Carbazole substituted boron dipyrromethenes

Article abstract of DOI:10.1039/c4dt01160k

meso-Substituted BODIPY with N-butylcarbazole (1) was prepared and derivatized. Dibromo BODIPY 2, α-formyl BODIPY 3 and β-formyl BODIPY 4 were synthesized. All compounds were characterized by HRMS, NMR, UV-vis absorption, electrochemical and fluorescence techniques. The crystal structures of BODIPY 1 and its dibromo derivative 2 were also solved. In both the X-ray structures, the dihedral angle between the meso-carbazole group and the dipyrrin plane was decreased, suggesting the increased interaction between the two units. meso-Substitution with the N-butylcarbazole group on the BODIPY core rendered huge Stokes shifts (111-168 nm) and higher quantum yields as compared to meso-aryl BODIPY. An efficient energy transfer from the carbazole unit to the BODIPY core was observed by fluorescence spectroscopy for all the compounds 1-4. CV studies of compounds 1-4 showed anodic shifts of the reduction and oxidation potentials, suggesting that the meso-carbazole group is affecting the electronic properties of the BODIPY core and making them easier to reduce.

Full text of DOI:10.1039/c4dt01160k

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: I. -. GUPTA and P.
E. Kesavan, Dalton Trans., 2014, DOI: 10.1039/C4DT01160K.
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 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
Carbazole Substituted Boron Dipyrromethenes
a
a
Praseetha E. Kesavan , Iti Gupta*
a
Indian Institute of Technology Gandhinagar, VGEC Campus, Chandkheda, Ahmedabad-382424, India
Abstract : Meso-substituted BODIPY with N-butylcarbazole (1) was prepared and
derivatized. Dibromo BODIPY 2, -formyl BODIPY 3 and -formyl BODIPY 4 were
synthesized. All compounds were characterized by HRMS mass, NMR, UV-vis absorption,
electrochemical and fluorescence techniques. Crystal structure of BODIPY 1 and its
dibromoderivative 2 were also solved. In both the X-ray structures, the dihedral angle
between the meso-carbazole group and dipyrrin plane was decreased, suggesting the
increased interaction between the two units. Meso-susbtitution with N-butylcarbazole
group on BODIPY core, rendered huge Stokes shifts (111-168 nm) and higher quantum
yields as compare to meso-aryl BODIPY. An efficient energy transfer from carbazole unit
to BODIPY core was observed by fluorescence spectroscopy for all the compouds 1-4. CV
studies of compounds 1-4 showed anodic shifts of the reduction and oxidation potentials,
suggesting that meso-carbazole group is affetcing the electronic properties of the BODIPY
core and making them easier to reduce.
Keywords: Carbazole BODIPY, Stokes Shifts, Carbazole Dipyrrane, BODIPY Crystals
*
Correspondence to: Dr. Iti Gupta, Indian Institute of Technology Gandhinagar, VGEC
Campus, Chandkheda, Ahmedabad-382424, India. Phone: +91-9925479623, Fax: +91-
2
†
3972324, E-mail: iti@iitgn.ac.in
Current address: Same as above.

Dalton Transactions
Page 2 of 21
View Article Online
DOI: 10.1039/C4DT01160K
Introduction
The BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes were first discovered by
1
Treibs and co-workers in 1968. The BODIPY (Boron dipyrrins) are a class of boron chelates
with dipyrrin units. This fluorescent dye has remarkable photophyical properties like: intense
absorption in the 480-600 nm region, high quantum yield, negligible triplet-state formation, good
2
thermal and photochemical stability. Good solubility and easy functionalization of the BODIPY
core has made them very popular among chemists. Due to their photo-stable nature and
3
insensitivity towards the environmental pH they gained attention as fluorescent labels (proteins
4
and DNA) inside the cell. BODIPYs have been shown useful for variety of applications such as
5
6
7
chemosensors, laser dyes, fluorescent switches etc. Halogenated BODIPY derivatives are also
8
used for the treatment of cancerous cells in PDT (photo dynamic therapy) due to low dark
toxicity and less photo-bleaching and good ISC (inter system crossing). Numerous reports are
9
10
11
available on BODIPY derivatives substituted with halogens, alkyl groups, aryl groups,
1
2
13
extended  systems, crown ether based sensors etc. In spite of having variety of applications,
the major limitations of such dyes are the emission range (about 600 nm) and small Stokes shifts
(
5-15 nm). In order to make them emit far in red region one has to either attach other
chromophores with the BODIPY core or make their dimers and higher oligomers to get good
1
4
15
Stokes shift (80 nm). Covalently linked BODIPY dimers (linked at and position)
have gained interest due to their good Stokes shift and red shifted absorption and emission bands.
Another simple way to induce bathochromic shift in their absorption and emission bands is the
1
6
introduction of electron donor moieties at the various position of BODIPY core. Its a known
fact, that carbazole is a good electron donor and that’s why its derivatives have been used for
17
various photovoltaic (OLEDs) and photosensitizers applications. Carbazole is popular among
chemists due to its facile functionalization, stability and its derivatives exhibits good absorption
1
8
and efficient emissive properties. Recently, Ooyama et al. have synthesized D-A BODIPYs
having diphelyaminocarbazole group attached to the meso-phenyl position of boron dipyrrin core
1
9, 20
for DSSC (dye sensitized solar cells) application.
BODIPY based nano-cars containing
21
carbazole and p-carborane groups have been prepared by Tour et al. NIR fluorescent BODIPYs
with two carbazole groups attached to their -pyrrole position, exhibiting reasonable two-photon
22, 23
absorption cross section were also reported.
In this paper, we report the synthesis and studies
of four Boron dipyrrins 1-4 having N-butylcarbazole group at their meso (C8) position. It is

Page 3 of 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
anticipated that substitution by electron rich carbazole moiety at the meso-position should affect
the electronic, photophysical and electrochemical properties of the BODIPY dyes. The first X-
ray crystal structures of BODIPYs 1 and 2 containing meso-N-butylcarbazole group at C8
position and its dibromo derivative are also reported.
C H
C H
4
9
4
9
C4H9
N
N
Br
N
i) DDQ
ii) Et N
NBS
3
DCM/ DMF
iii) BF .OEt
3
2
Br
N
N
NH HN
N
N
B
B
1
F
F
DPM
F
2
F
i) DMF, ii) DCE
POCl3
C H
4
9
C H
4
9
N
N
+
OHC
N
N
N
N
B
F
B
OHC
F
F
3
F
4
Scheme 1. Synthesis of Carbazole substituted BODIPYs
Results and Discussion
The carbazole substituted dipyrrane, DPM was synthesized by condensation of pyrrole
and 3-formyl carbazole in the presence of TFA (ESI). BODIPY 1 was synthesized from DPM as
shown in the Scheme 1. DPM was oxidized by DDQ and the resultant dipyrrin was complexed
1
.
1
with BF
3
.OEt
2
as per the literature reported method
Silica gel column chromatographic
purification in 35% DCM / Pet ether afforded 1 as orange solid in 50% yield. BODIPY 2 was
prepared by reacting 1 with NBS at room temperature for couple of hours in DCM/ DMF
24
mixture. Silica gel column purification in 25% DCM / Pet ether produced 2 as dark-orange
solid in 75% yield. Vilsmeier Haack formylation of 1 produced mixture of -formyl BODIPY 3
2
5
and -formyl BODIPY 4 in 25% and 50% yield respectively (ESI).

Dalton Transactions
Page 4 of 21
View Article Online
DOI: 10.1039/C4DT01160K
1
19
13
1
1
All BODIPYs 1-4 were characterized by HRMS, H, F, C, H- H COSY spectroscopy
1
(
ESI). DPM was confirmed by molecular ion peak at 366.1825 in HRMS. In H NMR of DPM,
four -pyrrole protons showed up as two singlets at 6.17 and 5.98 ppm and two -pyrrole
protons showed up as singlet at 6.68 ppm. The meso-carbazolyl proton showed up as singlet at
5
.66 ppm and seven carbazole aromatic protons appeared as four sets of multiplets between 8.02
to 7.17 ppm. The N-butyl aliphatic protons showed up as four set of signals ranging from 4.29 to
0
.93 ppm. Compounds 1-4 were confirmed by molecular ion peak in HRMS mass in the positive
1
ion mode. In H NMR of BODIPY 1, four -pyrrole protons showed up as two singlets at 7.04
and 6.58 ppm and two -pyrrole protons showed up as singlet at 7.95 ppm. The seven carbazole
aromatic protons appeared as five sets of signals between 8.02 to 7.17 ppm. The N-butyl
aliphatic protons showed up as four set of signals ranging from 4.29 to 0.93 ppm. The electronic
properties of the BODIPY core were affected by the introduction of N-buylcarbazole group at
1
the meso-position which resulted in the downfield shifts of -pyrrolic protons in H NMR
2
6
1
compared to the meso-tolyl BODIPY. The two -pyrrolic protons in H NMR of meso-tolyl
2
6
BODIPY appeared at 6.89 and 6.55 ppm. The X-ray crystal structure of 1 clearly shows that
aromatic carbazole group is more in plane with the BODIPY core, thereby increasing the -
1
electron delocalization in the molecule. In H NMR of BODIPY 2 due to one bromination at -
pyrrole position, the two -pyrrole protons showed up as two separate signals at 8.01 and 7.80
ppm and the remaining three -pyrrole protons showed up as three singlets at 7.08, 6.96 and 6.63
ppm respectively. The six carbazole aromatic protons were slightly downfield shifted w. r. t.
compound 1 and showed up as five sets of signals between 8.37 to 7.38 ppm. The N-butyl
aliphatic protons were also slightly downfield shifted and showed up as four set of signals
ranging from 4.37 to 1.01 ppm. In BODIPY 3 and 4, the formyl proton appeared as singlet at
10.43 and 9.88 ppm respectively. The chemical shifts for the rest of carbazole aromatic protons
1
9
and alkyl protons in BODIPY 3 and 4 were similar to compound 2. The F NMR spectra of
BODIPYs 1-4 were recorded in CDCl and the fluorine resonance signals splits into quartet due
to the coupling with adjacent boron atom ( B, I = 3/2). In F NMR spectra of compounds 1 and
3
1
1
19
19
19
2
, the F quartet appeared around -145.96 ppm whereas, in compound 3 the F signals appeared
1
9
at -137.75 ppm. This downfield shift in the F NMR of compound 3 is in accordance with the
2
7
literature reported BODIPYs having -formyl groups. The authors, reasoned that due to the H-

Page 5 of 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
1
9
bonding between F and H (of -CHO group) in CDCl
3
, F signal experienced this downfield
2
7
19
shift. In the case of BODIPY 4 having formyl group at the -position, the F signal appeared
at -144.98 ppm, here H-bonding between F and -CHO group is not possible.
Single Crystal X-ray Diffraction Studies
(
a)
(b)
Figure 1. X-ray crystal structures of (a) BODIPY 1 and (b) BODIPY 2, thermal ellipsoids are
shown at 50% probability level in Ortep diagrams.
The single crystals of compound 1 and 2 were obtained by slow evaporation of the n-
heptane/chloroform solution over a period of 10-12 days. Compound 1 gave orange needle shape
crystals in monoclinic form and compound 2 gave orange platelets in orthorhombic form (ESI).
The X-ray structures of compound 1 (CCDC 982777) and 2 (CCDC 979461) are shown in
Figure 1 and relevant data are given in ESI. The orientation of meso-N-butylcarbazole group
towards the plane of BODIPY core is clearly evident from both the crystal structures. In

Dalton Transactions
Page 6 of 21
View Article Online
DOI: 10.1039/C4DT01160K
2
8
agreement with the previously reported crystal data of meso-aryl BODIPYs, the X-ray
structures of 1 and 2 showed that the boron containing central six membered ring is coplanar
2
with the dipyrrin plane. Also the plane defining BF unit is perpendicular to the core BODIPY
plane. The interesting feature of X-ray structures of 1 and 2 is that the dihedral angle (C6-C5-
o
C13-C14) between meso-carbazole group and dipyrrin plane is 46 , which is much lesser to that
o
of meso-phenyl BODIPY crystal structure (reported value 60 ). In both the crystal structures the
C5-C13 bond lengths (the bond between dipyrrin and meso-carbazole group) are also affected
(
ESI) and are slightly shorter than that of meso-phenyl BODIPY crystal structure (the reported
28
value is 1.481Å). The bond lengths such as C1-C2, C2-C3, B-N, B-F, C-N and bond angles
such as N1-B1-N2 and C4-C5-C6 are also slightly altered compared to the meso-phenyl
BODIPY. Overall, the X-ray parameters revealed increased interactions between meso-carbazole
group and dipyrrin unit in both the compounds.
Photophysical Properties
Figure 2. Comparison of normalized absorption spectra of compounds 1-4 in chloroform.

Page 7 of 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
Table 1. Photophysical data of BODIPYs 1-4 in different solvents. The concentration used was
-6
2
.4 x 10 M and excitation wavelength was 488 nm.
Compound
Solvent
λ
abs
log 
fwhmabs-
λ
em
vst

f
1
-1
(
nm) (nm) (cm )
(nm) (nm) (cm )
BODIPY 1
Chloroform
Toluene
DCM
498, 345 4.87, 4.12 37 1563
499, 343 5.35, 4.57 37 1556
497, 345 4.99, 4.27 40 1656
496, 343 4.83, 4.12 38 1598
515, 354 5.04, 4.36 49 1934
515, 355 4.87, 4.08 48 1843
512, 354 4.76, 4.09 50 2007
510, 352 5.05, 4.38 50 2023
516, 347 5.18, 4.54 57 2255
518, 347 5.18, 4.54 52 2020
512, 347 4.56, 3.82 61 2388
511, 345 5.00, 2.39 59 2327
492, 346 4.57, 4.03 47 1995
498, 345 5.11, 4.46 44 1825
491, 346 4.87, 4.18 48 2046
492, 345 4.82, 4.24 46 1979
583
519
618
602
588
539
631
621
643
602
671
665
621
588
659
660
85
20
21
106
74
2928 0.18
772 0.33
3939 0.06
3549 0.09
2411 0.051
THF
BODIPY 2
BODIPY 3
BODIPY 4
Chloroform
Toluene
DCM
24
864
0.11
119
111
127
84
159
153
129
90
3683 0.017
3504 0.022
3828 0.07
2693 0.085
4628 0.002
4531 0.004
4222 0.05
3074 0.17
5192 0.012
5174 0.011
THF
Chloroform
Toluene
DCM
THF
Chloroform
Toluene
DCM
168
168
THF
_
____________________________________________________________________________________
The UV/vis absorption, fluorescence spectra and fluorescence lifetimes of BODIPY 1-4
were measured in chloroform. The absorption spectra of compounds 1-4 are presented in Figure
and photophysical properties are summarized in Table 1. BODIPYs 1-4 showed two absorption
2
bands, shorter wavelength band corresponding to the carbazole unit gave absorption maxima

between 347-354 nm. The longer wavelength band corresponding to the * transition of
BODIPY core appeared between 498-516 nm in all the compounds 1-4. This longer wavelength
2
9
band is blue shifted in compound 1 as compare to the meso-phenyl BODIPY and slightly red
shifted for compounds 2-4. The extinction coefficients were quite higher than the meso-phenyl
BODIPY (Table 1) for lower energy absorption band in all the compounds 1-4 and the
absorption maxima varied very little (2-4 nm) upon changing the solvent polarity from toluene to
1
6
THF (ESI), reflecting the typical behavior of BODIPY chromophores. The fwhmabs (full width
at half maxima of major absorption band) and quantum yields of all the compounds 1-4 were
calculated in different solvents (Table 1). Solvent polarity affected the broadening of the
absorption band and fwhmabs values were lower in non-polar solvent (toluene) and higher in
polar solvents (DCM, THF) for our compounds. This trend is in agreement with the meso-aryl
-1
BODIPYs. The meso-tolyl and meso-anisyl BODIPYs exhibited fwhmabs in the range of 697 cm

Dalton Transactions
Page 8 of 21
View Article Online
DOI: 10.1039/C4DT01160K
-1
29b
in non-polar solvents to 819 cm in polar solvents.
Whereas the fwhmabs of mono- and di-
-1
bromo derivatives of meso-anisyl BODIPYs were in the range of 975 cm in non-polar solvents
-
1
29c
to 1390 cm in polar solvents. The fwhmabs values of BODIPYs 1-4 were quite higher than
the reported meso-aryl BODIPYs, indicating that significant changes occurred in bond lengths /
2
9b
bond angles upon excitation.
Figure 3. Comparison of normalized emission spectra of BODIPYs 1-4 in CHCl (ex = 488
3
nm). Inset shows the fluorescence decay profile and weighted residuals, distribution fit of
compound 1 in chloroform. The excitation wavelength used was 440 nm, collected at 583 nm.
The fluorescence properties of compounds 1-4 were investigated in chloroform by both
steady state and time resolved fluorescence techniques. A comparison of emission spectra of 1-4
is shown in Figure 3 and solvatochromism data is given in Table 1. The typical mirror-image
relationship was observed for the lowest energy absorption band and emission spectra of all the
compounds 1-4. The emission maxima for compounds 1-4 were red shifted as compare to that of
2
9
meso-phenyl BODIPY. Compounds 1 and 2 showed 67 nm red shift w. r. t. meso-phenyl
BODIPY and compound 3 and 4 showed 120 nm red shifted emission bands. The large shift in

Page 9 of 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
emission maxima could be attributed to the carbazole group present at their meso position and
formyl group on the BODIPY core. Solvatochromic studies revealed that BODIYP 2 showed less
shifts (14- 29 nm) in emission maxima by changing the solvents polarity (Table 1). Whereas
change in the solvent polarity, resulted in significant shifts (45-70 nm) in the emission maxima
for BODIPYs 1, 3 and 4.
2 2
Figure 4. Normalized absorption (black) and emission (red) spectra of BODIPY 1 in CH Cl .
For all the compounds 1-4 Stokes shifts were small (20- 80 nm) in toluene and
chloroform (Table 1), whereas large Stokes shifts (111-168 nm) were observed in polar solvents
like DCM and THF. A comparison of absorption and emission spectra of BODIPY 1 is shown in
1
6
Figure 4. Usually the meso-aryl BODIPYs shows 10-15 nm Stokes shifts. For example, the
2
9b
-1
3
Stokes shift of meso-tolyl BODIPY in CHCl was 482 cm ; whereas for the mono- and di-
29c
-1
-1
bormo derivatives of meso-anisyl BODIPYs Stokes shifts were 526 cm and 394 cm
-1
respectively. The observed Stokes shifts for compound 1-4 were ranging from 2411 to 4222 cm
Table 1). The red shifted emission maxima in polar media indicate larges dipoles of the CT
(
2
9b
excited states. This is in agreement with the report by N. Boens et al.
of the BODIPY having
-1
N,N-dimethyl -amoniophenyl group at C-8 position, which showed Stokes shift of 3199 cm in

Dalton Transactions
Page 10 of 21
View Article Online
DOI: 10.1039/C4DT01160K
1
9a
CHCl
3
. Recent reports on BODIPYs having phenylcarbazole-diphenylamine
and
1
9b
-1
theinylcarbazole-diphenylamine groups at C-8 positions showed Stokes shifts of 388 cm and
-1
4
90 cm in 1,4-dioxane. Another report on meso-iodophenyl BODIPYs having one and two N-
-
enthynylcarbazole moieties at their C-3 and C-6 positions showed Stokes shifts of about 538 cm
1
-1
22
3
and 365 cm respectively in CHCl . Thus, the substitution at C-8 position of BODIPY with
carbazole moiety is affecting the Stokes shifts more than the substitution at C-3 and C-6
positions. The large Stokes shifts could be due to the effect of electron rich carbazole, which acts
2
2
an electron donor moiety in BODIPYs. The fluorescence quantum yields 
f 3
in CHCl for
BODIPY 1 (0.18) and 3 (0.07) were three and 1.2 times higher respectively than the meso-phenyl
2
9
f
BODIPY. The fluorescence quantum yields  for BODIPY 2 and 4 were slightly lesser than
the meso-phenyl BODIPY. The higher quantum yield of compounds 1 and 3 could be due to the
bulky nature of carbazole group at their meso-position, which hinders the free rotation in the
BODIPY molecules. The lower quantum yields for compounds 2 and 4 suggests, higher
intersystem crossing from S
were higher in non-polar solvent (toluene) and lower in polar solvents (DCM, CHCl
to the large dipole moment difference between CT excited state and ground state which in turn
1
to T
1
in these compounds. The quantum yields of compound 1-4
3
); this is due
29b
facilitate internal conversion in polar media.
The time-correlated single photon counting
technique was used to measure the singlet state life times  of BODIPYs 1-4. The fluorescence
decay of compounds 1-4 were fitted to a single exponential decay. The singlet state life times ,
r
the decrease in radiative decay constant k and the increase in non-radiative decay constant knr
are in line with the quantum yield data.
3
Table 2. Quantum yields and lifetime data of BODIPYs 1-4 in CHCl .
_
_________________________________________________________________
a
b
9 -1
9 -1
Compound

f

f
 (ns)
k
r
(10 s )
knr(10 s )
_
____________________________________________________________
BODIPY 1
BODIPY 2
BODIPY 3
BODIPY 4
Meso-Phenyl
0.18
0.045
0.07
0.043
0.06
0.163
0.038
0.062
0.037
_
3.37
1.08
1.47
3.15
0.45
0.053
0.042
0.047
0.014
0.14
0.24
0.88
0.63
0.30
2.08
c
BODIPY
_
__________________________________________________________________
k
r
=  / and knr = (1‐  )/; a: ex= 488 nm; b: ex= 347 nm; c: in toluene, taken from ref. (29)
f
f

Page 11 of 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
Figure 5. Comparison of normalized emission spectra of BODIPY 1, a 1:1 mixture of N-butyl
Carbazole and meso-Tolyl BODIPY and only N-butyl carbazole in CHCl (ex= 347 nm).
3
Since carbazole moiety absorbs between 300-450 nm and BODIPY dyes absorbs around
00-600 nm, an energy transfer from carbazole moiety to BODIPY core is expected. Indeed, all
5
the compounds 1-4 exhibited energy transfer phenomenon form carbazole unit to BODIPY core.
A comparison of emission spectra of BODIPY 1, N-butylcarbazole and a 1:1 mixture of N-Butyl
25
carbazole and meso-tolyl BODIPY is shown in Figure 5. In our systems, the meso-carbazole
unit act as energy donor and the BODIPY core act as energy acceptor. Therefore, upon excitation
of carbazole unit at 347 nm in all the compounds 1-4, the dominant emission was observed from
the BODIPY core in the range of 500-650 nm. N-butylcarbazole molecule emits in the range of
340-450 nm. It is very clear from Figure 5, that upon excitation of a 1:1 mixture of N-
butylcarbazole and meso-tolyl BODIPY at 347 nm, where N-butylcarbazole absorbs strongly,
emission was observed exclusively from N-butylcarbazole around 340 nm and no emission was
observed from the BODIPY core. However, in the case of BODIPY 1 the excitation of N-
butylcarbazole unit at 347 nm resulted in exclusive emission from BODIPY unit around 583 nm

Dalton Transactions
Page 12 of 21
View Article Online
DOI: 10.1039/C4DT01160K
and carbazole emission was drastically quenched (Figure 5). The large Stokes shifts could
possibly due to the through bond energy transfer from donor (meso-carbazole) to acceptor
3
0
(
BODIPY unit). The “energy transfer efficiency” (ETE, %) is a measure of through bond
energy transfer and it can be calculated as follows:
f of acceptor in the molecule excited at the donor
f of acceptor in the molecule excited at the acceptor
ETE % =
X 100
The quantum yields of BODIPY unit in all the compounds 1-4 were calculated at two
different wavelengths i. e. excited at donor (meso-carbazole, 347 nm) and excited at acceptor
(
BODIPY core, 488 nm) and data is given in Table 2. ETE gives the idea of the extent of energy
3
0
transfer including the loss in energy by nonradiatve process during the energy transfer. The
calculated values of ETE (%) were: BODIPY 1 (90 %), BODIPY 2 (85 %), BODIPY 3 (88 %)
and BODIPY 4 (86 %). X-ray crystal structure also support the fact that in the compounds 1 and
2
, the meso –carbazole (donor) and boron-dipyrrin core (acceptor) are not coplanar, therefore
possibility of energy transfer through other mechanism is not very favorable. However, more
detailed photophysical and electrochemical studies will be required to understand the mechanism
of energy transfer in these compounds. The ETE (%) values are between 85% to 90% indicating,
an efficient energy transfer from donor to acceptor in all the BODIPY 1-4.
Electrochemical Properties
Table 3. Electrochemical redox data (V) of compounds 1-4 in dichloromethane, containing 0.1
M TBAP as supporting electrolyte recorded at 50 mV/s scan speed.
_
__________________________________________________
ox(V vs SCE)
___________________________________
II II
__________________________________________________
E
_
I
Ered(V vs SCE)
Compound
I
_
1
2
3
4
1.29
1.32
1.44
1.41
1.03
1.05
1.17
1.15
-0.705
-0.56
-0.37
-0.51
-1.79
-1.60
-1.23
-1.53
_
__________________________________________________

Page 13 of 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
Figure 6. Comparison of cyclic voltamograms of compounds 1-4 in dichloromethane, containing
0
.1 M TBAP as supporting electrolyte recorded at 50 mV/s scan speed (V vs. SCE).
The cyclic voltammetry measurements of BODIPYs 1-4 were carried out at the scan rate
of 50 mV/s using tetrabutylammonium perchlorate as supporting electrolyte. The redox potential
data and a comparison of reduction waves are shown in the Table 3 and Figure 6 respectively.
The BODIPYs typically shows one reversible reduction and one quasi reversible reduction along
with one irreversible oxidation. Compounds 1-4 showed one reversible and one irreversible
reduction wave. The reduction potentials are showing anodic shift as compare to that of meso-
tolyl-BODIPY, indicating that compounds 1-4 are easier to reduce compare to the meso-tolyl-
2
6
BODIPY. Compounds 1 and 2 showed two irreversible oxidations, whereas compound 3
showed two quasi-reversible oxidations. Compound 4 showed one quasi-reversible oxidation at
1
.52 V and one irreversible oxidation at 1.15 V. The oxidation and reduction potential values of
compound 3 are very different from the parent BODIPY 1, suggesting that substitution by formyl
group at the -pyrrolic position affected the electronic properties of the compound more than the
substitution at-pyrrolic position. The oxidation potential values are more positive than the

Dalton Transactions
Page 14 of 21
View Article Online
DOI: 10.1039/C4DT01160K
typical meso-aryl BODIPY, suggesting that all the compounds 1-4 are difficult to oxidize
compared to their meso-aryl analogues.
Conclusion
In conclusion, we have synthesized and characterized four boron-dipyrrins containing
meso-carbazole group. Their absorption, emission, electrochemical and time resolved florescence
studies were carried out. Also, the X-ray crystal structures of two BODIPYs were solved. The
reduced dihedral angle between the meso-carbazole group and dipyrrin core in the both the
crystal structures revealed better interaction between the two moieties. It was found that, the
meso-carbazole group altered the electronic properties of the four BODIPYs which were
reflected in the higher extinction coefficient, red shifted emission maxima, increased quantum
yields and large Stokes shifts. Fluorescence studies indicated an efficient energy transfer from
meso-carbazole moiety to boron-dipyrrin core in all the compounds. Due to increased
conjugation with the electron donor meso-carbazole group, anodic shifts were observed in the
redox potentials of all four BODIPYs.
Experimental Section
Instrumentation and Reagents
Unless otherwise mentioned, all the reagents and solvents were purchased from Aldrich, Acros
Organics or Merck and used without further purification. Pyrrole was distilled under vacuum
prior to use. Silica gel (60-120 mesh size) and neutral alumina (Brockmann Grade I-II) used for
column chromatography were procured from Merck. The dipyrromethanes were visualized upon
2
exposure of TLC plate to Br vapors. The solution NMR spectra of compounds were recorded
with Bruker Avance III 500 MHz NMR spectrometer. The HRMS data for all the compounds
was recorded (in positive ion mode) with Waters Synapt-G2S ESI-Q-TOF Mass instrument.
Absorption spectra were recorded with Shimadzu UV-1700 and Fluorescence emission studies
were performed using Horiba-Jobin Yvon Fluolorog-3 Spectrofluorometer at IIT Gandhinagar.
f
The fluorescence quantum yields ( ) were estimated from the emission and absorption spectra
by comparative method at the excitation wavelength of 488 nm using Rhodamine 6B (
f
= 0.49)
in methanol as standard. The time-resolved fluorescence decay measurements were carried out at
the magic angle using a pico-second-diode-laser-based, time-correlated, single-photon counting

Page 15 of 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
(
TCSPC) fluorescence spectrometer from IBH, UK. Cyclic voltammetric (CV) and differential
pulse voltammetric (DPV) studies were carried out with an electrochemical system utilizing the
three electrode configuration consisting of a glassy carbon (working electrode), platinum wire
(
auxiliary electrode) and saturated calomel (reference electrode) electrodes. The experiments
were done in dry dichloromethane using 0.1 M tetrabutylammonium perchlorate as supporting
electrolyte. Half wave potentials were measured using DPV and also calculated manually by
taking the average of the cathodic and anodic peak potentials. All potentials were calibrated vs.
saturated calomel electrode by the addition of ferrocene as an internal standard, taking E ½
+
(
Fc/Fc ) = 0.51 V vs. SCE. The elemental analysis was done on Thermo Quest Microanalysis
instrument at IIT Bombay.
Synthesis and Characterization
9
-butyl-9H-carbazole: It was synthesized as reported before and the spectral data matches with
31
the reported one. Carbazole (16.7 g, 1mol) was taken in benzene (20 mL) and
tetrabutylammonium iodide (TABI, 1.11g, 3 mmol) was added. 1-Bromo butane (17.13 g, 125
mmol) and 50% NaOH aqueous solution (120 mL) were mixed in the RB. Reaction mixture was
o
stirred at 80 C for 2 h. Solvent was removed under reduced pressure on rotary evaporator. The
2 4
residue was extracted with DCM. The organic layer was dried over Na SO and filtered. After
removal of the solvent, product was recrystallized from ethanol to afford 9-butyl-9H- carbazole
in 83% yield (18.5g).
9
-butyl-9H-carbazole-3-carbaldehyde: It was synthesized as reported before and the spectral
32
data matches with the reported one. Phosphoril chloride (6.12 g, 40 mmol) was added slowly to
o
dry DMF (5 mL) at 0 C and the mixture was stirred for 1 h at RT then a solution of compound 1
(
5.6 g, 20 mmol) in dichloroethane was added and stirred for 1 hr. After this, reaction mixture
was refluxed for 15 h. Finally the solution was cooled and poured into water. The organic layer
was extracted with dichloromethane, dried with sodium sulfate and the solvent was removed
under reduced pressure. Desired compound was isolated via silica gel column chromatography
using ethyl acetate/ petroleum ether (5:95) mixture to afford 9-butyl-9H-carbazole-3-
1
carbaldehyde in 43% yield (4.32 g) H NMR (500 MHz, CDCl
3
,  ppm): 10.07 (s, 1H), 8.5 (s,
3
1
H), 8.13 (d, J = 7 Hz, 1H), 7.9 (d, J = 8 Hz, 1 H), 7.5 (m, 4H), 4.2 (t, J = 7.3 Hz, 2 H), 1.81 (q,

Dalton Transactions
Page 16 of 21
View Article Online
DOI: 10.1039/C4DT01160K
3
+
J = 7.3 Hz, 2H), 1.28 (m, 2H), 0.91 (t, J = 7.3 Hz, 3H). HRMS (ESI-Q-TOF): C17
H17NO
+
[
M+H] : calcd. m/z 252.131 found. m/z 252.1418.
9-butyl-carbazole dipyrromethane (Carbazole DPM)
9
-butyl-9H-carbazole-3-carbaldehyde (1g, 3.97 mmol) was dissolved in pyrrole (2.75 mL, 39.6
mmol) under nitrogen atmosphere. After 5 min. TFA (0.1 eq, 30 µL) was added and reaction
mixture was allowed to stir for half an hour. By vacuum distillation the excess pyrrole was
removed. Desired compound was isolated via silica gel column chromatography using
1
dichloromethane/petroleum ether (50:50) to afford Carbazole DPM in 54.8% (800 mg). H
NMR (500 MHz, CDCl ,  ppm): 8.01 (m, 4H, Ar-H), 7.45 (m, 2H, Ar-H), 7.34 (m, 2H, pyrrole
3
3
N-H), 7.19 (t, J = 7 Hz, 1H, Ar-H), 6.68 (s, 2H, pyrrole α-H), 6.17 (s, 2H, pyrrole β-H), 5.98 (s,
3
2
H, pyrrole β-H), 5.66 (s, 1H, meso-H), 4.29 (t, J = 6.5 Hz, 2H, N-CH
2
-C-), 1.85 (q, J = 7.5 Hz,
3
13
2H, C-CH
2
-C-), 1.42 (m, 2H, -C-CH
2
-CH
3
), 0.95 (t, J = 7 Hz, 3H, -C-CH
3
). C NMR (125.7
MHz, CDCl
3
,  ppm): 140.78, 139.57, 133.36, 132.44, 126.26, 125.69, 122.9, 122.56, 120.43,
119.96, 118.75, 117, 108.83, 108.72, 108.38, 107.06, 43.98, 42.89, 31.15, 20.54, 13.87. HRMS
-
-
(
ESI-Q-TOF): C25
24 3
H N [M-H] calcd. m/z 366.2048 found. m/z 366.1825. Anal. Calcd. (%) for
25 25 3
C H N : C, 81.71; H, 6.86; N, 11.43. Found: C, 81.79; H, 6.80; N, 11.23.
BODIPY 1: Carbazole DPM (100 mg 0.32 mmol) was dissolved in dichloromethane (38 mL)
and oxidized with DDQ (87.17 mg, 0.384 mmol) at RT under air. The reaction mixture was
allowed to stir at room temperature for 30 min. Triethyl amine (1.78 mL), followed by BF
.Et O
3 2
(
2.03 mL) was added to the reaction mixture successively without any time delay. The stirring
was continued at room temperature for an additional 30 min., the reaction mixture was
evaporated and the crude product was purified by using silica gel column chromatography and
eluted with dichloromethane/ petroleum ether (35:65) mixture to afford BODIPY 1 as orange
1
solid in 50.1% yield (66.3 mg). H NMR (500 MHz, CDCl
3
,  ppm): 8.35 (s, 1H, Ar-H), 8.14 (d,
J = 8 Hz, 1H, Ar-H), 7.94 (s, 2H, pyrrole α-H), 7.72 (d, J = 8 Hz, 1H, Ar-H ), 7.56 (m, 3H, Ar-
3
3
H), 7.32 (t, J = 7 Hz, 1H, Ar-H), 7.04 (s, 2H, pyrrole β-H), 6.57 (s, 2H, pyrrole β-H), 4.4 (t, J =
3
3
7
Hz, 2H, N-CH
2
-C-), 1.94 (t, J = 5 Hz, 2H, -C-CH
2
-C-), 1.49 (m, 2H, -C-CH
2 3
-CH ), 1.01 (t, J
13
=
7 Hz, 3H, -C-CH
3
). C NMR (125.7 MHz, CDCl ,  ppm): 142.85, 142.09, 141.1, 135.2,
3
131.81, 128.71, 126.72, 124.71, 123.55, 123, 122.53, 120.72, 119.93, 118.16, 109.29, 108.67,

Page 17 of 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
1
9
4
3.22, 31.15, 20.6, 13.87. F NMR (470.4 MHz, CDCl
3
,  ppm): -145.96 (q, 2F). HRMS (ESI-
[M ]: calcd. m/z 413.266 found. m/z 413.1875. Anal. Calcd. (%) for
: C, 72.66; H, 5.37; N, 10.17. Found: C, 72.32; H, 5.07; N, 10.07.
+
+
2 3
Q-TOF): C25H22BF N
C
25
H
2
22BF N
3
BODIPY 2: A solution of BODIPY 1 (50 mg, 0.12 mmol) in CH
2 2
Cl /DMF (3:3) was taken in
RB and a solution of NBS (51.24 mg, 2.4 eq) in CH Cl (1.8 mL) was added to it. The mixture
2
2
was stirred at room temperature for 2 h. The reaction mixture was washed with water and
organic layer was extracted with dichloromethane and dried over sodium sulfate. Evaporation of
solvent mixture under reduced pressure gave crude compound. Desired compound was isolated
via silica gel (100-200 mesh) column chromatography using dichloromethane/petroleum ether
1
(
25:75) mixture to afford BODIPY 2 as dark orange solid in 75% yield (51.7 mg) H NMR (500
MHz, CDCl ,  ppm): 8.27 (d, J = 5.5 Hz, 2H, Ar-H), 8.0 (s, 1H, pyrrole α-H), 7.8 (s, 1H,
3
pyrrole α-H), 7.72 (d, J = 8 Hz, 1H, Ar-H), 7.64 (d, J = 8.5 Hz, 1H, Ar-H), 7.55 (d, J = 8 Hz, 1H,
Ar-H), 7.38 (d, J = 8.5 Hz, 1H, Ar-H), 7.08 (s, 1H, pyrrole β-H), 6.96 (s, 1H, pyrrole β-H), 6.63
3
3
(
s, 1H, pyrrole β-H), 4.37 (t, J = 6.5 Hz, 2H, N-CH
2
-C-), 1.92 (t, J = 6.5 Hz, 2H, -C-CH
2
-C-),
, 
3
13
1
.46 (m, 2H, -C-CH
2
-CH
3
), 1.01 (t, J = 7 Hz, 3H, -C-CH
3
). C NMR (125.7 MHz, CDCl
3
ppm): 145, 142.43, 141.20, 139.77, 135.47, 134.50, 133.3, 130.47, 129.61, 129.22, 124.65,
124.16, 123.70, 123.58, 122.11, 119.31, 112.96, 110.81, 109.19, 43.41, 31.08, 29.69, 20.55,
1
9
1
3.82. F NMR (470.4 MHz, CDCl
3
,  ppm): -145.96 (q, 2F). HRMS (ESI-Q-TOF):
[M ]: calcd. m/z 569.0085 found. m/z 569.3715. Anal. Calcd. (%) for
: C, 52.58; H, 3.53; N, 7.36. Found: C, 52.32; H, 3.07; N, 7.23.
+
+
C
C
25
H
H
20BBr
20BBr
F
2 2
2
N
N
3
3
25
2
F
Synthesis of Mono-formyl BODIPYs 3 & 4
Phosphoril chloride (5 g, 32.6 mmol) was added slowly to dry DMF (3g) at 0 C and the mixture
was stirred for 5 min. under N atmosphere. The mixture was warmed to room temperature and
o
2
stirred for additional 30 min. BODIPY 1 (100 mg, 0.24 mmol) in 1,2-DCE was added to the
o
mixture and the resulting solution was stirred for 2 hours at 50 C. Then the reaction mixture was
o
cooled to room temperature and poured into saturated aqueous NaHCO
3
solution at 0 C. After
this, the mixture was warmed to room temperature and stirred for further 30 min. Reaction
mixture was washed with water and the organic layer was collected, dried over Na SO
2
4
.

Dalton Transactions
Page 18 of 21
View Article Online
DOI: 10.1039/C4DT01160K
Removal of solvent on rotary evaporator gave cure compounds. BODIPY 3 and 4 was separated
as first and second fraction respectively using silica gel column chromatography. BODIPY 3
was eluted with 50% dichloromethane/petroleum ether and BODIPY 4 was eluted with 80%
dichloromethane/petroleum ether.
1
BODIPY 3: Dark pink solid in 23% yield (25 mg) H NMR (500 MHz, CDCl
3
,  ppm): 10.43 (s,
1H, -CHO), 8.35 (s, 1H, Ar-H), 8.19 (s, 1H, pyrrole α-H), 8.15 (d, J = 7.5 Hz, 1H, Ar-H), 7.73
3
3
(
d, J = 8 Hz, 1H, Ar-H), 7.58 (t, J = 6.5 Hz, 2 H Ar-H), 7.51 (d, J = 8 Hz, 1H, Ar-H), 7.34 (t, J
=
7 Hz, 1H, Ar-H), 7. 24 (d, J = 4 Hz, 1H, pyrrole β-H), 7.15 (d, J = 5 Hz, 1H, pyrrole β-H),
3
6
.98, (d, J = 4 Hz, 1H, pyrrole β-H), 6.76 (d, J = 4 Hz, 1H, pyrrole β-H), 4.41 (t, J = 6.5 Hz, 2H,
3
N-CH
2
-C-), 1.96 (m, 2H, -C-CH
2
-C-), 1.55 (m, 2H, -C-CH
). C NMR (125.7 MHz, CDCl
37.1, 136.83, 135.34, 129, 128.91, 127.06, 124.32, 124.07, 123.28, 122.43, 121.23, 120.81,
2
-CH
3
), 1.01 (t, J = 7 Hz, 3H, -C-
1
3
CH
3
3
,  ppm): 184.57, 151.73, 147.99, 146.96, 142.53, 141.17,
1
19
1
20.29, 118.1, 109.49, 109.03, 52.33, 43.30, 31.15, 29.70, 20.6, 13.87. F NMR (470.4 MHz,
+
+
CDCl
3
,  ppm): -137.75 (q, 2F). HRMS (ESI-Q-TOF): C26
2
H23BF N
3
O [M+H] m/z: 442.1902
found. m/z 442.1822. Anal. Calcd. (%) for C26
H
22BF N O: C, 70.77; H, 5.03; N, 9.52. Found: C,
2 3
70.47; H, 5.09; N, 9.29.
1
BODIPY 4: Reddish maroon solid in 54% (57 mg) H NMR (500 MHz, CDCl
3
,  ppm): 9.88 (s,
1H, CHO), 8.36 (s, 1H, Ar-H), 8.29 (s, 1H, pyrrole α-H), 8.15 (m, J = 6 Hz, 2H, pyrrole α-H
3
+
Ar-H), 7.74 (d, J = 8 Hz, 1H, Ar-H), 7.58 (t, J = 8.5 Hz, 2H, Ar-H), 7.51 (d, J = 8 Hz, 1H, Ar-
3
H), 7.41(s, 1H, pyrrole β-H), 7.34 (t, J = 7 Hz, 1H, Ar-H) 7.25 (d, J = 8 Hz, 1H, pyrrole β-H),
6
1
.75 (d, J = 3 Hz, 1H, pyrrole β-H), 4.41 (t, J = 7 Hz, 2H, N-CH
2
-C-), 1.95 (m, 2H, -C-CH
2
-C-),
3
13
.48 (m,2H, -C-CH
2
-CH
3
), 1.02 (t, J = 7 Hz, 3H, -C-CH
3
). C NMR (125.7 MHz, CDCl , 
3
ppm): 185.03, 151.75, 151.15, 147.45, 142.62, 142.1, 141.18, 136.87, 135.14, 135.06, 131.74,
128.87, 127.06, 124, 123.93, 123.34, 122.41, 120.89, 120.27, 109.49, 109.15, 43.30, 31.14,
1
9
2
0.60, 13.88. F NMR (470.4 MHz, CDCl
3
,  ppm): -144.98 (q, 2F). HRMS (ESI-Q-TOF):
m/z: 442.1902 found. m/z 442.1893. Anal. Calcd. (%) for
O: C, 70.77; H, 5.03; N, 9.52. Found: C, 70.53; H, 5.14; N, 9.41.
+
+
C
C
26
H
H
23BF
2
N
N
3
3
O
[M+H]
26
22BF
2

Page 19 of 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
Acknowledgements
IG gratefully acknowledges DST (New Delhi), CSIR, (New Delhi) for financial support and IIT
Gandhinagar for infrastructure and research facility. IG thanks IIT Bombay, Chemistry
Department for Time Resolved Fluorescence, CHN analysis and CV studies. IG is grateful to
Prof. H. Furuta at Kyushu University, Fukuoka for X-ray measurements. PEK thanks IIT
Gandhinagar for fellowship.
Supporting Information
1
13
19
1
1
The characterization data like ESI-MS, H, C, F, H- H COSY NMR spectra, Fluorescence
and absorption spectra of reported compounds are available as supporting information.
References:
1
. A. Treibs and F. H. Kreuzer, Justus Liebigs Ann. Chem. 1968, 718, 208.
. G. Ulrich, R. Ziessel and A. Harriman, Angew. Chem. Int. Ed. 2008, 47, 1184.
. J. Karolin, L. B.-A. Johansson, L. Strandberg and T. Ny, J. Am. Chem. Soc.1994, 116, 7801.
. M.-C. Yee, S. C. Fas, M. M. Stohlmeyer, T. J. Wandless and K. A. Cimprich, J. Biol. Chem.
005, 280, 29053.
2
3
4
2
5
6
. A. Coskun and E. U. Akkaya, J. Am. Chem. Soc. 2006, 128, 14474.
. M. Shah, K. Thangraj, M. L. Soong, L. T. Wolford, J. H. Boyer, I. R. Politzer and T. G.
Pavlopoulos, Heteroat. Chem. 1990, 1, 389.
7
8
. T. A. Golovkova, D. V. Kozlov and D. C. Neckers, J. Org. Chem. 2005, 70, 5545.
. A. Kamkaew, S. H. Lim, H. B. Lee, L. V. Kiew, L. Y. Chung and K. Burgess, Chem. Soc.
Rev. 2013, 42, 77.
9
1
1
. T. Yogo, Y. Urano, Y. Ishitsuka, F. Maniwa and T. Nagano, J. Am. Chem. Soc. 2005, 127,
2162.
0. J. H. Boyer, A. M. Haag, G. Sathyamoorthi, M. L. Soong, K. Thangraj and T. G.
Pavlopoulos, Heteroat. Chem. 1993, 4, 39.
11. R. W. Wagner and J. S. Lindsey, Pure. Appl. Chem. 1996, 68, 1373.
12. G. Ulrich, S. Goeb, A. De Nicola, P. Retailleau and R. Ziessel, Synlett 2007, 1517.
13. A. Coskun and E. U. Akkaya, J. Am. Chem. Soc. 2005, 127, 10464.

Dalton Transactions
Page 20 of 21
View Article Online
DOI: 10.1039/C4DT01160K
14. M. Boring, R. Kruger, S. Link, C. Kleeberg, S. Kohler, X. Xie, B. Ventura and L. Flamigni,
Chem. Eur. J. 2008, 14, 2976.
1
1
1
5. C. Goze, G. Ulrich and R. Ziessel, Org. Lett. 2006, 8, 4445.
6. A. Laudet and K. Burgess, Chem. Rev. 2007, 107, 4891.
7. (a) V. Promarak, M. Ichikawa, T. Sudyoadsuk, S. Saengsuwan, S. Jungsuttiwong and T.
Keawin, Thin Solid Films 2008, 516, 2881; (b) S. Hwang, J. H. Lee, C. Park, H. Lee, C. Kim, C.
Park, M.-H. Lee, W. Lee, J. Park, K. Kim, N.-G. Park and C. Kim, Chem. Commun. 2007, 4887;
(
c) H. Choi, J. K. Lee, K. Song, S. O. Kan and J. Ko, Tetrahedron 2007, 63, 3115.
8. (a) A. Hameurlaine and W. Dehaen, Tetrahedron Lett. 2003, 44, 957; (b) Y. Li, J. Ding, M.
1
Day, Y. Tao, J. Lu and M. D’iorio, Chem. Mater. 2004, 16, 2165; (c) V. P. Barberis and J. A.
Mikroyannidis, Synth. Met. 2006, 156, 1408; (d) M. S. Mudadu, A. N. Singh and R. P. Thummel,
J. Org. Chem. 2008, 73, 6513.
1
1
3
2
2
2
9
2
9. (a) Y. Ooyama, Y. Hagiwara, T. Mizumo, Y. Harima and J. Oshita, RSC Adv. 2013, 3,
8099; (b) Y. Ooyama, Y. Hagiwara, T. Mizumo, Y. Harima and J. Oshita, New J. Chem. 2013,
7, 2479.
0. Y. Ooyama, Y. Hagiwara, Y. Oda, H. Fukuoka and J. Oshita, RSC Adv. 2014, 4, 1163.
1. J. Godoy, G. Vives and J. M. Tour, Org. Lett. 2010, 12, 1464.
2. X. Zhang, Y. Xiao, J. Qi, J. Qu, B. Kim, X. You and K. D. Belfield, J. Org. Chem., 2013, 78,
153.
3. D. Zhan, V. Martin, I. G. Moreno, A. Costela, M. E. Perez-Ojeda and Y. Xiao, Phys. Chem.
Chem. Phys. 2011, 13, 13026.
2
2
2
3
2
2
4. Y. Hayashi, S. Yamaguchi, W. Y. Cha, D. Kim and H. Shinokubo, Org. Lett. 2011, 13, 2992.
5. T. Kaur, V. Lakshmi and M. Ravikanth, RSC Adv. 2013, 3, 2736.
6. T. K. Khan, S. K. Jana, M. R. Rao, M. S. Shaikh and M. Ravikanth, Inorg. Chim. Acta 2012,
83, 257.
7. S. Madhu, M. R. Rao, M. S. Shaikh and M. Ravikanth, Inorg. Chem. 2011, 50, 4392.
8. H. L. Kee, C. Kirmaier, L. Yu, P. Thamyongkit, W. J. Youngblood, M. E. Calder, L. Ramos,
B. C. Noll, D. B. Bocian, R. Scheidt, R. R. Brige, J. S. Lindsey and D. Holten, J. Phys. Chem. B
005, 109, 20433.
2

Page 21 of 21
Dalton Transactions
View Article Online
DOI: 10.1039/C4DT01160K
29. (a) V. Lakshmi, M. Shaikh and M. Ravikanth, J. Fluoresc. 2013, 23, 519; (b) W. Qin, M.
Baruah, M. V. D. Auweraer, F. C. De Schryver and N. Boens, J. Phys. Chem. A 2005, 109,
7371; (c) V. Lakshmi and M. Ravikanth, Dalton Trans. 2012, 41, 5903.
30. C. Thivierge, J. Han, R. M. Jenkins and K. Burgess, J. Org. Chem. 2011, 76, 5219.
31. T. Zhao, Z. Liu, Y. Song, W. Xu, D. Zhang and D. Zhu, J. Org. Chem. 2006, 71, 7422.
32. T. H. Xu, R. Lu, C. H. Tan, X. P. Qiu, C. V. Bao, X. L. Liu, P. C. Xue and Y. Y. Zhao, Eur.
J. Org. Chem. 2006, 4014.