Synthesis, Photophysical and Electrochemical Studies on Triazole-Based Phthalimidodendrimers

Abstract

The synthesis of dendrimers with phthalimide as the surface group and 1,2,3-triazole as bridging unit is described using click chemistry in a convergent approach. The photophysical properties indicate an increase in the molar extinction coefficient as the generation of the dendrimer increases. In cyclic voltammetry studies, the dendrimers show two reversible redox peaks due to formation of a radical anion and a dianion of the phthalimido moiety.

Key words

dendrimer - 1,2,3-triazole - phthalimide - photophysical and electrochemical

• References and Notes

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• 28 General Procedure for the Cu-Catalyzed Huisgen Click Reaction: A mixture of azide [8 (0.50 equiv), 9 (0.33 equiv), 10 (0.25 equiv) or 11 (0.50 equiv)], alkyne 7 or 13 (1.0 equiv), CuSO₄·5H₂O (5 mol%), and sodium ascorbate (10 mol%) in a mixture of t-BuOH–H₂O (1:1, 20 mL) was stirred for 10 h at r.t. The residue obtained after evaporation of the solvent was washed thoroughly with H₂O and dissolved in CHCl₃ (150 mL). The organic layer was separated, washed with brine (150 mL), dried (anhyd Na₂SO₄), filtered and evaporated to give the crude triazole, which was purified by column chromatography (SiO₂) using the eluent as mentioned under each compound.
• 29 Phenolic Dendron 12: The crude product was purified by chromatography using CHCl₃–MeOH (9:2) as eluent to give the phenolic dendron 12 as a colorless solid in 87% yield; mp 124 ºC. ¹H NMR (300 MHz, CDCl₃): δ = 4.82 (s, 4 H), 5.43 (s, 4 H), 6.56 (s, 2 H), 6.70 (s, 1 H), 7.86–7.88 (m, 8 H), 8.10 (s, 2 H), 9.69 (s, 1 H). ¹³C NMR (75 MHz, CDCl₃): δ = 32.9, 52.5, 114.3, 117.8, 123.1, 123.3, 131.5, 134.5, 137.7, 142.4, 157.8, 167.8, 167.3. MS (ESI): m/z = 575.3 [M + 1]⁺. Anal Calcd for C₃₀H₂₂N₈O₅: C, 62.71; H, 3.86; N, 19.50. Found: C, 62.61; H, 3.74; N, 19.57.
• 30 Synthesis of Alkyne Dendron 13: A mixture of phenolic dendron 12 (0.32 g, 0.06 mmol) and propargyl bromide (0.07 mL, 0.72 mmol) and K₂CO₃ (1.0 g, 6.7 mmol) was stirred for 24 h in DMF (15 mL) at r.t. After completion of reaction, the reaction mixture was poured into H₂O and extracted with CHCl₃ (3 × 100 mL). The combined organic phases were washed with brine (2 × 50 mL), dried with anhyd Na₂SO₄ and filtered. The solvent was evaporated in vacuo and the residue was purified by chromatography, eluting with CHCl₃–MeOH (9:1) to yield the alkyne dendron 13 as a colorless solid in 88% yield; mp 164–166 ºC. ¹H NMR (300 MHz, CDCl₃): δ = 2.48 (t, J = 2.4 Hz, 1 H), 4.45 (d, J = 2.4 Hz, 2 H), 4.91 (s, 4 H), 5.36 (s, 4 H), 6.68 (s, 1 H), 6.71 (s, 2 H), 7.49 (2 H), 7.63–7.66 (m, 4 H), 7.76–7.79 (m, 4 H). ¹³C NMR (75 MHz, CDCl₃): δ = 33.1, 53.6, 55.9, 76.5, 77.5, 114.8, 120.3, 122.9, 123.5, 132.0, 134.1, 137.0, 143.3, 158.4, 167.7. MS (ESI): m/z = 614.3 [M + 1]⁺. Anal. Calcd for C₃₃H₂₄N₈O₅: C, 64.70; H, 3.95; N, 18.29. Found: C, 64.86; H, 3.79; N, 18.12.
• 31 Dendrimer 1: The crude product was purified by chromatography using CHCl₃–MeOH (9:2) as eluent to give the dendrimer 1 as a colorless solid in 91% yield; mp 204 ºC. ¹H NMR (300 MHz, DMSO-d ₆): δ = 4.84 (s, 4 H), 5.74 (s, 4 H), 7.09–7.12 (m, 2 H), 7.30–7.34 (m, 2 H), 7.83–7.91 (m, 8 H), 8.09 (s, 2 H). ¹³C NMR (75 MHz, DMSO-d ₆): δ = 32.9, 49.8, 123.2, 123.5, 128.8, 129.1, 131.6, 134.1, 134.5, 142.6, 167.3. MS (ESI): m/z = 559.3 [M + 1]⁺. Anal. Calcd for C₃₀H₂₂N₈O₄: C, 64.51; H, 3.97; N, 20.06. Found: C, 64.36; H, 4.12; N, 19.88.
• 32 Dendrimer 2: The crude product was purified by column chromatography using CHCl₃–MeOH (9:1) as eluent to give the dendrimer 2 as a colorless solid in 91% yield; mp 141 ºC. ¹H NMR (300 MHz, CDCl₃): δ = 2.36 (s, 9 H), 4.94 (s, 6 H), 5.57 (s, 6 H), 7.28 (s, 3 H), 7.71–7.73 (m, 6 H), 7.83–7.86 (m, 6 H). ¹³C NMR (75 MHz, CDCl₃): δ = 20.1, 32.9, 48.7, 122.0, 123.4, 129.2, 131.7, 132.0, 134.1, 139.3, 167.6. MS (ESI): m/z = 841.6 [M + 1]⁺. Anal. Calcd for C₄₅H₃₆N₁₂O₆: C, 64.28; H, 4.32; N, 19.99. Found: C, 64.42; H, 4.64; N, 19.79.
• 33 Dendrimer 3: The crude product was purified by chromatography using CHCl₃–MeOH (9:2) as eluent to give the dendrimer 3 as a colorless solid in 88% yield; mp 310–312 °C. ¹H NMR (300 MHz, DMSO-d ₆): δ = 4.82 (s, 8 H), 5.66 (s, 8 H), 6.88 (s, 2 H), 7.81–7.89 (m, 16 H), 8.02 (s, 4 H). ¹³C NMR (75 MHz, DMSO-d ₆): δ = 32.8, 49.4, 123.1, 123.5, 130.2, 131.5, 134.4, 134.7, 142.5, 167.3. MS (QTOF): m/z = 1039.8 [M⁺]. Anal. Calcd for C₅₄H₃₈N₁₆O₈: C, 62.42; H, 3.69; N, 21.57. Found: C, 62.24; H, 3.78; N, 21.62.
• 34 Dendrimer 4: The crude product was purified by column chromatography using CHCl₃–MeOH (9:2) as eluent to give the dendrimer 4 as a colorless solid in 89% yield; mp 171 ºC. ¹H NMR (300 MHz, DMSO-d ₆): δ = 4.82 (s, 8 H), 5.08 (s, 4 H), 5.49 (s, 8 H), 5.84 (s, 4 H), 6.87 (s, 2 H), 6.92 (s, 4 H), 7.12–7.14 (m, 2 H), 7.34–7.37 (m, 2 H), 7.80–7.88 (m, 16 H), 8.15 (s, 4 H), 8.27 (s, 2 H). ¹³C NMR (75 MHz, DMSO-d ₆): δ = 32.9, 49.9, 52.5, 61.1, 114.1, 120.0, 123.1, 123.4, 125.0, 128.9, 129.1, 131.5, 134.5, 134.4, 137.9, 142.5, 142.6, 158.3, 167.3. MS (QTOF): m/z = 1413 [M⁺]. Anal Calcd for C₇₄H₅₆N₂₂O₁₀: C, 62.88; H, 3.99; N, 21.80. Found: C, 62.79; H, 3.88; N, 21.80.
• 35 Dendrimer 5: The crude product was purified by chromatography using CHCl₃–MeOH (9:1) as eluent to give the dendrimer 5 as a colorless solid in 89% yield; mp 154–156 ºC. ¹H NMR (300 MHz, CDCl₃): δ = 2.29 (s, 9 H), 4.87 (s, 12 H), 4.95 (s, 6 H), 5.30 (s, 12 H), 5.52 (s, 6 H), 6.63 (s, 3 H), 6.69 (s, 6 H), 7.26 (s, 3 H), 7.52 (s, 6 H), 7.60–7.62 (m, 12 H), 7.72–7.74 (m, 12 H). ¹³C NMR (75 MHz, CDCl₃): δ = 20.1, 33.0, 48.7, 53.6, 61.9, 114.6, 119.9, 122.4, 123.1, 123.4, 129.3, 131.6, 131.9, 134.1, 137.1, 139.3, 143.2, 159.1, 167.7. MS (QTOF): m/z = 2122.5 [M⁺]. Anal. Calcd for C₁₁₁H₈₇N₃₃O₁₅: C, 62.79; H, 4.13; N, 21.77. Found: C, 62.69; H, 4.01; N, 21.84.
• 36 Dendrimer 6: The crude product was purified by column chromatography using CHCl₃–MeOH (9:2) as eluent to give the dendrimer 6 as a colorless solid in 86% yield; mp 176–178 ºC. ¹H NMR (300 MHz, DMSO-d ₆): δ = 4.80 (s, 16 H), 5.03 (s, 8 H), 5.45 (s, 16 H), 5.76 (s, 8 H), 6.84 (s, 4 H), 6.87 (s, 8 H), 7.04 (s, 2 H), 7.78–7.81 (m, 32 H), 8.13 (s, 8 H), 8.19 (s, 4 H). ¹³C NMR (75 MHz, DMSO-d ₆): δ = 32.8, 49.6, 52.5, 61.1, 114.0, 119.7, 119.9, 120.0, 121.6, 123.1, 123.4, 124.9, 131.4, 134.4, 137.8, 142.5, 158.3, 167.3. MS (QTOF): m/z = 2748.2 [M⁺]. Anal. Calcd for C₁₄₂H₁₀₆N₄₄O₂₀: C, 62.05; H, 3.89; N, 22.42. Found: C, 62.22; H, 3.78; N, 22.53.