S. Kolemen, G. Gulseren, T.
Nalbantoglu, H. Boyaci and E. U. Akkaya, J. Am. Chem. Soc., 2010, 132, 8029; (c) W. Pang, X.ꢀF.
Zhang, J. Zhou, C. Yu, E. Hao, L. Jiao, Chem. Commun., 2012, 48, 5437ꢀ5439; (d) X.ꢀF. Zhang, X.
Yang, J. Phys. Chem. B, 2013, 117, 9050ꢀ9055; (e) X.ꢀF. Zhang, X. Yang, J. Phys. Chem. B, 2013,
117, 5533ꢀ5539; (f) X.ꢀF. Zhang, X. Yang, K. Niu, H. Geng, J. Photochem. Photobiol. A: Chem.,
2014, 285, 16ꢀ20.
3 (a) A. B. Nepomnyashchii and A. J. Bard, Acc. Chem. Res., 2012, 45, 1844ꢀ1853; (b) N. Boens, V.
Leen and W. Dehaen, Chem. Soc. Rev., 2012, 41, 1130ꢀ1172; (c) A. Bessette and G. S. Hanan, Chem.
Soc. Rev., 2014, 43, 3342ꢀ3405; (d) G. Ulrich, R. Ziessel and A. Harriman, Angew. Chem., 2008, 120
,
1202ꢀ1219; Angew. Chem. Int. Ed., 2008, 47, 1184– 1201; (e) A. Wakamiya, T. Murakami and S.
20

Page 21 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
Yamaguchi, Chem. Sci., 2013, 4, 1002; (f) M. Wada, S. Ito, H. Uno, T. Murashima, N. Ono, T. Urano
and Y. Urano, Tetrahedron Lett., 2001, 42, 6711; (g) Z. Shen, H. Rohr, K. Rurack, H. Uno, M.
Spieles, B. Schulz, G. Reck and N. Ono, Chem.–Eur. J., 2004, 10, 4853; (h) C. Yu, Y. Xu, L. Jiao, J.
Zhou, Z. Wang, and E. Hao, Chem.–Eur. J., 2012, 18, 6437; (i) M. Nakamura, H. Tahara, K.
Takahashi, T. Nagata, H. Uoyama, D. Kuzuhara, S. Mori, T. Okujima, H. Yamada and H. Uno, Org.
Biomol. Chem., 2012, 10, 6840.
4
(a) R. Misra, B. Dhokale, T. Jadhav and S. M. Mobin, Dalton Trans., 2014, 43, 4854; (b) X. Yang,
X.ꢀF. Zhang, X. Lu, C. Yu, L. Jiao, J. Photochem. Photobiol. A: Chem., 2015, 297, 39ꢀ44.
5 (a) B. Dhokale, P. Gautam, S. M. Mobin and R. Misra, Dalton Trans., 2013, 42, 1512ꢀ1518; (b) P.
Gautam, B. Dhokale, S. M. Mobin and R. Misra, RSC Adv., 2012, 2, 12105ꢀ12107; (c) R. Misra, B.
Dhokale, T. Jadhav and S. M. Mobin, Dalton Trans., 2014, 43, 4854. (d) R. Misra, B. Dhokale, T.
Jadhav and S. M. Mobin, Organometallics, 2014, 33, 1867–1877. (e) R. Misra, B. Dhokale, T. Jadhav
and S. M. Mobin, New J. Chem. 2014, 38, 3579ꢀ3585. (f) R. Misra, T. Jadhav, B. Dhokale, P.
Gautam, R. Sharma, R. Maragani and S. M. Mobin, Dalton Trans., 2014, 43, 13076ꢀ13086.
6 B. Dhokale, T. Jadhav, S. M. Mobin and R. Misra, Chem. Commun., 2014, 50, 9119ꢀ9121.
7 Y. Liu, M. Nishiura, Y. Wang, Z. Hou, J. Am. Chem. Soc., 2006, 128, 5592–5593.
8 (a) A. Carpita and A. Ribecai, Tetrahedron Lett., 2009, 50, 204−207; (b) J. H. Olivier, F. Camerel,
R. Ziessel, P. Retailleau, J. Amadou and C. PhamꢀHuu, New J. Chem., 2008, 32, 920−924; (c) L.
Djakovitch, and P. Rollet, Adv. Synth. Catal., 2004, 346, 1782−1792.
9 (a) P. Arsenyan, K. Rubina, J. Vasiljeva and S. Belyakov, Tetrahedron Lett., 2013, 54, 6524−6528;
(b) M. Pal, R. Dakarapu, K. Parasuraman, V. Subramanian and K. R. Yeleswarapu, J. Org. Chem.,
2005, 70, 7179−7187. (c) Y. ꢀJ. Chen, G. ꢀH. Lee, S. ꢀM. Peng and C. Y. Yeh, Tetrahedron Lett.,
2005, 46, 1541−1544; Corrigendum: Tetrahedron Lett., 2005, 46, 3265; (d) J. J. Gonzalez, A.
Francesch, D. J. Cardenas and A. M. Echavarren, J. Org. Chem., 1998, 63, 2854−2857; (e) I. G. Stara,
I. Stary, A. Kollarovic, E. Teply, D. Saman and P. Fiedler, Tetrahedron, 1998, 54, 11209−11234; (f)
Y. Liu, S. Jin, Z. Wang, L. Song and Y. Hu, Org. Lett., 2014, 16, 3524–3527.
21

Dalton Transactions
Page 22 of 23
View Article Online
DOI: 10.1039/C5DT00565E
10 (a) R. H. Platel and L. L. Schafer, Chem. Commun., 2012, 48, 10609ꢀ10611; (b) G. Midya, B.
Parasar, K. Dharab and J. Dash, Org. Biomol. Chem., 2014, 12, 1812; (c) S. D. Wobser, C. J.
Stephenson, M. Delferro and T. J. Marks, Organometallics, 2013, 32, 1317−1327.
11 H. Wang, M. G. H. Vicente, F. R. Fronczek, K. M. Smith, Chem. Eur. J. 2014, 20, 5064−5074.
12 (a) N. K. Swamy, L. K. Tatini, J. M. Babu, P. Annamalai and M. Pal, Chem. Commun., 2007,
1035ꢀ1037; (b) X. Zeng, Chem. Rev., 2013, 113, 6864−6900.
13 (a) U. Mayerhcffer, M. Gsanger, M. Stolte, B. Fimmel and F. Wurthner, Chem. Eur. J., 2013, 19
,
218ꢀ232; (b) A. D. Laurent, C. Adamo and D. Jacquemin, Phys. Chem. Chem. Phys., 2014, 16, 14334ꢀ
14356.
14 (a) B. Dhokale, P. Gautam and R. Misra, Tetrahedron Lett., 2012, 53, 2352ꢀ2354; (b) P. Gautam,
B. Dhokale, V. Shukla, C. P. Singh, K. S. Bindra and R. Misra, J. Photochem. Photobiol. A, 2012,
239, 24ꢀ27; (c) R. Misra, P. Gautam, R. Sharma and S. M. Mobin, Tetrahedron Lett., 2013, 54, 381ꢀ
383; (d) T. Jadhav, R. Maragani, R, Misra, V. Sreeramulu, D. N. Rao and S. M. Mobin, Dalton
Trans., 2013, 42, 4340ꢀ4342; (e) R. Misra, P. Gautam, T. Jadhav and S. M. Mobin, J. Org.
Chem., 2013, 78, 4940ꢀ4948; (f) R. Sharma, R. Maragani, S. M. Mobin and R. Misra, RSC
Adv., 2013, 3, 5785; (g) R. Misra, T. Jadhav and S. M. Mobin, Dalton Trans., 2013, 42, 16614ꢀ16620.
(h) R. Maragani and R. Misra, Tetrahedron Lett., 2013, 54, 5399−5402; (i) R. Misra, T. Jadhav and S.
M. Mobin, Dalton Trans., 2014, 43, 2013ꢀ2022; (j) R. Misra, R. Sharma and S. M. Mobin, Dalton
Trans., 2014, 43, 6891ꢀ6896; (k) R. Misra, T. Jadhav, B. Dhokale and S. M. Mobin, Chem. Commun.,
2014, 50, 9076ꢀ9078; (l) V. A. Nadtochenko, N. N. Denisov, V. Y. Gak, N. V. Abramova, Loim, N.
M. Russ. Chem. Bull., 1999, 48, 1900; (m) S. Barlow and S. R. Marder, Chem. Commun., 2000, 1555ꢀ
1562.
22

Page 23 of 23
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00565E
Table of Content
Meso enyne substituted BODIPYs: synthesis, structure and
properties
Bhausaheb Dhokale, Thaksen Jadhav, Shaikh M. Mobin and Rajneesh Misra*.
Department of Chemistry, Indian Institute of Technology Indore,
IET-DAVV Campus, Khandwa Road, Indore 452 017 (India)
E-mail: rajneeshmisra@iiti.ac.in