Synthesis, spectral and electrochemical properties of phenylated boron-dipyrromethenes

Article abstract of DOI:10.1016/j.dyepig.2012.10.012

The synthesis, absorption, electrochemical and fluorescence properties of boron-dipyrromethenes (BODIPYs) containing one to six phenyl groups at the pyrrole carbons are described. The phenylated BODIPYs were prepared by coupling of appropriate brominated

Full text of DOI:10.1016/j.dyepig.2012.10.012

Accepted Manuscript
Synthesis, Spectral and Electrochemical Properties of Phenylated Boron-
Dipyrromethenes
V. Lakshmi, M. Ravikanth
PII:
S0143-7208(12)00298-7
10.1016/j.dyepig.2012.10.012
DYPI 3757
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 10 September 2012
Revised Date: 25 October 2012
Accepted Date: 28 October 2012
Please cite this article as: Lakshmi V, Ravikanth M, Synthesis, Spectral and Electrochemical Properties
of Phenylated Boron-Dipyrromethenes, Dyes and Pigments (2012), doi: 10.1016/j.dyepig.2012.10.012.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Synthesis, Spectral and Electrochemical Properties of Phenylated Boron-
Dipyrromethenes
V. Lakshmi and M. Ravikanth*
Department of Chemistry, Indian Institute of Technology, Bombay, Powai,
Mumbai 400 076, India. E-mail: ravikanth@chem.iitb.ac.in

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Synthesis, Spectral and Electrochemical Properties of Phenylated Boron-
Dipyrromethenes
V. Lakshmi and M. Ravikanth*
Department of Chemistry, Indian Institute of Technology, Bombay, Powai,
Mumbai 400 076, India. E-mail: ravikanth@chem.iitb.ac.in
Abstract:
The synthesis, absorption, electrochemical and fluorescence properties of boron-
dipyrromethenes (BODIPYs) containing one to six phenyl groups at the pyrrole carbons are
described. The phenylated BODIPYs were prepared by coupling of appropriate brominated
BODIPY with phenyl boronic acid in THF/toluene/H2O (1:1:1) mixture in the presence of
catalytic amount of Pd(PPh3)4/Na2CO3 at 80 °C for overnight. The effect of the number of
phenyl substituents at the pyrrole carbons of BODIPY framework on absorption, electrochemical
and fluorescence properties were investigated. The absorption and fluorescence studies showed
a bathochromic shift in absorption and emission bands, increase in quantum yield and singlet
state lifetime upto the presence of four phenyl groups at the pyrrole carbons of BODIPY but the
properties were reversed for five and six phenyl substituted BODIPYs. The electrochemical
studies indicated that with the increase of number of phenyl groups at the pyrrole carbons of
BODIPY framework, the electron rich nature of BODIPY increases.
Key words:
Boron-dipyrromethenes, Phenylated BODIPYs, absorption, emission,
electrochemical properties, electron rich systems.

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1. Introduction
4,4-Difluoro-4-bora-3a,4a-diaza-s-indacenes,
commonly
known
as
boron-
dipyrromethenes or BODIPYs are prominent fluorescent dyes owing to their numerous
applications in biological labeling and cell imaging, and also as artificial light harvesters,
sensitizers for solar cells, fluorescent sensors, molecular photonic wires, and solid state dye
lasers [1-4]. This is because of their excellent properties such as absorption and emission bands
in the visible region, large molar absorption coefficients, relatively high fluorescence quantum
yields and enhanced stability against chemicals and light [5-7]. Furthermore, the properties of
BODIPYs can be fine tuned by introducing appropriate substituents at BODIPY framework as
these dyes are amenable for easy modification [8-11]. Hence, the synthetic chemistry of
BODIPY dyes has rapidly grown in recent years and several new types of BODIPYs have been
synthesized by using functionalized BODIPYs. Specifically, the pyrrole substituted and pyrrole
fused BODIPY systems possesses excellent photophysical properties [12-18]. One approach to
synthesize pyrrole substituted BODIPYs is by using substituted pyrroles as key synthons [12-
16]. However, the substituted pyrroles are not easily accessible. Alternately, the functionalized
BODIPY dyes such as halogenated BODIPYs can be used to synthesize pyrrole substituted
BODIPYs [19-22]. Although several reports are available on pyrrole substituted BODIPYs, to
the best of our knowledge, there is no systematic study of the effect of increasing the number of
aryl groups at the pyrrole carbons of BODIPY core on the spectral, electrochemical and
photophysical properties of BODIPY. In this paper, we report synthesis, spectral and
electrochemical properties of pyrrole phenylated BODIPYs 1-6 where the number of phenyl
groups on the BODIPY core has been varied from one to six. Our studies indicated that spectral
and electrochemical properties were varied systematically upto introduction of four phenyl

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groups but the properties were reversed upon introduction of five and six phenyl groups at the
pyrrole carbons of BODIPY.
2. Experimental Section
2.1. General
THF and toluene were dried over sodium benzophenone ketyl and chloroform, ethyl-
acetate, methanol, acetonitrile were dried under calcium hydride. BF3·OEt2 and 2,3-dichloro-5,6-
dicyano-1,4-benzoquinone (DDQ) obtained from Sigma-Aldrich (USA) were used as obtained.
All other chemicals used for the synthesis were reagent grade unless otherwise specified.
Column chromatography was performed on silica (60-120 mesh).
2.2. Instrumentation
1H NMR spectra (
δ
in ppm) were recorded using Varian VXR 300 & 400 MHz and
13
Bruker 400 MHz NMR spectrometer. C NMR spectra were recorded on Varian and Bruker
spectrometer operating at 100.6 MHz. 19F NMR spectra were recorded on Varian and
11
spectrometer operating at 282.2 MHz. B NMR spectra were recorded on Varian spectrometer
1
operating at 96.3 MHz. TMS was used as an internal reference for recording H (of residual
proton; δ 7.26) and 13C (δ 77.0 signal) in CDCl3. Absorption and steady-state fluorescence
spectra were obtained with Perkin–Elmer Lambda-35, Varian and PC1 Photon Counting
Spectrofluorometer manufactured by ISS, USA instruments respectively. Fluorescence spectra
were recorded at 25 °C in a 1 cm quartz fluorescence cuvette. The fluorescence quantum yields
(Φf) were estimated from the emission and absorption spectra by comparative method at the
excitation wavelength of 488 nm in ethanol using Rhodamine 6G (Φf = 0.88) as standard [23].
High-resolution mass spectrum was obtained from Q-TOF instrument by electron spray
ionization (ESI) technique.

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Cyclic voltammetric (CV) and differential pulse voltammetric (DPV) studies were
carried out with electrochemical system utilizing the three electrode configuration consisting of a
glassy carbon (working electrode), platinum wire (auxillary 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 versus saturated calomel electrode by the
addition of ferrocene as an internal standard, taking E1/2 (Fc/Fc+) = 0.42 V, vs SCE [24].
2.4 General method for the synthesis of 8-(4-methoxyphenyl)-mono to hexaphenyl-4-bora-
3a,4a-diaza-s-indacenes (1-6)
Samples of 7-12 (100 mg, 0.13 mmol), phenylboronic acid (387 mg, ~ 2.6 mmol) and Na2CO3
(256 mg, 2.44 mmol), water/ THF / toluene (1:1:1) 15 ml were taken in a 100 ml round bottomed
flask fitted with a reflux condenser, stirred under N2 for 5 min. A catalytic amount of Pd(PPh3)4
(68 mg, ~ 5-10 mol%), was added and the reaction mixture was refluxed at 80 oC for 1 h to 6 h
depending on the number of phenyl groups on the BODIPY. After completion of the reaction as
judged by TLC analysis, the reaction mixture was diluted with water (5 ml) and extracted with
diethyl ether. The combined organic layers were washed with water, brine and dried over
MgSO4. The solvent was evaporated and the crude product was purified on a silica gel column
using petroleum ether/ethyl acetate (95:5) to afford phenylated BODIPYs 1- 4 in 50-55% yield.
2.4.1. 4,4-Difluoro-8-(4-methoxyphenyl)-3-phenyl-4-bora-3a,4a-diaza-s-indacene (1)
Yield 85%. 1H NMR (400 MHz, CDCl3, δ in ppm) 3.91 (s, 3H, -OCH3), 6.52 (m, 1H) 6.68 (d,
3
3
3
1H, J(H,H) = 4.3 Hz, Py), 6.90 (d, 1H, J(H,H) = 3.8 Hz, Py), 7.01 (d, 1H, , J(H,H) = 4.3 Hz,

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3
3
Py), 7.05 (d, 2H, , J(H,H) = 8.68 Hz, Ar), 7.48 (m, 3H, Ph), 7.55 (d, 2H, , J(H,H) = 8.69 Hz,
Ar), 7.82 (s, 1H, Py), 7.95 (m, 2H, Ph); 19F NMR (376.49 MHz, CDCl3, δ in ppm) -139.01 (q,
11
3
13
3J(B,F) = 64.0 Hz); B NMR (128.38 MHz, CDCl3, δ in ppm) 0.92 (t, J(B,F)= 30.8 Hz); C
NMR (100 MHz, CDCl3, δ in ppm) 55.68, 114.13, 118.08, 120.89, 126.72, 128.47, 129.57,
129.67, 130.01, 132.53, 132.77, 134.22, 137.21, 141.94, 145.89, 159.88, 161.93. HR-MS calcd
for C22H17BF2N2O 355.1418 (M-F)+, found 355.1434 (M-F)+.
2.4.2. 4,4-Difluoro-8-(4-methoxyphenyl)-3,5-diphenyl-4-bora-3a,4a-diaza-s-indacene (2)
3
Yield 87%. 1H NMR (400 MHz, CDCl3, δ in ppm) 3.93 (s, 3H, -OCH3), 6.62 (d, 2H, J(H,H) =
3
3
4.3 Hz, Py), 6.95 (d, 2H, J(H,H) = 3.8 Hz, Py), 7.07 (d, 2H, , J(H,H) = 8.6 Hz, Ar), 7.41 (m,
6H, Ph), 7.56 (d, 2H, , 3J(H,H) = 8.69 Hz, Ar), 7.87(m, 4H, Ph);19F NMR (376.49 MHz, CDCl3,
3
11
δ in ppm) -132.39 (q, J(B,F) = 64.0 Hz); B NMR (128.38 MHz, CDCl3, δ in ppm) 1.48 (t,
3J(B,F)= 30.8 Hz); 13C NMR (100 MHz, CDCl3, δ in ppm) 55.68, 114.13, 118.08, 120.89,
126.72, 128.47, 129.57, 129.67, 130.01, 132.53, 132.77, 134.22, 137.21, 141.94, 145.89, 159.88,
161.93. ES-MS calcd for C28H21BF2N2O 431.1731 (M-F)+, found 431.1747 (M-F)+.
2.4.3 4,4-Difluoro-8-(4-methoxyphenyl)-2,3,5-triphenyl-4-bora-3a,4a-diaza-s-indacene (3)
3
Yield 78%. 1H NMR (400 MHz, CDCl3, δ in ppm) 3.90 (s, 3H, -OCH3), 6.64 (d, 1H, J(H,H) =
4.3 Hz, Py), 6.95 (d, 1H, 3J(H,H) = 3.8 Hz, Py), 7.05 (m, 5H, Ph), 7.14(m, 3H, Py+ Ph), 7.36 (m,
6H, Ph), 7.49 (d, 2H, , 3J(H,H) = 8.69 Hz, Ar), 7.59 (d, 2H, , 3J(H,H) = 8.69 Hz, Ar), 7.84(m, 2H,
Ph);19F NMR (376.49 MHz, CDCl3, δ in ppm) -132.50 (q, 3J(B,F) = 64.0 Hz); 11B NMR (128.38
3
MHz, CDCl3, δ in ppm) 1.26 (t, J(B,F)= 30.8 Hz); 13C NMR (100 MHz, CDCl3, δ in ppm)
55.68, 114.09, 114.23, 120.99, 126.95, 127.97, 128.38, 129.14, 129.56, 130.60, 131.27, 132.15,

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132.55, 132.71, 134.13, 134.34, 134.50, 136.75, 144.33, 155.54, 159.01, 161.73. HR-MS calcd
for C34H35BF2N2O 507.2044 (M-F)+ , found 507.2046 (M-F)+.
2.4.4. 4,4-Difluoro-8-(4-methoxyphenyl)-2,3,5,6-teraphenyl-4-bora-3a,4a-diaza-s-indacene
(4)
Yield 51%. 1H NMR (400 MHz, CDCl3, δ in ppm) 3.92 (s, 3H, -OCH3), 7.05 (m, 9H, Ph + Py)
19
7.14 (m, 6H, Ph), 7.31 (m, 6H, Ar), 7.48(m, 4H, Ph), 7.65 (d, 2H, Ar); F NMR (376.49 MHz,
CDCl3, δ in ppm) -132.63 (q, 3J(B,F) = 64.0 Hz); 11B NMR (128.38 MHz, CDCl3, δ in ppm) 1.08
3
13
(t, J(B,F)= 30.8 Hz); C NMR (100 MHz, CDCl3, δ in ppm) 55.71, 114.20, 127.02, 128.34,
128.34, 128.46, 128.76, 129.20, 130.58, 132.02, 132.64, 134.15, 134.54, 134.79, 156.12, 161.84.
HR-MS calcd for C40H29BF2N2O 583.2357, found 583.2358 (M-F)+.
2.4.5. 4,4-Difluoro-8-(4-methoxyphenyl)-1,2,3,5,6-diphenyl-4-bora-3a,4a-diaza-s-indacene
(5)
3
Yield 70%. 1H NMR (400 MHz, CDCl3, δ in ppm) 3.72 (s, 3H, -OCH3), 6.51 (d, 2H, J(H,H) =
6.8 Hz, Ar), 6.66 (m, 4H, Ph + Py), 6.91 (m, 10H, Ph), 7.14 (m, 4H, Ph), 7.32 (m, 6H, Ph),
7.41(m, 2H, Ph), 7.49 (d, 2H, Ar);19F NMR (376.49 MHz, CDCl3, δ in ppm) -131.88 (q, 3J(B,F)
= 64.0 Hz); 11B NMR (128.38 MHz, CDCl3, δ in ppm) 1.17 (t, 3J(B,F)= 30.8 Hz); 13C NMR (100
MHz, CDCl3, δ in ppm) 55.68, 114.13, 118.08, 120.89, 126.72, 128.47, 129.57, 129.67, 130.01,
132.53, 132.77, 134.22, 137.21, 141.94, 145.89, 159.88, 161.93. HR-MS calcd for
C46H33BF2N2O 659.2670 (M-F)+, found 659.2699 (M-F)+.
2.4.6.
4,4-Difluoro-8-(4-methoxyphenyl)1,2,3,5,6,7-hexaphenyl-4-bora-3a,4a-diaza-s-
indacene (6)

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Yield 51%. 1H NMR (400 MHz, CDCl3, δ in ppm) 3.51 (s, 3H), 5.89 (d, 2H, 3J(H,H) = 8.76 Hz),
6.54-6.56 (m, 8H), 6.70-6.79 (m, 8H), 6.89-6.93 (m, 6H), 7.28-7.39 (m, 6H), 7.42 (d, 4H,
3
11
3J(H,H) = 5 Hz); 19F NMR (376.49 MHz, CDCl3, δ in ppm) -131.30 (q, J(B,F) = 64.0 Hz); B
NMR (128.38 MHz, CDCl3, δ in ppm) 1.20 (t, 3J(B,F)= 30.8 Hz); 13C NMR (100 MHz, CDCl3, δ
in ppm) 55.22, 112.4, 123.9, 125.5, 125.7, 126.3, 127.2, 127.5, 127.6, 128.4, 128.8, 129.2, 130.4,
130.9, 131.9, 132.4, 133.3, 133.6, 134.7, 134.9, 144.2, 156, 160; HRMS calcd for
C52H37BF2N2O 735.2983 (M-F)+, found 735.3001 (M-F)+.
3. Results and Discussion:
Although the synthesis of phenylated BODIPYs containing one to six phenyl groups at
pyrrole carbons of BODIPY have been reported earlier in different reports [25-31], we realized
that the synthetic routes which adopted were different and there is no single report that describes
the synthesis and properties of all BODIPYs 1-6 containing one to six phenyls at pyrrole
carbons. To provide complete synthetic information in one report, in this paper, we describe the
synthesis of all BODIPYs 1-6 containing one to six phenyl groups which were prepared from
their corresponding brominated BODIPYs 7-12 by coupling with phenylboronic acid under
Pd(0) coupling conditions. The BODIPYs containing one to six bromines 7-12 were prepared as
reported by us earlier [32]. The phenylated BODIPYs 1-6 were synthesized by coupling of their
corresponding brominated BODIPY compounds 7-12 with appropriate equivalents of
phenylboronic acid in THF/toluene/H2O (1:1:1) mixture in the presence of catalytic amount of
Pd(PPh3)4/Na2CO3 at 80 °C for overnight as shown in the Scheme 1. The reflux time was varied
from 1 h to 6 h depending on the number of phenyl groups on the BODIPY. For one and two
phenylated BODIPYs, the reaction was completed in 1 h whereas in case of three and four

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phenylated compounds, the reaction requires 3 h but for penta and hexaphenylated BODIPYs,
longer reaction times upto 6 h are required. The progress of the reaction was followed by TLC
analysis which clearly showed the spot corresponding to the required phenylated BODIPY along
with one or two minor spots corresponding to lower and higher analogues of phenylated
BODIPYs. For example, compound 10 on reaction with four equivalents of phenyl boronic acid
under Pd(0) coupling conditions showed four spots on tlc within 1 h corresponding to mono, di,
tri and tetraphenylated BODIPYs. However, as the reaction was progressed, the spots
corresponding to other phenylated BODIPys were almost disappeared and a spot corresponding
to tetraphenylated BODIPY was clearly appeared. Furthermore, we also noted that the bromo
groups present at the 3 and 5-positions of BODIPY were more reactive compared to bromines
present at the 2- and 6-positions of BODIPY. The penta and hexaphenylated BODIPYs requires
longer reaction times due to steric hindrance. The crude compounds were purified by silica gel
column chromatography and afforded pure fluorescent solids 1-6 in 60-80% yields. The
compounds 1-6 were freely soluble in common organic solvents and characterized by mass and
various spectroscopic techniques. The HR-MS mass spectra showed the corresponding expected
molecular ion peak confirming the identity of compounds 1-6.
19
11
1
The compounds 1-6 were characterized in detail by 1H, F and B NMR. H-1H COSY
also recorded for couple of compounds to identify all the signals in 1H NMR. The representative
1H NMR and 1H-1H COSY NMR spectra for compound 3 are shown in Figure 1. In 1H NMR of
pyrrole unsubstituted meso-anisyl BODIPY 13 [33], the six pyrrole protons appeared as three
sets of signals. The compounds 1-6 showed signals for pyrrole protons as well as for substituted
phenyl groups. However, the number of pyrrole signals in compounds 1-6 are either more or less
depending on the symmetric nature of the compound as well as on the number of phenyl groups.

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No pyrrole signal was observed for compound 6 due to presence of six phenyl groups at six
pyrrole carbons. The comparison of 19F and 11B NMR spectra of compounds 1-6 along with
compound 13 is shown in Figure 2 and the relevant data is tabulated in Table 1. Compounds 1-6
showed a typical quartet in 19F and triplet in 11B NMR due to coupling with each other.
11
However, compounds 1-6 exhibited slight shifts in 19F and B NMR compared to 13 indicating
that the π-delocalization is altered in the boron-dipyrrin core due to presence of phenyl groups at
the pyrrole carbons.
The absorption spectra of pyrrole phenylated BODIPYs 1-6 were recorded in five
different solvents of varying polarity and the data are presented in Table 2. The comparison of
absorption spectra of pyrrole phenylated BODIPYs 1-6 along with unsubstituted BODIPY 13
[33] recorded in toluene is shown in Figure 3. The pyrrole phenylated BODIPYs 1-6 showed
absorption features of typical of BODIPYs such as a strong band in the 500-600 nm region
corresponding to S0→ S1 transition with a vibronic transition on the higher energy side as a
shoulder and an ill-defined, weak band corresponding to the S0→S2 transition at about 400 nm.
The introduction of phenyl group at the pyrrole carbons of BODIPY core resulted in
bathochromic shift compared to unsubstituted meso-anisyl BODIPY 13 [33] and the magnitude
of red shift of absorption band depends on the number of phenyls substituted at the BODIPY
core However, this systematic red shift was observed only upto the presence of four phenyls at
the pyrrole carbons in compounds 1 to 4. In case of five and six phenyls substituted compounds 5
and 6 respectively, the absorption band was slightly blue shifted. This indicates that the phenyl
substituents at 1 and 7 positions induce steric crowding resulting in the decrease of effective π-
conjugation in the BODIPY core.

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A comparison of steady state fluorescence spectra of compounds 1-6 along with 13 in
toluene using same concentration is shown in Figure 4. Compounds 1-6 showed one single broad
emission band in the region of 540-650 nm. The emission band of compounds 1-4 experiences
bathochromic shift with the increase of number of phenyl groups upto four compared to 13 but
the emission band shifts towards blue for compounds 5 and 6 containing five and six phenyl
groups respectively at the pyrrole carbons of BODIPY (Table 2). The quantum yield Φf of
compounds 1-6 calculated by comparative method [23] indicated a steady increase in the
quantum yield on the increase of number of phenyl groups at the pyrrole carbons of BODIPY
compared to 13. Surprisingly, compound 5 showed a weak fluorescence with low quantum yield
compared to other phenylated BODIPYs which needs further investigation. The singlet state
lifetimes τ of compounds 1-6 along with compound 13 in toluene were measured using time-
correlated single photon counting (TCSPC) technique (Table 2). The fluorescence decays of
compounds 1-6 were fitted to single exponential and a representative fluorescence decay profile
for compound 4 is shown in Figure 5. The singlet state lifetimes of compounds 1-6 were in
agreement with their fluorescence quantum yields. The lifetimes τ of weakly fluorescent
compounds 1 and 5 were not obtained due to limitation of our instrument. Using the
experimental Фf and τ values, we calculated the radiative kr and nonradiative knr rate constants
which are in agreement with the quantum yield and singlet state life time data. The absorption
and fluorescence properties of compounds 1-6 were also investigated by changing the polarity of
the solvent. With the increase of solvent polarity, the absorption and emission bands of
compounds 1-6 experienced slight blue shift and the quantum yields and singlet state lifetimes
were decreased (Table 2).

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The redox properties of phenylated BODIPYs 1-6 are probed through cyclic
voltammetric and differential pulse voltammetric studies using tetrabutylammonium perchlorate
as supporting electrolyte (0.1 M) in dichloromethane as solvent. The comparison of cyclic
voltammograms and diffential pulse voltammograms of 1-6 are presented in Figure 6 and redox
potential data are tabulated in Table 3. In general, BODIPYs such as compound 13 show one
irreversible oxidation and one reversible reduction indicating that BODIPYs are electron
deficient. Since compounds 1-6 contain electron rich phenyl groups, we expected that
compounds 1-6 are stable under oxidation conditions. As clear from the Figure 6, the compounds
1-3 exhibited an irreversible oxidation but compounds 4-6 showed one reversible oxidation
supporting that the electron rich nature of BODIPY core increases with the increase of number of
phenyl groups. Furthermore compounds 1-6 showed one reversible reduction. However, the
reduction potential did not alter much with the increase of the number of phenyl groups in
compounds 1-6.
3. Conclusion
In conclusion, we synthesized BODIPYs containing one to six phenyl groups at the
pyrrole carbons of BODIPY framework to study the effect of number of phenyl groups on
spectral and electrochemical properties of BODIPY. The absorption and fluorescence bands
experienced systematic bathochromic shifts on introduction of phenyl groups but the systematic
trend was observed only upto introduction of four phenyl groups. However, BODIPYs
containing five and six phenyl groups showed hypsochromically shifted absorption and emission
bands. The fluorescence quantum yields and singlet state lifetimes were also follow same trend.
The electrochemical studies indicated that BODIPY core which is normally electron deficient in

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unsubstituted BODIPY changes to electron rich with the increase of number of phenyl groups at
the pyrrole carbons of BODIPY framework.
Acknowledgement. We thank Board of Research in Nuclear Sciences, Department of Atomic
Energy, Government of India for funding the project and VL thank CSIR for fellowship.
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Table 1: The 19F and 11B NMR spectra data of compounds 1-6 along with 13 recorded in CDCl3
(δ in ppm)
Compound
19F
11B
-145
-139
0.34
0.91
1.49
1.26
1.06
1.19
1.19
13
1
2
3
4
-132.4
-132.5
-132.6
-131.9
-131.3
5
6
\

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Table 2: The photophysical data of compounds 1-6 along with 13 in different solvents.
log
ε
τ
[ns]
λabs
λem
Фf
Kr
knr
109s-1 109s-1
Compd Solvent
[nm]
[nm]
Toluene 501
517
515
515
511
511
553
550
4.76
4.76
4.74
4.75
4.71
4.69
4.65
0.11
0.72
0.72
0.41
0.32
0.24
---
0.16
0.14
0.13
0.18
0.13
---
1.23
1.25
2.3
1.93
4.04
---
13
CHCl3
THF
EtOAc
MeCN
499
497
495
494
0.097
0.052
0.035
0.0013
0.05
Toluene 529
1
CHCl3
527
526
523
0.043
---
---
---
THF
548
545
4.67
4.69
0.029
0.023
---
---
---
---
---
---
EtOAc
MeCN
toluene
520
555
545
587
4.57
4.84
0.015
0.46
---
2.5
---
0.18
---
0.22
2
3
4
CHCl3
THF
552
552
547
543
586
585
581
580
604
603
600
598
598
616
616
614
611
4.82
4.84
4.82
4.78
4.79
4.79
4.67
4.78
4.73
4.52
4.51
4.51
4.48
0.29
0.27
0.29
0.17
0.49
0.34
0.36
0.32
0.22
0.66
0.48
0.39
0.37
2.2
1.8
1.5
1.0
3.4
3.7
2.9
2.7
2.0
3.8
4.1
3.3
3.2
0.13
0.15
0.19
0.17
0.14
0.09
0.12
0.12
0.11
0.17
0.12
0.12
0.11
0.32
0.41
0.47
0.83
0.15
0.15
0.22
0.25
0.39
0.09
0.13
0.18
0.19
EtOAc
MeCN
Toluene 570
CHCl3
THF
568
566
562
556
586
582
580
576
EtOAc
MeCN
toluene
CHCl3
THF
EtOAc
MeCN
toluene
CHCl3
THF
EtOAc
MeCN
toluene
CHCl3
THF
569
580
577
574
570
562
575
573
570
566
555
611
613
612
609
606
605
609
607
604
601
596
4.45
4.81
4.79
4.82
4.80
4.76
4.68
4.67
4.65
4.67
4.63
0.34
0.11
2.5
---
---
---
---
0.14
---
---
---
---
0.26
---
---
---
---
5
6
0.075
0.037
0.049
0.033
0.41
0.39
0.22
0.25
0.26
---
---
---
2.2
2.5
1.6
2.2
1.9
0.19
0.17
0.14
0.11
0.14
0.27
0.25
0.48
0.34
0.39
EtOAc
MeCN

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Table 3: Electrochemical data of compounds 1-6 recorded in CH2Cl2, measured with n-
-
Bu4N+P(ClO4)6 (0.1 M) as a electrolyte at a scan rate of 50 mV s-1. aIrrversible oxidation.
Compound
Oxidation Potential Reduction Potential
(V vs SCE)
1.68a
(V vs SCE)
-0.81
13
1
1.46a
-0.83
1.33a
-0.84
2
1.33a
-0.81
3
1.32
-0.79
4
1.32
-0.80
5
1.32
-0.86
6
Figure Captions
Figure 1: (a) 1H NMR (b) 1H-1H COSY NMR spectra of compound 3 recorded in CDCl3
Figure 2: Comparison of (a) 19F and (b) 11B NMR spectra of compounds 1-6 along with 13.

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Figure 3: The comparison of normalized absorption spectra of phenylated compounds 1-6 along
with 13 recorded in toluene
Figure 4: The comparison of normalized emission spectra of compounds 1-6 along with 13
recorded in toluene
Figure 5: A representative fluorescence decay profile and weighted residual distribution fit of 4
in toluene. The excitation wavelength used was 440 nm and emission was detected at 616 nm
Figure 6: The cyclic Voltammogram (solid line) and differential pulse voltammogram (dotted
-
line) of compounds 1-6 recorded in CH2Cl2 containing 0.1 M Bu4N+P(ClO4)6 as supporting
electrolyte recorded at 50 mV s-1 scan speed.
Scheme 1: Synthesis of phenylated BODIPY compounds 1-6. aPd(PPh3)4, Na2CO3,
phenylboronic acid; toluene, THF, water (1:1:1)

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Figure 1

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Figure 2

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5
6
1
2
13
3
4
1.0
0.8
0.6
0.4
0.2
0.0
350
400
450
500
550
600
650
Wavelength (nm)
Figure 3

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6
5
4
3
13
1
2
1.0
0.8
0.6
0.4
0.2
0.0
500
550
600
650
700
Wavelength (nm)
Figure 4

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1000
100
10
5
5
10
10
15
15
20
20
25
25
30
30
Time (ns)
Figure 5

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Figure 6

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Scheme 1

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Research Highlights
•
•
•
•
Synthesized a series of boron dipyrromethenes containing phenyl groups at the
pyrrole carbons.
The introduction of phenyl groups at the pyrrole carbon of the BODIPY core
alters the electronic properties.
Absorption and emission properties were systematically altered upto
introduction of four phenyl groups.
BODIPY core becomes electron rich and oxidation becomes easier with the
increase of number of phenyl groups.