Iptycene-Containing Azaacenes with Tunable Luminescence

A. Lennart Schleper; Constantin-Christian A. Voll; Jens U. Engelhart; Timothy M. Swager

doi:10.1055/s-0036-1589503

Synlett, Inhaltsverzeichnis

Synlett 2017; 28(20): 2783-2789
DOI: 10.1055/s-0036-1589503

letter

Iptycene-Containing Azaacenes with Tunable Luminescence

A. Lennart Schleper §

Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge MA, 02139, USA eMail: tswager@mit.edu

,

Constantin-Christian A. Voll §

Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge MA, 02139, USA eMail: tswager@mit.edu

,

Jens U. Engelhart

Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge MA, 02139, USA eMail: tswager@mit.edu

,

Timothy M. Swager*

Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge MA, 02139, USA eMail: tswager@mit.edu

› Institutsangaben

Abstract

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^§ These authors contributed equally

Abstract

An optimized route toward iptycene-capped, p-dibromo-quinoxalinophenazine was developed, increasing the yield significantly from literature procedures. New iptycene-containing symmetrical azaacenes were synthesized from this intermediate using Suzuki–Miyaura cross-coupling, and their photophysical properties were evaluated. Tuning the substituents allows modulating emission wavelengths across the visible spectrum. Substitution with 3-methoxy-2-methylthiophene exhibits a quantum yield of 35%. The (triisopropylsilyl)acetylene product has a quantum yield of 38% and serves as a model compound for the synthesis of polymers based on this electrooptically active molecular motif.

Key words

N-heteroiptycene - Suzuki–Miyaura cross-coupling - Sonogashira coupling - pyrazinoquinoxaline - luminescence

Volltext

Referenzen

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35 Preparation of Compounds 2 and 3 Following a literature procedure, see ref. 21.
36 Preparation of Compound 7 The optimized reaction was carried out in a 20 mL vial, containing zinc powder (470 mg, 7.19 mmol) suspended in AcOH (3.5 mL). Under stirring compound 5 (138 mg, 358 μmol) was added, and the reaction mixture was heated to 60 °C for 1 h. The reduced colorless intermediate 6 was separated from the zinc powder by filtration through a pad of Celite and added dropwise to a solution of 4 (61 mg, 260 μmol) in AcOH (1.5 mL) over 1 h. A yellow precipitate immediately formed. The solution was stirred for another 1 h and extracted several times with CH₂Cl₂ (20 mL) until the organic phase was colorless. The combined organic layers were washed with an aq NaHCO₃ solution (100 mL) and water (100 mL). After evaporation of the solvent, the crude product was purified via column chromatography (SiO₂, hexane–CH₂Cl₂ = 3:1 → 0:1). The product (7, 65 mg, 93.8 μmol, 72%) was obtained as a yellow powder. ¹H NMR (400 MHz, CDCl₃): δ = 7.59 (dd, J3 = 5.4 Hz, J4 = 3.2 Hz, 4 H, CH), 7.17 (dd, J3 = 5.4 Hz, J4 = 3.2 Hz, 4 H, CH), 5.84 (s, 4 H, CH) ppm.
37 Preparation of Compounds 8–13 (GP1) A Schlenk flask was filled with 7 (10 mg, 14.4 μmol), arylboronic acid (2.2 equiv, 31.7 μmol), and K₃PO₄ (12.3 mg, 57.8 μmol), evacuated, and purged with argon. A mixture of water–toluene–1,4-dioxane (1:1.8:5.5, 0.5 mL) was added, and the resulting suspension degassed with argon for 15 min. Subsequently, Pd₂(dba)₃ (0.4 mg, 0.437 μmol) and P(o-tol)₃ (1.1 mg, 3.61 μmol) were added, and the reaction was heated to 60 °C for 14 h. Upon full conversion of the starting material, the reaction was diluted with CH₂Cl₂ (10 mL) and washed with water (15 mL) three times. The organic phase was dried over MgSO₄, the solvent evaporated under reduced pressure, and the crude purified by column chromatography (SiO₂, gradient of hexane–CH₂Cl₂).
38 Preparation of Compound 14 In a heat-gun-dried Schlenk tube under an atmosphere of argon, a mixture of 7 (15 mg, 21.7 μmol), iminodibenzyl (9 mg, 47.7 μmol), and Pd-RuPhos-G4 (1.8 mg, 2.17 μmol) was dissolved in dry 1,4-dioxane (0.5 mL). The resulting mixture was degassed in a stream of argon for 10 min. At this point LiHMDS (0.1 M in THF, 54 μL, 54.2 μmol) was added. After heating to 60 °C for 16 h the reaction mixture was dissolved with CH₂Cl₂ and subsequently washed with water and brine. After drying over MgSO₄ and evaporating under reduced pressure, flash column chromatography (SiO₂, hexane–CH₂Cl₂= 1:1) afforded the product as a yellow solid in 56% yield. ¹H NMR (500 MHz, CD₂Cl₂): δ = 7.51 (dd, J = 5.4, 3.2 Hz, 8 H), 7.14 (ddd, J = 8.6, 6.5, 2.4 Hz, 12 H), 6.72 (td, J = 7.3, 1.2 Hz, 4 H), 6.54 (ddd, J = 8.7, 7.2, 1.7 Hz, 4 H), 6.37 (dd, J = 8.4, 1.2 Hz, 4 H), 5.61 (s, 4 H), 3.67 (s, 8 H) ppm. ESI-HRMS: m/z [M + H]⁺ = 921.3700; found: 921.3703.
39 Preparation of Compound 15 Compound 7 (20 mg, 28.9 μmol), Pd(PPh₃)₄ (6.4 mg, 5.54 μmol), and CuI (1.0 mg, 5.25 μmol) were suspended in THF–Et₃N (1:1, 1.5 mL). After degassing with argon for 15 min, TIPS acetylene (150 μL, 578 μmol) was added, and the resulting reaction mixture was stirred at 50 °C for 60 h. The green luminescent reaction mixture was quenched by addition of water (5 mL) and extracted three times with CH₂Cl₂ (10 mL). The combined organic layers were dried over MgSO₄, and the solvent was evaporated under reduced pressure. The crude was purified by column chromatography (SiO₂, hexane–CH₂Cl₂= 4:1 to 1:2). Compound 15 (15 mg, 57%) was obtained as a yellow solid. ¹H NMR (400 MHz, CDCl₃): δ = 7.54 (dd, J3 = 5.4 Hz, J4 = 3.2 Hz, 8H, CH), 7.14 (dd, J3 = 5.4 Hz, J4 = 3.2 Hz, 8 H, CH), 5.60 (s, 4 H, CH), 1.34 (s, 36 H, CH₃), 1.26 (s, 6 H, CH) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 157.7, 141.7, 140.2, 127.0, 125.4, 121.3, 107.6, 55.4, 19.1, 11.9 ppm. ESI-HRMS: m/z [M + H]⁺: 895.4586; found: 895.4566.

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