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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 Downloaded from pubs.acs.org on July 18, 2019

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is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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The Journal of Organic Chemistry

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

Abstract Graphic

Br

N Br

B

Ar

Ar

Ar Br

N

F F

Br

ArB(OH)2 Suzuki coupling

Ar

N Ar

B

R N

F F

rapid/efficient synthesis tunable neat-infrared (NIR) absorption/emission

Ar

R

FeCl3 N

N B F F

Ar

R R [b]-Phenanthrene-Fused BODIPYs

ACS Paragon Plus Environment

The Journal of Organic Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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 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. 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



via postfunctionalization, which showed intense NIR absorption and emission.

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. 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



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 further confirmed by 1H 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. 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. 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.

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

hexakis(4-alkoxyphenyl)benzene hexaalkoxytriphenylene.18a

oxidative

failed In

to

addition,

cyclodehydrogenation give

the

attempts

of

corresponding to

oxidize

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



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. 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

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.



Normalized Absorption

1.0

(a) a 2a 2d 3a 3d

0.5

0.0 400

500

600

700

800

Wavelength (nm)

Normalized Fluorescence

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.0 (b)

a 2a 2d 3a 3d

0.5

0.0 500

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. dyes

λabsmax (nm)

logεmaxa

ac

503

4.79

2a

592

2b

λemmax (nm)

Φb

Stokes Shift (cm-1)

515

0.82

500

4.81

629

0.75

1000

606

4.70

645

0.78

1000

2c

596

4.90

636

0.78

1100

2d

629

4.88

677

0.16

1100

2e

625

4.73

677

0.51

1200

2f

581

4.99

628

0.44

1300

3a

680

5.22

697

0.51

400

3b

698

5.24

715

0.29

300

3c

682

5.16

717

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. 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, 2H), 3.70 (s, 6H), 3.55 (s, 6H), 2.40 (s, 3H), 2.29 (s, 6H). 13C {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. 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.



Page 24 of 41

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 mg). Mp > 220℃. 1H 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).

13

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. [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



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 mg). Mp >220 ℃. 1H 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). Mp >220℃. 1H 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), 2.51 (s, 3H), 2.25 (s, 6H). 13C {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 ℃. 1

H 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. 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,



Page 28 of 41

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. 8-Phenyl-1,2,3,5,6,7-hexa(4-tert-butylphenyl)-BODIPY

round-bottom

flask

loaded

with

(4b).

compound 4a-Br (0.1

To mmol,

a

dry

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. [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.



[b]-Fused BODIPY 5a-Br. Compound 4a-Br (190 mg, 0.20 mmol) were dissolved

in dry dichloromethane (30 mL) then a solution of anhydrous ferric chloride (342 mg, 2.1 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-Br as solid in 42% yield (79 mg). Mp >220 ℃. 1H NMR (300 MHz, CDCl3) δ 9.30 (d, J = 9.0 Hz, 2H), 9.28 (d, J = 8.7 Hz, 2H), 8.57 (s, 2H), 8.52 (s, 2H), 7.86 (d, J = 9.0 Hz, 2H), 7.53-7.62 (m, 7H),

1.55 (s, 18), 1.47 (s, 18). 13C {1H} NMR (125 MHz, CDCl3) δ 153.5, 150.0, 149.7, 143.4, 134.6, 133.5, 133.2, 130.6, 129.9, 129.5, 129.6, 129.5, 127.7, 125.8, 125.0, 124.8, 124.4, 120.9, 119.8, 119.7, 115.9, 35.4, 35.1, 31.3, 31.2. HRMS (APCI) Calcd. for C55H53BBr2F2N2 [M + H]+, 949.2709, found 949.2759. [b]-Fused BODIPY 5b. Compound 4b (200 mg, 0.2 mmol) were dissolved in dry

dichloromethane (50 mL) then a solution of anhydrous ferric chloride (342mg, 1.2 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 5b as solid in 56% yield (112 mg). Mp >220 ℃. 1H NMR (500 MHz, CDCl3) δ 9.78 (d, J = 8.5 Hz, 2H), 8.57 (s, 2H), 8.45 (s, 2H), 7.90 (d, J = 8.5 Hz, 2H), 6.94-6.99 (m, 6H), 6.65-6.71 (m, 8H), 6.536.56 (m, 1H), 6.38-6.41 (m, 2H), 1.56 (s, 18H), 1.36 (s, 18H), 1.28 (s, 18H). 13C {1H}


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NMR was not available due to its poor solubility. HRMS (APCI) Calcd. for C75H79BF2N2, [M + H]+, 1057.6377, found 1057.6334. [b]-Fused BODIPY 5c. Compound 3c (215 mg, 0.2 mmol) were dissolved in dry

dichloromethane (50 mL) then a solution of anhydrous ferric chloride (342mg, 1.2 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 5c as solid in 53% yield (112 mg). Mp >220 ℃. 1H NMR (300 MHz, CDCl3) 1H NMR (500 MHz, CDCl3) δ 8.38 (s, 2H), 8.32 (d, J = 5.4 Hz, 2H), 7.55 (d, J = 4.8 Hz, 8H), 7.33-7.36 (m, 2H), 7.20-7.22 (m, 2H), 7.08-7.14 (m, 5H), 6.93-6.96 (m, 2H), 6.31 (d, J = 1.8 Hz, 2H), 3.37 (s, 6H), 1.40 (s, 36H). 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, 129.9, 129.8, 129.7, 128.5, 126.7, 126.5, 126.1, 125.5, 124.8, 124.7, 124.2, 123.4, 118.9, 118.7, 117.0, 111.3, 55.3, 35.0, 31.4. HRMS (APCI) Calcd. for C69H67BF2N2O2 [M + H]+, 1005.5356, found 1005.5332. [b]-Fused BODIPY 6. Compound 4f (210 mg, 0.20 mmol) were dissolved in dry

dichloromethane (50 mL) then a solution of anhydrous ferric chloride (342 mg, 2.1 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 6 as solid in 58% yield (121 mg).



Mp >220 ℃. 1H NMR (500 MHz, CDCl3) δ 9.19 (d, J = 9.5 Hz, 1H), 7.85-7.88 (m, 2H), 7.78 (d, J = 2.0 Hz, 1H), 7.64 (d, J = 7.5 Hz, 2H), 7.22-7.24 (m, 1H), 7.11 (s, 1H), 7.07-7.09 (m, 1H), 7.05 (s, 2H), 6.99 (d, J = 8.5 Hz, 2H), 6.96 (d, J = 9.0 Hz, 2H), 6.72 (d, J = 8.5 Hz, 2H), 6.69 (s, 1H), 4.00 (s, 3H), 3.96 (s, 3H), 3.91 (s, 3H), 3.76 (s, 3H), 2.44 (s, 3H), 2.27 (s, 6H).

13

C {1H} NMR was not available due to its

poor solubility. HRMS (APCI) Calcd. for C46H39BF2N2O4 [M + H]+, 733.3044, found 733.3046.

Supplementary Information (SI) available: Crystal structure data, additional

photophysical data and spectra, copies of NMR spectra, and high-resolution mass spectra. This material is available free of charge via the Internet at http://pubs.acs.org.

Notes

The authors declare no competing financial interest.

Acknowledgements We thank the National Nature Science Foundation of China (Grants Nos. 21672006, 21672007 and 21872002) for supporting this work. The calculations have been done on the supercomputing system in the Supercomputing Center of USTC.

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