Article pubs.acs.org/JPCC
Nanoscale Aggregates as Building Elements in a Biomimetic Living Self-Assembly Yingxuan Zheng,†,‡,§ Cheng Peng,†,‡,§ Wei Xiong,†,‡ Yifan Zhang,†,‡ Yin Liu,†,‡ Yanke Che,*,†,‡ and Jincai Zhao†,‡ †
Key Laboratory of Photochemistry, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China ‡ University of Chinese Academy of Sciences, Beijing, 100049, China S Supporting Information *
ABSTRACT: In this work, we report on a complex dynamic supramolecular assembly pathway for a perylene diimide (PDI) derivative; this pathway involves the sequential formation of three kinetically trapped assemblies (i.e., from smooth nanospheres to microspheres to nanofiber microspheres) and thermodynamically stable microribbons. Interestingly, the stable nuclei, which are formed via the fusion of densely entangled nanofibers on the microspheres, enabled the direct anchoring of nanospheres at the termini for the growth of microribbons. Furthermore, we demonstrate the living nature of this system by observing the direct terminal growth of nanospheres on added microribbon seeds under identical self-assembly conditions. Our findings represent a significant step toward artificial systems that are capable of resembling biological systems.
■
INTRODUCTION Among state-of-the-art self-assembly strategies for the construction of complex nano- and microarchitectures, living selfassembly represents a convenient and very powerful approach that has enabled access to various nanostructures with precise size and dimensional control.1−29 In particular, the crystallization-driven living self-assembly of block polymers (e.g., polyferrocenylsilane, PFS) pioneered by Manners et al. has led to the creation of various complex nanostructures with an unprecedented level of control.1−9 In recent years, living selfassembly has also been achieved for small organic molecules,10−24 of which living supramolecular assembly of a porphyrin-based monomer into nanoribbons was first reported by Takeuchi et al.10 However, despite impressive advances in this area, living supramolecular self-assembly that directly uses nanoscale aggregates rather than molecular monomers as building elements has never been reported, despite having been mastered by biological systems.31−33 Furthermore, revealing the nuclei formation for stable assemblies, particularly the real-time visualization of the nucleation processes that is essential to understanding and controlling a living self-assembly process, remains a great challenge. In the present work, we report on a complex dynamic supramolecular assembly pathway for a perylene diimide (PDI) derivative. This pathway involves the sequential formation of three kinetically trapped assemblies (i.e., from smooth nanospheres to microspheres to nanofiber microspheres) and thermodynamically stable microribbons, as shown in Figure 1. © XXXX American Chemical Society
Notably, the stable nuclei formed via the fusion of entangled nanofibers on the microspheres (i.e., the third metastable aggregates), as visualized by scanning electron microscopy (SEM) and confocal laser scanning optical microscopy (CLSM). More interestingly, the nuclei enabled the direct anchoring of nanospheres at the termini for the growth of the nanoribbons, suggesting living assembly of the nanoscale aggregates. Such a living nature of the system is further demonstrated by the observations of direct and quick terminal growth of nanospheres on the added microribbon seeds under identical self-assembly conditions (Figure 1). Considering the unique features of the self-assembly, i.e., nanoscale aggregates as building elements and the nucleation step that occurs only on the metastable nanofiber microsphere, our findings represent a substantial step toward complex artificial systems that may resemble biological systems.
■
EXPERIMENTAL SECTION Self-Assembly of Molecule 1. The self-assembly of 1 proceeded by injecting a chloroform solution (0.3 mL) of 1 (0.6, 1.2, 2.4, and 3.6 mM, respectively) into 4.5 mL of ethanol (poor solvent) in a test tube or vial followed by full mixing and aging. The assemblies suspended in solution were transferred Received: April 24, 2017 Revised: June 20, 2017 Published: June 22, 2017 A
DOI: 10.1021/acs.jpcc.7b03846 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
by drop-casting the suspending assemblies in ethanol onto silica substrates followed by sputtering Pt on the surface. The Pt sputtering was performed on a Leica EM SCD 500 instrument, and the current and time were set as 15 mA and 120 s, respectively. The thickness of the sputtered Pt layer was about 3 nm. Fluorescence images were recorded using an inverted CLSM (a Olympus FV1000) with 10×, 40×, and 100× magnification objective lenses. The samples were prepared by drop-casting the suspending assemblies in ethanol at different assembly times (2 min, 1 h, 3 h, 6 h, 9 h, 11 h, 24 h, 3 days, 5 days, 8 days, and 10 days) onto the glass substrates. The samples for in situ observations were prepared by transferring the initial mixed solution of 1 onto a Petri dish, then closing with a cap. The CLSM images were obtained at different assembly times (30 min, 1 h, 6 h, 10 h, 19 h, 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days, and 12 days). A continuous-wave laser of 488 nm was used to excite the CLSM samples. The emission of the assemblies was collected in the range from 500 to 780 nm with 2 nm resolution by using the lambda-mode option. The raw data were processed by Olympus Fluoview software. The dynamic light scattering (DLS) measurements were carried out on a commercial LLS spectrometer (ALV/DLS/ SLS-5022F) equipped with a multi-τ digital time correlator (ALV5000) and a cylindrical 22 mW He−Ne laser as the light source. All the DLS measurements were performed at a scattering angle of 90°. The sample was prepared by injecting 4.5 mL of ethanol into a 7 mL glass bottle through a 0.22 μm PTFE filter and then injecting 0.3 mL of 1 (3.6 mM) through a 0.22 μm PTFE filter into the bottle and mixing fully. The correlation function of scattering data was analyzed via the CONTIN method to obtain the distribution of diffusion coefficients (D) of the solutes. The apparent equivalent hydrodynamic radius (Rh) was determined using the Stokes− Einstein equation Rh = kT/6πηD, where k is the Boltzmann constant, T is the absolute temperature, and η is the solvent viscosity. All the measurements were performed at 25.00 ± 0.05 °C. The fluorescence quantum yields of the assemblies of 1 were performed on a Hamamatsu Absolute PL quantum yield spectrometer C11247 using an integrating sphere method.
Figure 1. Schematic representation of a complex supramolecular assembly pathway of molecule 1 and a living assembly of the initially formed nanospheres. Sequential formation of three kinetically trapped assemblies (i.e., from smooth nanospheres to microspheres to nanofiber microspheres) and thermodynamically stable microribbons are presented. Terminal anchoring of nanospheres on the added microribbon seeds is shown.
onto different substrates by simple drop-casting at different times for various characterizations. Prior to the living self-assembly process, microribbon seeds of 3−18 μm were prepared through ultrasonication (KQ-50DA, 50 W power) of the thermodynamically stable microribbons at −5 °C for 5 min. The living self-assembly proceeded by adding the seeds at certain amounts in a chloroform/ethanol mixture (volume ratio, 1:15) into the nanosphere solutions that were prefabricated by injecting 0.3 mL of chloroform solution of 1 (3.6 mM) into 4.5 mL of ethanol (poor solvent) in a test tube or vial followed by full mixing and aging for 1 h. Optical and Structural Characterization. SEM measurements were performed on a HITACHI S-4800 field-emission SEM, and the accelerating voltage and current were set as 10 kV and 10 μA, respectively. The SEM samples were prepared
Figure 2. SEM images of the assembly evolution of 1 at different time points. (a) Nanospheres that formed at 2 min after the beginning of the selfassembly process. (b) Microspheres formed by fusing nanospheres at 1.5 h. (c) Microspheres consisting of entangled nanofibers formed along with the dominant nanospheres at 6 h. (inset) Magnified image of a nanofiber microsphere. (d) Microspheres consisting of entangled nanofibers accompanied by nanoribbons fused by the nanofibers on the microsphere at 15 h. (e) More ribbons formed that were accompanied by a decrease in the number of nanospheres and microspheres at 24 h. (f) Remaining microribbons after 10 days of self-assembly. (g) Nanospheres anchored onto the termini of the nanoribbons for epitaxial growth. (h) Adjacent nanoribbons fusing together to form microribbons. B
DOI: 10.1021/acs.jpcc.7b03846 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
Figure 3. SEM images of the assembly evolution of 1 at various concentrations. (a) Morphological changes of 1 (2.4 mM) at different times (2 min, 1 day, 5 days, and 23 days) during the self-assembly process. (b) Morphological changes of 1 (1.2 mM) at different times (2 min, 6 h, 2 days, and 10 days) during the self-assembly process. (c) Morphological changes of 1 (0.6 mM) at different times (2 min, 6 h, 2 days, and 10 days) during the selfassembly process.
the nanospheres had an average diameter of 560 nm (Figure S1a). Interestingly, some nanospheres began to fuse together and grew into microscale spheres over the following hours (Figure 2b and Figure S2). After 6 h, some microspheres with a diameter of ca. 2 μm formed along with the existing nanospheres (Figure 2c). Magnified SEM images reveal that the smooth microspheres thus assembled and evolved into microspheres consisting of entangled nanofibers after 6 h (Figure 2c, inset, and Figure S3). Notably, only a small number of microspheres formed and the freestanding nanospheres dominated the assembly process, as shown in the following CLSM imaging. Interestingly, nanoribbons with widths ranging from 100 to 200 nm emerged on the nanofiber microspheres after 15 h (Figure 2d). Careful examinations of the nanoribbons on the surface of the nanofiber microsphere showed that the nanoribbons formed through fusion of the entangled nanofibers of the microsphere (Figure S4). As time progressed, more ribbons formed and elongated, which was accompanied by quick decreases in the number of nanospheres (Figure 2e). After 10 days of self-assembly, almost all the nanofiber microspheres disappeared, and only microribbons with widths ranging from 0.5 to 1 μm were observed (Figure 2f). The morphology of the resulting microribbons remained unchanged even after weeks of suspension in solution, indicating a thermodynamically stable nature. These observations led to the conclusion that the initially formed nanospheres, the second-stage microspheres, and the subsequent third-stage nanofiber microspheres were kinetically trapped assemblies that further evolved into thermodynamically stable microribbons. To gain insight into how the nanoribbon nuclei elongated and widened into the microribbons, we carefully monitored the morphological changes of the nanoribbon nuclei once they formed approximately 15 h after the beginning of the selfassembly process. Interestingly, the nanospheres were observed to be anchored onto the termini of the ribbons and to then be “assimilated” via conformational rearrangement for the growth of the nanoribbons (as shown by the circled areas in Figure 2g
Various excitation wavelengths ranging from 450 to 570 nm were employed for the fluorescence quantum measurements, and similar results were obtained.
■
RESULTS AND DISCUSSION Molecular Design. The designed molecule in this work is an asymmetric PDI derivative (1) that bears a bulky 2,6bis(pentan-3-yloxy)benzyl moiety as one side chain and a dodecyl group as the other side chain (Figure 1). This molecular design is inspired by our recent work in which appropriately bulky moieties at the 2-position of the benzyl substituent of PDI molecules gave rise to a morphological transition from kinetically trapped microribbons to thermodynamically stable nanotubes.30 Upon the introduction of two bulky pentan-3-yloxy moieties at the 2- and 6-positions of the benzyl substituent of 1 that may increase the molecular interaction complexity, we expect that molecule 1 will experience complex and attractive morphological transformation dynamics (e.g., involving more than three assemblies during the assembly process), which is rare in the field of biomimetic self-assembly.17 Furthermore, we expect that the increasing steric hindrance from the bulky moieties may slow the morphological transition between the assemblies and enable real-time observations of the entire processes. Indeed, a complex assemblage pathway involving sequential transformations from individual molecules to three metastable aggregates to thermodynamically stable microribbons was observed via SEM and CLSM imaging. Investigation of the Assembly Evolution of 1 by SEM. After flash injection of a 0.3 mL chloroform solution of 1 (3.6 mM) into 4.5 mL of ethanol and a quick stir, the resulting mixture was allowed to self-assemble at room temperature. The resulting assemblies from 1 at various times were agitated and drop-cast onto silicon for SEM imaging. As shown in Figure 2a, spherical nanoparticles with diameters ranging from 400 to 600 nm quickly formed after 2 min of the self-assembly process. Dynamic light scattering (DLS) measurements confirmed that C
DOI: 10.1021/acs.jpcc.7b03846 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
Figure 4. Real-time visualization and spectroscopic characterization of assembly evolution by CLSM. CLSM images of assemblies formed at 30 min (a), 1 h (b), 19 h (c), 3 days (d), 4 days (e), 7 days (f), and 12 days (g) after beginning of the self-assembly. (h) Fluorescence spectra of the circled areas 1−3 in (a) and (g) (top) and of the squared areas 4−6 in (e−g) (bottom).
and Figure S5). This result clearly indicates that nanospheres, rather than the molecular monomers, acted as the building elements to epitaxially grow onto the nanoribbon nuclei. Furthermore, we determined that the simultaneous widening of the nanoribbons into microribbons during self-assembly proceeded by the fusion of adjacent nanoribbons, as shown by the circled area in Figure 2h and Figure S6. These features are distinct from the previously reported living supramolecular polymerization, where molecular monomers that were disassembled from the kinetically trapped assemblies acted as the building blocks for the growth of the stable aggregates.10,17,23 Our system enables the self-assembly of nanoscale aggregates and resembles a biological system. We note that the transformation from metastable aggregates to stable ribbons is accelerated by mechanical agitation (even a slight shaking greatly accelerated the transformation), similar to the transformation observed for previously reported living supramolecular assemblies.10,18,21 To investigate the factors that control the formation of thermodynamically stable nuclei during the morphological evolution of the microspheres, we examined the assembly evolution of 1 at various concentrations. When a 0.3 mL chloroform solution of 1 (2.4 mM) was injected into 4.5 mL of ethanol, a similar assembly evolution, i.e., from metastable nanospheres to microspheres to nanofiber microspheres to stable microribbons, was observed (Figure 3a and Figure S7). The difference is that the resulting nanofiber microspheres that formed during the third stage were more loosely packed (Figure 3a) than those that formed during the self-assembly of 1 at the aforementioned higher concentration (Figure 2c,d). The fusion of loosely packed nanofibers into nanoribbons on the microspheres is clearly observed 5 days from the beginning of the self-assembly (see Figure 3a and Figure S7d), confirming that thermodynamically stable nuclei formed from the fusing of the nanofibers formed during the third stage of self-assembly. This phenomenon is distinct from that previously reported in
molecular systems, where individual monomers slowly nucleate by overcoming the energetic barrier.10−13,17,24 When the concentration of 1 was further decreased to 1.2 mM, the initially formed nanospheres decreased, with diameters ranging from 200 to 300 nm at 2 min after the beginning of the selfassembly process (Figure 3b) under identical self-assembly conditions. DLS measurements confirmed that the nanospheres exhibited an average diameter of ca. 220 nm (Figure S1b). Notably, these metastable nanospheres fused into microspheres along with irregular aggregates after 6 h (Figure 3b and Figure S8), which further evolved into irregular nanofiber rolls along with some flaky aggregates at 2 days from the beginning of the self-assembly process (Figure 3b and Figure S9). This morphology of the loosely packed nanofiber rolls and flaky aggregates remained unchanged even after 10 days of selfassembly (Figure 3b and Figure S10). These observations indicate that the formation of stable nanoribbon nuclei requires densely entangled nanofibers to overcome the energy barrier for the fusing process. This hypothesis is further supported by the results in the self-assembly of 1 at a further diluted concentration (0.6 mM), where the formed metastable nanospheres and irregular aggregates (containing entangled nanofibers and anchored nanospheres) only evolved into irregularly packed nanofibers, even after 10 days of selfassembly (Figure 3c and Figure S11). No fusing behavior was observed. Therefore, we conclude that the formed stable nanoribbon nuclei require densely packed nanofibers that formed during the third stage of self-assembly to overcome the energy barrier associated with fusion. These results also suggest that simple concentration controls may be an effective approach to steering the self-assembly pathway toward aggregates in and out of thermodynamic equilibrium. Real-Time Visualization and Spectroscopic Characterization of Assembly Evolution by CLSM. To gain additional insight into the assembly evolution of 1, we used a fluorescence confocal laser scanning microscope to monitor the D
DOI: 10.1021/acs.jpcc.7b03846 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
Figure 5. Living self-assembly of nanoscale aggregates. (a) SEM image of the microribbon seeds prepared using ultrasonication. (inset) Length distribution of the microribbon seeds (lengths of more than 100 microribbons were measured). (b) SEM image of the aggregates formed 15 min after the microribbon seeds were added to the stock solution of nanospheres at a molar ratio of 1:2. (c) SEM image of the aggregates that formed 4 h after the same living assembly. (d) SEM image of the aggregates that formed 1 day after the same living assembly. (inset) Length distribution of the formed nanoribbons. (e) SEM image of the termini of the seeds, showing the epitaxial growth of the nanospheres on the seed termini. (f) SEM image of the lateral fusion of the nanofiber microspheres on the microribbons.
assembly evolution. As shown in Figure 4h, the initially formed nanospheres and microspheres (corresponding to the circled areas 1 and 2 in Figure 4a) showed an identical fluorescence band centered at approximately 674 nm, indicating that molecular reorganization was negligible during the transformation of nanospheres into microspheres. Furthermore, no apparent changes in the fluorescence spectra were observed over the microspheres, even after 12 days (as shown by the circled area 3 in Figure 4g), suggesting that no dramatic molecular organization occurs during the transformation of smooth microspheres into nanofiber microspheres. However, the fluorescence of the bundled microspheres exhibited dramatic changes as nanoribbons appeared (as shown in square areas 4−6 in Figure 4e−g), where the maximum emission band was blue-shifted to 625 nm from 674 nm (Figure 4h) before stabilizing. Furthermore, the stable nanoribbons or microribbons exhibited a significantly enhanced emission efficiency (i.e., a fluorescence quantum yield of 7.5% was determined by the integrated sphere method) compared to the metastable nanospheres and microspheres (which exhibited a fluorescence quantum yield of ca. 0.5%). The blue-shifted fluorescence maximum and enhanced fluorescence intensity from the nanoribbons compared to those in the nanospheres and microspheres indicated that molecules of 1 adopted more Jtype stacking in the thermodynamically stable state. We noticed that the morphological evolution of 1 shown in Figure 4 is much slower than that shown in Figure 2. This difference in evolution speed is attributed to the assembly evolution under CLSM involving no agitation, whereas the assembly solution was often shaken during preparation of the SEM samples at various times, which greatly accelerated the assembly process. Living Self-Assembly of Nanoscale Aggregates. Motivated by the results showing that nanospheres can grow on the termini of the nanoribbons, we explored the possibility of living self-assembly of the nanospheres. Although impressive advances in the living supramolecular self-assembly of small molecules have been achieved,10−24 it still lags far behind the advances reported by Manners’ group1−9 for the living self-
assembly process. This approach enables not only real-time observation of the morphological transformation but also the observation of spatially resolved fluorescence spectral changes that are associated with molecular organization in the assemblies. We prepared the sample by injecting a chloroform solution (0.3 mL) of the corresponding compound (3.6 mM) into 4.5 mL of ethanol (poor solvent) and fully mixing. The mixture was then transferred onto a Petri dish and sealed with a cap for time-dependent in situ monitoring without any agitation. Given the dynamic movement of the aggregates, we focused on observations of the resulting aggregation on the bottom of the Petri dish. As shown in Figure 4, this scenario is dominated by redemitting particles at 3 days after the beginning of the selfassembly process. Careful analysis of the confocal images revealed that two kinds of particles (400−600 nm and ca. 2 μm in diameter, respectively) formed (as shown in areas 1 and 2 in Figure 4a), consistent with the nanospheres and microspheres observed by SEM (Figure 2a−c). We noticed that the relatively heavier microspheres sank to the bottom upon formation, whereas the lighter nanospheres mainly floated in the solution. This difference in behavior led to the illusion that most of the 1 formed microspheres from nanospheres over time. To reflect the real population of nanospheres and microspheres, we also prepared the dry CLSM samples by drop-casting the assembling solution at various times onto glass slides that were allowed to dry in the atmosphere. As shown in Figure S12, the resulting microspheres represented only a small number of the total microspheres and the nanospheres dominated during the entire self-assembly process. After 3 days, fiberlike aggregates emerged in the bundled microspheres (Figure 4d) and became elongated with time (Figure 4e−g), suggesting the formation of nanoribbon nuclei and epitaxial growth. These phenomena are consistent with those observed by SEM (Figure 2). The fluorescence spectral profile of the spatially resolved assemblies confirms a distinct molecular reorganization during E
DOI: 10.1021/acs.jpcc.7b03846 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
small molecules. Our findings represent a significant step toward artificial systems that resemble biological systems.
assembly of polymers and has not been reported to achieve the living assembly of nanoscale aggregates. Prior to the living self-assembly, we prepared the microribbon seeds of 1 by ultrasonicating the prefabricated stable microribbons at −5 °C for 5 min. SEM imaging confirmed that the length of the resulting seeds ranged from 3 to 18 μm (Figure 5a and Figure S13). Upon the addition of seeds of 1 (0.225 μmol, 0.1 mL) in a chloroform/ethanol mixture (volume ratio 1:15) to the prefabricated stock solution of nanospheres of 1 (0.45 μmol, 0.2 mL) assembled over 1 h in a chloroform/ethanol mixture (volume ratio 1:15), the living nature of the seeded self-assembly was investigated by SEM. As shown in Figure 5 and Figure S14, the microribbons became elongated as time progressed; simultaneously, the number of nanospheres decreased (Figure 5b−d). SEM images of the termini of the seeds reveal that all of the seeds anchored the nanospheres on their terminals, confirming the living epitaxial growth of the nanospheres on the seeds (as shown by the circled areas in Figure 5e). We note that a very small number of nanofiber microspheres (the third metastable aggregate) also formed during the living assembly process (Figure 5b,c). Interestingly, these nanofiber microspheres can fuse laterally onto the microribbon (as shown by the circled area in Figure 5f), indicative of the twodimensional (2D) living nature of the seeds. However, because of the very small amount of nanofiber microspheres that formed during the living self-assembly, the contribution to the width of the microribbon seeds was not noticeable. After 1 day of self-assembly, the nanospheres almost disappeared and the length of the nanoribbons stabilized (Figure 5d). The length of the resulting microribbons was approximately 3 times the length of the seeds. Likewise, when the molar ratio of 1 seeds to the precursor nanospheres was 1:1 and 1:5, the lengths of the resulting nanoribbons were approximately 2 and 6 times the length of the seeds, respectively (Figure S15), confirming the epitaxial elongation of the dominant nanospheres on the seeds. Notably, the completion of the living self-assembly with the molar ratio of 1 seeds to the precursor nanospheres at 1:1, 1:2, and 1:5 required only 9 h, 1 day, and 2 days, respectively. By contrast, the morphological evolution in the absence of seeds required more than 15 days to complete under identical assembly conditions. These results indicate that the addition of seeds allowed the assembly of nanospheres without a barrier and considerably accelerated the self-assembly process of 1, consistent with the autocatalytic characteristics of a living assembly.10−12,17,19,22,23
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.7b03846. Detailed synthesis of molecule 1, more optical and morphological characterizations (PDF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Yanke Che: 0000-0002-9671-3704 Author Contributions §
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Y.Z. and C.P. contributed equally to this work. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the 973 project (No. 2013CB632405), the National Natural Science Foundation of China (Nos. 21577147, 21590811, and 21521062), the “Strategic Priority Research Program” of the Chinese Academy of Sciences (No. XDA09030200), and the “Youth 1000 Talent Plan” Fund.
■
REFERENCES
(1) Qiu, H.; Hudson, Z. M.; Winnik, M. A.; Manners, I. Multidimensional Hierarchical Self-assembly of Amphiphilic Cylindrical Block Comicelles. Science 2015, 347, 1329−1332. (2) Hudson, Z. M.; Boott, C. E.; Robinson, M. E.; Rupar, P. A.; Winnik, M. A.; Manners, I. Tailored Hierarchical Micelle Architectures using Living Crystallization-driven Self-Assembly in Two Dimensions. Nat. Chem. 2014, 6, 893−898. (3) Rupar, P. A.; Chabanne, L.; Winnik, M. A.; Manners, I. NonCentrosymmetric Cylindrical Micelles by Unidirectional Growth. Science 2012, 337, 559−562. (4) Gilroy, J. B.; Gaedt, T.; Whittell, G. R.; Chabanne, L.; Mitchels, J. M.; Richardson, R. M.; Winnik, M. A.; Manners, I. Monodisperse Cylindrical Micelles by Crystallization-Driven Living Self-Assembly. Nat. Chem. 2010, 2, 566−570. (5) Gaedt, T.; Ieong, N. S.; Cambridge, G.; Winnik, M. A.; Manners, I. Complex and Hierarchical Micelle Architectures from Diblock Copolymers using Living, Crystallization-Driven Polymerizations. Nat. Mater. 2009, 8, 144−150. (6) Qiu, H.; Gao, Y.; Boott, C. E.; Gould, O. E. C.; Harniman, R. L.; Miles, M. J.; Webb, S. E. D.; Winnik, M. A.; Manners, I. Uniform Patchy and Hollow Rectangular Platelet Micelles from Crystallizable Polymer Blends. Science 2016, 352, 697−701. (7) Wang, X.; Guerin, G.; Wang, H.; Wang, Y.; Manners, I.; Winnik, M. A. Cylindrical Block Copolymer Micelles and Co-Micelles of Controlled Length and Architecture. Science 2007, 317, 644−647. (8) Qiu, H.; Russo, G.; Rupar, P. A.; Chabanne, L.; Winnik, M. A.; Manners, I. Tunable Supermicelle Architectures from the Hierarchical Self-Assembly of Amphiphilic Cylindrical B-A-B Triblock Co-Micelles. Angew. Chem., Int. Ed. 2012, 51, 11882−11885. (9) Robinson, M. E.; Lunn, D. J.; Nazemi, A.; Whittell, G. R.; De Cola, L.; Manners, I. Length Control of Supramolecular Polymeric Nanofibers based on Stacked Planar Platinum(II) Complexes by Seeded-Growth. Chem. Commun. 2015, 51, 15921−15924.
■
CONCLUSION In conclusion, we have demonstrated a novel biomimetic living assembly that uses nanoscale aggregates (i.e., nanospheres) as the building elements for growth on the nuclei once formed. Our system involved the sequential formation of three kinetically trapped (i.e., from smooth nanospheres to microspheres to nanofiber microspheres) and thermodynamically stable microribbons. Interestingly, the stable nuclei that formed via the fusion of densely entangled nanofibers on the microsphere enabled the direct anchoring of the nanospheres at the termini. Given the unique features of this living selfassembly, i.e., nanoscale aggregates as the building elements and a nucleation step that only occurred on the metastable nanofiber microspheres, these results are distinct from those previously reported for living supramolecular polymerization of F
DOI: 10.1021/acs.jpcc.7b03846 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C (10) Ogi, S.; Sugiyasu, K.; Manna, S.; Samitsu, S.; Takeuchi, M. Living Supramolecular Polymerization Realized through a Biomimetic Approach. Nat. Chem. 2014, 6, 188−195. (11) Ogi, S.; Stepanenko, V.; Sugiyasu, K.; Takeuchi, M.; Wuerthner, F. Mechanism of Self-Assembly Process and Seeded Supramolecular Polymerization of Perylene Bisimide Organogelator. J. Am. Chem. Soc. 2015, 137, 3300−3307. (12) Endo, M.; Fukui, T.; Jung, S. H.; Yagai, S.; Takeuchi, M.; Sugiyasu, K. Photoregulated Living Supramolecular Polymerization Established by Combining Energy Landscapes of Photoisomerization and Nucleation−Elongation Processes. J. Am. Chem. Soc. 2016, 138, 14347−14353. (13) Ogi, S.; Fukui, T.; Jue, M. L.; Takeuchi, M.; Sugiyasu, K. Kinetic Control over Pathway Complexity in Supramolecular Polymerization through Modulating the Energy Landscape by Rational Molecular Design. Angew. Chem., Int. Ed. 2014, 53, 14363−14367. (14) Kang, J.; Miyajima, D.; Mori, T.; Inoue, Y.; Itoh, Y.; Aida, T. A Rational Strategy for the Realization of Chain-Growth Supramolecular Polymerization. Science 2015, 347, 646−651. (15) Zhang, W.; Jin, W.; Fukushima, T.; Mori, T.; Aida, T. Helix Sense-Selective Supramolecular Polymerization Seeded by a OneHanded Helical Polymeric Assembly. J. Am. Chem. Soc. 2015, 137, 13792−13795. (16) Zhang, W.; Jin, W.; Fukushima, T.; Saeki, A.; Seki, S.; Aida, T. Supramolecular Linear Heterojunction Composed of Graphite-Like Semiconducting Nanotubular Segments. Science 2011, 334, 340. (17) Aliprandi, A.; Mauro, M.; De Cola, L. Controlling and Imaging Biomimetic Self-Assembly. Nat. Chem. 2016, 8, 10−15. (18) Colomb-Delsuc, M.; Mattia, E.; Sadownik, J. W.; Otto, S. Exponential Self-Replication Enabled through a Fibre Elongation/ Breakage Mechanism. Nat. Commun. 2015, 6, 7427. (19) Pal, A.; Malakoutikhah, M.; Leonetti, G.; Tezcan, M.; ColombDelsuc, M.; Nguyen, V. D.; van der Gucht, J.; Otto, S. Controlling the Structure and Length of Self-Synthesizing Supramolecular Polymers through Nucleated Growth and Disassembly. Angew. Chem., Int. Ed. 2015, 54, 7852−7856. (20) Sadownik, J. W.; Mattia, E.; Nowak, P.; Otto, S. Diversification of Self-Replicating Molecules. Nat. Chem. 2016, 8, 264−269. (21) Carnall, J. M. A.; Waudby, C. A.; Belenguer, A. M.; Stuart, M. C. A.; Peyralans, J. J. P.; Otto, S. Mechanosensitive Self-Replication Driven by Self-Organization. Science 2010, 327, 1502−1506. (22) Ogi, S.; Stepanenko, V.; Thein, J.; Würthner, F. Impact of Alkyl Spacer Length on Aggregation Pathways in Kinetically Controlled Supramolecular Polymerization. J. Am. Chem. Soc. 2016, 138, 670− 678. (23) Ma, X.; Zhang, Y.; Zhang, Y.; Liu, Y.; Che, Y.; Zhao, J. Fabrication of Chiral-Selective Nanotubular Heterojunctions through Living Supramolecular Polymerization. Angew. Chem., Int. Ed. 2016, 55, 9539−9543. (24) Haedler, A. T.; Meskers, S. C. J.; Zha, R. H.; Kivala, M.; Schmidt, H.-W.; Meijer, E. W. Pathway Complexity in the Enantioselective Self-Assembly of Functional Carbonyl-Bridged Triarylamine Trisamides. J. Am. Chem. Soc. 2016, 138, 10539−10545. (25) van der Zwaag, D.; de Greef, T. F. A.; Meijer, E. W. Programmable Supramolecular Polymerizations. Angew. Chem., Int. Ed. 2015, 54, 8334−8336. (26) De Greef, T. F. A.; Smulders, M. M. J.; Wolffs, M.; Schenning, A. P. H. J.; Sijbesma, R. P.; Meijer, E. W. Supramolecular Polymerization. Chem. Rev. 2009, 109, 5687−5754. (27) Korevaar, P. A.; George, S. J.; Markvoort, A. J.; Smulders, M. M. J.; Hilbers, P. A. J.; Schenning, A. P. H. J.; De Greef, T. F. A.; Meijer, E. W. Pathway Complexity in Supramolecular Polymerization. Nature 2012, 481, 492−496. (28) Mattia, E.; Otto, S. Supramolecular Systems Chemistry. Nat. Nanotechnol. 2015, 10, 111−119. (29) Jain, A.; George, S. J. New Directions in Supramolecular Electronics. Mater. Today 2015, 18, 206−214.
(30) Ma, X.; Zhang, Y.; Zhang, Y.; Peng, C.; Che, Y.; Zhao, J. Stepwise Formation of Photoconductive Nanotubes through a New Top-Down Method. Adv. Mater. 2015, 27, 7746−7751. (31) Kelm, J. M.; Lorber, V.; Snedeker, J. G.; Schmidt, D.; BrogginiTenzer, A.; Weisstanner, M.; Odermatt, B.; Mol, A.; Zünd, G.; Hoerstrup, S. P. A Novel Concept for Scaffold-Free Vessel Tissue Engineering: Self-Assembly of Microtissue Building Blocks. J. Biotechnol. 2010, 148, 46−55. (32) Kamei, M.; Saunders, W. B.; Bayless, K. J.; Dye, L.; Davis, G. E.; Weinstein, B. M. Endothelial Tubes Assemble from Intracellular Vacuoles in Vivo. Nature 2006, 442, 453−456. (33) Alajati, A.; Laib, A. M.; Weber, H.; Boos, A. M.; Bartol, A.; Ikenberg, K.; Korff, T.; Zentgraf, H.; Obodozie, C.; Graeser, R.; et al. Spheroid-based Engineering of a Human Vasculature in Mice. Nat. Methods 2008, 5, 439−445.
G
DOI: 10.1021/acs.jpcc.7b03846 J. Phys. Chem. C XXXX, XXX, XXX−XXX
