Carbonyl-to-Alkyne Electron Donation Effects in up to 10-nm-Long, Unimolecular Oligo(p-phenylene ethynylenes)

 

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Abstract

We synthesized some of the longest unimolecular oligo(p-phenylene ethynylenes) (OPEs), which are fully substituted with electron-withdrawing ester groups. An iterative convergent/divergent (a.k.a. iterative exponential growth – IEG) strategy based on Sonogashira couplings was utilized to access these sequence-defined macromolecules with up to 16 repeating units and 32 ester substituents. The carbonyl groups of the ester substituents interact with the triple bonds of the OPEs, leading to (i) unusual, angled triple bonds with increased rotational barrier, (ii) enhanced conformational disorder, and (iii) associated broadening of the UV/Vis absorption spectrum. Our results demonstrate that fully air-stable, unimolecular OPEs with ester groups can readily be accessed with IEG chemistry, providing new macromolecular backbones with unique geometrical, conformational, and photophysical properties.

Supporting Information

Supporting Information for this article is available online at https://doi.org/10.1055/s-0041-1730899.

^# These authors have contributed equally to this work.

Publication History

Received: 24 January 2021

Accepted: 30 April 2021

Article published online:
18 June 2021

© 2021. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/)

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany

• References and Notes

• 1 New address: Sinu C. Rajappan, School of Polymer Science and Engineering, University of Southern Mississippi, 118 College Drive, Hattiesburg, MS 39406, USA
  PubMed
• 2a Palmans A, Montali A, Weder C, Smith P. Proc. MRS 1999; 560: 265
  CrossrefPubMed
• 2b Sen CP, Valiyaveettil S. J. Polym. Sci., Part A: Polym. Chem. 2016; 54: 3652
  PubMed
• 2c Liang J, Wu P, Tan C, Jiang Y. RSC Adv. 2018; 8: 9218
  CrossrefPubMed
• 2d Braeken Y, Cheruku S, Seneca S, Smisdom N, Berden L, Kruyfhooft L, Penxten H, Lutsen L, Fron E, Vanderzande D, Ameloot M, Maes W, Ethirajan A. ACS Biomater. Sci. Eng. 2019; 5: 1967
  CrossrefPubMed
• 2e Hleli E, Mbarek M, Gouid Z, Ulbricsht C, Romdhane S, Ben Said R, Guesmi M, Egbe DA. M, Bouchriha H. J. Phys. Chem. Solids 2020; 136: 109157
  CrossrefPubMed
• 2f Jagadesan P, Yu Z, Barboza-Ramos I, Lara HH, Vazquez-Munoz R, Lopez-Ribot JL, Schanze KS. Chem. Mater. 2020; 32: 6186
  CrossrefPubMed
• 2g Nie J, Wang Z, Huang X, Lu G, Feng C. Macromolecules 2020; 53: 6299
  CrossrefPubMed
• 2h Wang Q, Zhong Y, Miller DP, Lu X, Tang Q, Lu Z.-L, Zurek E, Liu R, Gong B. J. Am. Chem. Soc. 2020; 142: 2915
  CrossrefPubMed
• 2i Zhang Y, Zhan H, Chen J, Sun L, Fan L.-J. J. Polym. Sci. 2020; 58: 2088
  PubMed
• 3a Remmers M, Schulze M, Wegner G. Macromol. Rapid Commun. 1996; 17: 239
  CrossrefPubMed
• 3b Levitsky IA, Kim J, Swager TM. J. Am. Chem. Soc. 1999; 121: 1466
  CrossrefPubMed
• 3c Brizius G, Pschirer NG, Steffen W, Stitzer K, zur Loye H.-C, Bunz UH. F. J. Am. Chem. Soc. 2000; 122: 12435
  CrossrefPubMed
• 3d Kim J, McQuade DT, McHugh SK, Swager TM. Angew. Chem. Int. Ed. 2000; 39: 3868
  CrossrefPubMed
• 3e McQuade DT, Hegedus AH, Swager TM. J. Am. Chem. Soc. 2000; 122: 12389
  CrossrefPubMed
• 3f McQuade DT, Kim J, Swager TM. J. Am. Chem. Soc. 2000; 122: 5885
  CrossrefPubMed
• 3g Kim J, Swager TM. Nature 2001; 411: 1030
  PubMed
• 3h Schmitz C, Posch P, Thelakkat M, Schmidt H.-W, Montali A, Feldman K, Smith P, Weder C. Adv. Funct. Mater. 2001; 11: 41
  CrossrefPubMed
• 3i Nesterov EE, Zhu Z, Swager TM. J. Am. Chem. Soc. 2005; 127: 10083
  CrossrefPubMed
• 3j Moon JH, McDaniel W, MacLean P, Hancock LF. Angew. Chem. Int. Ed. 2007; 46: 8223
  CrossrefPubMed
• 3k Satrijo A, Swager TM. J. Am. Chem. Soc. 2007; 129: 16020
  CrossrefPubMed
• 3l Egbe DA. M, Tuerk S, Rathgeber S, Kuehnlenz F, Jadhav R, Wild A, Birckner E, Adam G, Pivrikas A, Cimrova V, Knor G, Sariciftci NS, Hoppe H. Macromolecules 2010; 43: 1261
  CrossrefPubMed
• 3m Jagadesan P, Valandro SR, Schanze KS. Mater. Chem. Front. 2020; 4: 3649
  CrossrefPubMed
• 3n Liu K, Shen Y, Li X, Zhang Y, Quan Y, Cheng Y. Chem. Commun. 2020; 56: 12829
  CrossrefPubMed
• 3o Luo SL, Lin C.-J, Ku KH, Yoshinaga K, Swager TM. ACS Nano 2020; 14: 7297
  CrossrefPubMed
• 4a Liu X, Weinert ZJ, Sharafi M, Liao C, Li J, Schneebeli ST. Angew. Chem. Int. Ed. 2015; 54: 12772
  CrossrefPubMed
• 4b Beaudoin D, Rominger F, Mastalerz M. Angew. Chem. Int. Ed. 2016; 55: 15599
  CrossrefPubMed
• 4c Beaudoin D, Rominger F, Mastalerz M. Angew. Chem. Int. Ed. 2016; 55: 15599
  CrossrefPubMed
• 4d Sharafi M, Weinert ZJ, Cohen IM, Liao C, Ivancic M, Li J, Schneebeli ST. Synlett 2016; 27: 2145
  Article in Thieme ConnectPubMed
• 4e Rommelmann P, Greschner W, Ihrig S, Neumann B, Stammler H.-G, Groeger H, Kuck D. Eur. J. Org. Chem. 2018; 2018: 3891
  CrossrefPubMed
• 4f Campbell JP, Rajappan SC, Jaynes TJ, Sharafi M, Ma Y.-T, Li J, Schneebeli ST. Angew. Chem. Int. Ed. 2019; 58: 1035
  CrossrefPubMed
• 4g Campbell JP, Sharafi M, Murphy KE, Bocanegra JL, Schneebeli ST. Supramol. Chem. 2019; 31: 565
  CrossrefPubMed
• 5a Nielsen MB, Diederich F. Chem. Rev. 2005; 105: 1837
  CrossrefPubMed
• 5b Baker MA, Tsai C.-H, Noonan KJ. T. Chem. Eur. J. 2018; 24: 13078
  CrossrefPubMed
• 6a Breen CA, Deng T, Breiner T, Thomas EL, Swager TM. J. Am. Chem. Soc. 2003; 125: 9942
  CrossrefPubMed
• 6b Smith RC, Tennyson AG, Lim MH, Lippard SJ. Org. Lett. 2005; 7: 3573
  CrossrefPubMed
• 6c Boden BN, Jardine KJ, Leung AC. W, MacLachlan MJ. Org. Lett. 2006; 8: 1855
  CrossrefPubMed
• 6d VanVeller B, Miki K, Swager TM. Org. Lett. 2010; 12: 1292
  CrossrefPubMed
• 7a Remmers M, Neher D, Gruener J, Friend RH, Gelinck GH, Warman JM, Quattrocchi C, dos Santos DA, Bredas J.-L. Macromolecules 1996; 29: 7432
  CrossrefPubMed
• 7b Montali A, Smith P, Weder C. Synth. Met. 1998; 97: 123
  CrossrefPubMed
• 7c Rozanski LJ, Bunz UH. F, Vanden Bout DA. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 2007; 48: 288
  PubMed
• 7d Rozanski LJ, Vanden Bout DA, Bunz UH. F. In: Excimer Emission in Di-alkyl Poly(p-phenylene ethynylene) LEDs. American Chemical Society; Washington: 2007
• 7e Burnworth M, Mendez JD, Schroeter M, Rowan SJ, Weder C. Macromolecules 2008; 41: 2157
  CrossrefPubMed
• 8a Zheng J, Swager TM. Chem. Commun. 2004; 2798
  PubMed
• 8b Zhang L, Yin Q, Huang H, Wang B. J. Mater. Chem. B 2013; 1: 756
  CrossrefPubMed
• 8c Zhang L, Huang H, Xu N, Yin Q. J. Mater. Chem. B 2014; 2: 4935
  CrossrefPubMed
• 8d D'Olieslaeger L, Braeken Y, Cheruku S, Smits J, Ameloot M, Vanderzande D, Maes W, Ethirajan A. J. Colloid Interface Sci. 2017; 504: 527
  CrossrefPubMed
• 9a Grem G, Leditzky G, Ullrich B, Leising G. Adv. Mater. 1992; 4: 36
  CrossrefPubMed
• 9b Yamamoto T, Morita A, Miyazaki Y, Maruyama T, Wakayama H, Zhou ZH, Nakamura Y, Kanbara T, Sasaki S, Kubota K. Macromolecules 1992; 25: 1214
  CrossrefPubMed
• 9c Son S, Dodabalapur A, Lovinger AJ, Galvin ME. Science 1995; 269: 376
  CrossrefPubMed
• 9d Fou AC, Onitsuka O, Ferreira M, Rubner MF, Hsieh BR. J. Appl. Phys. 1996; 79: 7501
  PubMed
• 9e Van Duren JK. J, Yang X, Loos J, Bulle-Lieuwma CW. T, Sieval AB, Hummelen JC, Janssen RA. J. Adv. Funct. Mater. 2004; 14: 425
  CrossrefPubMed
• 9f Weber J, Thomas A. J. Am. Chem. Soc. 2008; 130: 6334
  CrossrefPubMed
• 9g Garcia JM, Garcia FC, Serna F, de la Pena JL. Prog. Polym. Sci. 2010; 35: 623
  CrossrefPubMed
• 9h Lei T, Dou J.-H, Cao X.-Y, Wang J.-Y, Pei J. J. Am. Chem. Soc. 2013; 135: 12168
  CrossrefPubMed
• 9i Lei T, Xia X, Wang J.-Y, Liu C.-J, Pei J. J. Am. Chem. Soc. 2014; 136: 2135
  CrossrefPubMed
• 9j Sun H, Martinez D, Li Z, Schanze KS. ACS Appl. Mater. Interfaces 2020; 12: 53310
  CrossrefPubMed
• 10 Pawle RH, Agarwal A, Malveira S, Smith ZC, Thomas III SW. Macromolecules 2014; 47: 2250
  CrossrefPubMed
• 11a Gao H. Macromol. Rapid Commun. 2012; 33: 722
  CrossrefPubMed
• 11b Landry E, Ye Z. Macromol. Rapid Commun. 2013; 34: 1493
  CrossrefPubMed
• 11c Mullner M, Muller AH. E. Polymer 2016; 98: 389
  CrossrefPubMed
• 11d Wang Y, Wang L, Chen G, Gong S. Macromol. Biosci. 2017; 17: 1600292
  CrossrefPubMed
• 11e Golder MR, Jiang Y, Teichen PE, Nguyen HV. T, Wang W, Milos N, Freedman SA, Willard AP, Johnson JA. J. Am. Chem. Soc. 2018; 140: 1596
  CrossrefPubMed
• 12a Soos ZG, Mukhopadhyay D, Hennessy MH. Chem. Phys. 1996; 210: 249
  CrossrefPubMed
• 12b Harrison MG, Moller S, Weiser G, Urbasch G, Mahrt RF, Bassler H, Scherf U. Phys. Rev. B: Condens. Matter 1999; 60: 8650
  CrossrefPubMed
• 12c Muller JG, Lemmer U, Raschke G, Anni M, Scherf U, Lupton JM, Feldmann J. Phys. Rev. Lett. 2003; 91: 267403/1
  PubMed
• 12d Yang X, Dykstra TE, Scholes GD. Phys. Rev. B: Condens. Matter 2005; 71: 045203/1
  PubMed
• 12e Furmanchuk Ao, Leszczynski J, Tretiak S, Kilina SV. J. Phys. Chem. C 2012; 116: 6831
  PubMed
• 13a Ickenroth D, Weissmann S, Rumpf N, Meier H. Eur. J. Org. Chem. 2002; 2808
  PubMed
• 13b Chen J, Vachon J, Feringa BL. J. Org. Chem. 2018; 83: 6025
  CrossrefPubMed
• 13c Hergert M, Bender M, Seehafer K, Bunz UH. F. Chem. Eur. J. 2018; 24: 3132
  CrossrefPubMed
• 13d Schneider RV, Waibel KA, Arndt AP, Lang M, Seim R, Busko D, Braese S, Lemmer U, Meier MA. R. Sci. Rep. 2018; 8: 1
  CrossrefPubMed
• 13e Eder T, Vogelsang J, Bange S, Remmerssen K, Schmitz D, Jester S.-S, Keller TJ, Hoeger S, Lupton JM. Angew. Chem. Int. Ed. 2019; 58: 18898
  CrossrefPubMed
• 14a Barnes JC, Ehrlich DJ. C, Gao AX, Leibfarth FA, Jiang Y, Zhou E, Jamison TF, Johnson JA. Nat. Chem. 2015; 7: 810
  CrossrefPubMed
• 14b Leibfarth FA, Johnson JA, Jamison TF. Proc. Natl. Acad. Sci. U.S.A 2015; 112: 10617
  CrossrefPubMed
• 15 All DFT calculations were carried out with the Jaguar software package, with fully analytical integrals (Jaguar keyword: nops = 1) as well as with maximum sized DFT grids (Jaguar keywords: gdftgrad = −14, gdftmed = −14, and gdftfine = −14). Geometries were optimized with the B3LYP-MM dispersion-corrected functional (see: Ref. 16) with the LACVP* basis set (for which the parameters of the functional have been carefully optimized to also account for basis set superposition error; see: Ref. 16e), followed by single point energy calculations at the B3LYP-MM/cc-pVDZ + + level of theory. The vibrational frequencies for all minimized structures were then calculated at the B3LYP-MM/LACVP* level, and the corresponding zero-point energies were included in the calculation of the relative energies. Solvation energies were calculated via single-point calculations at the B3LYP-MM/LACVP* level, with the PBF CHCl₃ solvent model implemented in the Jaguar software package. Torsional energy profiles were constructed by performing constrained structural optimizations with the dihedral angles ω (defined in Figure 2B) set to the specified values. Since the harmonic frequency approximation is only applicable to minimized structures (without constrained coordinates) zero-point energy corrections were not applied to the torsional energy profiles. Non-covalent interaction (NCI) plots as well as NCI interaction energies were obtained from the reduced density gradient at the B3LYP-MM/LACVP* level, following the methods of Johnson et al. (see: Ref. 17, Jaguar keyword: iplotnoncov = 1). Dipole moments were calculated at the B3LYP-MM/LACVP* level in vacuum
  PubMed
• 16a Vosko SH, Wilk L, Nusair M. Can. J. Phys. 1980; 58: 1200
  CrossrefPubMed
• 16b Lee C, Yang W, Parr RG. Phys. Rev. B Condens. Matter 1988; 37: 785
  CrossrefPubMed
• 16c Becke AD. J. Chem. Phys. 1993; 98: 5648
  CrossrefPubMed
• 16d Stephens PJ, Devlin FJ, Chabalowski CF, Frisch MJ. J. Phys. Chem. 1994; 98: 11623
  CrossrefPubMed
• 16e Schneebeli ST, Bochevarov AD, Friesner RA. J. Chem. Theory Comput. 2011; 7: 658
  CrossrefPubMed
• 17 Johnson ER, Keinan S, Mori-Sánchez P, Contreras-García J, Cohen AJ, Yang W. J. Am. Chem. Soc. 2010; 132: 6498
  CrossrefPubMed
• 18a Jaguar, version 10.4. Schrodinger, Inc.; New York, NY: 2019
  Google Scholar
• 18b Bochevarov AD, Harder E, Hughes TF, Greenwood JR, Braden DA, Philipp DM, Rinaldo D, Halls MD, Zhang J, Friesner RA. Int. J. Quantum Chem. 2013; 113: 2110
  CrossrefPubMed
• 19 Lingard H, Han JT, Thompson AL, Leung IK. H, Scott RT. W, Thompson S, Hamilton AD. Angew. Chem. Int. Ed. 2014; 53: 3650
  CrossrefPubMed
• 20 Zhang J, Moore JS, Xu Z, Aguirre RA. J. Am. Chem. Soc. 1992; 114: 2273
  CrossrefPubMed
• 21 Kim M, Boissonnault JA, Dau PV, Cohen SM. Angew. Chem. Int. Ed. 2011; 50: 12193
  CrossrefPubMed
• 22 General synthetic procedure for IEG growth deprotection: For TIPS deprotection, 4 M solutions of the TIPS-protected derivatives 3–6 (1.0 equiv) in anhydrous CH₂Cl₂ were prepared under an inert-gas atmosphere. Next, a 1 M solution of TBAF (1.5 equiv) in THF was added at room temperature and the reaction mixtures were stirred at room temperature for 1–2 h. Upon completion (monitored by TLC), the reaction mixtures were diluted with CH₂Cl₂ (25 mL) and then washed with water (3 × 20 mL) and brine (20 mL). Next, the organic layers were dried over anhydrous sodium sulfate, filtered, and the solvent was evaporated under reduced pressure. Any remaining catalyst was removed via a short flash column over silica gel (eluents: ethyl acetate/hexane mixtures). The TIPS-deprotected derivatives of the tetramer 5 and the octamer 6 were further purified with size-exclusion chromatography (stationary phase: Bio-Beads™ SX-1 Resin, eluent: CH₂Cl₂) before being carried forward to the Sonogashira coupling steps. Activation (via diazotization–iodination): Following a procedure adopted from Ref. 23, the aniline derivatives 3–6 (1.0 equiv) were dissolved in acetonitrile to form 0.1 M solutions. For compounds with low solubility in acetonitrile, toluene (10 vol%) was added as a co-solvent. Next, a 6 M aqueous HCl solution (10 vol% of the total reaction solvent) was added to the reaction mixtures and the reaction mixtures were cooled in an ice-bath. Diazotization was then initiated by adding an aqueous solution of NaNO₂ (1.1 equiv) dropwise to the reaction mixtures at a reaction temperature of <5 °C. The reaction mixtures were then stirred at ∼0 °C for 15 minutes and subsequently added to ice-cold solutions of KI (3 equiv) in water. The resulting mixtures were again stirred at 0 °C for 1 h and then extracted with ethyl acetate. The combined organic layers were washed with water and with brine, dried over anhydrous sodium sulfate, filtered, and the solvent was evaporated under reduced pressure. Finally, the crude activated (iodinated) derivatives of 3–6 obtained in this manner were run through short silica gel columns (eluent: ethyl acetate/hexane solvent mixtures) and then directly carried forward to the Sonogashira coupling reactions. Sonogashira couplings: To oven-dried reaction flasks were added (i) the iodo-derivative (1.0 equiv), (ii) Pd(PPh_{3 4} (3 mol%), and (iii) CuI (6 mol%). The reaction flasks were then evacuated and backfilled with argon three times with standard Schlenk techniques. Next, the reaction flasks were charged with anhydrous DMF (12 mL) and triethylamine (2.0 equiv) followed by the TIPS-deprotected acetylene compounds (1.3 equiv). Finally, the reaction mixtures were stirred overnight at 70 °C. The progress of the reactions was monitored by TLC. Upon completion, the reaction mixtures were cooled to room temperature, filtered through Celite® 545, and washed with ethyl acetate. The filtrates were diluted with water and the products were extracted with ethyl acetate. The combined organic layers were washed with water and brine, dried over anhydrous magnesium sulfate, filtered, and the solvent was evaporated under reduced pressure. The crude Sonogashira-coupled materials 4–7 were purified by flash column chromatography (eluents: ethyl acetate in hexane mixtures) and, for the longer derivatives 5–7, subsequent size-exclusion chromatography (stationary phase: Bio-Beads™ SX-1 Resin, eluent: CH₂Cl₂)
  PubMed
• 23 Droz AS, Neidlein U, Anderson S, Seiler P, Diederich F. Helv. Chim. Acta 2001; 84: 2243
  CrossrefPubMed
• 24a Schumm JS, Pearson DL, Tour JM. Angew. Chem. Int. Ed. Engl. 1994; 33: 1360
  CrossrefPubMed
• 24b Arias-Marin E, Arnault JC, Guillon D, Maillou T, Le Moigne J, Geffroy B, Nunzi JM. Langmuir 2000; 16: 4309
  CrossrefPubMed
• 24c Arias-Marin E, Le Moigne J, Maillou T, Guillon D, Moggio I, Geffroy B. Macromolecules 2003; 36: 3570
  CrossrefPubMed
• 25 Synthesis and characterization data of the dimer 4: Following the general reaction procedure for IEG growth (see: Ref. 22), the monomer 3 (2.0 mmol in 5 mL CH₂Cl₂) was deprotected with TBAF to afford 1.11 g (95% yield) of the TIPS-deprotected derivative of 3. At the same time, 3 (2.0 mmol) was activated following the general diazotization/iodination procedure to afford 1.06 g (57% yield) of the iodinated derivative of 3. The TIPS-deprotected (2.6 mmol) and iodinated (2.0 mmol) derivatives of 3 were then coupled together under Sonogashira coupling conditions to complete the IEG cycle, as detailed in the general IEG procedure. The crude product was purified by flash column chromatography (eluent: 0–20 vol% ethyl acetate in hexanes) to afford 1.72 g (88% yield) of the dimer 4. ¹H NMR (500 MHz, CDCl₃) δ 8.19 (s, 1 H), 8.11 (s, 1 H), 8.04 (s, 1 H), 7.22 (s, 1 H), 6.06 (s, 2 H), 4.29–4.20 (m, 8 H), 1.74 (dt, J = 12.0, 5.8 Hz, 2 H), 1.67 (td, J = 12.6, 6.3 Hz, 2 H), 1.55–1.28 (m, 28 H), 1.27–1.20 (m, 4 H), 1.16–1.14 (m, 21 H), 0.98–0.82 (m, 24 H). ¹³C (¹H) NMR (125 MHz, CDCl₃) δ 167.23, 165.90, 165.32, 165.22, 149.93, 137.99, 136.99, 136.85, 135.58, 135.15, 134.02, 123.84, 122.29, 118.67, 104.26, 99.30, 96.10, 89.23, 68.28, 68.19, 68.15, 67.49, 60.52, 38.95, 38.92, 38.87, 30.60, 30.48, 30.44, 29.12, 29.06, 29.05, 29.03, 24.06, 23.94, 23.90, 23.82, 23.08, 23.04, 18.79, 17.83, 14.18, 14.14, 12.42, 11.49, 11.14, 11.03. HRMS characterization for 4 was obtained after TIPS deprotection: HRMS (neg. ESI) calcd. for C₅₂H₇₄NO₈ ⁻: m/z = 840.5420 [M – H]⁻; found: 840.5421
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• 26 Synthesis and characterization data of the tetramer 5: Following the general reaction procedure for IEG growth (see: Ref. 22), the dimer 4 (1.0 mmol in 8 mL CH₂Cl₂) was deprotected with TBAF to afford 0.828 g (75% yield) of the TIPS-deprotected derivative of 4. At the same time, 4 (1.1 mmol) was activated following the general diazotization/iodination procedure to afford 1.038 g (62% yield) of the iodinated derivative of 4. The TIPS-deprotected (1.3 mmol) and iodinated (1.0 mmol) derivatives of 4 were then coupled together under Sonogashira coupling conditions to complete the IEG cycle, as detailed in the general IEG procedure. The crude product was purified by flash column chromatography (eluent: 0–20 vol% ethyl acetate in hexanes) to afford 0.910 g (82% yield) of the tetramer 5. ¹H NMR (500 MHz, CDCl₃) δ 8.28 (s, 1 H), 8.27 (s, 1 H), 8.24 (s, 1 H), 8.23 (s, 1 H), 8.21 (s, 1 H), 8.16 (s, 1 H), 8.12 (s, 1 H), 7.23 (s, 1 H), 6.07 (s, 2 H), 4.34–4.23 (m, 16 H), 1.79–1.67 (m, 8 H), 1.52–1.23 (m, 64 H), 1.16 (s, 21 H), 0.98–0.93 (m, 6 H), 0.91–0.84 (m, 42 H). ¹³C (¹H) NMR (125 MHz, CDCl₃) δ 167.09, 165.67, 165.01, 164.95, 164.91, 164.76, 149.82, 137.88, 136.87, 136.14, 136.01, 135.86, 135.61, 135.34, 134.54, 134.38, 134.07, 124.32, 123.24, 123.02, 122.57, 121.95, 118.55, 113.21, 109.86, 103.93, 100.16, 96.47, 95.07, 94.72, 94.47, 94.15, 89.19, 68.27, 68.25, 68.18, 68.06, 67.38, 38.82, 38.80, 38.78, 38.74, 30.47, 30.44, 30.32, 29.00, 28.95, 28.92, 23.94, 23.84, 23.78, 23.73, 22.95, 22.92, 18.66, 14.06, 14.03, 11.35, 11.00, 10.91. ∼46 ¹³C (¹H) NMR resonances coincide with other signals. HRMS (pos. ESI) calcd. for C₁₁₃H₁₆₈NO₁₆Si⁺: m/z = 1823.2127 [M + H]⁺; found: 1823.2124
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• 27 Synthesis and characterization data of the octamer 6: Following the general reaction procedure for IEG growth (see: Ref. 22), the tetramer 5 (0.50 mmol in 10 mL CH₂Cl₂) was deprotected with TBAF and the product was purified further via size exclusion chromatography (stationary phase: Bio-Beads™ SX-1 Resin, eluent: CH₂Cl₂) to afford 0.900 g (93% yield) of the TIPS-deprotected derivative of 5. At the same time, 5 (0.32 mmol) was activated following the general diazotization/iodination procedure to afford 0.413 g (67% yield) of the iodinated derivative of 5. The TIPS-deprotected (0.27 mmol) and iodinated (0.21 mmol) derivatives of 5 were then coupled together under Sonogashira coupling conditions to complete the IEG cycle, as detailed in the general IEG procedure. The crude product was purified by flash column chromatography (eluent: 0–20 vol% ethyl acetate in hexanes) to afford 0.200 g (27% yield) of the octamer 6. ¹H NMR (500 MHz, CDCl₃) δ 8.29 (dd, J = 5.0, 2.8 Hz, 10 H), 8.25 (s, 1 H), 8.23 (s, 1 H), 8.21 (s, 1 H), 8.16 (s, 1 H), 8.12 (s, 1 H), 7.24 (s, 1 H), 6.06 (s, 2 H), 4.34–4.22 (m, 32 H), 1.78–1.68 (m, 16 H), 1.52–1.22 (m, 128 H), 1.16 (s, 21 H), 0.98–0.93 (m, 9 H), 0.92–0.84 (m, 87 H). MS (MALDI, DCTB matrix) calcd. for C₂₁₇H₃₁₁NNaO₃₂Si⁺: m/z = 3494.2401 [M + Na]⁺; found: 3494.3000
  PubMed
• 28 Synthesis and characterization data of the hexadecamer 7: Following the general reaction procedure for IEG growth (see: Ref. 22), the tetramer 6 (0.017 mmol in 5 mL CH₂Cl₂) was deprotected with TBAF and the product was purified further via size exclusion chromatography (stationary phase: Bio-Beads™ SX-1 Resin, eluent: CH₂Cl₂) to afford 0.056 g (95% yield) of the TIPS-deprotected derivative of 6. At the same time, 6 (0.029 mmol) was activated following the general diazotization/iodination procedure to afford 0.073 g (53% yield) of the iodinated derivative of 6. The TIPS-deprotected (0.017 mmol) and iodinated (0.015 mmol) derivatives of 6 were then coupled together under Sonogashira coupling conditions to complete the IEG cycle, as detailed in the general IEG procedure. The crude product was purified by flash column chromatography (eluent: 0–20 vol% ethyl acetate in hexanes) and further via size exclusion chromatography (stationary phase: Bio-Beads™ SX-1 Resin, eluent: CH₂Cl₂) to afford 0.020 g (19% yield) of the hexadecamer 7. ¹H DOSY NMR (500 MHz, CDCl₃, polystyrene standard, see Figure S1 for the calibration curve): M̅ _w = 6.9 kDa (expected: 6.8 kDa)
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• 29 See Supplementary Figures S12 and S13 for the ¹³C (¹H) NMR spectra (125 MHz, CDCl₃, 298 K) as well as for the ¹H–¹³C HMBC NMR spectra (500 MHz, CDCl₃, 298 K) of 6 and 7. With over 200 carbon atoms in 6 and over 400 carbon atoms in 7, a large percentage of carbon signals is coinciding and/or is showing relatively weak signal-to-noise ratios. Yet, there are no carbon signals observed in the 80–85 ppm regions, where one would expect to find ¹³C resonances for potential homocoupled diacetylene byproducts (see, e.g., Ref. 33 for the ¹³C (¹H) NMR spectra of ester-containing diacetylene derivatives with similar structures). Taken together with the observed (see: Refs. 27 and 28) molecular weights – and the fact that the ¹H NMR resonances corresponding to the TIPS protecting groups are clearly observed at ∼1.16 ppm with the proper integrations – this finding excludes the formation of homocoupled diacetylene derivatives as potential side-products
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• 30 Xue C, Luo F.-T. Tetrahedron 2004; 60: 6285
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• 31 Sharafi M, Campbell JP, Rajappan SC, Dudkina N, Gray DL, Woods TJ, Li J, Schneebeli ST. Angew. Chem. Int. Ed. 2017; 56: 7097
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• 32 Since a racemic mixture of 2-ethylhexyl bromide was used for the synthesis, the OPEs are present as a mixture of diastereoisomers, which could further contribute to the observed line-broadening of the UV/Vis spectra
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• 33 Vestergaard M, Jennum K, Sørensen JK, Kilså K, Nielsen MB. J. Org. Chem. 2008; 73: 3175
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• Supplementary Material