Synthesis of Unsymmetrically Functionalized Violanthrenes by Reductive Aromatization of Violanthrone 79

Abstract

The commercially available n-type semiconductive dye Violanthrone 79 was used as starting material to synthesize previously unexplored substituted violanthrenes through a reductive aromatization and functionalization strategy. By using the low-cost reducing agents zinc and sodium dithionite in combination with suitable electrophilic trapping reagents, three violanthrenes functionalized with two pivalyloxy, trimethylsiloxy, or methoxy groups were selectively obtained in high yields. Due to their octyl ether moieties, these new red dyes are highly soluble. They were characterized by means of UV/vis and fluorescence spectroscopy, and their redox properties were studied by cyclic voltammetry. The spectroscopically determined frontier molecular orbital energies are compared to those calculated by density functional theory and suggest that electron-deficient Violanthrone 79 was transformed into three electron-rich violanthrenes with molecular characteristics typically observed in molecular precursors for p-type organic semiconductors.

Key words

arenes - violanthrenes - electron transfer - polycycles - reduction - dyes

• References and Notes

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• 16 VE3 Me₃SiCl (0.4 mL, 3.2 mmol, 16 equiv) was added to a mixture of VO79 (142 mg, 0.20 mmol, 1.0 equiv) and Zn dust (209 mg, 3.20 mmol, 16 equiv) in 1,4-dioxane (10 mL), and the mixture was heated at 80 °C under argon for 18 h while the suspension turned red. When the reaction was complete (TLC), all volatilities were removed in vacuo and the residue was taken up in hexane (20 mL). The mixture was filtered and the product was precipitated at –80 °C then dried in a vacuum to give a red powder; yield: 137 mg (0.16 mmol, 80%). The reaction was also performed on a 1 mmol scale; yield: 660 mg (0.77 mmol, 77%). IR (ATR): 3071 (w), 2925 (s), 2855 (m), 1578 (w), 1494 (w), 1462 (w), 1348 (s), 1314 (m), 1260 (w), 1033 (vs), 876 (vs), 756 (s), 628 (w) cm^–1. ¹H NMR (300.1 MHz, CDCl₃): δ = 0.44 [s, 18 H, Si(CH ₃)₃], 0.82–0.85 (m, 6 H, H_Oct ), 1.20–1.40 (m, 18 H, H_Oct ), 1.50–1.55 (m, 4 H, H_Oct ), 1.97 (quint, ³ J _H,_H = 7.5 Hz, 4 H, H_Oct ), 4.19–4.24 (m, 2 H, OCH ₂), 4.53–4.58 (m, 2 H, OCH ₂), 7.78–7.88 (m, 4 H, H3, H4), 8.37 (d, ³ J _H,_H = 9.6 Hz, 2 H, H6), 8.41 (s, 2 H, H1), 8.56 (dd, ³ J _H,_H = 9.4 Hz, ⁴ J _H,_H = 2.6 Hz, 2 H, H2), 8.75 (d, ³ J _H,_H = 9.7 Hz, 2 H, H7), 9.05 (dd, ³ J _H,_H = 9.2, ⁴ J _H,_H = 2.0 Hz, 2 H, H5). ¹³C NMR (75.5 MHz, CDCl₃): δ = 1.2, 14.2, 22.8, 26.4, 29.5, 29.7, 29.9, 32.0, 69.0, 101.5, 117.8, 119.9, 120.0, 122.2, 123.0, 123.7, 123.8, 125.1, 125.4, 125.7, 125.8, 126.2, 126.6, 128.8, 144.8, 156.0. HRMS (LIFDI+): m/z [M⁺] calcd for C₅₆H₆₆O₄Si₂: 858.44996; found: 858.44898.
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• 19 VE1 Pivalic anhydride (0.4 mL, 3.5 mmol, 16 equiv) was added to a mixture of VO79 (158 mg, 0.22 mmol, 1.0 equiv) and Zn dust (230 mg, 3.52mmol, 16 equiv) in 1,4-dioxane (15 mL), and the mixture was refluxed under argon for 18 h while the suspension turned brownish red. When the reaction was complete (TLC), the suspension was filtered, and all volatilities were removed in vacuo. The residue was taken up in CH₂Cl₂ (20 mL) and filtered over neutral alumina. The product was precipitated from hexane at –80 °C and dried in vacuo to give a red powder; yield: 163 mg (0.19 mmol, 85%). IR (ATR): 2926 (m), 2858 (m), 1751 (s), 1582 (w), 1516 (w), 1430 (w), 1383 (w), 1215 (m), 1109 (vs), 1031 (w), 787 (w), 637 (w) cm^–1. ¹H NMR (300.1 MHz, CDCl₃): δ = 0.79–0.85 (m, 6 H, H_Oct ), 1.20–1.43 (m, 18 H, H_Oct ), 1.47–1.53 (m, 4 H, H_Oct ), 1.74 [s, 18 H, C(CH ₃)₃], 1.96 (quint, ³ J _H,_H = 7.1 Hz, 4 H, H_Oct ), 4.15–4.25 (m, 2 H, OCH ₂), 4.50–4.62 (m, 2 H, OCH ₂), 7.79–7.89 (m, 4 H, H3, H4), 7.99 (d, ³ J _H,_H = 9.6 Hz, 2 H H6), 8.19 (dd, ³ J _H,_H = 9.2, ⁴ J _H,_H = 1.6 Hz, 2 H, H2), 8.42 (s, 2 H, H1), 8.71 (d, ³ J _H,_H = 9.6 Hz, 2 H, H7), 9.07 (dd, ³ J _H,_H = 8.6, ⁴ J _H,_H = 1.1 Hz, 2 H, H5). ¹³C NMR (75.5 MHz, CDCl₃): δ = 14.2, 22.8, 26.3, 26.7, 27.9, 29.5, 29.7, 29.8, 31.9, 40.0, 69.0, 101.7, 118.0, 118.9, 121.3, 121.5, 122.0, 123.9, 124.0, 125.6, 125.7, 125.7, 126.0, 126.9, 128.0, 128.5, 139.4, 156.8, 177.5. HRMS (APCI+): m/z [M + H]⁺ Calcd for C₆₀H₆₇O₆: 883.4932; found: 883.4953.
• 20 VE2
  VO79 (142 mg, 0.20 mmol, 1.0 equiv), KOH (400 mg; excess), and Na₂S₂O₄ (279 mg, 1.60 mmol, 8.0 equiv) were dissolved in toluene (10 mL) and H₂O (10 mL). Aliquat 336 (0.1 mL) was added, and the mixture was stirred for 1 h at 90 °C then cooled to r.t. MeI (0.12 mL, 2.0 mmol, 10 equiv) was added and the mixture was stirred for 30 min at 90 °C. When the reaction was complete (TLC), the organic phase was collected, dried (MgSO₄), filtered, and concentrated. The residue was taken up in CH₂Cl₂ (20 mL) and filtered over neutral alumina. The product was the precipitated at –80 °C from hexane and dried in vacuo to give a red powder; yield: 110 mg (0.15 mmol, 75%). IR (ATR), 3069 (m), 2926 (vs), 2854 (s), 1581 (m), 1492 (m), 1426 (w), 1345 (m), 1211 (vs), 1068 (m), 973 (w), 790 (m), 632 (w) cm^–1. ¹H NMR (300.1 MHz, CDCl₃): δ = 0.75–0.90 (m, 6 H, H_Oct ), 1.18–1.45 (m, 18 H, H_Oct ), 1.45–1.55 (m, 4 H, HOct), 1.97 (quint, ³ J _H,_H = 7.7 Hz, 4 H, HOct), 4.15–4.25 (m, 2 H, OCH2), 4.28 (s, 6 H, OCH3), 4.45–4.65 (m, 2 H, OCH2), 7.82–7.90 (m, 4 H, H3, H4), 8.43 (s, 2 H, H1), 8.48 (d, ³ J _H,_H = 9.5 Hz, 2 H, H6), 8.62 (dd, ³ J _H,_H = 9.5, ⁴ J _H,_H = 4.2 Hz, 2 H, H2), 8.82 (d, ³ J _H,_H = 9.7 Hz, 2 H, H7), 9.08 (dd, ³ J _H,_H = 9.5, ⁴ J _H,_H = 4.3 Hz, 2 H, H5). ¹³C NMR (75.5 MHz, CDCl₃): δ = 14.2, 22.8, 26.4, 29.5, 29.7, 29.9, 31.7, 31.9, 63.7, 69.0, 101.6, 117.8, 119.5, 122.3, 123.0, 123.2, 124.0, 125.7, 125.9, 126.1, 126.4, 126.7, 128.9, 156.5. HRMS (LIFDI+): m/z [M⁺] Calcd for C₅₂H₅₄O₄: 742.40221; found: 742.40214.
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