Synthesis and Optoelectronic Properties of Iptycene–Naphthazarin Dyes

Abstract

We report the synthesis and characterization of iptycene–naphthazarin dyes by using a sequential Diels–Alder approach. The tautomerization of naphthazarin was used as the key step in the synthesis, with structures confirmed by single-crystal X-ray and NMR analysis. The systematic trends in electronic properties were investigated by UV/Vis spectroscopy. BF₂ complexes of the dyes were prepared by reaction with BF₃·OEt₂ in CH₂Cl₂.

Key words

naphthazarin - iptycenes - Diels–Alder - tautomerization - epimerization

• References and Notes

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• 14 Only the general procedures for the synthesis of the target dyes 5–7 are reported here; all other details and protocols can be found in the Supporting Information. Synthesis of Iptycene–Naphthazarin Dyes 5–7; General Procedure: Dienophiles 1–3 (1 equiv) and diene 4 (1 equiv) were added to a flame-dried Schlenk flask with stirrer bar, and were dissolved in the minimal amount of anhydrous toluene (1–2 mL). The headspace was purged with argon, then heated to reflux overnight (111 °C). The solvent was evaporated under reduced pressure, and the crude material was redissolved in tetrahydrofuran (20 mL). After addition of KO^tBu (18 equiv) and stirring under ambient conditions for 1–3 h, the blue reaction mixture was poured over NH₄Cl (aq) and extracted with EtOAc. The organic layer was dried with MgSO₄, filtered and evaporated. Flash chromatography (SiO₂; hexanes/CH₂Cl₂, 1:1 or 1:2) gave 5–7 as orange solids in 30–53% yield. Compound 5: R_f = 0.35 (SiO₂; hexanes/CH₂Cl₂, 1:1); m.p. >300 °C; ¹H NMR (400 MHz, CD₂Cl₂, 298 K): δ = 5.68 (s, 2 H), 6.10 (s, 2 H), 7.01–7.09 (m, 8 H), 7.41–7.51 (m, 8 H), 8.26 (s, 2 H), 13.18 (s, 2 H); ¹³C NMR (100 MHz, CD₂Cl₂, 298 K): δ = 187.5, 153.6, 152.6, 146.6, 144.5, 144.0, 132.1, 126.5, 126.2, 124.73, 124.65, 122.0, 112.0, 54.5, 48.0; UV/Vis (CH₂Cl₂): λ _max (ε) = 496 (9570), 287 (50230), 259 nm (21130 M^–1 cm^–1); HRMS (ESI): m/z [M]⁺ calcd for C₄₂H₂₄O₄ ⁺: 592.1675; found: 592.1676. Compound 6: R_f = 0.59 (SiO₂; hexanes/CH₂Cl₂, 1:1); m.p. >300 °C; ¹H NMR (400 MHz, CD₂Cl₂, 298 K): δ = 1.20 (s, 12 H), 1.23 (s, 12 H), 1.61 (br. s, 8 H), 5.68 (s, 2 H), 5.94 (s, 2 H), 6.95–7.10 (m, 4 H), 7.40 (s, 4 H), 7.42–7.51 (m, 4 H), 8.27 (s, 2 H), 13.21 (s, 2 H); ¹³C NMR (100 MHz, CD₂Cl₂, 298 K): δ = 187.4, 153.5, 152.5, 147.0, 144.0, 142.7, 141.5, 132.2, 126.4, 124.6, 122.7, 122.0, 111.9, 54.5, 47.4, 35.6, 34.8, 32.2, 32.1; UV/Vis (CH₂Cl₂): λ _max (ε) = 497 (10130), 287 (40040), 257 nm (18420 M^–1 cm^–1); HRMS (ESI): m/z [M]⁺ calcd for C₅₈H₅₂O₄ ⁺: 812.3866; found: 812.3887. Compound 7: R_f = 0.41 (SiO₂; hexanes/CH₂Cl₂, 1:1); m.p. 288–289 °C; ¹H NMR (400 MHz, CD₂Cl₂, 298 K): δ = 2.14 (s, 12 H), 5.68 (s, 2 H), 5.92 (s, 2 H), 7.05 (br. dd, J = 5.5, 3.1 Hz, 4 H), 7.21 (s, 4 H), 7.45 (br. dd, J = 5.5, 3.1 Hz, 4 H), 8.26 (s, 2 H), 13.17 (s, 2 H); ¹³C NMR (100 MHz, CD₂Cl₂, 298 K): δ = 187.4, 153.4, 152.5, 147.3, 144.1, 142.3, 134.1, 132.2, 126.4, 125.9, 124.6, 122.0, 111.9, 54.5, 47.1, 19.7; UV/Vis (CH₂Cl₂): λ _max (ε) = 497 (9425), 288 (38750), 257 nm (17170 M^–1 cm^–1); HRMS (ESI): m/z [M + H]⁺ calcd for C₄₆H₃₃O₄ ⁺: 649.2379; found: 649.2401.