Synthesis and Studies of Aza-BODIPY-Based π-Conjugates for Organic Electronic Applications

Article abstract of DOI:10.1002/ejoc.201301300

Aza-boron-dipyromethene (aza-BODIPY) derivatives 1-6 were synthesized for the first time by employing the palladium catalyzed Suzuki-Miyaura coupling on dibromo-aza-BODIPY. Photophysical and electrochemical properties of these compounds were studied in solution. Absorption and emission maxima were observed in the near-infrared (NIR) region and were found to extend up to 754 and 751 nm, respectively. NIR fluorescence quantum yields in chloroform were as high as 0.45. Optical band gaps were measured from the onset of absorption spectra in thin films and were found to be low (ca. 1.2-1.4 eV). Electrochemical studies provided insight into the reduction potentials of these compounds and consequently the electron affinity (EA). High electron affinity (ca. 4.5) was observed for these dyes. NIR absorption and emission, good quantum yield, and high electron affinity of these compounds promise their applications in microscope imaging and optoelectronic devices, mainly in solar cells and field-effect transistors.

Full text of DOI:10.1002/ejoc.201301300

FULL PAPER
DOI: 10.1002/ejoc.201301300
Synthesis and Studies of Aza-BODIPY-Based π-Conjugates for Organic
Electronic Applications
Tamanna K. Khan,[a] Preeti Sheokand,[a] and Neeraj Agarwal*[a]
Keywords: Fluorescence / Dyes/pigments / C–C coupling / Organic electronics / Boron
Aza-boron-dipyromethene (aza-BODIPY) derivatives 1–6
were synthesized for the first time by employing the palla-
dium catalyzed Suzuki–Miyaura coupling on dibromo-aza-
BODIPY. Photophysical and electrochemical properties of
these compounds were studied in solution. Absorption and
emission maxima were observed in the near-infrared (NIR)
region and were found to extend up to 754 and 751 nm,
respectively. NIR fluorescence quantum yields in chloroform
were as high as 0.45. Optical band gaps were measured from
the onset of absorption spectra in thin films and were found
to be low (ca. 1.2–1.4 eV). Electrochemical studies provided
insight into the reduction potentials of these compounds and
consequently the electron affinity (EA). High electron affinity
(ca. 4.5) was observed for these dyes. NIR absorption and
emission, good quantum yield, and high electron affinity of
these compounds promise their applications in microscope
imaging and optoelectronic devices, mainly in solar cells and
field-effect transistors.
(methoxycarbonyl)propyl]-1-phenyl-[6.6]C61, PCBM} as
donor and acceptors, respectively.[9] Fullerene-based ac-
ceptors do not absorb significantly in the NIR region and
hence are unable to harvest photons of these wave-
lengths.[10] A few attempts have been made to develop alter-
natives to fullerene-based acceptors.[11–13] Electron-donors
such as Cu-phthalocyanine (CuPc), P3HT, and poly[4,8-bis-
substituted-benzo[1,2-b:4,5-bЈ]dithiophene-2,6-diyl-alt-4-sub-
stituted-thieno[3,4-b]thiophene-2,6-diyl] (PBDTTT)[14] are
quite popular in organic solar cells. Very few reports are
available on small, solution-processable n-type conjugated
compounds with low optical band gap.[15] Organic mo-
lecules having small energy gap and compatible energy
levels can be utilized in organic electronics to harvest NIR
photons. Intriguingly, organic solar cells with such mole-
cules could also be operated in the dark.
Here, we explore the chemical modification of aza-BOD-
IPY for n-type solution-processable organic materials with
low band gaps and high electron affinity. Aza-BODIPY de-
rivatives are particularly interesting because their photo-
physical and electrochemical properties can be easily ad-
justed by substituting them with electron-donating and elec-
tron-withdrawing groups and by increasing the π-conjuga-
tion along the dye molecule (Scheme 1).[15–19] The Suzuki–
Miyaura coupling has been successfully employed for the
first time on aza-BODIPY to achieve such chemical modifi-
cations. These molecules show absorption and emission in
the NIR region. Good fluorescence quantum yield in the
NIR region and high electron affinities of these compounds
make them potential materials for microscope imaging and
organic electronic devices.
Introduction
The application of near-infrared (NIR) dyes in biological
systems (e.g., bioimaging, sensing of cations and anions,
and photodynamic therapy), photovoltaics, organic light-
emitting devices and nonlinear optics is very attractive.[1–6]
Such applications have encouraged researchers to design
and synthesize new materials that incorporate chromo-
phores featuring absorption and emission beyond 700 nm.
Based on their physicoelectrochemical properties, applica-
tions of these dyes could include microscopic imaging,
whereby dyes emitting in the NIR region can provide
deeper penetration and high contrast, since it is less ab-
sorbed and scattered by biological tissues.[7,8] It is desirable
to have high quantum yields of NIR emitting dyes for appli-
cations in microscopic imaging. Such NIR dyes can also be
used in organic electronic applications, for which the elec-
tron-donating (p-type) and/or electron-accepting (n-type)
properties of the dye, absorption and/or emission properties
are important.
In organic electronic devices, various electron-donor and
electron-acceptor materials have been used, and many or-
ganic solar cells use polymer chains such as poly-3-hexyl-
thiophene (P3HT) and fullerene-based molecules {1-[3-
[a] Chemical Sciences, UM-DAE, Centre for Excellence in Basic
Sciences, Health Center Building,
Kalina Campus, Santacruz (East), Mumbai 400098, India
E-mail: na@cbs.ac.in
www.cbs.ac.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201301300.
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Synthesis and Studies of Aza-BODIPY-Based π-Conjugates
Results and Discussion
Aza-BOBIPY derivatives 1–6 were synthesized as shown
in Scheme 2. The synthesis of 1,7-dithienyl-3,5-di(4-
bromophenyl)borondifluoride-azadipyrromethene
(7)[16]
was carried out by using the classical procedure developed
by McDonnell and O’Shea.[17] Chalcone 8 was synthesized
by reacting thiophene 2-carbaldehyde with p-bromoaceto-
phenone in alcoholic KOH followed by reaction of 8 with
nitromethane, leading to the formation of 9 in good yields
(52 and 72%, respectively). Compound 9 was treated with
excess ammonium acetate at 120 °C in n-butanol to give aza-
dipyrromethene 10, as shown in Scheme 2;[16] the latter was
isolated after precipitation in moderate yield, and converted
into aza-BODIPY 7 by following a reported method.[16]
Thus, azadipyrromethene 10 was dissolved in chloroform,
and diisopropylethylamine (10 equiv.) was added dropwise
over 1 h, followed by the addition of BF3·Et2O (15 equiv.).
Overnight stirring of the reaction mixture at room tempera-
ture and usual work up produced the crude aza-BODIPY
7, which was purified by column chromatography on silica
(dichloromethane/petroleum ether, 1:4) to afford aza-
BODIPY 7 as a blue solid in 42% yield. Aza-BODIPY 7
was subsequently used for Suzuki–Miyaura coupling with
various substituted aryl boronic acids to prepare aza-
BODIPY derivatives 1–6 (Scheme 2). The well-known Su-
zuki–Miyaura coupling conditions [i.e., bromo aza-BOD-
IPY substrate, aryl boronic acids and Pd catalyst with
K2CO3 and 1,2-dimethoxyethane (DME)/H2O] did not give
Scheme 1. Structure of substituted aza-BODIPY derivatives I and
II having absorption and emission in the NIR spectral range.
Scheme 2. Synthetic scheme for compounds 1–10.
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T. K. Khan, P. Sheokand, N. Agarwal
FULL PAPER
the aryl-substituted aza-BODIPY. Under these conditions,
cleavage of the BF2 linkages of aza-BODIPY was observed.
It has been reported that BF2 linkages in aza-BODIPY
cleave when reacted under Sonogashira coupling condi-
tions.[18,20] The Suzuki–Miyaura coupling conditions were
therefore slightly modified, and aza-BODIPY 7 and the re-
spective aryl boronic acid were degassed with argon gas for
5 min. A mixture of tetrahydrofuran (THF), toluene and
water (1:1:1) was added to the reaction flask and the mix-
ture was stirred under argon gas. Pd(PPh3)4 was used as
catalyst and Na2CO3 as base to initiate the coupling of aryl
boronic acid with aza-BODIPY 7. After 2 h stirring at
80 °C, analysis of the reaction by TLC clearly indicated the
formation of a new spot corresponding to aryl coupled aza-
BODIPY along with the reactant. For the completion o
which we attribute to the formation of mono- and di-aryl-
substituted products. The reaction mixture was cooled and
successively washed with brine and water. The organic lay-
ers were dried with anhydrous sodium sulfate and the sol-
vent was evaporated. The crude product was purified by
chromatography on silica column to afford di-substituted
aza-BODIPY derivatives 1–6 as blue solids in 35–65%
yield. In addition to compounds 1–6, we also collected
small amounts of mono-substituted products and some un-
identified product in trace amounts.
All compounds were found to be reasonably soluble in
common organic solvents such as chloroform, dichloro-
methane, acetonitrile and dimethyl formamide. The identi-
ties of the compounds were confirmed by HRMS analysis,
1
Figure 1. H NMR spectrum of 1 recorded in CDCl3.
1
and by H, 13C and 19F NMR spectroscopy (see the Sup-
porting Information). The 1H NMR spectra of compounds
1–6 showed characteristic NMR signals corresponding to
the aza-BODIPY core with additional aryl proton signals
1
of substituted aryl groups. A representative H NMR spec-
trum for compound 1 recorded in CDCl3 is shown in Fig-
ure 1. Three sets of signals were obtained for the thienyl
group present at the 1- and 7-positions of aza-BODIPY at
δ = 7.22, 7.58 and 7.96 ppm. A singlet was observed for
beta protons of pyrrole at δ = 7.06 ppm. The biphenyl
groups attached at the 3- and 5-position of aza-BODIPY
exhibited five sets of signals with three doublets at δ = 7.65,
7.71 and 8.14 ppm corresponding to six aryl protons and
two multiplets at δ = 7.37 and 7.45 ppm corresponding to
1
four aryl protons. The H NMR spectra for compounds 2–
6 were found to be similar, with slight changes due to the
presence of substituents attached to the aryl group.
13C NMR spectroscopic analysis of compounds 1, 3 and 7
were recorded in CDCl3. Unfortunately, clear homogeneous
solutions of 2 and 4–6 in CDCl3 of the required concentra-
tion for 13C NMR could not be obtained, so we were un-
able to record good quality spectra for these compounds.
Melting points were not observed up to 220 °C in silicone
oil.
Compounds 1–6 were studied by absorption, fluores-
cence, and electrochemical techniques in solution. The ab-
sorption spectra were recorded in chloroform and are
shown in Figure 2, and the data were compared with those
Figure 2. Normalized absorption spectra for 1–7 in CHCl3 (top)
of reference aza-BODIPY;[18] the results are summarized in and in thin films (bottom).
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Synthesis and Studies of Aza-BODIPY-Based π-Conjugates
Table 1. Photophysical data for 1–7 recorded in CHCl3.
λabs [nm]
logε
λem [nm]
f[a]
τ [ns][a]
kr [108 s–1]
knr [108 s–1]
λabs [nm][b]
I
661
708
698
719
708
702
754
707
693
4.5
4.7
4.2
4.3
4.7
4.3
4.4
4.4
4.7
689
738
722
751
738
730
–
0.36
0.27
0.38
0.45
0.22
0.21
–
–
–
–
–
1
1.20
1.16
1.72
1.17
1.12
–
2.25
3.27
2.61
1.88
1.87
–
6.08
5.34
3.19
6.66
7.05
–
761
725
770
782
680
823
–
2
3
4
5
6
6+TFA
730
723
0.10
0.17
–
0.93
–
1.82
–
8.92
7
641
[a] Relative quantum yields were calculated by using aza-BODIPY I as reference (CHCl3, f = 0.36). [b] Absorption maxima recorded in
drop-cast films, τ is fluorescence lifetime, kr and knr are radiative and nonradiative constants, respectively.
Table 1. The absorption spectra of 1–6 showed two major edge, there is no other report of infrared emission and high
bands, one strong S0 ǞS1 transition at lower energy and a quantum yields of aza-BODIPY in the literature. Among
second weak S0 ǞS2 transition at higher energy. The refer- all the compounds 1–5, aza-BODIPY 3 showed that highest
ence aza-BODIPY 7 showed S0 ǞS1 transition at 693 nm, emission maxima (751 nm) with a high quantum yield of
which was shifted to longer wavelengths in 1–6 by 5–60 nm. 0.45. The aza-BODIPY 6 was completely nonfluorescent
Absorption maxima for 1–6 were observed at 698–754 nm due to electron transfer from the N,N-dimethylamine group
with high extinction coefficients. Thin-film absorption spec- to the aza-BODIPY core. However, compound 6 became
tra of 1–6 were recorded with a drop cast film on glass fluorescent upon the addition of trifluoroacetic acid (TFA),
surface. Compounds 1–6 showed broad and redshifted ab- as shown previously by McDonnell and O’Shea,[17] with a
sorption in thin films compared with solution spectra (Fig- quantum yield of 0.1 (see Figure S14 in the Supporting in-
ure 2). Optical band gaps were calculated from the onset of formation).
thin-film absorption spectra and are tabulated in Table 2.
Table 2. Electrochemical data for 1–7 recorded in CHCl3.
Ered [V] Eg [eV][a] ELUMO or (–EA) [eV][b] EHOMO [eV][c]
1
2
3
4
5
6
7
–0.413
–0.426
–0.415
–0.383
–0.394
–0.434
–0.427
1.28
1.38
1.33
1.26
1.44
1.18
1.39
–4.58
–4.57
–4.57
–4.62
–4.61
–4.57
–4.65
–5.86
–5.95
–5.90
–5.88
–6.05
–5.75
–6.04
[a] Optical band gap, calculated from absorption spectrum re-
corded in drop-cast films. [b] ELUMO were calculated from onset of
reduction potentials vs. ferrocene. [c] EHOMO = ELUMO – Eg.
The fluorescence spectra of 1–6 were recorded in chloro-
form and are shown in Figure 3; the data is presented in
Table 1. Compounds 1–5 showed strong emission peaks in
the range 722–751 nm. Compound 6 did not show any fluo-
rescence. Absorption and fluorescence spectra of 1–7 were
not mirror images of each other as in the case of BODIPY
dyes. Furthermore, it was found that these compounds pos-
sess considerable Stoke’s shift. This observation could be
accounted for by the possible differences in the ground and
excited state geometries of compounds 1–7. The fluores-
cence quantum yields of 1–5 in chloroform were calculated
by using I as reference compound (Scheme 1),[18] and it was
found that these compounds showed varying fluorescence
quantum yields (0.21–0.45). Recently, Maury et al. reported
that 3,5-nitrofluorenylethynyl-substituted aza-BODIPY (II)
showed emission at 740 nm with a high quantum yield of
0.36.[18] They attributed this redshift in the emission for
Figure 3. Normalized emission spectra for 1–5 and 7 recorded in
CHCl3 (top) and fluorescence decay profile and weighted, residual
distribution fit of 3 in CHCl3 (bottom). The excitation wavelength
used was 635 nm and emission was detected at 751 nm.
Fluorescence lifetime studies were carried out on 1–5 to
compound II to the longer π-conjugated skeleton understand their fluorescence properties in detail; the re-
(Scheme 1). Emission wavelengths and quantum yields of sults are presented in Table 1, and the fluorescence decay
1–7 are comparable to those of II. To the best of our knowl- profile for 3 is shown in Figure 3 (see also the Supporting
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T. K. Khan, P. Sheokand, N. Agarwal
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Information SI 15). Compounds 1–5 showed a single ex- tron-donating and electron-withdrawing properties. To the
ponential decay in CHCl3 solvent. The fluorescence life- best of our knowledge, this is the first example of Suzuki–
time, nonradiative and radiative decay constants for com- Miyaura coupling of aza-BODIPY. Absorption and emis-
pounds 1–5 were consistent with their fluorescence quan- sion maxima of these compounds are bathochromically
tum yields.
shifted and are in the near-infrared region. Extinction coef-
The electrochemical properties of 1–7 were investigated ficients and fluorescence quantum yields are found to be
by cyclic voltammetry and differential pulse voltammetry high. Electrochemical properties of compounds 1–5 and 7
in CHCl3 at a scan rate of 50 mV/s with tetrabutylammoni- exhibited one reversible reduction wave. HOMO and
umhexafluorophosphate (TBAHFP) as supporting electro- LUMO energy levels of these compounds were calculated
lyte. Compounds 1–7 were not oxidized under these experi- by using the onset of reduction potential and optical band
mental conditions and only reduction waves were observed. gaps. ELUMO values suggest that these compounds have
A comparison of the first reduction wave of compounds 4, high electron affinity and have potential applications in or-
5, and 7 is shown in Figure 4 and the data for 1–7 are pre- ganic field-effect transistors (OFET). Furthermore, we be-
sented in Table 2. The 3,5-diaryl-substituted aza-BODIPY lieve that the photophysical and electrochemical parameters
derivatives 1–6 are easier to reduce than 7, which is clearly of these compounds could be exploited for use in organic
evident from data presented in Table 2. The ELUMO of com- solar cells. We are in the process of establishing a facility
pounds 1–7 were calculated by using the reduction potential to explore the possible applications of these compounds in
onset and by using the Fc/Fc+ value at 5.1 eV vs. vacuum. organic solar cells and OFET.
EHOMO was calculated by using the ELUMO and optical
band gap for respective compounds 1–7 (Figure 2). The
Experimental Section
ELUMO of organic compounds is generally considered as
electron affinity (EA) or, in other words, it reflects how eas-
ily they can accept electrons. Electron affinity of more than
4.0 eV is considered to be high. The ELUMO values for 1–7
were observed at ca. –4.6 eV and because ELUMO also re-
Chemicals: All general chemicals and solvents were procured from
SD Fine Chemicals, India, or Sigma–Aldrich. Column chromatog-
raphy was performed using silica gel and basic alumina obtained
from Sisco Research Laboratories, India. Tetrabutylammoni-
flects the EA, we can say that these compounds have high umhexafluorophosphate was purchased from Aldrich and used
without further purifications. Solvents such as dichloromethane,
chloroform, tetrahydrofuran (THF), and toluene were purified and
distilled by standard procedures.
electron affinity.
Instrumentation: 1H and 13C NMR spectra (δ in ppm) were re-
corded with a Varian 600 MHz spectrometer. 19F NMR spectra
were recorded with a Bruker Avance III 376 MHz spectrometer.
Tetramethylsilane (TMS) was used as an internal reference for re-
cording 1H NMR spectra (residual proton; δ = 7.26 ppm) in
CDCl3. HRMS spectra were recorded with a Q-Tof micromass
spectrometer. UV/Vis spectra were acquired at room temperature
with a Shimadzu 1800 instrument. Fluorescence emission measure-
ments were carried out at room temperature with a Horiba Fluo-
romax 4 instrument. Cyclic voltammetry measurements were car-
ried out with an electrochemical analyzer (620 D, CH Instruments
Co.) at room temperature by utilizing the three-electrode configura-
tion consisting of glassy carbon (working electrode), platinum wire
(auxiliary electrode), and Ag/AgCl (reference electrode) electrodes.
The experiments were performed in anhydrous chloroform with
0.1 m tetrabutylammoniumhexafluorophosphate as the supporting
electrolyte. Fluorescence decay measurements were carried out at
the magic angle with a picosecond-diode-laser-based, time-corre-
lated single-photon-counting (TCSPC) fluorescence spectrometer
from IBH, UK. All the decays were fitted to a single exponential.
General Procedure for the Synthesis of Substituted Aza-BODIPY
Dyes 1–6
Compound 1: A 25 mL round-bottomed flask fitted with reflux con-
denser was filled with argon for 5 min. Compound 7 (0.1 g,
0.15 mmol), phenylboronic acid (0.055 g, 0.45 mmol) and Na2CO3
(0.063 g, 0.60 mmol) in water/THF/toluene (1:1:1, 15 mL) were
stirred under argon for 5 min. Pd(PPh3)4 (0.017 g, 0.015 mmol) was
added and the reaction mixture was heated to reflux at 80 °C. After
completion of the reaction as judged by TLC analysis, the reaction
mixture was diluted with water (5 mL) and extracted with dichloro-
Figure 4. Cyclic voltammograms of 5 (–), 4 (···) and 7 (–·–·–) in
CHCl3.
Conclusions
We have demonstrated the substitution of aza-BODIPY
at the 3- and 5-positions by various aryl groups having elec- methane. The combined organic layers were washed with water and
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Synthesis and Studies of Aza-BODIPY-Based π-Conjugates
brine, then dried with Na2SO4. The solvent was evaporated and the
crude product was purified on a silica gel column (petroleum ether/
dichloromethane, 80:20) to afford 1 (65%, 0.065 g) as a dark solid.
1H NMR (600 MHz, CDCl3): δ = 7.06 (s, 2 H, Py), 7.22–7.32 (m,
95:5) to afford 5 (35%, 0.042 g) as a dark solid. 1H NMR
(600 MHz, CDCl3): δ = 7.0 (s, 2 H, Py), 7.23–7.24 (m, 2 H, Th),
7.61 (d, J = 4.5 Hz, 2 H, Th), 7.71–7.78 (m, 12 H, Ph), 7.96–7.97
(m, 2 H, Th), 8.15 (d, J = 8.0 Hz, 4 H, Ph) ppm. 19F NMR
2 H, Th), 7.37–7.39 (m, 2 H, Ph), 7.45–7.48 (m, 4 H, Ph), 7.58 (d, (376.4 MHz, CDCl3): δ = –130.2 (q, JB–F = 64.0 Hz), –62.45
J = 4.5 Hz, 2 H, Th), 7.65 (d, J = 7.5 Hz, 4 H, Ph), 7.71 (d, J =
7.9 Hz, 4 H, Ph), 7.96 (s, 2 H, Th), 8.14 (d, J = 8 Hz, 4 H, Ph) ppm.
13C NMR (150.84 MHz, CDCl3): δ = 116.75, 126.80, 127.12,
127.19, 127.89, 128.25, 128.82, 129.61, 130.02, 130.18, 130.31,
133.28, 134.70, 140.06, 142.21, 143.46, 158.66, 161.66 ppm. 19F
NMR (376.4 MHz, CDCl3,): δ = –130.4 (q, JB–F = 64.0 Hz) ppm.
HRMS: calcd. for C40H26BF2N3S2 + K+ 700.1248; found 700.1268.
(s) ppm.
Compound 6: Compound 7 (0.1 g, 0.15 mmol), 4-(dimethylamino)-
phenylboronic acid (0.074 g, 0.45 mmol), and Na2CO3 (0.063 g,
0.60 mmol) in water/THF/toluene (1:1:1, 15 mL) were stirred under
argon for 5 min. Pd(PPh3)4 (0.017 g, 0.015 mmol) was added and
the reaction mixture was heated to reflux at 80 °C. After comple-
tion of the reaction, the crude product was purified on a silica gel
column (petroleum ether/dichloromethane, 50:50) to afford 6 (43%,
Compound 2: Compound 7 (0.1 g, 0.15 mmol), mesitylboronic acid
(0.074 g, 0.45 mmol), and Na2CO3 (0.063 g, 0.60 mmol) in water/
THF/toluene (1:1:1, 15 mL) were stirred under argon for 5 min.
Pd(PPh3)4 (0.017 g, 0.015 mmol) was added and the reaction mix-
ture was heated to reflux at 80 °C. After completion of the reaction
and purification of the crude product on silica gel column (petro-
leum ether/dichloromethane, 70:30), compound 2 (38%, 0.047 g)
was afforded as a dark solid. 1H NMR (600 MHz, CDCl3): δ =
2.04 (s, 12 H, CH3), 2.34 (s, 6 H, CH3), 6.95 (s, 4 H, Mesityl), 7.05
(s, 2 H, Ph), 7.22–7.24 (m, 2 H, Th), 7.27–7.29 (m, 4 H, Ph), 7.58
(d, J = 4.9 Hz, 2 H, Th), 7.96 (d, J = 3.4 Hz, 2 H, Th), 8.15 (d, J
= 8.0 Hz, 4 H, Ph) ppm. 19F NMR (376.4 MHz, CDCl3): δ =
–131.3 (q, JB–F = 60.2 Hz) ppm. HRMS: calcd. for C46H38BF2N3S2
+ K+ 784.2208; found 784.2211.
1
0.048 g) as a dark solid. H NMR (600 MHz, CDCl3): δ = 3.01 (s,
12 H, CH3), 7.01 (s, 2 H, Py), 7.20 (m, 2 H, Th), 7.48 (d, J =
6.9 Hz, 4 H, Ph), 7.55 (d, J = 4.9 Hz, 2 H, Th), 7.60 (d, J = 8.6 Hz,
4 H, Ph), 7.68 (d, J = 8.3 Hz, 4 H, Ph), 7.94 (d, J = 3.4 Hz, 2 H,
Th), 8.12 (d, J = 8.3 Hz, 4 H, Ph) ppm. 19F NMR (376.4 MHz,
CDCl3): δ = –130.6 (q, JB–F = 64.0 Hz) ppm. HRMS: calcd. for
C44H36BF2N5S2 + K+ 786.2105; found 786.2112.
Compound 7: Compound 7 was synthesized according to a reported
procedure.[16] Yield 53%. H NMR (600 MHz, CDCl3): δ = 6.8 (s,
1
2 H, Py), 7.20–7.22 (m, 2 H. Th), 7.60–7.66 (m, 6 H, Th + Ph),
7.86 (d, 3J = 8 Hz, 4 H, Ph), 7.93 (s, 2 H, Th) ppm. 13C NMR
(150.84 MHz, CDCl3): δ = 116.41, 125.79, 128.34, 129.95, 130.69,
130.82, 131.84, 134.48, 138.70, 145.06 ppm. 19F NMR (376.4 MHz,
CDCl3): δ = –130.2 (q, JB–F = 64.0 Hz) ppm.
Compound 3: Compound 7 (0.10 g, 0.15 mmol), 4-anisylphenyl-
boronic acid (0.068 g, 0.45 mmol), and Na2CO3 (0.063 g,
0.60 mmol) in water/THF/toluene (1:1:1, 15 mL) were stirred under
argon for 5 min. Pd(PPh3)4 (0.017 g, 0.015 mmol) was added and
the reaction mixture was heated to reflux at 80 °C for 18 h. Workup
as described above and purification of the crude product on silica
gel column (petroleum ether/dichloromethane, 40:60) gave 3 (45%,
Supporting Information (see footnote on the first page of this arti-
cle): NMR, mass spectra, and fluorescence decay profile of selected
compounds.
Acknowledgments
1
0.049 g) as a dark solid. H NMR (600 MHz, CDCl3): δ = 3.87 (s,
The authors thank the Centre for Excellence in Basic Sciences,
Mumbai for providing research facilities. Partial funding was pro-
vided by the Department of Science and Technology, India (SR/
FT/CS-87/2010). The authors thank Dr. Sudha Srivastava, the Tata
Institute of Fundamental Research, Mumbai for providing the
NMR facility. Prof. M. Ravikanth, Indian Institute of Technology,
Bombay, is thanked for helping us to obtain HRMS and 19F NMR
spectra. Prof. Anindya Datta of IIT Bombay is acknowledged for
allowing us to record fluorescence decay.
6 H, OCH3), 6.93–7.0 (m, 6 H, Py+Ph), 7.22 (s, 2 H, Th), 7.57 (d,
J = 4.6 Hz, 2 H, Th), 7.60 (d, J = 8.1 Hz, 4 H, Ph), 7.67 (d, J =
7.9 Hz, 4 H, Ph), 7.95 (s, 2 H, Th), 8.12 (d, J = 7.9 Hz, 4 H,
Ph) ppm. 13C NMR (150.84 MHz, CDCl3): δ = 55.56, 114.54,
117.02, 126.89, 128.47, 129.77, 130.31, 130.41, 159.92 ppm. 19F
NMR (376.4 MHz, CDCl3): δ = –130.5 (q, JB–F = 60.2 Hz) ppm.
HRMS: calcd. for C42H30BF2N3O2S2 + K+ 760.1467; found
760.1479.
Compound 4: Compound 7 (0.1 g, 0.15 mmol), 4-acetylphenylbor-
onic acid (0.074 g, 0.45 mmol), and Na2CO3 (0.063 g, 0.60 mmol)
in water/THF/toluene (1:1:1, 15 mL) were stirred under argon for
5 min. Pd(PPh3)4 (0.017 g, 0.015 mmol) was added and the reaction
mixture was heated to reflux. Upon completion of the reaction, the
crude product was purified on a silica gel column (petroleum ether/
dichloromethane, 40:60) to afford 4 (60%, 0.07 g) as a dark solid.
1H NMR (600 MHz, CDCl3): δ = 2.65 (s, 6 H, COCH3), 7.0 (s, 2
H, Py), 7.23 (s, 2 H, Th), 7.60 (d, J = 4.5 Hz, 2 H, Th), 7.74–7.76
(m, 8 H, Ph), 7.96 (d, J = 3.1 Hz, 2 H, Th), 8.05 (d, J = 7.8 Hz, 4
H, Ph), 8.15 (d, J = 7.8 Hz, 4 H, Ph) ppm. 19F NMR (376.4 MHz,
CDCl3): δ = –130.2 (q, JB–F = 64.0 Hz) ppm. HRMS: calcd. for
C44H30BF2N3O2S2 + Na+ 768.1725; found 768.1740.
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Received: August 28, 2013
Published Online: December 19, 2013
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