Synthesis and Unique Optical Properties of Selenophene-BODIPYs

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Synthesis and Unique Optical Properties of Selenophene-BODIPYs and Their Linear Oligomers Daisuke Taguchi, Takashi Nakamura, Hiroaki Horiuchi, Makoto Saikawa, and Tatsuya Nabeshima J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b00782 • Publication Date (Web): 10 Apr 2018 Downloaded from http://pubs.acs.org on April 10, 2018

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The Journal of Organic Chemistry

Synthesis and Unique Optical Properties of Selenophene-BODIPYs and Their Linear Oligomers Daisuke Taguchi,† Takashi Nakamura,† Hiroaki Horiuchi,‡ Makoto Saikawa,† Tatsuya Nabeshima*,† †

Graduate School of Pure and Applied Sciences and Tsukuba Research Center for Energy Materials Science (TREMS), University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan

‡

Division of Molecular Science, Graduate School of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan

ABSTRACT: A series of selenophene-substituted BODIPY monomers and selenophene-linked BODIPY oligomers was synthesized. The synthesized BODIPYs show good absorption/emission properties in the red to near-infrared region. Furthermore, some of the selenophenyl BODIPYs are not only useful fluorophores, but also good photosensitizers to produce singlet oxygen.

Boron-dipyrrin complexes (BODIPYs) show a strong absorption/emission and high chemical stability, thus they have been studied for applications in various fields such as bioimaging, sensors, and solar cells.1–3 The unsubstituted BODIPY, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, shows an absorption and emission at 505 nm and 526 nm in chloroform, respectively.4 Recently, the BODIPYs that have absorptions and emissions in the red to near-infrared region (650–900 nm) have attracted more increasing attention.5,6 To increase the absorption and emission wavelengths, various chemical modifications of BODIPY have been applied, such as the introduction of substituents to its 3,5-positions,7–9 fusion of the aromatic rings to its pyrroles,10,11 replacement of the methine group at the 8-position with nitrogen (azaBODIPY),12 oligomerization/polymerization of its core,13–15 and their combination.16,17 We have reported that linking of the BODIPY cores by benzene rings or thiophene rings is effective to shift the absorption/emission to the near-infrared region.18,19 In this study, we introduced selenophene as a substituent into the BODIPY skeleton. Emission of the fluorescent molecules containing selenophene often appears at a longer wave-

length compared to that of the thiophene analogs.20,21 Generally, heavier elements usually result in significant spin-orbit coupling interactions to promote the intersystem crossing, which quenches the fluorescence. Actually, selenium contributes to effectively quench the fluorescence compared to sulfur.20–22 Very interestingly, however, some selenium compounds show higher fluorescence quantum yields than the sulfur analogs.23 BODIPYs containing heavy atoms exhibit a photosensitizing effect,24,25 which is applicable to photodynamic therapy for cancer.26 When such sensitizers absorb red to near-infrared light that is transparent to biological tissue, they become more valuable.27 Thus, we were encouraged to synthesize selenophenyl BODIPYs that would show unique photophysical properties. We have synthesized selenophenyl BODIPY monomers SB1a–e and selenophene-linked BODIPY oligomers SB2a– SB3a (Schemes 1 and 2). The synthesized BODIPYs showed good absorption/emission properties in the red to near-infrared region and photosensitized generation of singlet oxygen.

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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

Scheme 1. Synthesis of selenophene-BODIPY monomers

The introduction of thiophenyl groups into the 3,5-position of BODIPY resulted in larger bathochromic shifts in their absorption and emission compared to the 3,5-diphenyl substituted BODIPYs.19 Hence, the BODIPY’s 3,5-positions were expected to be the most appropriate to connect selenophene units to achieve larger bathochromic shifts. In order to investigate the influence of substituents at the 8-position on the optical properties, we synthesized 3,5-diselenophenyl BODIPYs bearing aryl substituents, SB1a and SB1b. 2,6Diselenophenyl BODIPY SB1c and 2,3,5,6-tetraselenophenyl BODIPY SB1d were synthesized to clarify the effect of the position of the selenophenyl group on the optical properties. Iodoselenophenyl BODIPY SB1e was also prepared to examine a combination effect of the substituents on the photophysical properties and sensitizing efficiency. Synthesis of the BODIPY monomers is shown in Scheme 1. SB1a and SB1b were synthesized from 3,5-dibromo BODIPY 428 and 529, respectively, by the Suzuki-Miyaura cross coupling reaction with 2-selenenopheneboronic acid. SB1c was similarly obtained from 2,6-dibromo BODIPY 630. Tetraselenophenyl BODIPY SB1d was synthesized from 2,6-dibromo3,5-diselenophenyl BODIPY 8, which was derived via bromination and boron complexation of the diselenophenyl dipyrrin 7. The iodinated selenophene-BODIPY SB1e was prepared by selective iodination of the α-position of the selenophene ring of SB1a with N-iodosuccinimide. Selenophene-linked BODIPY oligomers SB2a and SB3a (dimer and trimer) were synthesized in 8% and 4% yields, respectively, by the cross coupling of 3,5-dichloro BODIPY 931 and selenophene via direct C–H activation of the 2-position of selenophene,32 followed by purification with silica gel, then gel permeation chromatography (Scheme 2). The modified method of direct arylation polymerization reported by Ozawa and coworkers33,34 was employed for this oligomerization. In a previous study,19 the thiophene-linked BODIPY oligomers were synthesized from the corresponding dipyrrin oligomers, which were obtained via condensation of 3 components, that

is, mono-pyrrolyl thiophene, bis-pyrrolyl thiophene, and arylaldehyde. This route required multiple steps and gave rise to a very low overall yield (1% from thiophene). The thiophenelinked BODIPY dimer TB2a and trimer TB3a were also obtained by this C-H activation method using 9 and thiophene in a one-pot reaction (TB2a 4%, TB3a 3%). The structure of 3,5-diselenophenyl BODIPY SB1a in solution was characterized by NMR measurements. In the 1H NMR spectrum of 3,5-diselenophenyl BODIPY SB1a, the proton signal at the 3-position of selenophene was shifted downfield (8.23 ppm) compared to that of 2,6-diselenophenyl BODIPY SB1c (7.31 ppm) (see SI, Figures S1, S5). Furthermore, the 1H–19F HOESY NMR spectrum of SB1a showed a correlation peak only between the proton at the 3-position of the selenophene and the fluorine of the BODIPY core (SI Figure S19). These observations suggest that the Se atoms of the selenophenes of SB1a should face away from the BODIPY unit due to the C-H ··· F-B hydrogen bonds. This hydrogen bond between the selenophenyl C-H and BF2 unit was also supported by the single-crystal X-ray diffraction analysis of SB1a (SI Figure S28). Scheme 2. Synthesis of selenophene-BODIPY oligomers


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The Journal of Organic Chemistry Table 1. Optical properties of selenophene-BODIPYs (CHCl3, 298 K). BODIPY

λabs / nm

ε / M−1cm−1

λem / nm

ΦF

Stokes shift / cm−1

Φ∆

SB1a

631

67000

657

0.69

630

0.050

SB1b

626

69000

656

0.65

730

–

SB1c

634

70000

695

0.063

1380

0.065

SB1d

653

53000

704

0.11

1110

0.27

SB1e

651

69000

676

0.51

570

0.30

SB2a

785

88000

842

0.012

810

0.29

TB1a19

623

72000

643

0.78

500

0.0042a

TB1b19

618

142000

643

0.75

630

–

19

TB1c

630

36000

684

0.11

1250

0.019a

TB1d19

640

55000

699

0.21

1320

0.028a

TB2a19

780

74000

820

0.08

630

0.13a

a ··· Measurement in this study.

Selenophene-substituted BODIPYs showed their absorption and emission in the far-red or near-infrared region (Table 1). SB1a showed an absorption maximum λabs at 631 nm and emission maximum λem at 657 nm. The absorption and emission were red-shifted by 8 nm and 14 nm, respectively, compared to the thiophene-substituted BODIPY TB1a19 (Figures 1, 2, and Table 1). The fluorescence quantum yield ΦF of SB1a was 0.69, which was very high in spite of bearing heavy selenium atoms. A larger bathochromic shift of the selenophenyl groups in comparison to the thiophenyl analogue was also observed for SB1b, which has a 4-methoxyphenyl group at the meso position. SB1b showed a high fluorescence quantum yield (ΦF = 0.65) like SB1a despite possessing rotatable aryl substituents. A small effect of the meso-aryl substituent on the emission properties would be useful to design more functionalized BODIPYs.

phene with selenophene increases the HOMO level but does not affect the LUMO level. The emission maximum of 2,6-diselenophenyl BODIPY SB1c (695 nm) was red-shifted compared to 3,5diselenophenyl BODIPYs SB1a and SB1b by about 40 nm (Figures 1, 2, and Table 1). However, the fluorescence quantum yield of SB1c is much lower (ΦF = 0.063). This significant decrease in the fluorescence intensity is probably attributable to the free rotation of the selenophene units. In SB1a and SB1b, the rotation of the selenophene rings is suppressed by the intramolecular hydrogen bonds between the C-H of the 3position of the selenophene and B-F of the BODIPY core. In contrast to the 3,5-diselenophenyl BODIPYs, the selenophene rings in 2,6-diselenophenyl BODIPY SB1c can rotate in the excited state35 because SB1c does not have internal hydrogen bonds to fix the conformation of the selenophene groups. This free rotation in SB1c would also result in the large Stokes shift.

Figure 1. Structures of thiophene-BODIPYs19

The redox behavior of the selenophene-substituted BODIPY was examined by cyclic voltammetry in CH2Cl2 containing 0.1 M nBu4NPF6 (SI Figure S25). SB1a displayed an irreversible oxidation wave at Ep = +0.58 V (vs. Fc/Fc+) and a reversible reduction wave at E1/2 = −1.33 V. In comparison, the thiophene BODIPY TB1a exhibited an irreversible oxidation wave at Ep = +0.65 V and a reversible reduction wave at E1/2 = −1.33 V. These results suggest that the replacement of thio-



Figure 2. (a) Absorption and (b) emission spectra of selenophene-BODIPY monomers. SB1a (black), SB1b (blue), SB1c (red), SB1d (green), SB1e (purple) (CHCl3, 298 K).

2,3,5,6-Tetraselenophenyl BODIPY SB1d exhibited an absorption and emission at 653 nm and 704 nm, respectively, which are in the target wavelength region (> 650 nm). The fluorescence quantum yield (ΦF = 0.11) of SB1d is smaller than those of 3,5-diselenophenyl BODIPYs SB1a and SB1b. It is also noted that the fluorescence quenching of the selenophenyl BODIPYs is more significant than that of the thiophene analog TB1d19 (ΦF = 0.21). The fluorescence quenching of SB1d implies the efficient formation of the triplet excited state due to the heavy atom effect of selenium. Intriguingly, SB1e, which contains iodinated selenophene units, has a relatively strong emission (ΦF = 0.51) in spite of the fact that SB1e possesses two kinds of heavy atoms, I and Se. The absorption and emission of the iodinated selenophenyl BODIPY, SB1e is red-shifted by 20 nm and 19 nm compared to SB1a. Linking BODIPY units with selenophene caused a red shift of the absorption/emission to the near-infrared region. The absorption maximum of the selenophene-linked BODIPY dimer SB2a appears at 785 nm (Figure 3, Table 1). Furthermore, SB2a shows an emission in spite of possessing selenium atoms (ΦF = 0.012), and the maximum emission (842 nm) is red-shifted by 22 nm compared to that of TB2a19.

Figure 3. Absorption (solid line) and emission (dotted line) spectra of selenophene-BODIPY dimer SB2a (CHCl3, 298 K).

Selenophene BODIPYs were found to be effective photosensitizers of singlet oxygen using far red and near-infrared light. The quantum yield of the singlet oxygen formation sensitized by SB1a is Φ∆ = 0.050, which is much higher than that of the thiophene derivative TB1a (Φ∆ = 0.0042) (Table 1). All the selenophenyl BODIPYs measured in this study have higher Φ∆ values than those of the thiophene analogs (Table 1). This result suggests that the selenium atoms contribute to the efficient intersystem crossing. Next, we examined the influence of the position and the number of selenophene units. The Φ∆ values of the selenophene BODIPY monomers are in the order of SB1d>SB1c>SB1a. Thus, connecting the selenophene units at the 2,6-positions of the BODIPY core is more effective to generate singlet oxygen than at its 3,5-positions. Moreover, the more selenophene units that are introduced, the higher the sensitization efficiency becomes. With regard to the number of BODIPY units, the selenophene BODIPY dimer SB2a generated singlet oxygen more effectively (Φ∆ = 0.29) than the monomer SB1a (Φ∆ = 0.050).

SB1e, which contains iodine atoms, showed the highest quantum yield of singlet oxygen generation (Φ∆ = 0.30) among the investigated selenophene BODIPYs. As already mentioned, SB1e, which has two kinds of heavy atoms (Se and I), is still highly emissive. SB1e is an interesting compound that possesses seemingly contradictory characters: Efficient singlet oxygen generation (Φ∆ = 0.30) from triplet excited state and still strong emission (ΦF = 0.51) from singlet excited state. To summarize, we synthesized a series of selenophenesubstituted BODIPYs. They emit fluorescence in far-red or near-infrared region in spite of possessing selenium atoms. The emission of the selenophene-substituted BODIPYs is redshifted compared to the thiophene-substituted analogs. Furthermore, some of the selenophenyl BODIPYs are not only useful fluorophores, but also good photosensitizers to produce singlet oxygen. The results obtained in this study should be very useful to develop a variety of new near-infrared photofunctional materials containing selenophene units.

EXPERIMENTAL SECTION General. All chemicals were reagent grade, and used without further purification unless otherwise noted. Dry THF was purified with Nikko Hansen Ultimate Solvent System 3S-TCN 1. Silica gel column chromatography was performed with Kanto Chemical silica gel 60 N (spherical, neutral). Alumina for column chromatography was purchased from Wako Pure Chemical Industries, Ltd. (alumina, activated (about 75 µm)). GPC purification was performed on a JAI LC-9210 II NEXT system with JAIGEL-1HH/2HH columns using CHCl3 as an eluent. M.BRAUN UNILAB system under N2 atmosphere was used for the synthesis using a glove box. Melting points were determined on a Yanaco MP-J3 melting point apparatus. Elemental analysis was performed on a Yanaco MT-6 analyzer with tin boats purchased from Elementar. We appreciate Mr. Ikuo Iida and Mr. Masao Sasaki for the elemental analysis. 1H, 13C, 11B, 19F NMR, and 2D NMR spectra were recorded on a Bruker AVANCE 300, 400, or 600 spectrometers. Tetramethylsilane was used as an internal standard (δ 0.00 ppm) for 1 H and 13C NMR measurements when CDCl3 was used as a solvent. Hexafluorobenzene in CDCl3 (1 wt%) was used as an external standard (δ –163.0 ppm) for 19F NMR measurements. BF3·Et2O in CDCl3 (1 wt%) was used as an external standard (δ 0.0 ppm) for 11B NMR measurements. MALDI-TOF mass data were recorded on an AB SCIEX TOF/TOF 5800 system. Dithranol was used for the matrix. ESI-TOF mass data were recorded on an AB SCIEX TripleTOF 4600 system. HRMS value was calculated for the strongest peak using PeakView 1.2.0.3 software (AB SCIEX, 2012). UV-Vis spectra were recorded on a JASCO V-660 or V-670 spectrophotometer. Emission spectra were recorded on a JASCO FP-8600 fluorescence spectrophotometer. Absolute fluorescence quantum yields were determined with a Hamamatsu Photonics absolute PL quantum yield measurement system C9920-02. Solvents used for measurements were airsaturated. Cyclic voltammetry was performed on an BAS ALS model 750A electrochemical analyzer using a three-electrode system (working electrode, a 1 mm glassy carbon electrode; counter electrode, a platinum wire; reference electrode, Ag+/Ag electrode (a silver wire immersed in 0.01 M AgNO3 and 0.1 M nBu4NPF6 in CH3CN)). The solution was deaerated by bubbling nitrogen prior to the measurements. Phosphorescence spectra of singlet oxygen was measured by a time-resolved near-IR emission measurement system. As an excitation light source, output from an Nd3+: YAG laser (Tokyo Instruments Lotis II, 532 nm, 0.4 mJ/pulse, pulse width: 8 ns, 10 Hz) was used. Phosphorescence of singlet oxygen was detected with a photomultiplier tube (Hamamatsu R5509-42) after dispersion with a monochromator (Ritsu MC-10N, blaze wavelength: 1250 nm and slit width: 1.0 mm). Signals from the photomultiplier tube were recorded on a digital oscilloscope (Tektronix TDS380P) or processed with a gated photon counter (Stanford Research Systems SR400) after the amplifi-


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The Journal of Organic Chemistry cation with a DC-300 MHz amplifier (Stanford Research Systems SR445). Quantum yield of singlet oxygen formation were determined by measuring phosphorescence spectra of singlet oxygen. CHCl3 (Wako Pure Chemical, Spectrochemical Analysis grade) was used as solvent. Absorbance of sample solutions was set to 0.1 at the excitation wavelength (532 nm). Tetraphenylporphyrin in CHCl3 was used as a standard (Φ∆ = 0.55)36. Synthesis of SB1a. A 5 mL 2 neck flask was charged with 428 (50.6 mg, 108 µmol), 2-selenopheneboronic acid37 (41.2 mg, 236 µmol), cesium carbonate (141 mg, 431 µmol), tri-t-butylphosphonium tetrafluoroborate (12.5 mg, 43.1 µmol), tris(dibenzylideneacetone)dipalladium(0) (10.0 mg, 10.9 µmol), dry THF (5.0 mL) and deaerated water (50 µL). The mixture was stirred for 8 h at ambient temperature under an argon atmosphere in a dark condition. Brine (40 mL) was added to the mixture, which was extracted with chloroform (30 mL×3). The combined organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The obtained residue was purified by column chromatography on silica-gel using dichloromethane/n-hexane (1:1) as the eluent to give SB1a (46.6 mg, 82.0 µmol, 76%). Gold crystal; m.p. 273–275 °C; 1H NMR (400 MHz, CDCl3): δ 8.25–8.22 (4H), 7.42 (dd, J = 5.6, 4.0 Hz, 2H), 6.96 (s, 2H), 6.70 (d, J = 4.3 Hz, 2H), 6.54 (d, J = 4.3 Hz, 2H), 2.37 (s, 3H), 2.16 (s, 6H); 19F NMR (376 MHz, CDCl3): δ –138.2 (1:1:1:1 quartet, JBF = 33 Hz); 11B NMR (128 MHz, CDCl3): δ 1.7 (t, JBF = 33 Hz); 13C NMR (151 MHz, CDCl3): δ 152.2, 140.5, 139.0, 138.5, 137.0, 136.97, 136.93, 135.6, 133.5, 131.2, 130.3, 128.6, 128.2, 121.4, 21.1, 20.1; HRMS (ESI-TOF) m/z: [M+Na]+ Calcd for C26H21BF2N2NaSe2 592.9998; Found 592.9976. Synthesis of SB1b. A 5 mL 2 neck flask was charged with 529 (30.7 mg, 67.3 µmol), 2-selenopheneboronic acid37 (23.5 mg, 134 µmol), cesium carbonate (86.6 mg, 266 µmol), tri-tbutylphosphonium tetrafluoroborate (8.7 mg, 30 µmol), tris(dibenzylideneacetone)dipalladium (0) (8.0 mg, 8.7 µmol), dry THF (3.0 mL) and deaerated water (18 µL). The mixture was stirred for 4 h at ambient temperature under an argon atmosphere in a dark condition. The reaction mixture was filtered through a Celite pad and washed with chloroform. The filtered solution was washed with brine (20 mL), water (40 mL) and brine (40 mL). The combined organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The obtained residue was purified by column chromatography on silicagel using dichloromethane/n-hexane (1:1) as the eluent to give SB1b (15.4 mg, 27.7 µmol, 42%). Gold crystal; m.p. 213–214 °C; 1H NMR (400 MHz, CDCl3): δ 8.23–8.21 (4H), 7.49 (d, J = 8.7 Hz, 2H), 7.42 (dd, J = 5.0, 5.0 Hz, 2H), 7.04 (d, J = 8.7 Hz, 2H), 6.83 (d, J = 4.4 Hz, 2H), 6.77 (d, J = 4.4 Hz, 2H), 3.91 (s, 3H); 19F NMR (376 MHz, CDCl3): δ –137.4 (1:1:1:1 quartet, JBF = 33 Hz); 11B NMR (128 MHz, CDCl3): δ 1.6 (t, JBF = 33 Hz); 13C NMR (151 MHz, CDCl3): δ 161.3, 151.9, 141.1, 139.0, 136.8, 135.5, 133.4, 132.1, 131.1, 129.9, 126.8, 121.3, 113.8, 55.5; MALDI-TOF MS m/z: [M+H]+ Calcd for C24H18BF2N2OSe2 599.0; Found 559.2; Elemental analysis, calcd for C24H17BF2N2OSe2•0.5H2O: C 51.01, H 3.21, N 4.96; found: C 51.29, H 3.06, N 4.97. Synthesis of SB1c. A 5 mL 2 neck flask was charged with 630 (30.0 mg, 64.1 µmol), 2-selenopheneboronic acid (22.5 mg, 129 µmol), cesium carbonate (83.0 mg, 255 µmol), tri-tbutylphosphonium tetrafluoroborate (8.3 mg, 29 µmol), tris(dibenzylideneacetone)dipalladium(0) (7.2 mg, 7.9 µmol), dry THF (3.0 mL) and degassed water (20 µL). The mixture was stirred for 24 h at ambient temperature under an argon atmosphere in a dark condition. Brine (40 mL) was added to the mixture, which was extracted with chloroform (30 mL×3). The combined organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The obtained residue was purified by column chromatography on silica-gel using dichloromethane/n-hexane (1:1) as the eluent to give SB1c (9.1 mg, 16.0 µmol, 25%). Blue solid; m.p. 220–221 °C; 1H NMR (400 MHz, CDCl3): δ 8.13 (s, 2H), 7.88 (dd, J = 5.5, 0.85 Hz, 2H), 7.30 (dd, J = 3.8, 0.85 Hz, 2H), 7.24 (dd, J = 5.5, 3.8 Hz, 2H), 7.02 (s, 2H), 6.63 (s, 2H), 2.41 (s, 3H), 2.17 (s, 6H); 19F NMR (376 MHz, CDCl3): δ –145.8 (1:1:1:1 quartet, JBF = 29 Hz); 11B NMR (128 MHz, CDCl3):

δ 0.14 (t, JBF = 29 Hz); 13C NMR (151 MHz, CDCl3): δ 146.7, 142.2, 141.0, 139.2, 136.4, 136.1, 130.6, 130.4, 129.7, 129.4, 128.4, 125.7, 123.4, 21.2, 20.1; MALDI-TOF MS m/z: [M+H]+ Calcd for C26H21BF2N2Se2 570.0; Found 570.2; Elemental analysis, calcd for C26H21BF2N2Se2: C 54.96, H 3.73, N 4.93; found: C 54.88, H 3.72, N 4.77. Synthesis of 7. A 200 mL 2 neck flask was charged with SB1a (163.3 mg, 287.4 µmol), toluene (46 mL), and trifluoroacetic acid (4.4 mL, 57.4 mmol). The mixture was stirred at 100 °C for 10 h and then washed with sat. NaHCO3 aq (100 mL×2). The combined aqueous layer was extracted with ethyl acetate (100 mL). The combined organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The residue was washed with n-hexane to give 7 (126.9 mg, 243.9 µmol, 85%). Purple solid; m.p. 227–229 °C; 1H NMR (400 MHz, CDCl3): δ 8.06 (dd, J = 5.6, 1.2 Hz, 2H), 7.63 (dd, J = 4.0, 1.2 Hz, 2H), 7.37 (dd, J = 5.6, 4.0 Hz, 2H), 6.93 (s, 2H), 6.63 (d, J = 4.4 Hz, 2H), 6.40 (d, J = 4.4 Hz, 2H), 2.36 (s, 3H), 2.14 (s, 6H); 13C NMR (101 MHz, CDCl3): δ 150.1, 143.2, 141.6, 137.5, 137.0, 136.9, 133.1, 131.7, 130.8, 128.4, 127.8, 127.5, 115.7, 21.1, 20.1; HRMS (ESI-TOF) m/z: [M+H]+ Calcd for C26H23N2Se2 523.0191; Found 523.0163. Synthesis of 8. A 100 mL 3 neck flask was charged with 7 (64.6 mg, 124.1 µmol), N-bromosuccinimide (43.2 mg, 243 µmol) and dry dichloromethane (40 mL) at 0 °C and then the mixture stirred at room temperature for 3 h. The mixture was diluted with chloroform (30 mL), and then washed with H2O (30 mL). The combined organic layer was dried over MgSO4, filtered, and concentrated in vacuo. To the obtained residues, dichloromethane (25 mL) and N,Ndiisopropylethylamine (1.0 mL, 5.7 mmol), and trifluoroborane ethylether complex (1.0 mL, 8.1 mmol) were added. Then, the reaction mixture was stirred at room temperature for 7.5 h. The mixture was diluted with chloroform (30 mL), and then washed with H2O (30 mL). The aqueous layer was extracted with chloroform (30 mL). The combined organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The obtained residue was purified by column chromatography on silica-gel using dichloromethane/n-hexane (1:1) as the eluent to give 8 (27.8 mg, 33.6 µmol, 27%). Blue solid; m.p. > 300 °C; 1 H NMR (400 MHz, CDCl3): δ 8.35 (dd, J = 5.6, 0.80 Hz, 2H), 8.04 (dd, J = 3.6, 0.80 Hz, 2H), 7.42 (dd, J = 5.6, 3.6 Hz, 2H), 6.99 (s, 2H), 6.74 (s, 2H), 2.38 (s, 3H), 2.19 (s, 6H); 19F NMR (376 MHz, CDCl3): δ –138.2 (1:1:1:1 quartet, JBF = 33 Hz); 11B NMR (128 MHz, CDCl3): δ 1.7 (t, JBF = 33 Hz); 13C NMR (101 MHz, CDCl3): δ 151.0, 141.8, 139.2, 137.0, 136.6, 135.7, 134.8, 134.3, 130.3, 129.7, 129.1, 128.3, 110.1, 21.1, 20.1; HRMS (ESI-TOF) m/z: [M+Na]+ Calcd for C26H19BBr2F2N2NaSe2 748.8201; Found 748.8168. Synthesis of SB1d. A 50 mL 2 neck flask was charged with 8 (27.8 mg, 33.6 µmol), 2-selenopheneboronic acid (14.7 mg, 84.1 µmol), cesium carbonate (44.1 mg, 135 µmol), tri-tbutylphosphonium tetrafluoroborate (3.9 mg, 13 µmol), tris(dibenzylideneacetone)dipalladium(0) (3.5 mg, 3.4 µmol), THF (8.4 mL) and degassed water (50 µL) was stirred for 21 h at ambient temperature under an argon atmosphere. Chloroform (30 mL) was added to the mixture, which was washed with brine (30 mL). The aqueous layer was extracted three times with chloroform (30 mL). The combined organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The residue was purified by column chromatography on silica-gel using dichloromethane/n-hexane (1:1) as the eluent and reprecipitation from dichloromethane/n-hexane to give SB1d (14.0 mg, 16.9 µmol, 50%). Green solid; m.p. > 300 °C; 1H NMR (400 MHz; CDCl3): δ 8.27 (dd, J = 5.6, 1.1 Hz, 2H), 7.87 (dd, J = 5.6, 1.1 Hz, 1H), 7.70 (dd, J = 3.8, 1.1 Hz, 2H), 7.34 (dd, J = 5.6, 3.8 Hz, 2H), 7.13 (dd, J = 5.6, 3.8 Hz, 2H), 7.04 (dd, J = 3.8, 1.1 Hz, 2H), 7.01 (s, 2H), 6.67 (s, 2H), 2.40 (s, 3H), 2.26 (s, 6H); 19F NMR (376 MHz, CDCl3): δ –134.9 (1:1:1:1 quartet, JBF = 31 Hz); 11B NMR (128 MHz, CDCl3): δ 1.0 (t, JBF = 31 Hz); 13C NMR (151 MHz, CDCl3): δ 151.1, 143.1, 140.6, 138.9, 136.8, 136.4, 135.8, 135.3, 135.1, 131.5, 131.2, 129.9, 129.6, 129.5, 128.6, 128.3, 125.7, 21.2, 20.4; MALDI-TOF MS m/z: [M]+ Calcd for C34H25BF2N2Se4 827.9;



Found 827.8; Elemental analysis, calcd for C34H25BF2N2Se4•1.5H2O: C 47.86, H 3.31, N 3.28; found: C 47.72, H 3.02, N 3.20. Synthesis of SB1e. A 200 mL recovery flask was charged SB1a (42.0 mg, 73.8 µmol), N-iodosuccinimide (35.4 mg, 157.3 µmol) and dichloromethane (12.0 mL). The mixture was stirred for 4 h at ambient temperature. Water (30 mL) was added to the flask, and the mixture was extracted with chloroform (30 mL×2). The organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The residue was purified by column chromatography on silica-gel using dichloromethane/n-hexane (1:1) as the eluent. The obtained green solid was purified by GPC and reprecipitation from dichloromethane/nhexane to give SB1e (14.2 mg, 17.3 µmol, 23%). Green solid; m.p. > 300 °C; 1H NMR (300 MHz, CDCl3): δ 7.67 (d, J = 4.2 Hz, 2H), 7.61 (d, J = 4.2 Hz, 2H), 6.96 (s, 2H), 6.65 (d, J = 4.4 Hz, 2H), 6.55 (d, J = 4.4 Hz, 2H), 2.36 (s, 3H), 2.14 (s, 6H); 19F NMR (376 MHz, CDCl3): δ –136.9 (1:1:1:1 quartet, JBF = 34 Hz); 11B NMR (128 MHz, CDCl3): δ 1.5 (t, JBF = 34 Hz); 13C NMR (151 MHz, CDCl3): δ 151.2, 144.8, 141.3, 140.8, 138.7, 137.1, 136.8, 134.4, 130.1, 128.7, 128.2, 120.8, 83.6, 21.1, 20.1; HRMS (ESI-TOF) m/z: [M+Na]+ Calcd for C26H19BF2I2N2NaSe2 844.7936; Found 844.7903. Synthesis of BODIPY oligomers SB2a and SB3a. A 10 mL Schlenk flask with a magnetic stirring bar was flame-dried under vacuum and filled with argon after cooling to room temperature. In a glovebox, cesium carbonate (1.958 g, 6.009 mmol, dried in vacuo at 120 °C before use) and pivalic acid (204 mg, 2.00 mmol, distilled before use) were added to the flask. Then, 931 (762.8 mg, 2.012 mmol), tris(o-methoxyphenyl)phosphine (141.7 mg, 402.1 µmol), tris(dibenzylideneacetone)dipalladium(0) (104.7 mg, 101.1 µmol) were added with Ar flow. After the reaction vessel was evacuated and backfilled with argon, dry THF (2.0 mL) and selenophene (485 µL, 6.00 mmol) were added to this flask. The reaction mixture was stirred in 100 °C oil bath for 40 min, and cooled to room temperature, and then stirred again in 100 °C oil bath for another 30 min. The mixture was poured into CHCl3 (50 mL), washed with brine (50 mL). The aqueous layer was extracted three times with CHCl3. The combined organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The obtained residue was purified by column chromatography on silica-gel using dichloromethane/n-hexane (1:1) as the eluent and by GPC to give SB2a (83.7 mg, 83.3 µmol, 8%), SB3a (36.5 mg, 25.3 µmol, 4%). SB2a: purple powder; m.p. > 300 °C; 1H NMR (600 MHz, CDCl3): δ 8.33 (s, 2H), 8.30 (dd, J = 4.0, 1.0 Hz, 2H), 8.24 (dd, J = 5.6, 1.0 Hz, 2H), 7.44 (dd, J = 5.6, 4.0 Hz, 2H), 6.96 (s, 4H), 6.84 (d, J = 4.4 Hz, 2H), 6.73 (d, J = 4.4 Hz, 2H), 6.55 (d, J = 4.4 Hz, 2H), 6.54 (d, J = 4.4 Hz, 2H), 2.37 (s, 6H), 2.17 (s, 12H); 19F NMR (376 MHz, CDCl3): δ –138.1 (1:1:1:1 quartet, JFB = 34 Hz); 11B NMR (128 MHz, CDCl3): δ 1.8 (t, JBF = 34 Hz); 13C NMR (101 MHz, CDCl3): δ 152.6, 150.9, 143.0, 139.8, 138.9, 138.5, 137.6, 137.4, 136.9, 136.1, 135.0, 133.8, 131.3, 130.3, 128.7, 128.2, 121.8, 121.7, 21.1, 20.1; HRMS (ESI-TOF) m/z: [M+Na]+ Calcd for C48H38B2F4N4NaSe3 1029.0647; Found 1029.0603. SB3a: blue powder; m.p. > 300 °C; 1H NMR (400 MHz, CDCl3): δ 8.36 (d, J = 4.0 Hz, 2H), 8.34 (d, J = 4.0 Hz, 2H), 8.29 (d, J = 4.0 Hz, 2H), 8.22 (d, J = 8.0 Hz, 2H), 7.41 (dd, J = 8.0, 4.0 Hz, 2H), 6.98 (s, 2H), 6.97 (s, 4H) 6.90 (d, J = 4.0 Hz, 2H), 6.85 (d, J = 4.0 Hz, 2H), 6.74 (d, J = 4.0 Hz, 2H), 6.58 (d, J = 4.0 Hz, 2H), 6.56 (d, J = 4.0 Hz, 2H), 6.53 (d, J = 4.0 Hz, 2H), 2.383 (s, 3H), 2.374 (s, 6H), 2.173 (s, 6H), 2.165 (s, 12H); 19F NMR (376 MHz, CDCl3): δ –137.7 (1:1:1:1 quartet, JFB = 34 Hz, 2F), –138.0 (1:1:1:1 quartet, JFB = 34 Hz, 4F); 11B NMR (128 MHz, CDCl3): δ 1.8 (t, JBF = 34 Hz); 13C NMR (151 MHz, CDCl3): δ 152.6, 151.3, 150.9, 143.4, 143.0, 139.6, 138.9, 138.8, 138.6, 138.5, 138.1, 137.6, 137.4, 137.0, 136.9, 136.1, 135.3, 135.2, 135.1, 135.0, 133.8, 133.7, 131.3, 130.3, 128.7, 128.3, 128.2, 128.1, 122.0, 121.8, 21.2, 21.1, 20.1, 20.0; MALDI-TOF MS m/z: [M]+ Calcd for C70H55B3F6N6Se4 1444.1; Found 1444.0; Elemental analysis, calcd for C70H55B3F6N6Se4: C 58.278, H 3.84, N 5.83; found: C 58.04, H 3.80, N 5.75.

ASSOCIATED CONTENT Supporting Information

The Supporting Information is available free of charge on the ACS Publications website at DOI: ##.####/####### Spectral data for 1H, 13C NMR and other measurements (PDF) Crystallographic data for SB1a (CIF)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected].

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT We would like to thank Prof. Fumiyuki Ozawa of Kyoto University for the advice on the C-H activated coupling reaction. This research was supported by JSPS KAKENHI (grant numbers 15H00723 and 15H00914) and the Mitsubishi Foundation.

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Synthesis and Unique Optical Properties of Selenophene-BODIPYs

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