Helically Twisted Tetracene: Synthesis, Crystal Structure, and Photophysical Properties of Hexabenzo[a,c,fg,j,l,op]tetracene

Abstract

The synthesis, X-ray crystal structure, and photophysical properties of unsubstituted hexabenzo[a,c,fg,j,l,op]tetracene are described. Unlike the previously reported tert-butyl-substituted analogues, unsubstituted hexabenzo[a,c,fg,j,l,op]tetracene showed a helically twisted conformation in the solid state. Density functional theory calculations on the possible conformers were also studied.

Key words

hexabenzotetracene - twisted acenes - polycyclic aromatic hydrocarbons - nonplanar π-system

• References and Notes

• 1a Pascal RA. Chem. Rev. 2006; 106: 4809
• 1b Rickhaus M, Mayor M, Juricek M. Chem. Soc. Rev. 2016; 45: 1542

Reviews on nonplanar π-systems:
• 2a Rieger R, Müllen K. J. Phys. Org. Chem. 2010; 23: 315
• 2b Dodziuk H. Strained Hydrocarbons: Beyond the van’t Hoff and Le Bel Hypothesis. Wiley-VCH; Weinheim: 2009
• 2c Harvey RG. Polycyclic Aromatic Hydrocarbons . Wiley-VCH; New York: 1997
• 2d Tsefrikas VM, Scott LT. Chem. Rev. 2006; 106: 4868
• 2e Wu Y.-T, Siegel JS. Chem. Rev. 2006; 106: 4843

Reviews on C–H arylation of PAHs:
• 3a Wencel-Delord J, Glorius F. Nat. Chem. 2013; 5: 369
• 3b Segawa Y, Maekawa T, Itami K. Angew. Chem. Int. Ed. 2015; 54: 66
• 4 Ozaki K, Kawasumi K, Shibata M, Ito H, Itami K. Nat. Commun. 2015; 6: 6251
• 5 Kumar B, Strasser CE, King BT. J. Org. Chem. 2012; 77: 311
• 6a Zhong Y, Kumar B, Oh S, Trinh MT, Wu Y, Elbert K, Li P, Zhu X, Xiao S, Ng F, Steigerwald ML, Nuckolls C. J. Am. Chem. Soc. 2014; 136: 8122
• 6b Qian H, Negri F, Wang C, Wang Z. J. Am. Chem. Soc. 2008; 130: 17970
• 7 Synthesis of Hexabenzo[a,c,fg,j,l,op]tetracene (1) To a 10 mL Schlenk tube containing a magnetic stirring bar were added pyrene (81.0 mg, 400 μmol), 5,5-dimethyldibenzo[b,d]silole (253 mg, 1.20 mmol), o-chloranil (394 mg, 1.60 mmol), and Pd(MeCN)₄(BF₄)₂ (8.9 mg, 20 μmol). After dry DCE (4 mL) was added via a syringe through the septum, the septum was then replaced with argon-balloon-equipped condenser. The resultant mixture was stirred at reflux for 2.5 h. After the reaction mixture was cooled down to room temperature, this mixture was passed through a short pad of silica gel, washed with CH₂Cl₂, and solvents were removed under reduced pressure. The residue was subjected to silica gel chromatography (hexane–CH₂Cl₂, 10:1) to afford 1 (116 mg, 58%) as a white solid. ¹H NMR (600 MHz, CD₂Cl₂): δ = 7.70 (t, J = 7.1 Hz, 4 H), 7.77 (t, J = 7.1 Hz, 4 H), 8.12 (t, J = 7.5 Hz, 2 H), 8.81 (d, J = 8.2 Hz, 4 H), 8.88 (d, J = 8.2 Hz, 4 H), 8.99 (d, J = 7.5 Hz, 4 H). ¹³C NMR (150 MHz, C₂D₂Cl₄): δ = 123.6 (CH), 124.2 (C_q), 125.6 (CH), 125.8 (CH), 126.8 (CH), 127.0 (CH), 127.7 (C_q), 128.1 (C_q), 128.5 (CH), 129.3 (C_q), 130.8 (C_q). HRMS–FAB: m/z calcd for C₄₀H₂₂ [M]⁺: 502.1716; found: 502.1719; mp >300 °C. All other experimental procedures and characterization data of 1 can be found in the Supporting Information.
• 8 Crystal Data of 1 Rigaku MicroMax007HF with PILATUS diffractometer, graphite-monochromated Mo Kα radiation (λ = 0.71075 Å), formula: C₄₄H₂₂, FW = 502.58, T = 123(2) K, monoclinic, P2₁/a, a = 7.839(4) Å, b = 26.538(11) Å, c = 11.640(5) Å, β = 98.627(12)°, V = 2394.1(19) ų, Z = 4, D _calc = 1.394 g/cm³, μ = 0.079 mm^–1, F(000) = 1048, crystal size: 0.20 × 0.20 × 0.01 mm³, θ range: 3.04–25.00°, reflections collected: 29984, independent reflections: 4172, R _int = 0.0760, param.: 361, GOF on F ²: 1.121, R ₁ = 0.0832, wR ₂ = 0.2285 (I > 2σ(I)), R ₁ = 0.1036, wR ₂ = 0.2634 (all data) The structures were solved by direct methods with SIR-97 and refined by full-matrix least-squares techniques against F ² (SHELXL-97). The intensities were corrected for Lorentz and polarization effects. The nonhydrogen atoms were refined anisotropically. Hydrogen atoms were placed using AFIX instructions. CCDC 1450739 contains the supplementary crystallographic data for this paper. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/getstructures.
• 9a Muir KW, Robertson JM. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1972; 28: 879
• 9b Fujisawa S, Oonishi I, Aoki J, Ohashi Y, Sasada Y. Bull. Chem. Soc. Jpn. 1982; 55: 3424
• 9c Marsh RE, Herbstein FH. Acta Crystallogr., Sect. B: Struct. Sci. 1988; 44: 77
• 9d Rossman MG. J. Chem. Soc. 1959; 2607
• 9e Izuoka A, Wakui K, Fukuda T, Sato N, Sugawara T. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1992; 48: 900
• 9f Robertson JM, Trotter J. J. Chem. Soc. 1959; 2614
• 10a Herbstein F. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1979; 35: 1661
• 10b Thulstrup EW, Spanget-Larsen J, Waluk J. Theor. Chim. Acta 1994; 89: 301
• 11 Zöphel L, Berger R, Gao P, Enkelmann V, Baumgarten M, Wagner M, Müllen K. Chem. Eur. J. 2013; 19: 17821