A Versatile Synthesis of Long-Wavelength-Excitable BODIPY Dyes from Readily Modifiable Cyclopenta[2,1-b:3,4-b′]dithiophenes

Abstract

Knoevenagel condensation of a simple methylated ­borondipyrromethene (Bodipy) with 4,4′-dihexyl-4H-cyclopenta-[2,1-b:3,4-b′]dithiophenes functionalized at one end by a triphenylamine residue and at the other by a carbaldehyde fragment leads to novel dye species. These bisvinylic derivatives exhibit pronounced absorption in the visible range extending above 850 nm. Addition of other Bodipy units by coupling to a central iodophenyl entity enables filling of the gaps in absorption of the pivotal starting material. Efficient cascade energy transfer between the Bodipys is facilitated by spectral overlap between the energy donor and the energy acceptor. All photons between 350 nm and 750 nm are channeled to the distyryl centers which emit at 864 nm.

Key words

BODIPY - dithiophene - pyrene - energy transfer - panchromatic dyes

• References and Notes

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• 17 Preparation of Compound 13: To a solution of BODIPY 12 (207.9 mg, 0.46 mmol) in toluene (70 mL) were added 6-[4-(diphenylamino)phenyl]-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2-carbaldehyde (11; 856.3 mg, 1.39 mmol), piperidine (1 mL) and p-toluenesulfonic acid (p-TsOH). The resulting mixture was stirred at reflux and the solvent was distilled to dryness using a Dean–Starck apparatus. Afterwards, the organic product was extracted with CH₂Cl₂, washed with H₂O and brine. The organic layer was dried over anhyd MgSO₄ and evaporated under vacuum. The crude product was purified by silica gel chromatography (from 80:20 → 50:50 petroleum ether–CH₂Cl₂) and recrystallized by evaporation in CH₂Cl₂–EtOH and washed with pentane to afford a deep-brown red compound (745.8 mg, 98%). ¹H NMR (400 MHz, CD₂Cl₂): δ = 7.88 (d, ³ J = 8.1 Hz, 2 H), 7.52 (d, ³ J = 8.5 Hz, 4 H), 7.42 (s, 4 H), 7.29 (t, ³ J = 7.9 Hz, 8 H), 7.17 (d, ⁴ J = 4.0 Hz, 4 H), 7.15 (d, ³ J = 8.4 Hz, 2 H), 7.12 (d, ³ J = 7.7 Hz, 8 H), 7.02–7.08 (m, 8 H), 6.65 (s, 2 H), 1.88–1.96 (m, 8 H), 1.50 (s, 6 H), 1.13–1.24 (m, 24 H), 0.95–1.05 (m, 8 H), 0.81 (t, ³ J = 6.7 Hz, 12 H). ¹³C NMR (101 MHz, CD₂Cl₂): δ = 161.4, 159.5, 152.3, 148.0, 147.8, 146.9, 143.5, 141.8, 140.6, 138.8, 135.7, 135.5, 135.1, 134.1, 131.5, 130.4, 129.9, 129.6, 126.6, 125.1, 124.2, 123.8, 123.3, 118.5, 117.6, 116.2, 95.2, 38.6, 34.7, 32.2, 30.3, 25.1, 23.2, 22.9, 15.3, 14.4. MS (EI): m/z (%) = 1649.5 (100.0), 1629.5 (30). Anal. Calcd for C₉₉H₁₀₀BF₂IN₄S₄: C, 72.07; H, 6.11; N, 3.40. Found: C, 71.85; H, 5.80; N, 3.11.
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• 21 Preparation of Compound 16: To a degassed solution of 13 (63 mg, 0.038 mmol) and 15 (22 mg, 0.046 mmol) in benzene (10 mL) and Et₃N (2 mL) was added [Pd(PPh₃)₄] (10 mg). The resulting mixture was stirred for 19 h at 70 °C and then cooled to r.t. After evaporation of the solvent under vacuum, the organic product was extracted with CH₂Cl₂, washed with H₂O and brine. The organic layer was dried over anhyd Na₂SO₄ and evaporated under vacuum. The crude product was purified by silica gel chromatography (from 50:50 → 40:60 petroleum ether–CH₂Cl₂) to obtain a brown compound (62 mg, 81%) and recrystallized by evaporation in THF–pentane and washed with pentane to afford a brown compound (54 mg, 71%). ¹H NMR (400 MHz, CDCl₃): δ = 7.71 (d, ³ J = 8.1 Hz, 4 H), 7.47–7.56 (m, 8 H), 7.33–7.41 (m, 6 H), 7.20–7.31 (m, 12 H), 7.02–7.16 (m, 18 H), 6.69 (d, ³ J = 9.0 Hz, 2 H), 6.62 (s, 1 H), 6.61 (s, 2 H), 5.99 (s, 1 H), 3.04 (s, 6 H), 2.61 (s, 3 H), 1.82–1.95 (m, 8 H), 1.50 (s, 9 H), 1.45 (s, 3 H), 1.11–1.25 (m, 24 H), 0.94–1.07 (m, 8 H), 0.83 (t, J = 6.9 Hz, 12 H). ¹³C NMR (101 MHz, CDCl₃): δ = 160.5, 158.7, 155.2, 153.1, 151.9, 151.1, 147.4, 147.1, 146.2, 143.0, 142.6, 140.7, 140.4, 140.0, 138.2, 137.7, 135.9, 135.8, 135.3, 134.7, 133.6, 132.9, 132.2, 132.2, 130.9, 129.7, 129.3, 129.3, 129.2, 129.1, 128.8, 126.1, 124.6, 124.4, 123.9, 123.5, 123.5, 123.1, 122.4, 120.6, 117.9, 116.8, 116.1, 114.2, 112.0, 90.0, 68.0, 54.0, 53.4, 40.2, 38.0, 34.1, 31.6, 29.7, 25.6, 24.5, 22.7, 22.3, 14.9, 14.8, 14.6, 14.5, 14.0. MS (EI): m/z (%) = 2000.1 (100.0), 1981.1 (35), 1963.2 (15). Anal. Calcd for C₁₂₉H₁₂₇B₂F₄N₇S₄: C, 77.42; H, 6.40; N, 4.90. Found: C, 77.20; H, 6.09; N, 4.68
• 22 Preparation of Compound 17: To a degassed solution of 13 (92 mg, 0.056 mmol) and 14 (43 mg, 0.056 mmol) in benzene (20 mL) and Et₃N (2 mL) was added [Pd(PPh₃)₄] (10 mg). The resulting mixture was stirred for 19 h at 80 °C and then cooled to r.t. After evaporation of the solvent under vacuum, the organic product was extracted with CH₂Cl₂, washed with H₂O and brine. The organic layer was dried over anhyd Na₂SO₄ and evaporated under vacuum. The crude product was purified by silica gel chromatography (from 80:20 → 50:50 petroleum ether–CH₂Cl₂) to obtain a grey compound (119 mg, 93%) and recrystallized by evaporation in THF–pentane and washed with pentane to afford a brown compound (112 mg, 88%). ¹H NMR (400 MHz, CDCl₃): δ = 8.80 (d, ³ J = 9.0 Hz, 2 H), 8.60 (d, ³ J = 9.2 Hz, 2 H), 7.96–8.29 (m, 18 H), 7.77 (d, ³ J = 7.9 Hz, 2 H), 7.66–7.74 (m, 2 H), 7.51 (d, ³ J = 7.9 Hz, 2 H), 7.39 (d, ³ J = 7.1 Hz, 2 H), 7.21–7.31 (m, 10 H), 6.99–7.17 (m, 24 H), 6.22 (s, 2 H), 3.18 (s, 6 H), 1.80–1.97 (m, 8 H), 1.56 (s, 6 H), 1.54 (s, 6 H), 1.11–1.31 (m, 24 H), 0.94–1.07 (m, 8 H), 0.82 (t, ³ J = 6.5 Hz, 12 H). ¹³C NMR (101 MHz, CDCl₃): δ = 158.7, 155.9, 147.4, 141.2, 132.5, 132.3, 132.2, 132.1, 131.6, 131.3, 131.2, 131.0, 130.5, 130.2, 129.7, 129.3, 128.7, 128.6, 128.5, 128.4, 127.9, 127.5, 127.3, 127.2, 126.3, 126.2, 126.0, 125.7, 125.7, 125.3, 125.2, 124.6, 124.4, 124.4, 124.4, 124.2, 123.9, 123.1, 122.4, 122.0, 120.3, 116.5, 82.7, 82.6, 38.0, 31.6, 29.7, 26.9, 24.5, 22.7, 16.6, 15.0, 14.9, 14.6, 14.1. MS (EI): m/z (%) = 2281.1 (100.0), 2262.1. (30) Anal. Calcd for C₁₅₆H₁₃₆B₂F₂N₆S₄: C, 82.08; H, 6.01; N, 3.68. Found: C, 81.74; H, 5.78; N, 3.51.
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