Phenanthro[ b]-Fused BODIPYs through Tandem Suzuki and Oxidative Aromatic Couplings: Synthesis and Photophysical Properties

Article abstract of DOI:10.1021/acs.joc.9b01425

A new synthetic method to build phenanthrene-fused boron dipyrromethenes (BODIPYs) through tandem Suzuki couplings on readily available 2,3,5,6-tetrabromoBODIPYs, followed by an intramolecular oxidative aromatic coupling mediated by iron(III) chloride is

Full text of DOI:10.1021/acs.joc.9b01425

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Article
Phenanthro[b]-Fused BODIPYs through Tandem Suzuki and Oxidative
Aromatic Couplings: Synthesis and Photophysical Properties
Wei Miao, Yuanmei Feng, Qinghua Wu, Wanle Sheng, Mao Li, Qing-Yun Liu, Erhong Hao, and Lijuan Jiao
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b01425 • Publication Date (Web): 09 Jul 2019
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Phenanthro[b]-Fused BODIPYs through
Tandem Suzuki and Oxidative Aromatic
Couplings: Synthesis and Photophysical
Properties
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Wei Miao,a Yuanmei Feng,a Qinghua Wu,a Wanle Sheng, a Mao Li,a Qingyun Liu,b
Erhong Hao,*a and Lijuan Jiao*a
a
Laboratory of Functional Molecular Solids, Ministry of Education; School of Chemistry and
Materials Science, Anhui Normal University, Wuhu, 241002, China;
b
College of Chemistry and Environmental Engineering, Shandong University of Science and
Technology, Qingdao, China.
*To whom correspondence should be addressed.
E-mail: haoehong@ahnu.edu.cn, jiao421@ahnu.edu.cn
Abstract Graphic
Ar
Ar
B
Ar
R
R
FeCl3
ArB(OH)2
Ar
Ar
Br
Br
N
N
N
N
N
N
Suzuki
coupling
B
B
F
F
Ar
Ar
Br
Br
F
F
F
F
rapid/efficient synthesis
tunable neat-infrared (NIR) absorption/emission
R
R
[b]-Phenanthrene-Fused BODIPYs
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Abstract: A new synthetic method to build phenanthrene-fused BODIPYs through
tandem Suzuki couplings on readily available 2,3,5,6-tetrabromoBODIPYs, followed
by an intramolecular oxidative aromatic coupling mediated by iron(III) chloride is
reported. This efficient synthesis allows a very straightforward approach for tuning
the absorption and emission of BODIPYs in the red/NIR range. These resultant
phenanthrene-fused BODIPYs exhibit strong absorption (extinction coefficients up to
2.2 × 105 M−1 cm−1) and emission in the near-infrared (NIR) range (688-754 nm).
Substituents on the resultant phenanthrene rings have significant impact on the
photophysical properties of these phenanthrene-fused BODIPYs.
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INTRODUCTION
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Near-infrared (NIR) absorbing/emitting dyes have received diverse applications, for
example, as efficient photosensitizers in photovoltaic devices and photodynamic
therapy, and as fluorophores in sensors, energy-transfer cassettes and biological
imaging.1 These intense demands have motivated scientists to synthesize new NIR
dyes with high molar extinction coefficients in this wavelength range (650-1000 nm)
over the past few decades.2 In this context, their diverse applications require robust
dyes with highly synthetic efficiency and diversity. Boron dipyrromethene (BODIPY)
dyes are promising candidates for building new NIR dyes because they have excellent
photophysical properties such as large molar absorption coefficients, tunable
fluorescence quantum yields and good photostability, and their rich functionalization
chemistry.3 In particular, almost unlimited structural modifications on every position
of BODIPY core lead to sophisticated derivatives with finely tuneable chemical and
photophysical properties, including NIR absorption/emission.
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To this end, various elegant methods have been developed to modify BODIPY core
for achieving NIR absorption/emission through de nova synthesis or
postfunctionalization,4-6 such as introducing linear aromatic groups at peripheral
positions, aromatic ring fusion and conjugated oligomers. Among them, π-extension by
fusing aromatic rings to BODIPY core is particularly promising, and has resulted in
significant redshifts in the absorption and emission properties of the BODIPY dyes.7-8
For example, several methods have been developed to construct benzo[a]-fused
BODIPYs (A9 in Figure 1), which often have redshifted absorption/emission with
modest fluorescent quantum yields. Phenanthro[a]-fused BODIPYs B10 and C11 were
obtained by condensation of a π-extended phenanthro-fused pyrrole with aldehyde via
de nova synthesis or obtained through a rapid Pd(0)-catalyzed intramolecular cyclization
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via postfunctionalization, which showed intense NIR absorption and emission.
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Figure 1. Chemical structures of aromatic ring-fused BODIPYs A-E and reported
synthesis of BODIPY F.
Importantly, comparing with [a]-fused BODIPYs, [b]-fused BODIPYs have been
reported to have better stability due to the effective decrease in the LUMO level. Indeed,
benzo[b]-fused BODIPYs (for example, D12) were synthesized by condensation of
indoles or dihydroindoles, and showed broad and intense absorption bands with lowered
LUMO energy levels. Naphtho[b]-fused BODIPY E13 was recently synthesized via an
efficient one-pot Suzuki-Miyaura-Knoevenagel reaction and showed maximum
absorption/emission at 630/640 nm, respectively, due to markedly stabilized LUMO
energy. However, both benzo[b]-fused and naphtho[b]-fused BODIPYs exhibited
negligible or weak fluorescence.
Interestingly, a sole example of phenanthro[b]-fused BODIPY F14 reported by
Shinokubo and co-workers, showed intense fluorescence in the NIR region and
photocurrent conversion ability on the basis of its n-type semiconducting property due
to the low LUMO level. Phenanthro[b]-fused F was synthesized through
.
PIFA/BF3 Et2O promoted cyclization from BODIPY G, while the later was obtained
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from Suzuki coupling between 2,6-dibromoBODIPY and 2-biphenylboronic acid.
This method, although elegant, is difficult to obtain phenanthro[b]-fused BODIPY
derivatives due to limited 2-biphenylboronic acid derivatives available.
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As part of our chemistry of the fully ring-fused planar π-conjugated dyes,15 we are
interested in developing an efficient method to synthesized phenanthro[b]-fused
BODIPYs with diverse substituents. Following our previous reports on regioselective
and stepwise synthesis of brominated BODIPYs and their regioselective and stepwise
functionalization,16 herein, we report an efficient and versatile method to synthesize
phenanthro[b]-fused BODIPYs through tandem Suzuki couplings on readily available
2,3,5,6-tetrabromoBODIPYs, followed by an intramolecular oxidative aromatic
coupling mediated by iron(III) chloride. The electronic and optical properties of these
resultant dyes were investigated.
RESULTS AND DISCUSSION
Syntheses. Oxidative aromatic coupling has been a powerful method to furnish
various polycyclic aromatic compounds, allowing to form multiple C-C bonds at
once.17 We reasoned that 2,3,5,6-tetraaryl substituted BODIPYs offer an ideal,
electronic-tunable reacting site for building phenanthro[b]-fused BODIPYs through
intramolecular oxidative aromatic coupling. To prove this hypothesis, key
intermediate 2,3,5,6-tetraphenylBODIPY 2a was synthesized in 74% yield (Scheme 1)
through Suzuki coupling between BODIPY 1a and 5 equiv of phenylboronic acid.
The starting 2,3,5,6-tetrabromoBODIPY 1a was prepared in 90% yield by reacting
meso-(2,4,6-trimethylphenyl)BODIPY with 6 equiv of liquid bromine at room
temperature. BODIPY 2a was then subjected to intramolecular oxidative aromatic
coupling using the classical one-electron oxidant, i.e., iron(III) chloride. This reaction
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in dichloromethane smoothly gave π-expanded phenanthro[b]-fused BODIPY 3a in
73% yield in less than 5 mins. HRMS showed a parent ion peak at m/z 591.2391
(Calcd. for C42H29BFN2 [M-F]+, 591.2408) for this compound, indicating that only
four protons have been eliminated from this reaction. This loss of four protons was
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further confirmed by H NMR spectra. The absorption maximum of BODIPY 3a in
dichloromethane is 673 nm, which is in agreement with previously reported result.14
In addition, PIFA (4 equiv) in the presence of BF3·OEt2 (4 equiv) at -40 ℃14 was also
able to oxidize 2a to the phenanthro[b]-fused BODIPY 3a. However, only 46% yield
for 3a was obtained in this condition.
Scheme 1. Synthesis of phenanthro[b]-fused BODIPYs 3a-d
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To study the scope of this reaction, we further applied BODIPY 1a with different
boronic acids and obtained 2,3,5,6-tetraaryl BODIPYs 2b-d in similar good yields
(77-79%, Scheme 1). Subsequent intramolecular oxidative aromatic couplings
mediated by iron(III) chloride on BODIPYs 2b-d with various aryl substitutes all
proceed smoothly, giving phenanthro[b]-fused BODIPYs 3b-d in 60-75% yields.
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After successful fusion of 2,3,5,6-tetraaryl substituted BODIPYs, we then decided
to synthesize 1,2,3,5,6,7-hexaaryl substituted BODIPYs to further study the
selectivity of FeCl3 mediated intramolecular oxidative aromatic couplings (Scheme 2).
2,3,5,6-Tetraaryl substituted BODIPY 4a was first obtained in 75% yield by Suzuki
coupling between 2,3,5,6-tetrabromoBODIPY 1b and 4-tert-butylphenylboronic acid.
1,7-DibromoBODIPY 4a-Br was then obtained regioselectively in 95% yield from
the bromination of 4a with 3 equiv of liquid bromine. Further Suzuki coupling
reaction
between
4a-Br
and
4-tert-butylphenylboronic
acid
or
3-methoxylphenylboronic acid gave 1,2,3,5,6,7-hexaaryl substituted BODIPYs 4b
and 4c in 81% and 79%, respectively. The structure was confirmed by single X-ray
crystal structure analysis (Figure S1). Finally, both 4b and 4c were then subjected to
intramolecular oxidative aromatic coupling using the above condition. Interestingly,
both oxidative ring fusion reactions with 6 equiv of FeCl3 in CH2Cl2/CH3NO2 at room
temperature generated exclusively phenanthro[b]-fused BODIPYs 5b and 5c in 56%
and 53% yields, respectively. No corresponding phenanthro[a]-fused BODIPYs were
isolated. Further oxidation products, such as fully fused BODIPYs, were not found in
this reaction by increasing the amount of FeCl3. Both HRMS data of 5b and 5c
indicated loss of four protons during oxidative ring fusion reactions. The
regiochemistry was assigned by their NMR spectra. To further confirm the
regioselectivity of this reaction, we carried out the de nova synthesis of 5b from
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4a-Br. In the presence of FeCl3, intramolecular oxidative aromatic coupling reactions
of BODIPYs 4a and 4a-Br both successfully gave the corresponding
phenanthro[b]-fused BODIPYs 5a and 5a-Br in 70% and 42% yields, respectively.
Bromination of 5a to form 5a-Br was attempted, but the reaction was sluggish.
Standard Suzuki coupling between 5a-Br and 4-tert-butylphenylboronic acid also
gave phenanthro[b]-fused BODIPY 5b, which is the same product from the
intramolecular oxidative aromatic coupling of 4b.
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Scheme 2. Synthesis of phenanthro[b]-fused BODIPYs 5a - c
Crystals of 4b suitable for X-ray analysis were obtained from the slow diffusion of
anhydrous hexane into their dichloromethane solutions at room temperature. The
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plane defined by F−B−F atoms for 4b is perpendicular to that of dipyrrin core as usual
with the B−N distance of 1.54 Å. 4b shows an almost planar structure for the
BODIPY core (the central six-membered ring with two adjacent five-membered rings).
The dihedral angles of aryl rings A, B, C, D and the BODIPY core were 64.37°,
60.52°, 61.10° and 66.02°, respectively (Figure 2 and Table S1), which indicated that
almost all benzene rings on 4b are arranged in parallel.
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Figure 2. X-Ray structure of 4b. C grey, N blue, F green, B dark yellow. Hydrogen
atoms were omitted for clarity.
It
has
been
reported
that
failed
oxidative
to
cyclodehydrogenation
give the corresponding
attempts to oxidize
of
hexakis(4-alkoxyphenyl)benzene
hexaalkoxytriphenylene.18a
In
addition,
4,4′′-dimethoxy-o-terphenyl by King et. al also gave only intractable reaction
mixtures.18b In order to gain more insight into the utility of this reaction,
2,3,5,6-tetra(4-methoxyphenyl)BODIPY 2e was obtained via above Suzuki reaction
and was further applied with FeCl3 using the optimized conditions (Scheme 3). This
reaction only gave one-fold cyclized product 6 in 58% yield, but did not isolate the
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expected two-fold cyclized phenanthro[b]-fused product. Other attempts such as
increasing the reaction time and the amount of FeCl3 also failed and some
decompositions of compound 6 were observed. Cyclic voltammetry of both BODIPYs
2e and 6 were then measured in anhydrous dichloromethane containing 0.1 M
tetrabutylammonium hexafluorophosphate (TBAPF6) as the supporting electrolyte
(Figure S2 and Table S3). In comparison with that of the starting BODIPY 2e which
has a reversible oxidation at 0.92 V, BODIPY 6 showed an increased reversible
oxidation peak at 1.01V and a decreased HOMO-LUMO gap (2.00 eV). This data
indicates that this unusual reactivity may result from the rapid ring-closure followed
by one-electron over-oxidation of the produced phenanthrol[b]-fused moiety in the
one-fold cyclized product 6.
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Scheme 3. Synthesis of BODIPYs 6 and 7
Spectroscopic Properties.
Next, treatment of 2,3,5,6-tetra(3-methylphenyl)BODIPY 2f with FeCl3 lead to
phenanthro[b]-fused 7 with a mixture of ortho- and para-methyl substituents (Scheme
3) as indicated by 1H NMR. The formation of 7 was further confirmed by HRMS data,
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which showed a parent ion peak at m/z 667.3093 (Calcd. for C46H38BF2N2 [M + H]+,
667.3096) for this compound. This result indicated very reactive intermediates
involved in this oxidative ring forming reaction which cannot distinguish strongly
between the two positions. A similar problem was also observed during the synthesis
of polycyclic aromatic hydrocarbons and graphene fragments.19
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The optical properties of these BODIPYs 2a-d and 3a-d were investigated in
toluene (Figure 3) and were summarized in Table 1. As expected, in comparison to the
starting meso-mesitylphenyl-BODIPY a, the installation of phenyl substituents on the
BODIPY core in BODIPYs 2a-d lead to red-shift of the absorption maximum and
emission maximum up to 126 nm and 162 nm, respectively. Moreover, after oxidative
ring fusion, phenanthro[b]-fused BODIPY 3a gave additional red-shifts of the
absorption maximum and emission maxima in relation to 2,3,5,6-tetraphenylBODIPY
2a in 88 nm and 68 nm, respectively. The photophysical properties of 3a is in good
agreement with that previously reported by Shinokubo.14 In comparision with
BODIPY 3a, phenanthro[b]-fused BODIPYs 3b-d with electron-donating substituents
all showed redshifts of their absorption and emission maxima. In particular, the
phenanthro[b]-fused BODIPY 3d has large redshifts of their absorption (from 680 nm
to 740 nm) and emission maxima (from 697 nm to 767 nm). This ring-fusion process
also leads to a significant increase in the extinction coefficients of the resultant dyes
(Table 1). For example, the excitation coefficients value for phenanthro[b]-fused
BODIPY 3b is increased to more than three times as compared to that of
2,3,5,6-tetraphenylBODIPY 2b.
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1.0
0.5
0.0
(a)
a
2a
2d
3a
3d
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400
500
600
700
800
Wavelength (nm)
1.0
0.5
0.0
a
(b)
2a
2d
3a
3d
500
600
700
800
Wavelength (nm)
Figure 3. Normalized absorption (a) and fluorescence emission (b) spectra of
meso-mesitylphenylBODIPY a, 2a, 2d, 3a and 3d in toluene.
Compared to starting meso-mesitylphenylBODIPY a and the corresponding
2,3,5,6-tetraarylBODIPYs 2a-d, the phenanthro[b]-fused BODIPYs 3a-d showed
lower fluorescence quantum yields. However, their quantum yields generally depend
on the electronic characters of substituents on the newly formed phenanthrene rings.
For example, phenanthro[b]-fused BODIPY 3a has good fluorescence quantum yield
of 0.51 in toluene.14 Phenanthro[b]-fused BODIPY 3b with tert-butyl groups also
exhibits decreased fluorescence quantum yield of 0.29 in toluene. However, the
fluorescence quantum yields of phenanthro[b]-fused BODIPYs 3c and 3d with
methoxy groups dramatically decrease to less than 0.01 in toluene.
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Table 1. Photophysical properties of BODIPYs a, 2a-f, 3a-d, 4a-c, 5a-c, 6 in
toluene at room temperature.
7
8
λemmax (nm)
a
dyes
λabsmax (nm)
logεmax
Φb
Stokes Shift (cm-1)
9
ac
2a
503
592
606
596
629
625
581
680
698
682
740
605
581
591
593
694
691
687
682
675
4.79
4.81
4.70
4.90
4.88
4.73
4.99
5.22
5.24
5.16
5.29
4.80
4.92
4.83
4.84
5.22
5.11
4.83
4.95
4.93
515
629
645
636
677
677
628
697
715
717
767
649
618
639
640
713
715
714
730
712
0.82
0.75
0.78
0.78
0.16
0.51
0.44
0.51
0.29
<0.01
<0.01
0.43
0.10
0.57
0.54
0.68
0.03
0.46
0.43
0.54
500
1000
1000
1100
1100
1200
1300
400
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2b
2c
2d
2e
2f
3a
3b
3c
300
700
3d
4a
400
1100
1000
1300
1200
400
4a-Br
4b
4c
5a
5a-Br
5b
5c
500
500
1000
800
6
aMolar extinction coefficients are in the maximum of the highest peak. the
fluorescence quantum yields (Φ) of 2a-f, 4a-c were calculated using Cresyl violet
perchlorate in anhydrous methanol (Φ = 0.54) as the standard. The fluorescence
b
quantum
yields
(Φ)
of
3a-d,
5a-c,
6
were
calculated
using
1,7-diphenyl-3,5-di(p-methoxyphenyl)-azadipyrromethene in trichloromethane (Φ =
0.36) as the standard. cFrom reference 21
Further investigation showed that the phenanthro[b]-fused BODIPY 5a also has a
typical narrow absorption band, with the absorption maximum and emission maxima
centered at 694 nm and 713 nm in toluene, respectively (Table 1 and Figure S17 in the
Supporting Information). Interestingly, phenanthro[b]-fused BODIPY 5a showed
intense fluorescence (Φ = 0.68) in toluene, while its parent 4a showed a moderate
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fluorescence emission (Φ = 0.43). The origin of the weak fluorescence for 4a may be
associated with the internal conversion due to the rotation of substituted aryl
groups.15d In comparison with 5a, introducing a bromine or aryl group at the
1,7-positions only gave slight blueshifts of absorption maxima for resultant 5a-Br, 5b
and 5c (Table 1). Both 5b and 5c maintain good fluorescence quantum yields (0.46
and 0.43 in toluene, respectively). These fluorescence quantum yields of 5b and 5c
are significantly higher than those previously reported phenanthro[b]-fused
azaBODIPYs which had absorption maxima around 800 nm and very small Stoke
shifts (200 and 300 cm-1). In contrast, phenanthro[b]-fused BODIPYs 5b and 5c have
absorption maxima over 680 nm and larger Stoke shifts (500 and 1000 cm-1,
respectively).
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Phenanthro[b]-fused BODIPY 5a-Br with two bromine atoms at 1,7-positions only
has very weak fluorescence with fluorescence quantum yield of 0.03 in toluene. The
low fluorescence quantum yield of phenanthro[b]-fused BODIPY 5a-Br could be
partially attributed to the heavy atom effect of Br atoms at 1,7-positions, indicating
the potential application of phenanthro[b]-fused BODIPYs 5a-Br as a photosensitizer.
Under irritation with 660 nm laser, we found phenanthro[b]-fused BODIPY 5a-Br can
efficiently generate singlet oxygen which was trapped by 1,3-diphenylisobenzofuran
(DPBF) as shown in Figure 4. The decrease of the absorbance band of DPBF at 415
nm was monitored (Figure S23 in the Supporting Information) and shows a ׽1.38
times higher efficiency for singlet oxygen generation than that of
2,6-dibromo-1,7-diphenyl-3,5-di(4-methoxylphenyl)-azaBODIPY20 (H, ΦΔ = 0.77 in
toluene).
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1.0
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0.0
0s
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60
300
400
500
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700
Wavelength (nm)
Figure 4. Absorption spectra changes of DPBF upon irradiation with 660 nm laser in
the presence of 5a-Br for 60 s (recorded at 10 s interval) in toluene.
The solvatochromic effects of these BODIPYs were investigated in cyclohexane,
toluene, dichloromethane, tetrahydrofuran and acetonitrile (Figures S3-S21) and were
summarized in Table S4 (Supporting Information). The influence of the solvent on
λabs(max) and λem(max) of these dyes is less than 21 nm and 22 nm, respectively. Most
of these dyes show slight decreases of fluorescence quantum yields, especially for
these with electron donating substituted groups. For example, the absorption maxima
of 3d were blue-shifted from toluene (740 nm), cyclohexane (733 nm),
dichloromethane (727 nm), tetrahydrofuran (730 nm) to acetonitrile (718 nm), and the
fluorescence quantum yields were reduced from 0.10 (in cyclohexane) to less than
0.01 (in acetonitrile).
DFT Calculations.
For a better understanding of the remarkable regioselectivity of this oxidative fusion
reaction and the properties of the resultant phenanthro[b]-fused BODIPYs, theoretical
calculations based on density functional theory (DFT) and time-dependent DFT
(TD-DFT) were performed for 4b and 5b and the results are summarized in Table S5
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and Figure 5. In comparison with 4b, the calculated LUMO energy levels of 5b
decreased from -3.0 eV to -3.2 eV, while the HOMO energy basically unchanged. The
slight stabilization of HOMO and the destabilization of LUMO led to the decrease of
the HOMO-LUMO gap. The electron densities in the HOMO of 4b are mainly located
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Figure 5. (a) LUMO and (c) HOMO orbitals of 4b, (b) LUMO and (d) HOMO
orbitals of 5b, (e) 4b and (f) 5b with NICS(0) values (ppm) at the geometric center
points of corresponding five-/six-membered rings. All hydrogen atoms and tert-butyl
groups are removed for clarity in (e) and (f).
on the 2,6-diphenyls, 3,5-diphenyls and the dipyrrin unit. However, 1,7-phenyls has
almost no electron densities (Figure 5a-d). The oxidative ring fusion reaction
normally involved the nucleophilic attack of the cation radical by an electron-rich aryl
group.15e The high electron density on 3,5-phenyls may facilitate the formation of
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cation radicals at these two phenyls in the presence of FeCl3, which may then undergo
nucleophilic attack by the adjacent 2,6-phenyls to form the ring-fused product 5b. The
TD-DFT calculations at the B3LYP/6-31+G(d, p) level on both BODIPYs 4b and 5b
show strong absorption with the lowest energy mostly consisting of the
HOMO-LUMO transition (Table S5 in the Supporting Information). The TD-DFT
calculations also predict that phenanthro[b]-fused 5b are 79 nm red-shift for the first
excited state compared with that of 4b, which is in good agreement with the
experimental data.
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Nucleus independent chemical shift (NICS) calculations of 4b and 5b were
conducted to provide the trend of aromaticity of each ring (Figure 5e-f). Calculated
structure of phenanthro[b]-fused 5b has a nearly planar core structure composed of
nine fused rings. The NICS(0) values of 3.2, –4.8, –0.2, –10.6, and -6.0 ppm (Figure
5f) are predicted for the six- and five-membered rings in 5b, respectively, indicating
the high aromaticity of newly formed rings and a well extended π-conjugation after
ring fusion.22
CONCLUSION
In summary, we have synthesized a series of phenanthro[b]-fused BODIPYs in good
yield by an intramolecular oxidative aromatic coupling mediated by iron(III) chloride.
The X-ray structures, optical properties and DFT calculation of these π-extended
systems were investigated. These BODIPYs show strong sharp absorption (up to 754
nm in toluene) and fluorescence emission (up to 771 nm in toluene) tunable up to NIR
region and tunable fluorescence quantum yields (up to 0.68 in toluene), which
render them potential applications as promising NIR emitting or theranostic materials.
Further researches along this line are underway in our group.
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EXPERIMENTAL SECTION
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General. Reagents and solvents were used as received from commercial suppliers
unless noted otherwise. All reactions were performed in oven-dried or flame-dried
glassware unless otherwise stated, and were monitored by TLC using 0.25 mm silica
gel plates with a UV indicator (HSGF 254) for thin-layer chromatography (TLC).
All heating reactions were carried out in an oil bath. Flash column chromatography
was performed using silica gel (300-400 mesh). 1H and 13C {1H} NMR were recorded
on a 300 or 500 MHz NMR spectrometer at room temperature. Chemical shifts (δ) are
given in ppm relative to CDCl3 (7.26 ppm for 1H) or to internal TMS. High-resolution
mass spectra (HRMS) were obtained using APCI (or MALDI)-TOF in positive mode.
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Cyclic Voltammograms. Cyclic voltammograms of 1 mM BODIPYs were measured
in degassed dichloromethane solution containing 0.1 M TBAPF6 as the supporting
electrolyte, glassy carbon electrode as a working electrode, Pt wire as a counter
electrode, and a saturated calomel electrode (SCE) as reference electrode at 20 mV
s–1 as the scanning rate at room temperature.
Photophysical Measurements. UV-visible absorption and fluorescence emission
spectra were recorded on commercial spectrophotometers (190-870 nm scan range) at
room temperature (10 mm quartz cuvette). Relative fluorescence quantum efficiencies
of BODIPY derivatives were obtained by comparing the areas under the corrected
emission spectrum of the test sample in various organic solvents with Cresyl violet
perchlorate (Φ = 0.54 in methanol) and 1,7-diphenyl-3,5-di(4-methoxyphenyl)-
azadipyrromethene (Φ = 0.36 in CHCl3). Quantum yields were determined by the
formula below.23
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nx2
nr2
1-10-A
(
λex
)
)
r
F
x
Φ = Φ ×
×
×
x
r
(
λex
F 1-10-A
x
r
6
7
8
9
where the subscripts x and r refer, respectively, to our sample x and reference
(standard) fluorophore r with known quantum yield Φr in a specific solvent, F stands
for the spectrally corrected, integrated fluorescence spectra, A(λex) denotes the
absorbance at the used excitation wavelength λex, and n represents the refractive index
of the solvent (in principle at the average emission wavelength).
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Singlet Oxygen Trap Experiments. In singlet oxygen measurements,
1,3-diphenylisobenzofuran (DPBF) was used as a singlet oxygen trap molecule.
2,6-Dibromo-1,7-diphenyl-3,5-di(4-methoxylphenyl)-azaBODIPY (H, ΦΔ = 0.77 in
toluene) was used as the reference compound with singlet oxygen quantum yield. In
brief, photosensitizer and a trap molecule were mixed in toluene, followed by
irradiation (660 nm laser with 0.5 mW/cm2) at a 10 s interval. Absorbance decrease of
DPBF at 415 nm was monitored and recorded indicating singlet oxygen generation
and consumption in the presence of light and 5a-Br.
The singlet oxygen quantum yield (ΦΔ) of 5a-Br was calculated by the formula
below.
H
k 1−10−A
600
Φ△＝ΦH
kH 1−10−A
600
Where ΦH is the singlet oxygen quantum yield of the H in toluene (0.77), k and kH
are slopes of plots, which represent the absorbance at 415 nm of DPBF in the 5a-Br
and H, respectively. A6H00 and A600 is absorbance at the irradiation wavelength (660
nm) of the H and 5a-Br at the beginning.
Crystallography. Crystals of 4b (CCDC 1903259) suitable for X-ray analysis
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were obtained by slow evaporation of dichloromethane solution at room temperature.
Data were collected using a diffractometer equipped with a graphite crystal
monochromator situated in the incident beam for data collection at room temperature.
Cell parameters were retrieved using SMART24 software and refined using SAINT25
on all observed reflections. The determination of unit cell parameters and data
collections were performed with Mo Kα radiation (λ) at 0.71073 Å. Data reduction
was performed using the SAINT software, which corrects for Lp and decay. The
structure was solved by the direct method using the SHELXS-974 program and
refined by least squares method on F2, SHELXL-9726, incorporated in SHELXTL
V5.10.
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Computational Details. The ground state geometry of BODIPY 4b and the
corresponding aryl-fused BODIPY 5b was optimized by using DFT method. The
same method was used for vibrational analysis to verify that the optimized structures
correspond to local minima on the energy surface. Time-Dependent Density
Functional Theory (TD-DFT) computations at the B3LYP/6-31+G (d, p) level were
used to obtain the vertical excitation energies and oscillator strengths. The geometry
optimizations of all the molecules in dichloromethane were done using the
Self-Consistent Reaction Field (SCRF) method and the Polarizable Continuum Model
1
(PCM). The H NMR spectra of the optimized structures were calculated by a GIAO
(gauge-independent atomic orbital) method using the same level. All calculations
were performed employing the Gaussian 09 suit of programs.27
Synthesis. BODIPYs 1a16a and 1b16b were synthesized according to the literature.
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8-(2,4,6-Trimethylphenyl)-2,3,5,6-tetraphenyl-BODIPY
(2a).
To
a
dry
5
6
7
8
round-bottom flask loaded with compound 1a (0.1 mmol, 62 mg), phenylboronic acid
(0.5 mmol, 61 mg), Na2CO3 (5 mL, 1M) and Pd(PPh3)4 (0.01 mmol, 11 mg) were
added toluene (5 mL). Freeze-pump-thaw cycle was carried out three times. After that,
the mixture was warmed to 70 ℃ under argon and stirred for 8 hours. After cooling to
room temperature, the reaction mixture was extracted with CH2Cl2 and dried over
anhydrous Na2SO4. The organic layers were combined and evaporated under vacuum.
The residue was purified through column chromatography (silica, petroleum
ether/ethyl acetate = 6/1, v/v) to afford 2a as solid in 74% yield (46 mg). Mp >220 ℃.
1H NMR (300 MHz, CDCl3) δ 7.51 (d, J = 6.3 Hz, 4H), 7.31-7.36(m, 6H), 7.12-7.14
(m, 6H), 7.02 (s, 2H), 6.96-6.98 (m, 4H), 6.76 (s, 2H), 2.40 (s, 3H), 2.31 (s, 6H). 13C
{1H} NMR (125 MHz, CDCl3) δ 156.4, 143.9, 138.7, 136.9, 135.0, 134.9, 134.6,
133.8, 131.8, 130.4, 130.3, 129.1, 128.3, 128.1, 127.9, 127.0, 126.9, 21.2, 20.4.
HRMS (APCI) Calcd. for C42H33BFN2 [M-F]+, 595.2721, found 595.5735.
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8-(2,4,6-Trimethylphenyl)-2,3,5,6-tetra(4-tert-butylphenyl)-BODIPY (2b). To a dry
round-bottom flask loaded with compound 1a (0.1 mmol, 62 mg),
(4-tert-butylphenyl)boronic acid (0.5 mmol, 89 mg), Na2CO3 (5 mL, 1M) and
Pd(PPh3)4 (0.01 mmol, 11 mg) were added toluene (5 mL). Freeze-pump-thaw cycle
was carried out three times. After that, the mixture was warmed to 70 ℃ under argon
and stirred for 8 hours. After cooling to room temperature, the reaction mixture was
extracted with CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were
combined and evaporated under vacuum. The residue was purified through column
chromatography (silica, petroleum ether/ethyl acetate = 5/1, v/v) to afford 2b as solid
in 79% yield (67 mg). Mp >220 ℃. 1H NMR (500 MHz, CDCl3) δ 7.46 (s, 2H), 7.44
(s, 2H), 7.34 (s, 2H), 7.33 (s, 2H), 7.12 (s, 2H), 7.11 (s, 2H), 6.99 (s, 2H), 6.87 (s, 2H),
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6.86 (s, 2H), 6.70 (s, 2H), 2.39 (s, 3H), 2.29 (s, 6H), 1.32 (s, 18H), 1.24 (s, 18H). 13C
{1H} NMR (125 MHz, CDCl3) δ 156.5, 151.9, 149.6, 142.7, 138.5, 137.0, 134.8,
134.4, 131.2, 130.5, 130.1, 129.0, 128.1, 127.8, 126.7, 124.9, 124.8, 34.8, 34.4, 31.3,
31.2, 21.2, 20.4. HRMS (APCI) Calcd. for C58H65BFN2 [M-F]+, 819.5225, found
819.5235.
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8-(2,4,6-Trimethylphenyl)-2,3,5,6-tetra(3-methoxyphenyl)-BODIPY (2c). To a dry
round-bottom flask loaded with compound 1a (0.1 mmol, 62 mg),
(3-methoxyphenyl)boronic acid (0.5 mmol, 76 mg), Na2CO3 (5 mL, 1M) and
Pd(PPh3)4 (0.01 mmol, 11 mg) were added toluene (5 mL). Freeze-pump-thaw cycle
was carried out three times. After that, the mixture was warmed to 70 ℃ under argon
and stirred for 8 hours. After cooling to room temperature, the reaction mixture was
extracted with CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were
combined and evaporated under vacuum. The residue was purified through column
chromatography (silica, petroleum ether/ethyl acetate = 4/1, v/v) to afford 2c as solid
in 77% yield (57 mg). Mp >220 ℃. 1H NMR (300 MHz, CDCl3) δ 7.20-7.23 (m, 2H),
7.02-7.11 (m, 8H), 6.90 (d, J = 8.4 Hz, 2H), 6.76 (s, 2H), 6.62-6.69 (m, 4H), 6.49 (s,
13
2H), 3.70 (s, 6H), 3.55 (s, 6H), 2.40 (s, 3H), 2.29 (s, 6H). C {1H} NMR (75 MHz,
CDCl3) δ 159.2, 158.9, 156.2, 144.1, 138.8, 136.8, 135.1, 134.8, 134.3, 133.0, 130.2,
129.1, 128.9, 128.3, 126.9, 123.0, 120.7, 115.7, 115.4, 113.4, 113.0, 55.2, 55.0, 21.2,
20.4. HRMS (APCI) Calcd. for C46H41BF2N2O4 [M + H]+, 735.3200, found 735.3197.
8-(2,4,6-Trimethylphenyl)-2,3,5,6-tetra(3,4,5-trimethoxyphenyl)-BODIPY (2d). To a
dry round-bottom flask loaded with compound 1a (0.1 mmol, 62 mg),
(3,4,5-trimethoxyphenyl)boronic acid (0.5 mmol, 106 mg), Na2CO3 (5 mL, 1M) and
Pd(PPh3)4 (0.01 mmol, 11 mg) were added toluene (5 mL). Freeze-pump-thaw cycle
was carried out three times. After that, the mixture was warmed to 70 ℃ under argon
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and stirred for 8 hours. After cooling to room temperature, the reaction mixture was
extracted with CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were
combined and evaporated under vacuum. The residue was purified through column
chromatography (silica, petroleum ether/ethyl acetate = 5/1, v/v) to afford 2d as solid
in 77% yield (74 mg). Mp >220 ℃. 1H NMR (500 MHz, CDCl3) δ 7.07 (s, 2H), 6.85
(s, 4H), 6.72 (s, 2H), 6.24 (s, 4H), 3.87 (s, 6H), 3.78 (s, 6H), 3.70 (s, 12H), 3.62 (s,
12H), 2.43 (s, 3H), 2.32 (s, 6H).3C {1H} NMR (125 MHz, CDCl3) δ 155.9, 152.9,
152.6, 143.3, 138.9, 138.8, 137.4, 136.9, 134.8, 134.4, 130.2, 129.3, 128.4, 126.9,
126.2, 108.3, 105.8, 60.9, 56.1, 21.3, 20.4. HRMS (APCI) Calcd. for C54H57BF2N2O12
[M + H]+, 975.4045, found 975.4046.
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8-(2,4,6-Trimethylphenyl)-2,3,5,6-tetra(4-methoxyphenyl)-BODIPY (2e). To a dry
round-bottom flask loaded with compound 1a (0.1 mmol, 62 mg),
(4-methoxyphenyl)boronic acid (0.5 mmol, 76 mg), Na2CO3 (5 mL, 1M) and
Pd(PPh3)4 (0.01 mmol, 11 mg) were added toluene (5 mL). Freeze-pump-thaw cycle
was carried out three times. After that, the mixture was warmed to 70 ℃ under argon
and stirred for 8 hours. After cooling to room temperature, the reaction mixture was
extracted with CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were
combined and evaporated under vacuum. The residue was purified through column
chromatography (silica, petroleum ether/ethyl acetate = 5/1, v/v) to afford 2e as solid
in 78% yield (57 mg). Mp >220 ℃. 1H NMR (300 MHz, CDCl3) δ 7.47 (d, J = 7.8 Hz,
4H), 7.00 (s, 2H), 6.91 (d, J = 7.8 Hz, 4H), 6.85 (d, J = 8.1 Hz, 4H), 6.69 (d, J = 7.8
Hz, 4H), 6.64 (s, 2H), 3.82 (s, 6H), 3.74 (s, 6H), 2.39 (s, 3H), 2.29 (s, 6H). 13C {1H}
NMR (75 MHz, CDCl3) δ 160.1, 158.5, 155.8, 141.9, 138.5, 136.9, 134.7, 134.07,
132.1, 130.5, 129.5, 128.2, 126.7, 126.0, 124.3, 113.6, 113.4, 55.2, 55.1, 21.2, 20.3.
HRMS (APCI) Calcd. for C46H41BF2N2O4 [M + H]+, 735.3200, found 735.3197.
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8-(2,4,6-Trimethylphenyl)-2,3,5,6-tetra(3-methylphenyl)-BODIPY (2f). To a dry
round-bottom flask loaded with compound 1a (0.1 mmol, 62 mg),
(3-methylphenyl)boronic acid (0.5 mmol, 68 mg), Na2CO3 (5 mL, 1M) and Pd(PPh3)4
(0.01 mmol, 11 mg) were added toluene (5 mL). Freeze-pump-thaw cycle was carried
out three times. After that, the mixture was warmed to 70 ℃ under argon and stirred for
8 hours. After cooling to room temperature, the reaction mixture was extracted with
CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were combined and
evaporated under vacuum. The residue was purified through column chromatography
(silica, petroleum ether/ethyl acetate = 5/1, v/v) to afford 2f as solid in 76% yield (52
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mg). Mp > 220℃. H NMR (300 MHz, CDCl3) δ 7.28-7.35 (m, 4H), 7.14-7.22 (m,
4H), 7.03 (s, 2H), 6.92-6.99 (m, 4H), 6.83 (s, 2H), 6.73 (s, 2H), 6.69 (d, J = 7.2 Hz,
2H), 2.41 (s, 3H), 2.30 (s, 6H), 2.27 (s, 6H), 2.19 (s, 6H). 13C {1H} NMR (125 MHz,
CDCl3) δ 155.8, 149.8, 148.4, 148.1, 142.1, 138.6, 137.0, 134.8, 134.2, 130.5, 129.0,
128.3, 126.9, 126.0, 124.4, 123.9, 120.8, 114.1, 111.9, 111.0, 110.5, 55.8, 55.7, 21.2,
20.4. HRMS (APCI) Calcd. for C46H42BF2N2 [M + H]+, 671.3404, found 671.3403.
[b]-Fused BODIPY 3a. Compound 2a (120 mg, 0.20 mmol) were dissolved in dry
dichloromethane (50 mL) then a solution of anhydrous ferric chloride (275 mg, 1.7
mmol) in nitromethane (3 mL) was added to the solution and the mixture was stirred
for 5 mins at room temperature. Then the reaction was quenched by addition of
MeOH (20 mL). The organic phase was washed with H2O (2 × 50 mL) extracted with
CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were combined and
evaporated under vacuum. The residue was purified through column chromatography
(silica, petroleum ether/ethyl acetate = 6/1, v/v) to afford 3a as solid in 73% yield (86
mg). Mp >220 ℃. 1H NMR (300 MHz, CDCl3) δ 9.68 (d, J = 8.4 Hz, 2H), 8.59 (d, J
= 8.1 Hz, 2H), 8.48 (d, J = 8.1 Hz, 2H), 7.99 (d, J = 9.0 Hz, 2H), 7.72-7.85 (m, 4H),
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7.46-7.55 (m, 4H), 7.33 (s, 2H), 7.11 (s, 2H), 2.49 (s, 3H), 2.26 (s, 6H). C {1H}
NMR (125MHz, CDCl3) δ 150.5, 145.1, 139.1, 138.8, 137.3, 134.2, 131.0, 130.6,
123.0, 129.3, 129.2, 128.7, 128.4, 127.9, 127.7, 127.2, 127.0, 124.1, 123.9, 123.6,
121.2, 21.3, 20.4. HRMS (APCI) Calcd. for C42H29BFN2 [M-F]+, 591.2408, found
591.2391.
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[b]-Fused BODIPY 3b. Compound 2b (165 mg, 0.20 mmol) were dissolved in dry
dichloromethane (30 mL) then a solution of anhydrous ferric chloride (275 mg, 1.7
mmol) in nitromethane (3 mL) was added to the solution and the mixture was stirred
for 5 mins at room temperature. Then the reaction was quenched by addition of
MeOH (20 mL). The organic phase was washed with H2O (2 × 50 mL) extracted with
CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were combined and
evaporated under vacuum. The residue was purified through column chromatography
(silica, petroleum ether/ethyl acetate = 6/1, v/v) to afford 3b as solid in 70% yield
(115 mg). Mp >220 ℃. 1H NMR (500 MHz, CDCl3) δ 9.59 (d, J = 9.0 Hz, 2H), 8.58
(s, 2H), 8.48 (d, J = 1.5 Hz, 2H), 7.87-7.90 (m, 4H), 7.50-7.52 (m, 2H), 7.24 (d, J =12
Hz, 2H), 7.10 (s, 2H), 2.49 (s, 3H), 2.25 (s, 6H), 1.55 (s, 18H), 1.46 (s, 18H). 13C {1H}
NMR (125 MHz, CDCl3) δ 152.8, 150.2, 149.6, 143.5, 138.8, 138.6, 137.4, 134.3,
131.3, 130.3, 129.0, 128.5, 128.3, 125.8, 125.4, 125.0, 123.9, 121.9, 120.4, 119.7,
119.4, 35.4, 35.41, 31.44, 31.3, 21.3, 20.3. HRMS (APCI) Calcd. for C58H61BFN2
[M-F]+, 815.4912, found 815.4922.
[b]-Fused BODIPY 3c. Compound 2c (146 mg, 0.20 mmol) were dissolved in dry
dichloromethane (50 mL) then a solution of anhydrous ferric chloride (272 mg, 1.7
mmol) in nitromethane (3 mL) was added to the solution and the mixture was stirred
for 5 mins at room temperature. Then the reaction was quenched by addition of
MeOH (20 mL). The organic phase was washed with H2O (2 × 50 mL) extracted with
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CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were combined and
evaporated under vacuum. The residue was purified through column chromatography
(silica, petroleum ether/ethyl acetate = 6/1, v/v) to afford 3c as solid in 75% yield (104
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mg). Mp >220 ℃. H NMR (300 MHz, CDCl3) δ 9.19 (s, 2H), 8.22-8.34 (m, 4H),
7.23-7.30 (m, 6H), 7.05-7.13 (m, 4H), 4.13 (s, 6H), 3.91 (s, 6H), 2.50 (s, 3H), 2.27 (s,
6H). 13C {1H} NMR (125 MHz, CDCl3) δ 158.6, 158.2, 150.7, 144.8, 139.0, 138.6,
137.5, 131.1, 130.8, 128.5, 128.36, 127.6, 124.8, 124.6, 124.0, 122.9, 121.2, 117.8,
115.6, 113.2, 113.1, 113.0, 106.5, 56.0, 55.6, 21.3, 20.4. HRMS (APCI) Calcd. for
C46H37BF2N2O4 [M + H]+, 731.2887, found 731.2888.
[b]-Fused BODIPY 3d. Compound 2d (195 mg, 0.20 mmol) were dissolved in dry
dichloromethane (30 mL) then a solution of anhydrous ferric chloride (129 mg, 0.8
mmol) in nitromethane (3 mL) was added to the ice bath cooled solution and the
mixture was stirred for 5 mins. Then the reaction was quenched by addition of MeOH
(20 mL). The organic phase was washed with H2O (2 × 50 mL) extracted with CH2Cl2
and dried over anhydrous Na2SO4. The organic layers were combined and evaporated
under vacuum. The residue was purified through column chromatography (silica,
petroleum ether/ethyl acetate = 6/1, v/v) to afford 3d as solid in 60% yield (116 mg).
1
Mp >220℃. H NMR (300 MHz, CDCl3) δ 8.88 (s, 2H), 7.14 (s, 2H), 7.03-7.04 (m,
4H), 4.16 (s, 6H), 4.09 (s, 6H), 3.99 (d, J = 2.1 Hz, 12H), 3.73 (s, 6H), 3.67 (s, 6H),
13
2.51 (s, 3H), 2.25 (s, 6H). C {1H} NMR (125 MHz, CDCl3) δ 153.3, 153.0, 152.3,
152.3, 150.6, 145.1, 142.3, 141.8, 138.9, 138.8, 137.6, 131.3, 130.9, 128.4, 123.9,
123.0, 120.8, 119.8, 115.5, 107.6, 100.3, 61.4, 61.3, 57.1, 56.4, 21.4, 20.3. HRMS
(APCI) Calcd. for C54H54BF2N2O12 [M + H]+, 971.3732, found 971.3735.
8-Phenyl-2,3,5,6-tetra(4-tert-butylphenyl)-BODIPY (4a). To a dry round-bottom
flask loaded with compound 1b (0.1 mmol, 58 mg), (4-tert-butylphenyl)boronic acid
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(0.5 mmol, 89 mg), Na2CO3 (5 mL, 1M) and Pd(PPh3)4 (0.01 mmol, 11 mg) were
added toluene (5 mL). Freeze-pump-thaw cycle was carried out three times. After that,
the mixture was warmed to 70 ℃ under argon and stirred for 8 hours. After cooling to
room temperature, the reaction mixture was extracted with CH2Cl2 and dried over
anhydrous Na2SO4. The organic layers were combined and evaporated under vacuum.
The residue was purified through column chromatography (silica, petroleum
ether/ethyl acetate = 5/1, v/v) to afford 4a as solid in 75% yield (60 mg). Mp >220 ℃.
1H NMR (300 MHz, CDCl3) δ 7.66 (d, J = 6.6 Hz, 2H), 7.54-7.59 (m, 3H), 7.43 (d, J
= 8.1 Hz, 4H), 7.34 (d, J = 8.1 Hz, 4H), 7.15 (d, J = 8.1 Hz, 4H), 6.90-6.97 (m, 6H),
1.31 (s, 18H), 1.25 (s, 18H). 13C {1H} NMR (125 MHz, CDCl3) δ 156.7, 156.7, 151.9,
149.8, 142.9, 134.6, 134.5, 131.2, 130.8, 130.1, 129.0, 128.3, 128.3, 128.0, 127.8,
125.0, 124.8, 34.7, 34.4, 31.3. HRMS (APCI) Calcd. for C55H59BF2N2 [M + H]+,
797.4812, found 797.4809.
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8-Phenyl-2,3,5,6-tetra(4-tert-butylphenyl)-1,7-dibromo-BODIPY
(4a-Br).
To
compound 4a (88 mg, 0.11 mmol) in 40 mL of dry CH2Cl2 was added liquid bromine
(18 μL, 0.34 mmol) in CH2Cl2 (5 mL), the mixture was left stirring for an 0.5 h,
washed with an aqueous solution of sodium thiosulfate, and extracted by CH2Cl2.
Organic layers were combined, dried over Na2SO4, and evaporated to dryness.
Purification was performed by column chromatography on silica gel using petroleum
ether/ethyl acetate (4:1, v/v) as eluent, from which the desired product 4a-Br was
obtained as red solid in 93% yield (97 mg). Mp >220 ℃. 1H NMR (500 MHz, CDCl3)
δ 7.52-7.54 (m, 3H), 7.45-7.47 (m, 2H), 7.28-7.24 (m, 4H), 7.20 (d, J = 8.5 Hz, 4H),
7.16 (d, J = 8.5 Hz, 4H), 6.89 (d, J = 8.5 Hz, 4H), 1.24 (s, 18H), 1.24 (s, 18H). 13C
{1H} NMR (125MHz, CDCl3) δ 156.9, 152.1, 150.2, 143.8, 136.3, 132.2, 130.3,
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130.1, 130.1, 129.7, 129.5, 129.4, 129.0, 128.1, 124.6, 124.4, 120.3, 34.7, 34.5, 31.2.
HRMS (APCI) Calcd. for C55H57BBr2F2N2 [M + H]+, 953.3022, found 953.3046.
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8-Phenyl-1,2,3,5,6,7-hexa(4-tert-butylphenyl)-BODIPY
(4b).
To
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round-bottom flask loaded with compound 4a-Br (0.1 mmol, 95 mg),
(4-tert-butylphenyl)boronic acid (0.3 mmol, 54 mg), Na2CO3 (5 mL, 1M) and
Pd(PPh3)4 (0.01 mmol, 11 mg) were added toluene (5 mL). Freeze-pump-thaw cycle
was carried out three times. After that, the mixture was warmed to 70 ℃ under argon
and stirred for 8 hours. After cooling to room temperature, the reaction mixture was
extracted with CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were
combined and evaporated under vacuum. The residue was purified through column
chromatography (silica, petroleum ether/ethyl acetate = 6/1, v/v) to afford 4b as solid
in 81% yield (85 mg). Mp >220 ℃. 1H NMR (500 MHz, CDCl3) δ 7.32 (d, J = 4.8 Hz,
4H), 7.26 (s, 1H), 7.21 (d, J = 4.8 Hz, 4H), 6.88 (d, J = 5.1 Hz, 4H), 6.76 (d, J = 4.5
Hz, 2H), 6.65 (d, J = 3.9 Hz, 4H), 6.50 (d, J = 4.2 Hz, 4H), 6.45 (d, J = 3.9 Hz, 4H),
6.30-6.33 (m, 2H), 1.25 (s, 18H), 1.14 (s, 18H), 1.12 (s, 18H). 13C {1H} NMR (125
MHz, CDCl3) δ 156.2, 151.2, 148.6 147.7, 146.4, 143.9, 134.6, 132.3, 131.9 131.7,
131.3, 130.4, 130.3, 129.8, 129.1, 128.3, 126.1, 125.0, 124.3, 123.9, 123.7, 34.6, 34.2,
34.1, 31.2, 31.1. HRMS (APCI) Calcd. for C75H83BF2N2 [M + H]+, 1061.6690, found
1061.6703.
8-Phenyl-2,3,5,6-tetra(4-tert-butylphenyl)-1,7-di(3-methoxyphenyl)-BODIPY (4c).
To a dry round-bottom flask loaded with compound 4a-Br (0.1 mmol, 95 mg),
(3-methoxyphenyl)boronic acid (0.3 mmol, 46 mg), Na2CO3 (5 mL, 1M) and
Pd(PPh3)4 (0.01 mmol, 11 mg) were added toluene (5 mL). Freeze-pump-thaw cycle
was carried out three times. After that, the mixture was warmed to 70 ℃ under argon
and stirred for 8 hours. After cooling to room temperature, the reaction mixture was
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extracted with CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were
combined and evaporated under vacuum. The residue was purified through column
chromatography (silica, petroleum ether/ethyl acetate = 6/1, v/v) to afford 4c as solid
in 79% yield (85 mg). Mp >220 ℃. 1H NMR (500 MHz, CDCl3) δ 7.33 (d, J = 8.0Hz,
4H), 7.22 (d, J = 9.0 Hz, 4H), 6.89 (d, J = 9.0 Hz, 6H), 6.59-6.65 (m, 3H), 6.45-6.50
(m, 6H), 6.31-6.33 (m, 2H), 6.17-6.21 (m, 2H), 6.07 (s, 2H), 3.44 (s, 3H), 3.42 (s, 3H),
1.26 (s, 18H), 1.14 (s, 18H). 13C {1H} NMR (125 MHz, CDCl3) δ 157.0, 154.4, 152.4,
148.7, 141.5, 136.1, 135.8, 134.0, 130.8, 130.6, 130.1, 129.69, 129.8, 128.5, 126.5,
125.5, 124.8, 124.7, 124.2, 123.4, 118.7, 117.0, 111.3, 55.3, 35.0, 34.9, 31.4. HRMS
(APCI) Calcd. for C69H71BF2N2O2 [M + H]+, 1009.5649, found 1009.5696.
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[b]-Fused BODIPY 5a. Compound 4a (160 mg, 0.20 mmol) were dissolved in dry
dichloromethane (30 mL) then a solution of anhydrous ferric chloride (360 mg, 1.6
mmol) in nitromethane (4 mL) was added to the solution and the mixture was stirred
for 5 mins at room temperature. Then the reaction was quenched by addition of
MeOH (20 mL). The organic phase was washed with H2O (2 × 50 mL) extracted with
CH2Cl2 and dried over anhydrous Na2SO4. The organic layers were combined and
evaporated under vacuum. The residue was purified through column chromatography
(silica, petroleum ether/ethyl acetate = 5/1, v/v) to afford 5a as solid in 70% yield (110
mg). Mp >220 ℃. 1H NMR (300 MHz, CDCl3) δ 9.51-9.70 (m, 2H), 9.26 (d, J = 8.4
Hz, 1H), 8.47-8.60 (m, 4H), 7.86-7.95 (m, 4H), 7.45-7.68 (m, 8H), 1.55 (s, 18H), 1.48
(s, 18H). 13C {1H} NMR (75 MHz, CDCl3) δ 152.8, 150.1, 149.6, 143.6, 138.6, 135.3,
134.2, 131.3, 130.1, 129.1, 128.5, 128.3, 125.8, 125.5, 125.0, 123.8, 122.1, 121.9,
119.8, 119.4, 35.4, 35.1, 31.4, 31.3. HRMS (APCI) Calcd. for C55H55BF2N2 [M + H]+,
793.4499, found 793.4498.
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