Synthesis and properties of hexaarylated AzaBODIPYs

Accepted Manuscript Synthesis and Properties of Hexaarylated AzaBODIPYs Sunit Kumar, Tamanna K. Khan, Mangalampalli Ravikanth PII:

S0040-4020(15)01151-5

DOI:

10.1016/j.tet.2015.07.074

Reference:

TET 27019

To appear in:

Tetrahedron

Received Date: 22 June 2015 Revised Date:

24 July 2015

Accepted Date: 28 July 2015

Please cite this article as: Kumar S, Khan TK, Ravikanth M, Synthesis and Properties of Hexaarylated AzaBODIPYs, Tetrahedron (2015), doi: 10.1016/j.tet.2015.07.074. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Synthesis and Properties of Hexaarylated AzaBODIPYs Sunit Kumar, Tamanna K. Khan and Mangalampalli Ravikanth* Indian Institute of Technology, Powai, Mumbai, 400076, India, Fax:91-22-5723480;

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Tel: 91-22-5767176; E-mail: [email protected].

Abstract:

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Sterically crowded 1,2,3,5,6,7-hexaarylated azaBODIPYs were synthesized in 2535% yields by coupling 1,3,5,7-tetraaryl azaBODIPYs with six different aryl boronic acids

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under Pd(0) coupling conditions. The moderate reaction yields were attributed to steric congestion caused by two additional aryl groups introduced at the tetraaryl azaBODIPY core. The compounds were characterized by HR-MS, 1D and 2D NMR spectroscopic techniques. The 1H, 19F and 11B NMR studies of hexaarylated azaBODIPYs showed slight upfield shifts

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compared to tetraaryl azaBODIPY indicating the slight alteration of electronic properties of azaBODIPY core upon introduction of two additional aryl groups on tetrararyl azaBODIPY. The absorption and fluorescence bands of hexaarylated azaBODIPYs experienced 7-10 nm

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hypsochromic shifts compared to tetraaryl azaBODIPY. The hexaarylated azaBODIPYs are

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weakly fluorescent with significant reduction in quantum yields and singlet state lifetimes compared to tetraarylated azaBODIPY.

Keywords: AzaBODIPY, hexaarylated azaBODIPY, electronic properties, redox properties and C-C coupling.

1

ACCEPTED MANUSCRIPT Introduction The 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes, popularly known as borondipyrromethanes or BODIPYs, hold great promise for variety of applications in the fields ranging from materials to biology owing to their favorable properties such as high stability,

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absorption and emission in visible region, high extinction coefficients and fluorescence quantum yields and negligible photobleaching.1 One of the best modifications that carried out on BODIPYs is replacing the meso-carbon with nitrogen and the resulted azaBODIPYs2

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exhibit all the valuable characteristics of BODIPYs and also absorbs and emits in NIR region which is important for their potential use in the areas of photodynamic therapy3, sensors4 and

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photosynthetic model systems capable of harvesting energy5.

Recently, we have shown that the electronic and photophysical properties of BODIPYs can be altered significantly by introducing aryl groups at all six pyrrole carbon of the dye.6 The aryl groups at all six pyrrole carbons of BODIPY causes steric crowding at the

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BODIPY core and induces deformation in the BODIPY plane leading to alteration in electronic properties.7 A perusal of literature revealed that azaBODIPYs are generally synthesized as 1,3,5,7-tetraaryl azaBODIPY derivatives and the 2,6-positions of azaBODIPY

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always remained unsubstituted.8 Furthermore, the reports on tetraaryl azaBODIPYs where

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the 2,6-positions were used effectively for synthesis of new azaBODIPY dyes are very few.9 This may be due to the low reactivity of 2,6-positions of azaBODIPY because of steric crowding caused by aryl groups present at the 1,3,5,7-positions. Herein, we made an attempt to introduce two additional aryl groups at 2- and 6- positions to synthesize sterically crowded 1,2,3,5,6,7-hexaarylated azaBODIPYs. Thus, we report our successful synthesis of 1,2,3,5,6,7-hexaarylated

azaBODIPYs

by

coupling

2,6-dibromo-1,3,5,7-tetraaryl

azaBODIPY10 with six different aryl boronic acids under Pd(0) catalyzed Suzuki coupling conditions. The introduction of two additional aryl groups at 2- and 6-positions of 1,3,5,7-

2

ACCEPTED MANUSCRIPT tetraaryl azaBODIPY slightly alters the electronic properties which clearly reflected in their NMR, absorption, fluorescence and electrochemical properties. Results and Discussion: The key precursor, 2,8-dibromo-4,4-difluoro-1,7-bis(4-methoxyphenyl)-3,5-diphenyl4,4-difluoro-1,7-bis(4-

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4-bora-3a,4a,8-triaza-s-indancene 2 was synthesized by treating

methoxyphenyl)-3,5-diphenyl-4-bora-3a,4a,8-triaza-s-indancene 1 with 2.2 equivalents of Nbromosuccinimide in CHCl3 at room temperature and afforded in 90% yield. The 1,2,3,5,6,7-

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hexaaryl azaBODIPYs 3-8 were prepared by reacting 2 in toluene/THF/H2O mixture (1:1:1) with six different aryl boronic acids in the presence of Pd(PPh3)4/Na2CO3 at 80º C for 12 h

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(scheme 1). The progress of the reaction was monitored by TLC analysis.

Scheme 1 As the reaction progressed, the TLC analysis showed an appearance of more polar spot corresponding to the desired hexaaryl azaBODIPY along with small amounts of unreacted starting material and the debrominated azaBODIPY compound. The crude reaction mixtures 3

ACCEPTED MANUSCRIPT were subjected to silica gel column chromatographic purification and afforded pure compounds 3-8 in 25-35% yields.

We varied the reaction conditions by changing the

catalyst, reaction time, temperature etc. but no improvement in the yields of hexaarylated azaBODIPYs 3-8 was noticed. The steric congestion at the azaBODIPY core could be one of

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the reasons for moderate yields of hexaarylated azaBODIPYs 3-8. The identities of compounds 3-8 were confirmed by corresponding molecular ion peak in HR-MS spectra. The 13

C,

techniques. The comparison of

H,

11

B and

19

B and

19

F NMR spectroscopic

F NMR spectra 1,2,3,5,6,7-hexaaryl

3,5-diphenyl-1,7-di(p-anisyl) azaBODIPY 1 recorded in CDCl3 are

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azaBODIPY 5 and

1

11

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compounds 3-8 were further characterized by 1H,

shown in fig. 1 and the relevant comparison data for all compounds 1-8 are presented in Table 1. In 1H NMR of 3,5-diphenyl-1,7-di(p-anisyl) aza-BODIPY 1, the four aryl groups present at the azaBODIPY core appeared as five sets of resonances which were identified and

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assigned using 1H-1H COSY and NOESY NMR spectra.

Table 11H NMR (type b and type d), 11B NMR and 19F NMR data of compound 1 and 3-8

Compound

1

H NMR (ppm)

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recorded in CDCl3.

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B NMR

19

F

NMR type d

(ppm)

(ppm)

1

8.18

8.10

1.22

-130.95

3

7.45

7.98

0.83

-131.40

4

7.46

7.40

0.82

-131.47

5

7.48

7.42

0.80

-131.44

6

7.43

7.39

0.79

-131.41

7

8.01

7.96

0.41

-131.54

8

7.58

7.45

0.62

-131.62

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type b

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ACCEPTED MANUSCRIPT The 2,6-pyrrole protons (c type) in compound 1 appear as singlet at 6.90 ppm. However, upon introduction of two aryl groups at 2,6-positions in compound 5, the resonance at 6.90

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ppm was absent due to substitution of aryl groups and the aryl protons present at the

Fig. 1

1,3,5,7-positions also experienced upfield shifts compared to 1. For example, in compound 1, the type b and type d protons of aryl groups appear at 8.18 and 8.10 ppm, respectively. However, in hexaarylated azaBODIPYs such as 5, these two types of protons (type b and type d) experienced upfield shifts and appear at 7.48 and 7.42 ppm respectively. The other aryl protons also showed slight upfileld shifts in hexaarylated azaBODIPY 5 compared to tetrarayl azaBODIPY 1. The compounds 3-8 also showed similar upfield shifts (Table 1).

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ACCEPTED MANUSCRIPT Furthermore, the typical triplet observed at 0.80 ppm in 11B NMR and quartet at -131.42 ppm in 19F NMR of compound 5 were also slightly upfield shifted as compared to compound 1. All these observations indicate that the introduction of two additional aryl groups at 2,6positions of 1,3,5,7-tetraryl azaBODIPY induces steric congestion at the azaBODIPY core

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leading to alteration in electronic properties. Spectral and electrochemical properties

The spectral and electrochemical properties of hexaarylated aza-BODIPYs 3-8 were

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studied along with reference compound tetraaryl aza-BODIPY 1 and data are tabulated in Table 2. The comparison of absorption spectra of compound 3 with compound 1 recorded

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using same concentration is shown in Fig. 2a. The compounds 3-8 showed same absorption

Table 2. Absorption and fluorescence data of compounds 1-8 recorded in toluene. Concentration of solution used is 1x10-5 M. Electrochemical (V) data of compounds 1-8

scan speed. λem

(nm)

(nm)

663

2

654

Φ

τ

Electrochemical data

(ns)

E1/2ox(V)

E1/2red (V)

697

4.86

0.24

1.56

1.33

-0.24

-1.04

691

4.91

≤ 0.01

-

1.64

-0.08

-0.94

656

695

4.92

0.04

0.26

1.48

-0.25

-1.11

656

709

4.70

≤ 0.01

0.23

1.49

-0.25

-1.14

654

750

4.74

≤ 0.01

0.08

1.39

-0.26

-1.14

653

692

4.49

≤ 0.01

0.07

1.48

-0.21

-1.08

7

654

688

4.88

0.05

0.06

1.59

-0.12

-0.96

8

656

716

4.84

≤ 0.01

0.14

1.45

-0.25

-1.11

3 4 5 6

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1

log ε

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λabs

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recorded in CH2Cl2 using 0.1 M TBAP as the supporting electrolyte recorded at 50 mVs-1

log(ε/mol-1dm3 cm-1)-molar extinction coefficient, λabs (absorption maxima), λem (emission maxima), Φ (quantum yield), τ (lifetime).

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ACCEPTED MANUSCRIPT features like compound 1 but experienced 7-10 nm blue shift and slight changes in the absorption coefficients which is attributed to the slight alteration of electronic properties because of steric congestion caused by additional two aryl groups at the 2,6-positions of 1,3,5,7-tetraaryl azaBODIPY. The comparison of steady state fluorescence spectra of

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compound 3 with compound 1 is shown in Fig. 2b. The compound 1 showed one broad emission band at 663 nm with a quantum yield of 0.32. The hexaarylated azaBODIPYs 3-8 showed similar broad emission band which either experienced bathochromic or

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hypsochromic shift with significant reduction in quantum yields. Thus, the hexaarylated

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azaBODIPYs 3-8 are weakly fluorescent than tetraarylated azaBODIPY 1.

Fig. 2

The weak fluorescence of hexaarylated azaBODIPYs was tentatively attributed to the distortion of azaBODIPY core because of steric crowding caused by aryl groups which enhances non-radiative decay processes leading to low quantum yields.

The singlet state

lifetimes of compounds 3-8 and compound 1 were measured using time correlated single photon counting (TCSPC) technique. All compounds 3-8 and 1 were excited at 635 nm and emissions were detected at emission wavelengths depending on the emission peak position of

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ACCEPTED MANUSCRIPT the hexaarylated aza_BODIPYs. The representative fluorescence decay profile of compound 3 is shown in Fig. 3. The tetraarylated aza-BODIPY 1 showed single exponential decay with singlet state lifetime of 1.54 ns. However, the hexaarylated BODIPYs 3-8 showed either mono- or bi-exponential decays with lifetimes ranging from 0.06 to 0.26 ns. The significant

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decrease in singlet state lifetime of compounds 3-8 compared to compound 1 is in agreement

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with the steady state fluorescence data

Counts

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1000

100

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3 2 1 0 -1 -2 -3 -4 5.5

.

AC C

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Ri

10

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

Time (ns) Fig. 3

The redox properties of compounds 3-8 along with compound 1 are probed through cyclic voltammetric studies using terrabutylammonium perchlorate as supporting electrolyte in dichloromethane solvent. The comparison of cyclic voltamograms of compound 1 and 3 are shown in Fig. 4 and the relevant data are included in Table 2. The compound 1 showed

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ACCEPTED MANUSCRIPT one reversible reduction at -0.24 V, one quasi reversible reduction at -1.04 V and one

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irreversible oxidation at 1.13 V.

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Fig. 4

The compounds 3-8 also showed one reversible and one quasi reversible reductions and one quasi reversible oxidation with negligible shifts in redox potentials indicating the compounds

Summary

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3-8 are robust and stable under redox conditions.

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In conclusion, we prepared a series of hexaarylated azaBODIPYs by coupling 2,6-

dibromo-1,3,5,7-tetraphenyl azaBODIPY 2 with various aryl boronic acids under Pd(0) coupling conditions. The yields of the products were low to moderate because of low reactivity due to steric congestion at the azaBODIPY core. The absorption and fluorescence bands of hexaarylated azaBODIPYs experienced 7-10 nm hypsochromic shift compared to tetraarylated azaBODIPYs. The hexaarylated azaBODIPYs are weakly fluorescent with low quantum yields and singlet state lifetimes compared to tetraarylated azaBODIPYs. Thus, the

9

ACCEPTED MANUSCRIPT studies indicated that the introduction of two additional aryl groups at the 2,6-positions of 1,3,5,7-tetraaryl azaBODIPY alters the electronic properties because of steric congestion at the azaBODIPY core. Experimental Section

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General The chemicals such as BF3·OEt2, Triethylamine (TEA), and 2, 3-dichloro-5,6dicyano-1,4-benzoquinone (DDQ) were used as obtained from Aldrich. All other chemicals used for the synthesis were reagent grade unless otherwise specified. Column

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chromatography was performed on silica (60-120 mesh). The 1D, 2D, 13C, 11B and 19F NMR

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spectra were recorded in CDCl3 on Bruker 400 and 500 MHz instrument. The frequency for 13

C nucleus is 100 MHz, 470.54 MHz for

19

F nucleus, and 160.46 MHz for

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Tetramethylsilane [Si(CH3)4] was used as an internal standard for 1H and

B nucleus.

13

C NMR,

tetrafluorotoluene as a external standard for 19F NMR and boric acid as an external standard 11

B NMR. Absorption and steady state fluorescence spectra were obtained by Varian

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for

instruments. The fluorescence quantum yields (Φ) were estimated from the emission and absorption spectra by comparative method at the excitation wavelength of 630 nm using 3,5-

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dianisyl -1,7-di(p-phenyl) azaBODIPY (Φ = 0.36 in chloroform)11 as standard. The time resolved fluorescence decay measurements were carried out at magic angle using a

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picosecond diode laser based time correlated single photon counting (TCSPC) fluorescence spectrometer from IBH, UK. All decays were fitted to single exponential. The good fit criteria were low chi-square (1.0) and random distributions of residuals cyclic voltammetric (CV) studies were carried out with BAS electrochemical system utilizing the three electrode configuration consisting of a glassy carbon (working electrode), platinum wire (auxiliary electrode) and saturated calomel (reference electrode) electrodes. The experiments were done in dry dichloromethane using 0.1 M tetrabutylammonium perchlorate as supporting electrolyte. The high resolution mass spectra (HRMS) were recorded with a Bruker maxis 10

ACCEPTED MANUSCRIPT Impact and Q-Tof micro mass spectrometer. For UV-vis and fluorescence titrations, the stock solution of all compounds (1×10-5 M) were prepared by using HPLC grade toluene solvent.

General Method for the synthesis of compounds 3-8: 2,8-dibromo-4,4-difluoro-1,7-bis(4-

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methoxyphenyl)-3,5-diphenyl-4-bora-3a,4a,8-triaza-s-indancene 2 (100 mg, 0.14 mmol), appropriate arylboronic acid (55-85 mg, 0.42 mmol), and Na2CO3 (60 mg, 0.56 mmol) were taken in a 1:1:1 mixture of water/THF/toluene (20 mL) in a 100 mL round-bottomed flask

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fitted with a reflux condenser and stirred under N2 for 5 min. A catalytic amount of Pd(PPh3)4 (16 mg, 0.014 mmol) was added and the reaction mixture was refluxed at 80° C for 6-10 h.

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After completion of the reaction, as judged by TLC analysis, the reaction mixture was diluted with water (5 mL) and extracted with dichloromethane. The combined organic layers were washed with water and brine and dried over anhydrous Na2SO4. The solvent was evaporated, and the crude product was purified on a silica gel column chromatography (80:15, petroleum

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ether/ethyl acetate) to afford polyarylated azaBODIPYs 3-8 (25-35%) as brown solids. 4,4-difluoro-1,7-bis(4-methoxyphenyl)-2,3,5,6-tetraphenyl-4-bora-3a,4a,8-triaza-sindancene (3). Yield 30% (31 mg); 1H NMR (400 MHz, CDCl3, δ in ppm) 3.81 (6H, s,

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OMe), 6.79 (2H, q, 3J (H, H) = 6.9 Hz, Ar), 6.96-6.99 (4H, m, Ar), 7.17-7.19 (6H, m, Ar), 7.21-7.24 (2H, m, Ar), 7.27-7.31 (4H, m, Ar), 7.40-7.42 (4H, m, Ar), 7.45-7.48 (6H, m, Ar); F NMR (470 MHz, CDCl3, δ in ppm) -131.40 (q, 3J (B, F) = 31 Hz);

AC C

19

MHz, CDCl3, δ in ppm) 0.84 (t, 3J (B, F)= 30 Hz);

13

11

B NMR (160.46

C NMR (100 MHz, CDCl3, δ in ppm)

55.4, 113.6, 114.4, 124.6, 127.4, 127.8, 128.5 129.8, 130.5, 130.8, 130.9, 131.1, 132.8, 133.4, 160.2.; HRMS (ESI, m/z) [M+-H] found 710.2797 C46H35BF2N3O2 requires 710.2793. 4,4-difluoro-1,7-bis(4-methoxyphenyl)-3,5-diphenyl-2,6-di-p-tolyl-4-bora-3a,4a,8-triazas-indancene (4). Yield 29% (28 mg); 1H NMR (400 MHz, CDCl3, δ in ppm) 2.30 (3H, s, CH3), 2.40 (3H, s, CH3), 3.80 (3H, s, OCH3), 3.81 (3H, s, OCH3), 6.71-6.74 (2H, q, 3J (H, H)

11

ACCEPTED MANUSCRIPT = 6.9 Hz, Ar), 6.79 (2H, d, 3J (H, H) = 6.9 Hz, Ar), 6.95 (d, 2H, 3J (H, H) = 6.9 Hz), 7.307.62 (4H, m, Ar), 7.23-7.25 (2H, m, Ar), 7.28-7.32 (4H, m, Ar), 7.38-7.42 (4H, m, Ar), 7.457.48 (4H, m, Ar); 19F NMR (470 MHz, CDCl3, δ in ppm) -131.97 (q, 3J (B, F) = 30 Hz); 11B NMR (160.46 MHz, CDCl3, δ in ppm) 0.82 (t, 3J (B, F)= 30 Hz);

13

C NMR (100 MHz,

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CDCl3, δ in ppm) 55.1, 55.3, 113.7, 113.5, 113.8, 114.32, 124.6, 128.5, 129.5, 130.4, 130.9, 131.27, 132.5, 140.4, 145.3, 158.7, 159.9.; HRMS (ESI, m/z) [M+-H] found 738.3113 C48H39BF2N3O2 requires 738.3106.

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4,4-difluoro-1,2,6,7-tetrakis(4-methoxyphenyl)-3,5-diphenyl-4-bora-3a,4a,8-triaza-sindancene (5). yield 35 % (33 mg); 1H NMR (400 MHz, CDCl3, δ in ppm) 3.76 (6H, s,

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OCH3), 3.81 (6H, s, OCH3), 6.71 (4H, q, 3J(H,H) = 6.8 Hz, Ar), 6.80 (4H, q, 3J (H,H) = 6.9 Hz, Ar), 6.88 (4H, q, 3J (H,H) = 6.7 Hz, Ar), 7.24-7.30 (6H, m, Ar), 7.41-7.43 (4H, m, Ar), 7.48 (4H, q, 3J (H,H) = 7.0 Hz, Ar); 19F NMR (470 MHz, CDCl3, δ in ppm) -131.44 (q, 3J (B, F) = 30 Hz); 11B NMR (160.46 MHz, CDCl3, δ in ppm) 1.20 (t, 3J (B, F)= 31Hz); 13C NMR

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(100 MHz, CDCl3, δ in ppm) 55.1, 55.3, 113.7, 113.5, 113.8, 114.32, 124.6, 128.5, 129.5, 130.4, 130.9, 131.27, 132.5, 140.4, 145.3, 158.7, 159.9; HRMS (ESI, m/z) [M+-Na] found 792.2824 C48H38BF2N3NaO4 requires 792.2825.

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4,4-difluoro-2,6-bis(4-fluorophenyl)-1,7-bis(4-methoxyphenyl)-3,5-diphenyl-4-bora3a,4a,8-triaza-s-indancene (6). Yield 25% (24 mg); 1H NMR (400 MHz, CDCl3, δ in ppm)

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3.79 (3H, s, OCH3), 3.82 (3H, s, OCH3), 6.75 (2H, q, 3J(H, H) = 6.8 Hz, Ar), 6.80 (2H, q, 3J (H, H) = 6.9 Hz, Ar), 6.86-6.89 (2H, m, Ar), 6.92-6.95 (2H, m, Ar), 6.99-7.02 (2H, m, Ar), 7.15-7.18 (2H, m, Ar), 7.23-7.27 (2H, m, Ar), 7.30-7.36 (6H, m, Ar), 7.39-7.40 (2H, m, Ar), 7.40-7.45 (4H, m, Ar); 19F NMR (470 MHz, CDCl3, δ in ppm) -131.44 (q, 3J (B, F) = 30 Hz), -114.3 (m, Ar), -114.8 (m, Ar); 11B NMR (160.46 MHz, CDCl3, δ in ppm) 0.79 (t, 3J (B, F)= 30 Hz);

13

C NMR (100 MHz, CDCl3, δ in ppm) 55.4, 55.5, 113.2, 113.7, 114.3, 115.6,

115.27, 115.9, 124.4, 128.0, 128.7, 128.8, 129.3, 129.4, 129.9, 130.5, 131.4, 132.4, 132.5,

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ACCEPTED MANUSCRIPT 132.7, 139.5, 141.2, 145.4, 154.4, 158.9, 159.7, 160.4, 161.2, 163.1; HRMS (ESI, m/z) [M+Na] found 746.2604 C46H33BF4N3O2 requires 746.2586. 4,4-difluoro-1,7-bis(4-methoxyphenyl)-2,6-bis(4-nitroophenyl)-3,5-diphenyl-4-bora3a,4a,8-triaza-s-indancene (7). Yield 33% (30 mg); 1H NMR (400 MHz, CDCl3, δ in ppm)

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3.82 (3H, s, OCH3), 3.90 (3H, s, OCH3), 6.81 (2H, d, 3J (H, H) = 6.9 Hz, Ar), 7.01 (2H, q, 3J (H, H) = 7.0 Hz, Ar), 7.09 (2H, q, 3J (H, H) = 6.9 Hz, Ar), 7.24-7.28 (2H, m, Ar), 7.33-7.37 (8H ,m, Ar), 7.46-7.51 (4H, m, Ar), 7.72-7.74 (2H, m, Ar), 7.96 (2H, q, 3J (H, H) = 6.9 Hz,

(q, 3J (B, F) = 64.0 Hz);

B NMR (128.38 MHz, CDCl3, δ in ppm) 0.41 (t, 3J (B, F)= 30.8

13

C NMR (100 MHz, CDCl3, δ in ppm) 55.5, 55.6, 113.9, 114.0, 123.5, 123.7, 127.8,

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Hz);

11

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Ar), 8.01 (2H, q, 3J (H, H) = 6.9 Hz, Ar); 19F NMR (376.49 MHz, CDCl3, δ in ppm) 131.54

128.1, 128.3, 129.4, 129.8, 130.0, 130.2, 130.5, 130.6, 130.8, 131.5, 132.7, 132.7, 140.5, 142.8, 144.7, 146.9, 160.9, 161,2; HRMS (ESI, m/z) [M+] found 799.2416 C46H32BF2N5O6 requires 799.2395.

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2,6-di([1,1’-biphenyl]-4-yl)4,4-difluoro-1,7-bis(4-methoxyphenyl)-3,5-diphenyl-4-bora3a,4a,8-triaza-s-indancene (8). Yield 31% (26 mg); 1H NMR (400 MHz, CDCl3, δ in ppm) 3.80 (3H, s, OCH3), 3.90 (3H, s, OCH3), 6.78-6.82 (2H, m, Ar), 6.99-7.04 (5H, m, Ar),

EP

7.23-7.30 (5H, m, Ar), 7.31-7.34 (2H, m, Ar), 7.39-7.52 (14H, m, Ar), 7.55-7.59 (4H, m, Ar), 7.72-7.74 (2H, m, Ar), 7.95 (2H, q, 3J (H, H) = 6.9 Hz, Ar); 19F NMR (470 MHz, CDCl3, δ in

AC C

ppm) -131.62 (q, 3J(B,F) = 29 Hz); 11B NMR (160.46 MHz, CDCl3, δ in ppm) 0.62 (t, 3J (B, F)= 29 Hz). 13C NMR (100 MHz, CDCl3, δ in ppm) 55.5, 55.6, 113.7, 114.4, 124.8, 125.3, 126.9, 127.0, 127.5, 127.9, 128.7, 128.9, 129.7, 130.6, 130.9, 131.0, 131.1, 132.8, 139.7, 140.5, 160.2, 161.3; HRMS (ESI, m/z) [M+-H] found 862.3410 C58H43BF2N3O2 requires 862.3420.

13

ACCEPTED MANUSCRIPT Acknowledgements We thank the Department of Science and Technology, Government of India for financial support and S. K thanks the UGC for fellowship.

1.

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References a) Treibs, A.; Kreuzer, F. H. Liebigs Ann. Chem. 1968, 718, 208; b) Loudet, A.; Burgess, K. Chem. Rev. 2007, 107, 4891; c) Boens, N.; Leen, V.; Dehaen, W. Chem. Soc. Rev.

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2012, 41, 1130; d) Ulrich, G.; Ziessel, R.; Harriman, A. Angew. Chem. Int. Ed. 2008, 47, 1184; e) Lakshmi, V.; Rao, M. R.; Ravikanth, M. Org. Biomol. Chem. 2015, 13, 2501. a) Tasior, M.; O'Shea, D. F. Bioconjugate Chem. 2010, 21, 1130; b) Grossi, M.; Palma,

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A.; McDonnell, S. O.; Hall, M. J.; Rai, D. K.; Muldoon, J.; O’Shea, D. F. J. Org. Chem. 2012, 77, 9304; c) Lu, H.; Shimizu, S.; Mack, J.; Shen, Z.; Kobayashi, N. Chem. -Asian J. 2011, 6, 1026.

a) Kamkaew, A.; Lim, S. H.; Lee, H. B.; Kiew, L. V.; Chung, L. Y.; Burgess, K. Chem.

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Soc. Rev. 2013, 42, 77; b) Awuah, S. G.; You, Y. RSC Advances 2012, 2, 11169; b) Oleinick, N. L.; Morris, R. L.; Belichenko, I. Photochem. Photobiol. Sci. 2002, 1, 1; c)

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Dougherty, T. J. Semin. Surg. Oncol. 1986, 2, 24. 4. a) Liu, H.; Mack, J.; Guo, Q.; Lu, H.; Kobayashi, N.; Shen, Z. Chem. Commun. 2011, 47,

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12092; b) Adarsh, N.; Krishnan, M. S.; Ramaiah, D. Anal. Chem. 2014, 86, 9335; c) Wu, D.; O’Shea, D. F.; Org. Lett. 2013, 15, 13; d) Jokic, T.; Borisov, S. M.; Saf, R.; Nielsen, D. A.; Kühl, M.; Klimant, I. Anal. Chem. 2012, 84, 6723; e) Zou, B.; Liu, H.; Mack, J.; Wang, S.; Tian, J.; Lu, H.; Liaand, Z.; Shen, Z. RSC Adv. 2014, 4, 53864. 5.

a) Ulrich, G.; Ziessel, R.; Harriman, A. Angew. Chem. Int. Ed. 2008, 47, 1184; b) Ziessel, R.; Harriman, A. Chem. Commun. 2011, 47, 611; c) El-Khouly, M. E.; Fukuzumi, S.; D’Souza, F.; ChemPhysChem 2014, 15, 30; d) Bessette, A.; Hanan, G. S. Chem. Soc. Rev. 2014, 43, 3342; e) Bottari, G.; de la Torre, G.; Guldi, D. M.; Torres, T. 14

ACCEPTED MANUSCRIPT Chem. Rev. 2010, 110, 6768; f) Balzani, V.; Credi, A.; Venturi, M. ChemSusChem 2008, 1, 26; g) Imahori, H.; Umeyama, T.; Kei, K.; Yuta, T. Chem. Commun. 2012, 48, 4032; h) D’Souza, F.; Ito, O. Chem. Soc. Rev. 2012, 41, 86; c) Guldi, D. M.; Costa, R. D. J. Phys. Chem. Letts. 2013, 4, 1489; i) Satake, A.; Kobuke, Y. Org. Biomol. Chem. 2007, 5, 1679.

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6. a) Lakshmi, V.; Ravikanth, M. Chem. Phys. Lett. 2013, 564, 93; b) Lakshmi, V.; Ravikanth, M. Eur. J. Org. Chem. 2014, 5757; c) Lakshmi V.; Ravikanth, M. RSC Adv. 2014, 4, 44327.

Lakshmi, V.; Ravikanth, M. Chem. Phys. Lett. 2013, 564, 93.

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8. a) Bandi, V.; Ohkubo, K.; Fikuzumi, S.; D’Souza, F. Chem. Commun. 2013, 49, 2867; b)

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Khan, T. K.; Sheokand, Agarawal, P. N. Eur. J. Org. Chem. 2014, 1416; c) Bandi, V.; Gobeze, H. B.; Karr, P. A.; D’Souza, F. J. Phys. Chem. C. 2014, 118, 18969; d) Yoshii, R.; Yamane, H.; Nagai, A.; Tanaka, K.; Taka, H.; Kita, H.; Chujo, Y. Macromolecules. 2014, 47, 2316; e) Zhang, X. –X.; Wang, Z.; Yue, X.; Ma, Y.; Kiesewetter, D. O.; Chen,

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X. Mol. Pharmaceutics. 2013, 10, 1910; f) Murtagh, J.; Frimannsson, D. O.; O’Shea, D. F. Org. Lett. 2009, 11, 23.

9. a) Gao, L.; Tang, S.; Zhu, L.; Sauvé, G. Macromolecules. 2012, 45, 7404; b) Yang, P.;

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Zhao, W. J.; Huang, D.; Yi, X. J. Mater. Chem. 2012, 22, 20273; c) Ma, X.; Mao, X.;

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Zhang, S.; Huang, X.; Cheng, Y.; Zhu, C. Polym. Chem. 2013, 4, 520; d) Senevirathna, W.; Sauvé, G. J. Mater. Chem. C. 2013, 1, 6684. 10. Gorman, A.; Killoran, J.; O’Shea, C.; Kenna, T.; Gallagher, W. M.; O’Shea, D. F. J. Am. Chem. Soc. 2004, 126, 10619. 11. Killoran, J.; Allen, L.; Gallagher, J. F.; Gallagherb, W. M.; O’Shea, D. F. Chem. Commun. 2002, 17, 1862.

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Legends Scheme 1. Synthesis of compounds 3-8. Table 1. 1H NMR (type b and type d), 11B NMR and 19F NMR data of compound 1 and 3-8

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recorded in CDCl3.

Table 2. Absorption and fluorescence data of compounds 1-8 recorded in toluene. Concentration of solution used is 1x10-5 M. Electrochemical (V) data of compounds 1-8

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recorded in CH2Cl2 using 0.1 M TBAP as the supporting electrolyte recorded at 50 mVs-1 scan speed.

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Fig. 1. Comparison of (i) partial 1H, (ii) 11B and (iii) 19F NMR spectra of AzaBODIPY 1 and 5 recorded in CDCl3.

Fig. 2. Comparison of absorption (a) and fluorescence spectra (b) of tetraaryl azaBODIPY 1 (red line) and hexaaryl azaBODIPY 3 (black line) recorded in toluene.

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Fig. 3. Fluorescence-decay profile and the corresponding weighted residual-distribution fit of the fluorescence decay of azaBODIPY 3 in toluene. The excitation wavelength used was 635

toluene.

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nm and emission was detected at the emission-peak maxima (695 nm) of azaBODIPY 3 in

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Fig. 4. Comparison of cyclic voltammogram spectra of tetraaryl azaBODIPY 1 (red line) and hexaaryl azaBODIPY 3 (black line) recorded in CH2Cl2 using 0.1 M TBAP as the supporting electrolyte recorded at 50 mVs-1 scan rate.

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Graphical Abstract Synthesis and Properties of Hexaarylated AzaBODIPYs Sunit Kumar, Tamanna K. Khan and Mangalampalli Ravikanth*

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Indian Institute of Technology, Powai, Mumbai, 400076, India, Fax:91-22-5723480; Tel: 9122-5767176; E-mail: [email protected].

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A series of 1,2,3,5,6,7-hexaarylated azaBODIPYs were synthesized by coupling of 2,6-

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dibromo-1,3,5,7-tetraaryl azaBODIPY with different substituted aryl boronic acids under

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Pd(0) coupling conditions and their spectral and electrochemical properties were investigated.

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Supporting Information Synthesis and Properties of Hexaarylated AzaBODIPYs

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Sunit Kumar, Tamanna K. Khan and Mangalampalli Ravikanth*

Indian Institute of Technology, Powai, Mumbai, 400076, India, Fax:91-22-5723480;

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Contents

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Tel: 91-22-5767176; E-mail: [email protected].

Page No.

Figure S1. HR mass spectrum of compound 3

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Figure S2.1H NMR spectrum of compound 3 in CDCl3

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Figure S3.13C NMR spectrum of compound 3 in CDCl3

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Figure S4.19F NMR spectrum of compound 3 in CDCl3

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5

Figure S5.11B NMR spectrum of compound 3 in CDCl3

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Figure S6. HR mass spectrum of compound 4

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Figure S7.1H NMR spectrum of compound 4 in CDCl3

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Figure S8.13C NMR spectrum of compound 4 in CDCl3

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Figure S9.19F NMR spectrum of compound 4 in CDCl3

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Figure S10.11B NMR spectrum of compound 4 in CDCl3

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Figure S11.HR mass spectrum of compound 5

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Figure S12.13C NMR spectrum of compound 5 in CDCl3

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Figure S13.HR mass spectrum of compound 6

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Figure S14.1H NMR spectrum of compound 6 in CDCl3

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Figure S15. 13C NMR spectrum of compound 6 in CDCl3

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Figure S16. 19F NMR spectrum of compound 6 in CDCl3

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Figure S1711B NMR spectrum of compound 6 in CDCl3

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Figure S18 HR mass spectrum of compound 7

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Figure S19 1H NMR spectrum of compound 7 in CDCl3

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Figure S20 13C NMR spectrum of compound 7 in CDCl3

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Figure S21 19F NMR spectrum of compound 7 in CDCl3

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Figure S22 11B NMR spectrum of compound 7 in CDCl3

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Figure S23 HR mass spectrum of compound 8

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Figure S241H NMR spectrum of compound 8 in CDCl3

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Figure S25 13C NMR spectrum of compound 8 in CDCl3

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Figure S2619F NMR spectrum of compound 8 in CDCl3

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Figure S2711B NMR spectrum of compound 8 in CDCl3

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Figure S1. HR mass spectrum of compound 3

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N N

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OCH 3

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H3CO

Figure S2. 1H NMR spectrum of compound 3 in CDCl3

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N N

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OCH 3

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Figure S3. 13C NMR spectrum of compound 3 in CDCl3

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Figure S4. 19F NMR spectrum of compound 3 in CDCl3

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H3CO

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3

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Figure S5. 11B NMR spectrum of compound 3 in CDCl3

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H3CO

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CH3

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Figure S6. HR mass spectrum of compound 4

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H3CO

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CH3

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Figure S7.1H NMR spectrum of compound 4 in CDCl3

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H3CO

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4

CH3

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Figure S8.13C NMR spectrum of compound 4 in CDCl3

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Figure S9.19F NMR spectrum of compound 4 in CDCl3

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OCH 3

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CH3

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Figure S10.11B NMR spectrum of compound 4 in CDCl3

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Figure S11.HR mass spectrum of compound 5

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Figure S12.13C NMR spectrum of compound 5 in CDCl3

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Figure S13.HR mass spectrum of compound 6

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Figure S14. 1H NMR spectrum of compound 6 in CDCl3

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Figure S15. 13C NMR spectrum of compound 6 in CDCl3

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Figure S16. 19F NMR spectrum of compound 6 in CDCl3

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Figure S1711B NMR spectrum of compound 6 in CDCl3

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Figure S18 HR mass spectrum of compound 7

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Figure S19 1H NMR spectrum of compound 7 in CDCl3

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Figure S20 13C NMR spectrum of compound 7 in CDCl3

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Figure S21 19F NMR spectrum of compound 7 in CDCl3

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Figure S22 11B NMR spectrum of compound 7 in CDCl3

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Figure S23 HR mass spectrum of compound 8

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Figure S231H NMR spectrum of compound 8 in CDCl3

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Figure S25 13C NMR spectrum of compound 8 in CDCl3

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Figure S2419F NMR spectrum of compound 8 in CDCl3

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Figure S2511B NMR spectrum of compound 8 in CDCl3