Iptycene-Containing Azaacenes with Tunable Luminescence

^§ 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

• References and Notes

• 1 Krebs FC. Sol. Energy Mater. Sol. Cells 2009; 93: 394
• 2 Burgues-Ceballos I. Stella M. Lacharmoise P. Martinez-Ferrero E. J. Mater. Chem. A 2014; 2: 17711
• 3 Segal M. Baldo M. Holmes R. Forrest S. Soos Z. Phys. Rev. B 2003; 68: 1
• 4 Adachi C. Baldo MA. Thompson ME. Forrest SR. J. Appl. Phys. 2001; 90: 5048
• 5 Hashimoto M. Igawa S. Yashima M. Kawata I. Hoshino M. Osawa M. J. Am. Chem. Soc. 2011; 133: 10348
• 6 Baldo MA. Adachi C. Forrest SR. Phys. Rev. B: Condens. Matter Mater. Phys. 2000; 62: 10967
• 7 Peng Q. Obolda A. Zhang M. Li F. Angew. Chem. Int. Ed. 2015; 54: 7091
• 8 Obolda A. Ai X. Zhang M. Li F. ACS Appl. Mater. Interfaces 2016; 8: 35472
• 9 Uoyama H. Goushi K. Shizu K. Nomura H. Adachi C. Nature (London, U.K.) 2012; 492: 234
• 10 Luo Y. Aziz H. Adv. Funct. Mater. 2010; 20: 1285
• 11 Kondakov DY. Pawlik TD. Hatwar TK. Spindler JP. J. Appl. Phys. 2009; 106: 124510
• 12 Li W. Pan Y. Xiao R. Peng Q. Zhang S. Ma D. Li F. Shen F. Wang Y. Yang B. Ma Y. Adv. Funct. Mater. 2014; 24: 1609
• 13 Cui L.-S. Nomura H. Geng Y. Kim JU. Nakanotani H. Adachi C. Angew. Chem. Int. Ed. 2017; 56: 1571
• 14 Turro NJ. Modern Molecular Photophysics. Benjamin Cummings; San Francisco CA: 1978
• 15 Nakanotani H. Higuchi T. Furukawa T. Masui K. Morimoto K. Numata M. Tanaka H. Sagara Y. Yasuda T. Adachi C. Nat. Commun. 2014; 5: 4016
• 16 Goushi K. Yoshida K. Sato K. Adachi C. Nat. Photonics 2012; 6: 253
• 17 Kawasumi K. Wu T. Zhu T. Chae HS. Van Voorhis T. Baldo MA. Swager TM. J. Am. Chem. Soc. 2015; 137: 11908
• 18 Chavez III R. Cai M. Tlach B. Wheeler DL. Kaudal R. Tsyrenova A. Tomlinson AL. Shinar R. Shinar J. Jeffries-EL M. J. Mater. Chem. 2016; 4: 3765
• 19 Lim J. Albright TA. Martin BR. Miljanić OS. J. Org. Chem. 2011; 76: 10207
• 20 Marsden JA. Miller JJ. Shirtcliff LD. Haley MM. J. Am. Chem. Soc. 2005; 127: 2464
• 21 Zucchero AJ. McGrier PL. Bunz UH. F. Acc. Chem. Res. 2010; 43: 397
• 22 Kivala M. Diederich F. Acc. Chem. Res. 2009; 42: 235
• 23 Endo A. Sato K. Yoshimura K. Kai T. Kawada A. Miyazaki H. Adachi C. Appl. Phys. Lett. 2011; 98: 10
• 24 Hirata S. Sakai Y. Masui K. Tanaka H. Lee SY. Nomura H. Nakamura N. Yasumatsu M. Nakanotani H. Zhang Q. Shizu K. Miyazaki H. Adachi C. Nat. Mater. 2015; 14: 330
• 25 Anthony JE. Chem. Rev. 2006; 106: 5028
• 26 Li J. Zhang Q. ACS Appl. Mater. Interfaces 2015; 7: 28049
• 27 Swager TM. Acc. Chem. Res. 2008; 41: 1181
• 28 Wright MW. Welker ME. J. Org. Chem. 1996; 61: 133
• 29 Zhang L. Jiang K. Li G. Zhang Q. Yang L. J. Mater. Chem. A 2014; 2: 14852
• 30 Wang E. Hou L. Wang Z. Hellström S. Mammo W. Zhang F. Inganäs O. Andersson MR. Org. Lett. 2010; 12: 4470
• 31 Huang W. Buchwald SL. Chem. Eur. J. 2016; 22: 14186
• 32 Ganschow M. Koser S. Hahn S. Rominger F. Freudenberg J. Bunz UH. F. Chem. Eur. J. 2017; 23: 4415
• 33 Tao Y. Yuan K. Chen T. Xu P. Li H. Chen R. Zheng C. Zhang L. Huang W. Adv. Mater. 2014; 26: 7931
• 34 Zhang Q. Li J. Shizu K. Huang S. Hirata S. Miyazaki H. Adachi C. J. Am. Chem. Soc. 2012; 134: 14706
• 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_2­).
• 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.