Synlett 2017; 28(20): 2783-2789
DOI: 10.1055/s-0036-1589503
letter
© Georg Thieme Verlag Stuttgart · New York

Iptycene-Containing Azaacenes with Tunable Luminescence

A. Lennart Schleper §, Constantin-Christian A. Voll §, Jens U. Engelhart, Timothy M. Swager*
  • Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge MA, 02139, USA   Email: tswager@mit.edu
Financial support was provided through the Airforce Office of Scientific Research, a Cusanuswerk scholarship of ALS, a MITei fellowship of CCAV sponsored by Eni S.p.A., and the German Research Foundation (DFG) of JUE
Further Information

Publication History

Received: 05 April 2017

Accepted after revision: 15 May 2017

Publication Date:
19 July 2017 (eFirst)

§ 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.

Supporting Information

 
  • References and Notes

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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–CH2Cl).
  • 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.