Angewandte Eine Zeitschrift der Gesellschaft Deutscher Chemiker Chemie www.angewandte.de Akzeptierter Artikel Titel: Living Supramolecular Polymerization of a Perylene Bisimide Dye into Fluorescent J-Aggregates Autoren: Wolfgang Wagner, Marius Wehner, Vladimir Stepanenko, Soichiro Ogi, and Frank Würthner Dieser Beitrag wurde nach Begutachtung und Überarbeitung sofort als "akzeptierter Artikel" (Accepted Article; AA) publiziert und kann unter Angabe der unten stehenden Digitalobjekt-Identifizierungsnummer (DOI) zitiert werden. Die deutsche Übersetzung wird gemeinsam mit der endgültigen englischen Fassung erscheinen. Die endgültige englische Fassung (Version of Record) wird ehestmöglich nach dem Redigieren und einem Korrekturgang als Early-View-Beitrag erscheinen und kann sich naturgemäß von der AA-Fassung unterscheiden. Leser sollten daher die endgültige Fassung, sobald sie veröffentlicht ist, verwenden. Für die AA-Fassung trägt der Autor die alleinige Verantwortung. Zitierweise: Angew. Chem. Int. Ed. 10.1002/anie.201709307 Angew. Chem. 10.1002/ange.201709307 Link zur VoR: http://dx.doi.org/10.1002/anie.201709307 http://dx.doi.org/10.1002/ange.201709307 10.1002/ange.201709307 Angewandte Chemie COMMUNICATION Living Supramolecular Polymerization of a Perylene Bisimide Dye into Fluorescent J-Aggregates Abstract: Self-assembly of a new, in bay-position 1,7- dimethoxysubstituted perylene bisimide (PBI) organogelator affords nonfluorescent H-aggregates at fast cooling rates and fluorescent Jaggregates at slow cooling rates. Under properly adjusted conditions the kinetically trapped “off-pathway” H-aggregates transform into the thermodynamically favored J-aggregates, a process that can be accelerated by the addition of J-aggregate seeds. Spectroscopic studies revealed a subtle interplay of - interactions and intra- and intermolecular hydrogen bonding for monomeric, H- and Jaggregated PBIs. Multiple polymerization cycles initiated from the seed termini demonstrate the living character of this chain-growth supramolecular polymerization process. Although living covalent polymerization was introduced as early as in the late 1950s, and since then this research field has undergone a comprehensive development,  its supramolecular counterpart has emerged only recently. Spearheaded by research on seeded “living” block copolymer self-assembly from crystal facets by Manners,  Sugiyasu, Takeuchi and coworkers demonstrated for the first time in 2014 the seed-initiated living supramolecular polymerization of a single aggregate chain with a porphyrin dye. This step marks the logical advancement of a research field that has initially been established based on thermodynamic considerations, i.e. formation of equilibrium structures, and only later on developed toward kinetic control leading to “off-pathway” products, i.e. out-of-equilibrium species. The final step towards living supramolecular polymerization has been achieved recently by both the seed-induced[4,9] as well as the initiator moleculeinduced approach, where either added seeds or properly designed molecules function as initiators for the chain growth of monomers into one-dimensional non-covalently bound molecular aggregates. A crucial requirement for the chain-growth supramolecular polymerization is the retardation of the competing spontaneous self-assembly of monomers which can be accomplished by kinetically trapped “inactive” species.[3, 4, 8-10] We have recently shown that such kinetically trapped species can be programed by molecular design.[9a,b] Thus, simple perylene bisimide (PBI) organogelator molecules bearing terminal amide groups are kinetically trapped by intramolecular hydrogen bonding under appropriate conditions either in unimolecular [9a] or “off-pathway” aggregate[9b] states, and hence inactivated for spontaneous supramolecular polymerization but active upon addition of seeds. With a similar design, Miyajima and Aida demonstrated that the spontaneous polymerization of a bowl-shaped corannulene bearing multiple amide groups can be retarded by intramolecular hydrogen bonding and its chain-growth polymerization can be initiated by addition of a non-hydrogen bonded derivative. [*] W. Wagner, M. Wehner, Dr. V. Stepanenko, Prof. Dr. F. Würthner Universität Würzburg, Institut für Organische Chemie, Am Hubland, 97074 Würzburg (Germany) E-mail: firstname.lastname@example.org Dr. V. Stepanenko, Dr. S. Ogi, Prof. Dr. F. Würthner Universität Würzburg, Center for Nanosystems Chemistry (CNC) and Bavarian Polymer Institute (BPI) Theodor-Boveri-Weg, 97074 Würzburg (Germany) Supporting information for this article is given via a link at the end of the document. Chart 1. Chemical structures of the dimethoxy-substituted MeO-PBI, [9a, 12] reference PBI organogelator H-PBI and benzamide 1. A unique feature of “living” polymers is their active termini that enable initiation of repeated growth cycles of monomers until the “living” ends being terminated. Until to-date, such repeated cycles have been shown only for very few living supramolecular polymerization systems,[4,10] that are, however, not yet exciting from the functional point of view. Here we report the first example of a PBI dye for which the multicycle living supramolecular polymerization is successfully demonstrated and a fluorescent J-aggregate is obtained. Our present studies revealed that the newly designed core-twisted PBI organogelator MeO-PBI (Chart 1) self-assembles into kinetically trapped nonfluorescent H-type aggregates, which can be transformed into thermodynamically favored fluorescent J-aggregates by seedinduced living polymerization. More significantly, the polymerization cycle could be repeated for several times by using the “living” polymer of the preceding cycle. The PBI organogelator MeO-PBI was synthesized by imidization of 1,7-dimethoxy-perylene-3,4:9,10-tetracarboxylic acid bisanhydride with N-(2-aminoethyl)-3,4,5-tris(dodecyloxy)benzamide in imidazole using Zn(OAc)2 as a catalyst. The respective bisanhydride precursor was synthesized by a recently developed copper-mediated cross-coupling reaction from tetrabutyl 1,7-dibromoperylene-3,4,9,10-tetracarboxylate. The detailed synthetic procedure and characterization data are provided in the Supporting Information. The optical properties of the monomeric MeO-PBI were investigated by UV/vis absorption and steady state fluorescence spectroscopy in 1,1,2,2-tetrachloroethane (TCE). In this solvent the absorption spectrum of MeO-PBI shows the characteristic vibronic structure of bay-substituted PBIs with an absorption maximum at λmax = 577 nm (Figure S5), which is bathochromically shifted compared to that of the previously reported core-unsubstituted H-PBI (λmax = 533 nm). The methoxy substituents at 1,7 bay-position lead to a twist of the perylene core of 11° according to DFT calculations (Figure S4). This distortion of the perylene core evokes a decrease of the extinction coefficient of MeO-PBI ( = 6.0 104 M-1 cm-1 in TCE) compared with the core-planar reference H-PBI ( = 8.1 104 M1 cm-1 in TCE). The fluorescence spectrum of MeO-PBI shows a maximum at 598 nm and resembles a mirror image shape of the absorption spectrum (Figure S5). Interestingly, MeO-PBI exhibits a remarkably higher fluorescence quantum yield of fl = 0.68 than H-PBI (fl = 0.10) in TCE. The appreciably intense fluorescence of the former might be explained by a less electron-deficient character of the dimethoxy-substituted PBI core, which makes the photoinduced electron transfer from the electron-rich tridodecyloxyphenyl side groups to the core unfavorable. The supramolecular polymerization of MeO-PBI was studied by temperature-dependent UV/vis spectroscopy in a 2:1 (v/v) solvent mixture of methylcyclohexane (MCH) and toluene (Tol) with varying cooling/heating rates (Figure 1). Upon cooling the monomer solution of MeO-PBI from 90 to 10 °C with a cooling rate of 5 °C/min, the absorption maximum is hypsochromically This article is protected by copyright. All rights reserved. Accepted Manuscript Wolfgang Wagner, Marius Wehner, Vladimir Stepanenko, Soichiro Ogi, and Frank Würthner* 10.1002/ange.201709307 Angewandte Chemie Figure 1. Temperature-dependent absorption spectra of MeO-PBI (cT = 15 10 M) in MCH/Tol (2:1, v/v) upon cooling from 90 to 10 °C with a cooling rate of 5 °C/min (a) and with a slower cooling rate of 1 °C/min (b). The plots of the extinction coefficients ( at 560 nm against temperature for the respective cooling (black dots) and heating (orange dots) processes are shown in the insets; cooling and heating rates are for (a) 5 °C/min and for (b) 1 °C/min. (c) Timedependent UV/vis absorption (solid lines) and emission spectra (dashed lines, λex = 487 nm) of the spontaneous transformation from the H-aggregate MeOPBIagg I (cT = 15 10-6 M) into the J-aggregate MeO-PBIagg II at 20 °C. -6 shifted with a loss of vibronic fine structure and concomitant appearance of a weak transition at higher wavelength (620 nm). These spectral features are typical for the formation of PBI Haggregates (denoted here as MeO-PBIagg I). The plot of the apparent extinction coefficients (ε) at the absorption maximum of the monomer (560 nm) against the temperature reveals a sigmoidal transition, which is indicative of an isodesmic aggregation mechanism[5b] (Figure 1, inset). Surprisingly, upon cooling the same solution from 90 to 10 °C with a slower cooling rate of 1 °C/min the formation of a J-type aggregate (denoted as MeO-PBIagg II) with a strongly bathochromically shifted absorption maximum at 655 nm was observed (Figure 1b). The plot of the ε values at 560 nm against the temperature for the aggregation of MeO-PBIagg II shows, in contrast to that of MeOPBIagg I, a pronounced hysteresis of ca. 25 °C between the thermodynamically controlled heating and the kinetically controlled cooling process (Figure 1a,b insets). The thermodynamically controlled non-sigmoidal (Figure 1b inset) transition upon heating could be fitted by using the cooperative nucleation-elongation model introduced by Smulders et al., giving a critical temperature of Te = 359 K and elongation enthalpy of ΔHe = -88.6 kJ mol-1 at cT = 15 10-6 M (Figure S6, Table S1). Upon diluting the total concentration, the elongation temperature Te decreased with a linear relationship as the van’t Hoff plot illustrates (Figure S7). From this plot the standard enthalpy (ΔH0) and entropy (ΔS0) were determined to be -97.6 kJ mol-1 and -179.7 J mol-1 K-1, respectively; the former value is in good agreement with ΔHe determined by fitting of the temperature-dependent data with the cooperative model (Figure S6). The monitoring of a solution of the kinetically formed Haggregate MeO-PBIagg I (cT = 15 10-6 M) in MCH/Tol (2:1, v/v) by time-dependent UV/vis spectroscopy at 20 °C revealed an interesting transformation of the H-aggregate MeO-PBIagg I into the J-aggregate MeO-PBIagg II (Figure 1c, solid lines). The timedependent absorption data clearly confirm that MeO-PBIagg I is a kinetically metastable aggregate, which is completely transformed into the thermodynamically favored MeO-PBIagg II within a period of about 6 h. Repeating the measurements revealed a faster transformation of MeO-PBIagg I into MeOPBIagg II with decreasing total concentration from 20 10-6 M to 10 10-6 M (Figure S8). This concentration-dependence indicates that MeO-PBIagg I is an “off-pathway” (kinetically trapped) aggregate.[4, 7a] The transformation of H- into Jaggregate caused a drastic change in fluorescence. While the H-aggregate MeO-PBIagg I is nearly non-fluorescent, MeOPBIagg II is appreciably fluorescent with a quantum yield of fl = 0.14 (Figure 1c, S12). Time-dependent fluorescence spectra (Figure 1c, dashed lines) with an excitation at the isosbestic point of MeO-PBIagg I and MeO-PBIagg II (λex = 487 nm) reveal a transformation of the non-fluorescent H-aggregate MeO-PBIagg I into the emissive J-aggregate MeO-PBIagg II with a strong increase of the fluorescence. Such unique change in fluorescence properties upon transformation of a kinetically trapped H-aggregate into the thermodynamically stable Jaggregate has been rarely reported. The influence of hydrogen bonding for the stabilization of the different aggregated species was investigated by Fouriertransform infrared (FT-IR) spectroscopy (for details see Supporting Information and Figures S13, S14). These FT-IR studies revealed that the aggregates of MeO-PBIagg II are formed from monomers with extended conformation (denoted as MeOPBIopen) by intermolecular hydrogen bonding between the amide groups, while MeO-PBIagg I consists of intramolecularly hydrogen-bonded monomers MeO-PBIclosed that are selfassembled by π-π interactions between the PBI molecules (Figure 2). Figure 2. Schematic illustration of the equilibrium between the open (MeO-PBIopen) and the closed conformation (MeO-PBIclosed) and the formation of metastable H-aggregate MeO-PBIagg I and the thermodynamically favored J-aggregate MeO-PBIagg II. As discussed before, MeO-PBI shows an interesting interplay between kinetically trapped state and thermodynamically stable aggregate states. Therefore, we have explored the seedinduced living supramolecular polymerization of this PBI. For this purpose, seeds of MeO-PBIagg II with different lengths were produced by treating solutions of MeO-PBIagg II in an ultrasonic bath for various time intervals. Increasing the sonication time from 2 to 10 min leads to a decreased length of the seeds of MeO-PBIagg II from 55-200 nm (2 min) to 45-170 nm (5 min) and This article is protected by copyright. All rights reserved. Accepted Manuscript COMMUNICATION 10.1002/ange.201709307 Angewandte Chemie 20-80 nm (10 min) as revealed by AFM (Supporting Information, Figure S16). However, the morphology, i.e. the helical structure of the individual strands of the seeds is similar to that of the polymer (MeO-PBIagg II) and also the UV/vis spectrum of MeOPBIagg II-seed resembles that of freshly prepared MeO-PBIagg II. The addition of MeO-PBIagg II-seed (ratio 1:100, sonication time: 10 min) induces the transformation of MeO-PBIagg I into MeOPBIagg II instantaneously (Figure S10), which indicates that polymers with controlled length and size dispersion can be obtained. Thus, the seeded polymerization occurs without a lag time and the transformation rate is remarkably higher compared with the spontaneous aggregation process. Stirring (400 rpm) of MeO-PBIagg I solution is another option to accelerate the transformation of MeO-PBIagg I into MeO-PBIagg II, however, only after an induction period of ca. 30 min that is obviously needed to afford the nucleation (Figure S10b). Final proof for the living growth of the supramolecular polymer chain of MeO-PBI from the seed termini was derived by UV/vis absorption spectroscopy in MCH/Tol (2:1, v/v) applying the experimental protocol schematically illustrated in Figure 3a and S1. For this purpose, 1 equivalent (equiv.) of a freshly prepared solution of the kinetically trapped MeO-PBIagg I in this solvent mixture (cT = 15 10-6 M) was added to 1 equiv. of a solution of MeO-PBIagg II-seed (sonication time 10 min) at 20 °C. Upon mixing of these two stock solutions, the supramolecular polymerization occurred instantaneously and completed after few minutes because of the high fraction of “active” seeds that function as initiators. Subsequently, 1 equiv. of the supramolecular polymer solution obtained after the first cycle was removed to keep the overall volume of the sample constant. For a second cycle, another 1 equiv. of MeO-PBIagg I was added to the remaining polymer solution (1 equiv.), which is now acting as the seed for the subsequent polymerization cycle. This procedure was repeated for another three cycles. With this experiment the living supramolecular polymerization process could be followed very easily by monitoring the apparent absorbance at 655 nm (absorption maximum of MeO-PBIagg II) during the whole experiment and plotting the absorbance data against the time (Figure 3b). After the first addition of MeO-PBIagg I the apparent absorbance at 655 nm drops to 0.22 and subsequently a very fast seeded supramolecular polymerization process occurs, accompanied by an increase of the absorption nearly reaching the initial value of 0.33. This observation confirms the transformation of the kinetically trapped aggregates MeOPBIagg I into a “first generation” thermodynamically stable polymer MeO-PBIagg II. The obtained polymers after the first cycle can now act as the nuclei for the second cycle and so on. Interestingly, the rate of the polymerization into MeO-PBIagg II gets slower with increasing cycle number because the number of “active termini” of the seed is reduced by half after each cycle. The initial slopes of the graphs determined by fitting the respective first data points with a linear relationship are supportive of this conclusion. The values of the initial slopes can be fitted by the exponential equation y = 0.0303 min-1 (1/2)n-1 with the cycle number n (Figure S11), clearly showing that the values of the initial slopes are reduced by half for each cycle. Concomitantly, the fiber length should increase which is confirmed by atomic force microscopy (AFM). Indeed, AFM images of the samples prepared by spin-coating of the solutions of the polymers obtained after each cycle (Figure 3c-e, S17) show a successive increase of polymer length from 35-130 nm (1st cycle) to 50-300 nm (2nd cycle), 150-600 nm (3rd cycle) and extended µm long polymer networks (4th and 5th cycles). These remarkable results clearly prove that the polymers MeO-PBIagg II can indeed act as seeds for the kinetically trapped MeO-PBIagg I and that the formed polymers stay unchanged during the time course of experiments. Our highly interesting results discussed above clearly revealed the living character by chain-growth mechanism from the fiber termini for this supramolecular polymerization of MeO-PBI through a precise kinetic control of the aggregation process. In conclusion, we have presented here the first example for a living supramolecular polymerization leading to a fluorescent Jaggregate. This progress became possible by the molecular design of a slightly core-twisted PBI that self-assembles preferentially into metastable “off-pathway” H-aggregates (MeOPBIagg I) that could be transformed into thermodynamically more stable fluorescent J-aggregates (MeO-PBIagg II) by seed-induced Figure 3. (a) Schematic illustration of a stepwise living supramolecular polymerization process of MeO-PBI. (b) Time course of the apparent absorbance at 655 nm (λmax of MeO-PBIagg II) during the living polymerization of MeO-PBI. The grey areas indicate the time for opening the sample compartment to add the respective equivalent of MeO-PBIagg I. AFM height images of the supramolecular polymers (MeO-PBIagg II) obtained after the first (c), second (d) and fourth cycle (e) prepared by spin-coating of the respective solutions on HOPG. The Z scale is 12 nm (c, d, e). This article is protected by copyright. All rights reserved. Accepted Manuscript COMMUNICATION 10.1002/ange.201709307 Angewandte Chemie living supramolecular polymerization. The experimental protocol developed for the living polymerization has potential for the construction of interesting functional supramolecular polymers and even supramolecular block copolymers that may serve as highly promising architectures for the investigation of exciton and charge carrier transport phenomena on the nanoscale.   Acknowledgements We thank the Bavarian State Ministry of Education, Science and the Arts for generous support for the newly established Key Laboratory for Supramolecular Polymers at the Center for Nanosystems Chemistry.  Keywords: J-aggregates • Living polymerization • Perylene dyes/pigments • Self-assembly • Supramolecular chemistry       M. Szwarc, M. Levy, R. Milkovich, J. Am. Chem. Soc. 1956, 78, 2656-2657. a) O. W. Webster, Science 1991, 251, 887-893; b) G. Odian, Principles of Polymerization, 4th ed., Wiley-VCH, Hoboken, NJ, 2004; c) J. M. G. Cowie, V. Arrighi, Polymerization: Chemistry and Physics of Modern Materials, Taylor & Francis Inc, CRC Press, Boca Raton, 2007. a) X. Wang, G. Guerin, H. Wang, Y. Wang, I. Manners, M. A. Winnik, Science 2007, 317, 644-647; b) P. A. Rupar, L. Chabanne, M. A. Winnik, I. Manners, Science 2012, 337, 559562. S. Ogi, K. Sugiyasu, S. Manna, S. Samitsu, M. Takeuchi, Nat. Chem. 2014, 6, 188-195. a) L. Brunsveld, B. J. B. Folmer, E. W. Meijer, R. P. Sijbesma, Chem. Rev. 2001, 101, 4071-4098; b) T. F. A. De Greef, M. M. J. Smulders, M. Wolffs, A. P. H. J. Schenning, R. P. Sijbesma, E. W. Meijer, Chem. Rev. 2009, 109, 5687-5754; c) T. Aida, E. W. Meijer, S. I. Stupp, Science 2012, 335, 813-817. a) A. Lohr, F. Würthner, Isr. J. Chem. 2011, 51,1052-1066; b) L. Yang, X. Tan, Z. Wang, X. Zhang, Chem. Rev. 2015, 115, 7196-7239; c) E. Krieg, M. M. C. Bastings, P. Besenius, B. Rybtchinski, Chem. Rev. 2016, 116, 2414-2477.       a) P. A. Korevaar, S. J. George, A. J. Markvoort, M. M. J. Smulders, P. A. J. Hilbers, A. P. H. J. Schenning, T. F. A. De Greef, E. W. Meijer, Nature 2012, 481, 492-496; b) P. A. Korevaar, T. F. A. de Greef, E. W. Meijer, Chem. Mater. 2014, 26, 576-586; c) J. Baram, H. Weissman, B. Rybtchinski, J. Phys. Chem. B 2014, 118, 12068-12073; d) D. Görl, X. Zhang, V. Stepanenko, F. Würthner, Nat. Commun. 2015, 6, 7009-7017. a) F. Würthner, Nat. Chem. 2014, 6, 171-173; b) D. van der Zwaag, T. F. A. de Greef, E. W. Meijer, Angew. Chem. 2015, 127, 8452-8454; Angew. Chem. Int. Ed. 2015, 54, 8334-8336; c) R. D. Mukhopadhyay, A. Ajayaghosh, Science 2015, 349, 241-242. a) S. Ogi, V. Stepanenko, K. Sugiyasu, M. Takeuchi, F. Würthner, J. Am. Chem. Soc. 2015, 137, 3300-3307; b) S. Ogi, V. Stepanenko, J. Thein, F. Würthner, J. Am. Chem. Soc. 2016, 138, 670-678; c) A. Pal, M. Malakoutikhah, G. Leonetti, M. Tezcan, M. Colomb-Delsuc, V. D. Nguyen, J. van der Gucht, S. Otto, Angew. Chem. 2015, 127, 7963-7967; Angew. Chem. Int. Ed. 2015, 54, 7852-7856; d) W. Zhang, W. Jin, T. Fukushima, T. Mori, T. Aida, J. Am. Chem. Soc. 2015, 137, 13792-13795; e) M. E. Robinson, D. J. Lunn, A. Nazemi, G. R. Whittell, L. De Cola, I. Manners, Chem. Commun. 2015, 51, 15921-15924. f) H. Frisch, E.-C. Fritz, F. Stricker, L. Schmüser, D. Spitzer, T. Weidner, B. J. Ravoo, P. Besenius, , Angew. Chem. 2016, 128,7358-7362; Angew. Chem. Int. Ed. 2016, 55, 7242-7246. g) T. Fukui, S. Kawai, S. Fujinuma, Y. Matsushita, T. Yasuda, T. Sakurai, S. Seki, M. Takeuchi, K. Sugiyasu, Nat. Chem., 2017, 9, 493-499. J. Kang, D. Miyajima, T. Mori, Y. Inoue, Y. Itoh, T. Aida, Science 2015, 347, 646-651. F. Würthner, T. E. Kaiser, C. R. Saha-Möller, Angew. Chem. 2011, 123, 3436-3473; Angew. Chem. Int. Ed. 2011, 50, 33763410. a) S. Ghosh, X.-Q. Li, V. Stepanenko, F. Würthner, Chem. Eur. J. 2008, 14, 11343-11357; b) V. Stepanenko, X.-Q. Li, J. Gershberg, F. Würthner, Chem. Eur. J. 2013, 19, 4176-4183. P. Leowanawat, A. Nowak-Krol, F. Würthner, Org. Chem. Front. 2016, 3, 537-544. M. M. J. Smulders, M. M. L. Nieuwenhuizen, T. F. A. de Greef, P. van der Schoot, A. P. H. J. Schenning, E. W. Meijer, Chem. Eur. J. 2010, 16, 362-367 Z. Chen, Y. Liu, W. Wagner, V. Stepanenko, X. Ren, S. Ogi, F. Würthner, Angew. Chem. 2017, 129, 5823-5827; Angew. Chem. Int. Ed. 2017, 56, 5729-5733. This article is protected by copyright. All rights reserved. Accepted Manuscript COMMUNICATION 10.1002/ange.201709307 Angewandte Chemie COMMUNICATION COMMUNICATION Wolfgang Wagner, Marius Wehner, Vladimir Stepanenko, Soichiro Ogi and Frank Würthner* Page No. – Page No. Living Supramolecular Polymerization of a Perylene Bisimide Dye into Fluorescent J-Aggregates Accepted Manuscript Living supramolecular polymerization. First example of a perylene bisimide (PBI) based multicycle living polymerization system is reported. The baysubstituted PBI organogelator forms “off-pathway” H-aggregates that are transformed into thermodynamically favored fluorescent J-aggregates by a living seeded polymerization. This article is protected by copyright. All rights reserved.