Synthesis and Characterization of Near-Infrared Emissive BODIPY-Based Conjugated Polymers

Abstract

Three novel BODIPY-based conjugated polymers could be synthesized via palladium-catalyzed Sonogashira coupling reaction. Compared with BODIPY model derivatives, the polymers can emit in the range from deep-red to near-infrared region with emission spectral maxima at λ = 640-660 nm and exhibit moderate fluorescent quantum yield from 0.23 to 0.26. Density functional theory (DFT) calculations are performed on three polymers repeat units, and HOMO and LUMO energy levels of the conjugated polymers are estimated.

Key words

organoboron dye - conjugated polymer - BODIPY - near-infrared

References and Notes

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11

General Procedure for Polymerization via Sonogashira Polymerization Reaction
A 20 mL Schlenk flask was charged with monomers, catalyst Pd(PPh₃)₄, (CuI), and a magnetic stirrer. A 1:1 mixture of degassed anhyd Et₃N and anhyd toluene solvent was then added to the monomers, and the reaction temperature was raised to 80 ˚C. The polymerization was continued for 72 h. Then the solvent was evaporated under vacuum. The residue was dissolved in CH₂Cl₂ (100 mL) and washed with H₂O (3×). The organic layer was collected, dried over anhyd Na₂SO₄, and filtered. The filtrate was concentrated and added to MeOH to precipitate the polymer. A dark powder was obtained by filtration, further purified with MeOH, and then dried under vacuum for 24 h to afford polymers.
P1 BODIPY dye 2 (57 mg, 0.1 mol), monomer 5 (103 mg, 0.1 mmol), Pd(PPh₃)₄ (12.0 mg, 0.01 mmol), and CuI (1.9 mg, 0.01mmol) were added to a mixture of toluene (3 mL) and Et₃N (3 mL). The mixture was stirred under N₂ atmosphere at 80 ˚C for 72 h, and then the solvent was evaporated under vacuum. The residue was dissolved in CH₂Cl₂ (100 mL) and washed with H₂O (3×). The organic layer was collected, dried over anhyd Na₂SO₄, and filtered. The filtrate was concentrated and added to MeOH to precipitate the polymer. A dark powder was obtained by filtration, further washed with MeOH, and then dried under vacuum for 24 h to afford a yield of 59%. ^¹H NMR (300 MHz, CDCl₃): δ = 7.71-7.65 (br, 5 H), 7.57-7.42 (br, 6 H), 4.24-4.15 (br 12 H), 3.92-3.84 (br, 12 H), 3.76-3.68 (br, 12 H), 3.52 (br, 6 H), 3.68-3.65 (br, 12 H), 3.52 (br, 6 H), 3.37 (br, 6 H), 3.20 (br, 6 H), 2.70 (br, 6 H), 1.42 (br, 6 H). FT-IR (KBr): 3441, 2923, 2823, 1630, 1529, 1384, 1317, 1261, 1095, 1014, 862, 724, 535 cm^-¹. P2 BODIPY dye 2 (57 mg, 0.1 mol) and monomer 6 (36 mg, 0.1 mmol) were added to a 5 mL Schlenk flask. Pd(PPh₃)₄ (12.0 mg, 0.01 mmol) and CuI (1.9 mg, 0.01 mmol) were added to a mixture of toluene (3 mL) and Et₃N (3 mL). The mixture was stirred under N₂ atmosphere at 80 ˚C for 72 h, and then the solvent was evaporated under vacuum. The polymeriza-tion was carried out according to the method for polymer P1. A dark blue powder was obtained by filtration, further washed with MeOH, and then dried under vacuum for 24 h to afford a yield of 54%. ^¹H NMR (300 MHz, CDCl₃): δ = 7.55-7.51 (br, 5 H), 7.32-7.31 (br, 2 H), 4.17-4.15 (br, 12 H), 3.83-3.80 (br, 12 H), 3.65-3.64 (br, 12 H), 3.52-3.50 (br, 12 H), 3.39-3.40 (br, 18 H), 2.75-2.68 (br, 6 H), 1.55 (br, 6 H). FT-IR (KBr): 3445, 2922, 2853, 1530, 1399, 1315, 1272, 1237, 1182, 1011, 1107, 725, 586 cm^-¹. P3 BODIPY dye 3 (37 mg, 0.1 mol) and monomer 10 (37 mg, 0.1 mmol) were added to a 5 mL Schlenk flask. Pd(PPh₃)₄ (12.0 mg, 0.01 mmol) and CuI (1.9 mg, 0.01 mmol) were added to a mixture of toluene (3 mL) and Et₃N (3 mL). The mixture was stirred under N₂ atmosphere at 80 ˚C for 72 h, and then the solvent was evaporated under vacuum. The polymerization was carried out according to the method for polymer P1. A dark blue powder was obtained by filtration, further washed with MeOH, and then dried under vacuum for 24 h to afford a yield of 62%. ^¹H NMR (300 MHz, CDCl₃): δ = 7.71-7.70 (br, 2 H), 7.53-7.54 (br, 5 H), 4.05-4.02 (br, 4 H), 2.70-2.65 (br, 12 H), 2.05 (br, 3 H), 1.55-1.65 (br, 15 H), 1.28-1.27 (br, 6 H). FT-IR (KBr): 3438, 2924, 2363, 1637, 1527, 1384, 1315, 1261, 1097, 804 cm^-¹.