Internationale Ausgabe: DOI: 10.1002/anie.201904749Supramolecular Structures Hot PaperDeutsche Ausgabe: DOI: 10.1002/ange.201904749

Breaking Parallel Orientation of Rods via a Dendritic Architecturetoward Diverse Supramolecular StructuresRuimeng Zhang, Xueyan Feng, Rui Zhang, Wenpeng Shan, Zebin Su, Jialin Mao,Chrys Wesdemiotis, Jiahao Huang, Xiao-Yun Yan, Tong Liu, Tao Li, Mingjun Huang,Zhiwei Lin,* An-Chang Shi* und Stephen Z. D. Cheng*

Abstract: Self-assembled nanostructures of rod-like moleculesare commonly limited to nematic or layered smectic structuresdominated by the parallel arrangement of the rod-like compo-nents. Distinct self-assembly behavior of four categories ofdendritic rods constructed by placing a tri(hydroxy) group atthe apex of dendritic oligo-fluorenes is observed. Designedhydrogen bonding and dendritic architecture break the parallelarrangement of the rods, resulting in molecules with specific(fan-like or cone-like) shapes. While the fan-shaped moleculestend to form hexagonal packing cylindrical phases, the cone-shaped molecules could form spherical motifs to pack intovarious ordered structures, including the Frank–Kasper A15phase and dodecagonal quasicrystal. This study providesa model system to engineer diverse supramolecular structuresby rod-like molecules and sheds new light into the mechanismsof the formation of unconventional spherical packing struc-tures in soft matter.

Introduction

In the past forty years, great efforts on the investigation ofstructural self-assemblies have been made in various materialsystems such as block copolymers,[1] dendrons,[2] giant mole-cules,[3] hybrids,[4] and many others.[5] In flexible AB diblockcopolymers, the competition between the repulsive interac-tion between the A and B blocks, quantified by the Flory–Huggins interaction parameter, the overall degree of poly-merization, and the chain connectivity lead to microphaseseparation of the two blocks forming polymeric domains. Theshape of the polymeric domains (for example, lamellae,cylinders, or spheres) with different preferred interfacial

curvatures is determined by the composition (volume frac-tion) of the blocks and allows various ordered phases in blockcopolymers.[1a,b] In general, the preferred interfaces could beflat, curved one-dimensional (1D), or two-dimensional (2D),resulting in the formation of lamella (LAM), hexagonalcylindrical (HEX), or body-centered cubic (BCC) phases,respectively. Besides using flexible blocks as basic compo-nents of the self-assemblies, rod-like components, such asrigid macromolecules and liquid crystals, could also beintroduced into the systems. Different from flexible compo-nents, rod-like molecules prefer parallel arrangement formingstructures with orientational order (liquid crystal-like or-ders).[6]

In supramolecular science and technology, macroscopicproperties are largely directed by these assembled struc-tures.[7] To precisely control the assembled structures, themolecules must possess precise stereochemistry, composition,sequence, topology, and molecular mass.[3b,c,8] They wouldassemble into mesoscopic motifs, and simultaneously packinto diverse ordered structures. This process is commonlyreferred to as the molecular building block approach. Theself-assembled mesoscopic structures are critically dependenton the geometry of the motifs. For example, disc-like motifsusually pack into HEX phases, while spherical motifs are ableto pack into a wide range of spherical structures such as BCCand hexagonally close packing (HCP) phases as well ascomplex Frank–Kasper (F-K) phases or quasicrystals.[1c–e,

2, 3b,c,8, 9]

In this study, we explore the possibility to obtain motifswith curved interfaces consisting of, at least, a partially non-parallel arrangement of rod-like components and the result-

[*] R.-M. Zhang, Prof. R. Zhang, Prof. M. Huang, Prof. S. Z. D. ChengSouth China Advanced Institute for Soft Matter Science andTechnology, School of Molecular Science and EngineeringSouth China University of TechnologyGuangzhou 510640 (China)

R.-M. Zhang, Dr. X. Feng, Dr. W. Shan, Z. Su, Prof. C. Wesdemiotis,J. Huang, X.-Y. Yan, T. Liu, Dr. Z. Lin, Prof. S. Z. D. ChengDepartment of Polymer Science, College of Polymer Science andPolymer Engineering, The University of AkronAkron, OH 44325-3909 (USA)E-Mail: zl21@zips.uakron.edu

scheng@uakron.edu

Prof. A.-C. ShiDepartment of Physics and Astronomy, McMaster UniversityHamilton, Ontario L8S 4M1 (Canada)E-Mail: shi@mcmaster.ca

J. Mao, Prof. C. WesdemiotisDepartment of Chemistry, The University of AkronAkron, OH 44325 (USA)

Prof. T. LiDepartment of Chemistry and BiochemistryNorthern Illinois UniversityDeKalb, IL 60115 (USA),andX-ray Science Division, Advanced Photon SourceArgonne National LaboratoryArgonne, IL 60439 (USA)

Supporting information and the ORCID identification number(s) forthe author(s) of this article can be found under:https://doi.org/10.1002/anie.201904749.

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ing ordered phases. In general, rod-like molecules preferparallel arrangement to minimize the excluded volume(maximize the free volume) and thus maximize the transla-tional entropy of the molecules. It is noted that the parallelarrangement is at the expense of decreasing orientationalentropy, but in many cases the gain in translational entropydominates, resulting in an overall entropy maximum.[6c] As anexample, in our previous work that the hydroxy-functional-ized fullerene is linearly tethered with one or two rod-likeoligo-fluorene(s) (OF), the rod-like OF units are parallel toeach other and only highly asymmetric LAM phases areobserved.[8b]

To disrupt the tendency of parallel arrangement of rod-like components, we need to introduce extra interactions,which prefer the unparallel arrangements of rod-like compo-nents that could largely minimize enthalpy at the expense ofdecreasing entropy. For the purpose of validating this idea, wedesigned and synthesized four categories (a total of 16) ofmolecules based on the dendritic OF rods capped by a tri-(hydroxy) group. The molecule is designated as 3OH-XOFn-(P), where X (from 2 to 4) is the number of the OF rods,n (from 1 to 4) is the number of repeating units of the OF rods,and P refers to the substituted position of benzoic ester core(3,5 adapted for X = 2; 3,4,5 adapted for X = 3; and 3,4 or 3,5adapted for X = 4). The tri(hydroxy) group will provide thedriving force for the self-assembly. Owing to the largelyincommensurate cross-section area between the tri(hydroxy)group and multi-OF rods, the curved interface is preferred.Moreover, in previous reported dendrimers, that consist ofconformationally flexible AB2 rod-like building blocks con-nected by long flexible spacers, only nematic, smectic, andcrystalline phases could be observed;[10] while in our design,rigid OF rods are attached to benzoic ester core throughrelatively shorter spacers, therefore the rigidity of the back-

bone of the molecules is increased, beneficial to hold the fan-like and cone-like molecular shape. We also put two sidechains into each OF rod unit. On the one hand, the large sterichindrance between side chains may lead to weaker ornegligible p–p interaction between OF rods (see details inthe Supporting Information); and on the other hand, the sidechains are necessities for filling space if the molecules takefan-like or cone-like shape with a curved interface. Thesynergistic effects of the above factors may endow themolecules with the ability to partially break the preferredparallel orientation of OF rods and acquire a fan-like or cone-like geometry during self-assemblies. As shown in Figure 1,three strategies are developed to tune the molecular shape.The first one is to increase the length of the OF rods (n from1 to 4), the second one is to increase the number of the OFrods (X from 2 to 3), and the third one is to vary thesubstituted position of benzoic ester core of 3OH-4OFn (Pfrom 3,5 to 3,4). It is intriguing to investigate what kinds ofnanostructures could be achieved and how these structuresare formed if we could partially break the parallel orientationof the OF rods.

Results and Discussion

The detailed routes used to synthesize this set ofmolecules are given in the Supporting Information, Schem-es S1–S4. In brief, OF rods with tunable and uniform lengthwere first synthesized based on previously reported proce-dures.[8b] Then, spacers with identical length but differentnumber or position of substitution were adopted to conjugatethe tri(hydroxy) group and OF rods together via the copper-catalyzed azide–alkyne cycloaddition (CuAAC) click chemis-try.[11] The precisely defined chemical structures of synthe-sized molecules were unambiguously characterized (see de-tailed characterization in the Supporting Information). Nota-bly, with the same n value, two series of molecules with fourrods but with different substituted positions of benzoic estercore, 3OH-4OFn(3,5) and 3OH-4OFn(3,4), were obtained anddesignated as pairs of constitutional isomers.[12]

All of the samples were thermally annealed to generatesupramolecular structures. Details of sample preparation aregiven in the Supporting Information. The samples weresubsequently examined by a combination of small-angle X-ray scattering (SAXS) and the bright-field (BF) transmissionelectron microscopy (TEM).

Starting from the simplest molecules, 3OH-2OFn(3,5) (n =

1–4), with increasing OF rods length, all samples of thesemolecules exhibit HEX phases with a plane group of P6mm.This conclusion is based on the diffraction peaks having qratios of 1:

p3:2 (Figure 2A(i–iv)) in the SAXS patterns and

BF TEM images (Figure 2A (v–viii)) showing a hexagonalpacking of columns.[3c] Taking 3OH-2OF1(3,5) as an example,the experimentally determined diameter (Dexp, 5.83 nm) ofthe column is smaller than the double apex-to-peripherylength of the molecule (2L, 8.10 nm, Figure 2A(ix)). Inaddition, with increasing the length of OF rods, the incrementof Dexp (Table 1, see detailed calculations in the SupportingInformation) is less than the double length of an OF rod

Figure 1. Chemical structures of 3OH-2OFn(3,5), 3OH-3OFn(3,4,5),3OH-4OFn(3,5), and 3OH-4OFn(3,4).

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repeat unit (1.66 nm).[8b] It is plausible to attribute thisdiscrepancy to the overlapping of the coronas consisting ofOF rods along the radial direction. However, this model maynot be feasible to afford uniform space filling, particularlywhen the OF rods become longer. Given spacers between theapex and the OF rods is flexible, we expect that the OF rodsare not completely arranged along the radial direction andthus, OF rods are not mainly interdigitated with neighbors,rather tilted an angle toward the tangential direction dictatedby more uniform space filling.[13] The formation of HEXphases for all the molecules in this category could beattributed to the same AB2 dendritic architecture.[12a] Specif-ically, this architecture results in the fan-like conformation of3OH-2OFn(3,5), which preferentially assembles into disc-likemotifs and pack into HEX phases (Figure 2A(x)).

A drastic change of the phase behavior is observed whenthe number of the OF rods is increased to three. For 3OH-3OF1(3,4,5) with the shortest OF rods length, the positions ofthe SAXS peaks shown in Figure 2B (i) have q ratios of

p2:p

4:p

5:p

6:p

8:p

10:p

12:p

13:p

14:p

16:p

17:p

18:p

20:-p21:p

22:p

24:p

26:p

29. This pattern could be assigned to theF-K A15 phase with a space group of Pm3̄n (see detailed peakassignments in the Supporting Information, Figure S13 andTable S3).[3b,9a] The F-K A15 phase is one of the so-calledtopologically close packing structures, and it usually has anA3B stoichiometry with B units in CN12 icosahedra and Aunits in CN14 polyhedra.[14] In dendrimers and dendrons, itwas first observed by Percec et al. , who determined itsspherical model rather than a columnar model by thecomputation of electron density profiles and direct visual-ization in TEM images.[9a,b] The packing model of 3OH-3OF1(3,4,5) is further determined by the BF TEM image(Figure 2B (v)), showing a square 44 tiling pattern witha bright spot at the intersection of the dark lines, in agreementwith the spherical model along the [001] direction.[3c,9b] Thelattice parameter of the cubic unit cell for this phase is a =

11.98 nm as calculated from the d200. In addition, the sphericalmotifs usually could be generated from conical or crown-like

Figure 2. Supramolecular structures self-assembled from 3OH-2OFn(3,5) and 3OH-3OFn(3,4,5). A) SAXS patterns (i to iv) and thin-sectioned BF-TEM images (v to viii) of 3OH-2OFn(3,5) (n = 1–4), where HEX phases are formed; (ix) molecular model of 3OH-2OF1(3,5); (x) packing model of3OH-2OFn(3,5) (n = 1–4). B) SAXS patterns (i to iv) and thin-sectioned BF-TEM images (v to viii) of the 3OH-3OFn(3,4,5) (n = 1–4), where orderedphases change from F-K A15 to DQC, and finally to BCC; (ix) molecular model of 3OH-3OF1(3,4,5); (x) packing model of 3OH-3OFn(3,4,5)(n = 1–4). TEM images are taken along the [001] direction of the HEX phase, the [001] direction of the A15 phase, the [00001] direction of theDQC phase and the [001] direction of the BCC phase and provided after Fourier filtering (the originals are given in the Supporting Information,Figures S16 and S17). The lattice parameters obtained in the TEM images (the scale bars represent 50 nm) are consistent with these determinedbased on the SAXS patterns. In molecular models, the side chains (-C6H13) are not completely shown for clarity. O red, N blue, C gray, H white. Inpacking models, the red coronas are mainly composed of OF rods while the blue cores mainly consist of tri(hydroxy) groups.

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molecular conformation, which can be confirmed by X-raydiffraction and corresponding electron density profiles anal-ysis.[15] For 3OH-3OF1(3,4,5), the experimentally determinedaverage diameter of each sphere is about 7.43 nm (Dexp),which is smaller than double the apex-to-periphery length ofthe molecule (8.08 nm, 2L, Figure 2B (ix)) in the conicalconformation; however the crown-like conformation is lesslikely since the average number of molecules per supra-molecular spheres is estimated as 67 (based on the measureddensity (1) of the A15 sample (1 = 1.10 gcm@3)), thus wespeculate that the molecules are in conical conformation withcone angle about 28.0788 (Table 1, see detailed calculations inthe Supporting Information). The OF rods may tilt an angletoward the tangential direction, which appears to be impor-tant for uniform packing of the coronas.[13]

A distinct phase emerges when the length of the OF rodsis increased by one OF unit to 3OH-3OF2(3,4,5). Thismorphology can be assigned as a dodecagonal quasicrystalline(DQC) phase, which exhibits a SAXS pattern with typicaldiffraction peaks (the 00002, 12100, 10102, and 12101diffractions in Figure 2B (ii)) characterizing the DQC phaseas reported in previous work.[1e, 3c,9e] The DQC phase is closelyrelated to the F-K phases. In the two-dimensional ab plane,the DQC only possesses 3-fold, 4-fold, and 6-fold rotationalsymmetry and without translational operations.[16] From theBF TEM image along the [00001] direction (Figure 2B (vi)),representative tiling patterns (36, 44, 33.42 and 32.4.3.4) withsimilar abundance corresponding to DQC phase as reportedbefore can be identified, further confirming the formation ofthe DQC phase.[3c,17]

When the length of OF rods is further increased to 3OH-3OF3(3,4,5), a BCC phase (space group Im3̄m) with a latticeparameter of a = 9.31 nm is identified by a combination of the

SAXS pattern exhibiting q ratios of 1:p

2:p

3:p

4:p

5:p

6:p

7(Figure 2B (iii)) and the BF TEM image showing typicalsquarely packed spheres along the [001] direction (Fig-ure 2B (vii)).[3c] The density is measured to be 1 =

1.04 gcm@3. The estimated average diameter of the assembledspheres is 9.17 nm, the average number of molecules in eachsphere is 62, and the cone angle is calculated to be q =

29.1988(Table 1, for detailed calculations, see the SupportingInformation). The 3OH-3OF4(3,4,5) with the longest OF rodsstill forms a BCC phase as shown in the SAXS pattern(Figure 2B (iv)) and the BF TEM image (Figure 2B (viii)). Itis interesting to note that our calculation indicates that, withn increasing from three to four, the diameter of the assembledsphere increases by 1.28 nm, which is also less than the doublelength of an OF rod repeat unit (1.66 nm).[8b]

To explore the effect of molecular geometry on the phasebehavior, we specifically design a set of constitutionalisomers, 3OH-4OFn(3,5) and 3OH-4OFn(3,4). The pair ofconstitutional isomers have an identical composition for thesame number of n (Supporting Information, Figures S9, S10).However, these two molecules self-assemble to form com-pletely different supramolecular structures. Regardless of thelength of the OF rods (n = 1–4), the HEX phases (plane groupof P6mm) are observed in 3OH-4OFn(3,5), as identified bythe SAXS patterns with a q ratio of 1:

p3:2 (Figures 3 (i, ii);

Supporting Information, Figure S11). Compared with theHEX phases formed by 3OH-2OFn(3,5), the HEX lattice sizeof the 3OH-4OFn(3,5) (5.23 nm, 5.99 nm, 7.08 nm, and8.42 nm, respectively) is slightly smaller at the same OF rodslength. This could be attributed to the smaller size of thehydrogen bonded core resulted from a smaller number ofmolecules per hexagonal column stratum in HEX lattice. Theincreasing trend of the average diameter of the column inHEX lattices of 3OH-4OFn(3,5) is similar to that of 3OH-2OFn(3,5) (Table 1, see detailed calculations in the Support-

Tabelle 1: Supramolecular structure analysis of 3OH-2OFn(3,5), 3OH-3OFn(3,4,5), 3OH-4OFn(3,5), and 3OH-4OFn(3,4).

Molecules Phase a [nm][a] Dexp[b] m[c] a or q [88][d]

3OH-2OF1(3,5) HEX 5.83 5.83 6 603OH-2OF2(3,5) HEX 6.59 6.59 5 723OH-2OF3(3,5) HEX 7.77 7.77 5 723OH-2OF4(3,5) HEX 9.16 9.16 6 603OH-3OF1(3,4,5) A15 11.98 7.43 67 28.073OH-3OF2(3,4,5) DQC 6.17 – – –3OH-3OF3(3,4,5) BCC 9.31 9.17 62 29.193OH-3OF4(3,4,5) BCC 10.61 10.45 70 27.463OH-4OF1(3,5) HEX 5.23 5.23 2 1803OH-4OF2(3,5) HEX 5.99 5.99 2 1803OH-4OF3(3,5) HEX 7.08 7.08 2 1803OH-4OF4(3,5) HEX 8.42 8.42 2 1803OH-4OF1(3,4) DQC 5.70 – – –3OH-4OF2(3,4) DQC 6.22 – – –3OH-4OF3(3,4) – – – – –3OH-4OF4(3,4) – – – – –

[a] Hexagonal columnar lattice parameters of HEX phases, cubic latticeparameters of F-K A15 and BCC phases, and the d-spacing value of thefirst peak in DQC phases. [b] Average diameter of the column in HEXphases or average diameter of the spheres in F-K A15 and BCC phases.[c] Average number of molecules per hexagonal column stratum in HEXphases or the average number of molecules per supramolecular spherein F-K A15 and BCC phases. [d] Fan-angle (a) or cone angle (q).

Figure 3. Constitution directed assemblies of 3OH-4OFn(3,5) and3OH-4OFn(3,4) (n = 1–2). 3OH-4OFn(3,5) (n =1,2) shows HEX phasesin the SAXS patterns (i) and (ii). 3OH-4OFn(3,4) (n =1,2) shows DQCphases in the SAXS patterns (iii) and (iv).

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ing Information). Distinguished from HEX lattices construct-ed by 3OH-4OFn(3,5), their constitutional isomers, 3OH-4OFn(3,4), self-assemble to form spherical packing DQCphases for n = 1 and 2 (the d-spacing value of the first peak inthe DQC phases is 5.70 nm and 6.22 nm, respectively), asidentified by the SAXS patterns exhibiting typical diffractionpeaks (the 00002, 12100, 10102, and 12101 diffractions inFigure 3(iii, iv)).[1e, 3c,9e] When the repeating units numbern increases to three and four, the sample becomes disordereddespite extensive thermal and solvent annealing treatments(SAXS patterns are given in the Supporting Information,Figure S12). The distinct assembly behaviors of this set ofconstitutional isomers are consistent with previous work indendron systems where dendrons with 3,5-substitution usuallyshow columnar structures, while dendrons with 3,4-substitu-tion generally display spherical structures and should beoriginated from the different molecular shape.[12, 18] For 3OH-4OFn(3,5), we speculate that they should assume a fan-likeshape, whereas a much more crowded conformation could beexpected for the 3OH-4OFn(3,4), resulting in a cone-likeshape.

To understand the origin of the rich variety of mesoscopicphases formed by the four categories of dendritic OF rodscapped by a tri(hydroxy) group, we propose a thermodynamicmodel that includes a number of contributions to the Gibbsfree energy of the system in the form [Eq. (1)]:

G ¼ H@TS ¼ HHB@TðSSC þ SRÞ ð1Þ

where HHB represents the hydrogen bonding interactions inthe core, SSC represents the conformational entropy of theside chains, and SR represents the entropy of the OF rods.Similar to many dendrons systems,[2a] the HHB is a stronginteraction, which would drive the molecules to aggregateinto core-coronas structures; and at the same time, theparallel arrangement of the rods is assumed to be partiallybroken to afford the curved interface. The SSC is a largecontribution to the entropy of the coronas[19] and wouldincrease with increasing available packing space for sidechains. This entropic contribution could approach a constantwhen most molecular conformations of the side chainsassume their preferred states; after that, a further increaseof packing space for the side chains would induce large voidspace in coronas, thus it is unfavorable. Compared with SSC,the SR of the rods, which is consisting of orientational entropySRo and translational entropy SRt,

[6c] has a smaller contributionto the entropy of the coronas. However, this contribution isstill important, especially when the side chains have reachedtheir optimum conformations.

The molecular shape (fan-like or cone-like shape), whichappears to be related to the packing of OF rods and sidechains in coronas, is assumed to be determined by maximizingthe entropy of coronas (SSC and SR).[19] For 3OH-2OFn(3,5)and 3OH-4OFn(3,5), when the fan-like molecular shape isassumed to be able to provide enough available packing spacefor the side chains to afford their most conformations, thecone-like molecular shape may generate extra void space incoronas. Besides that, the fan-like shape could minimize theexclude volume, thus also increase the SRt at the expense of

a lowering of the SRo. In this case, the fan-like molecular shapewould be expected, and the molecules could pack into disc-like motifs, which generally allow the formation of columnarstructures, consistent with our experimental observations.

When the number of the OF rods increases from two tothree or substituted position of 3OH-4OFn changes from 3,5-position to 3,4-position, large crowdedness appears to begenerated for the packing of side chains if the molecules stillhold fan-like shape. To avoid this and increase SSC, cone-likemolecular shape, which would release more packing space forside chains, is preferred.

In the spherical packing phases observed in the currentstudy, the 3OH-3OFn(3,4,5) molecules are simple and preciseoligomers. Nevertheless, these molecules exhibit a phasesequence from A15 to BCC phases with increasing rodslength. It should be noted that a similar sequence has beenobserved in dendrons with flexible chains at the end as eitherincreasing annealing temperature or increasing the number ofbranches near the periphery.[2a, 9d, 18, 20] When the sphericalmotifs form an ordered structure, the spherical symmetry ofthe motifs is broken by the lattice symmetry. In this case, thegeometric shapes of the deformed spherical motifs wouldfollow the polyhedral shapes of the Wigner–Seitz cells(WSCs). The sphericity of the deformed sphere could bequantified by the isoperimetric quotient (IQ = 36pV2/S3,where V and S are the volume and area of the WSC). Forthe structure consisting of more than one type of WSCs, theaverage value of IQ (IQ) of all the WSCs is used to quantifyits average sphericity. The IQ of the cubic phase is independ-ent on the size of the unit cell and can be calculated as IQ =

0.7534 and 0.7617 for the BCC and F-K A15 phases,respectively.[21] It is generally believed that the tendency forminimizing the surface area of these soft spherical motifsdrives the formation of the A15 phase.[21a,22] To explain therich phase behaviors observed in dendrons, Ungar and his co-workers calculated the average radial distribution functions ofvolume dV/dr for different phases with spherical motifs.[9d,20]

The dV/dr curves give the ideal shapes of molecules thatwould fill the unit cell of different phases perfectly uniformly.By comparing dV/dr curves of A15 and BCC phases in termsof space filling, one can anticipate that widening and short-ening the arms of dendrons would usually lead to thevariation from A15 to BCC phases.[9d, 20] For 3OH-3OFn-(3,4,5), we did observe the phase sequence from A15 to BCCphases when n values increase from one to three or four.Specifically, the 3OH-3OF1(3,4,5) with shortest OF rodslength forms the A15 phase with smaller surface area, whileBCC phases with the larger surface area are more favorablefor 3OH-3OF3(4)(3,4,5) with longer OF rods. These resultsmay support the hypothesis that the OF rods are tilted anangle toward the tangential direction of the spherical motifs.

Conclusion

In summary, we have designed a series of preciselydefined fan-shaped or cone-shaped dendritic OF rods cappedby a tri(hydroxy) group with tunable rods length. Theincorporation of hydrogen bonding and special dendritic

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architecture into the rod-like molecules successfully breaksthe preferred parallel arrangement of the rods and moreoverleads to controllable supramolecular structures. In particular,completely different structural behaviors of two rods (3OH-2OFn(3,5)) and three rods molecules (3OH-3OFn(3,4,5)) aswell as the constitutional isomers (3OH-4OFn(3,5) and 3OH-4OFn(3,4)) have been observed. In the spherical packingregion, the deformation tendency of the spherical motifscould be regulated by varying the length of the OF rods,resulting in a sequence of phases from F-K A15 to DQC andBCC phases (the analysis of supramolecular structures forthese molecules are summarized in Table 1). This set ofsamples not only provides a novel model system to study howwe can break the preferred parallel arrangement of rod-likemolecules and achieve diverse anticipated supramolecularstructures, but also offers an opportunity to understand thestructural evolution pathways of spherical packing phases.

Acknowledgements

This work was supported by the National Science Foundation(DMR-1408872 to S.Z.D.C., CHE-1808115 to C.W.), theIntroduced Innovative R&D Team Project of „The PearlRiver Talent Recruitment Program“ of Guangdong Province(no. 2016ZT06C322), the National Natural Science Founda-tion of China (U1832220 to S.Z.D.C.), and the NaturalScience and Engineering Research Council (NSERC) ofCanada. This research used resources of the AdvancedPhoton Source, a U.S. Department of Energy (DOE) Officeof Science User Facility operated for the DOE Office ofScience by Argonne National Laboratory under Contract No.DE-AC02-06CH11357.

Conflict of interest

The authors declare no conflict of interest.

Stichwçrter: Frank-Kasper-Phase · Nanostrukturen ·Oligofluorene · Selbstorganisation · St-bchenfçrmige Molekfle

Zitierweise: Angew. Chem. Int. Ed. 2019, 58, 11879–11885Angew. Chem. 2019, 131, 12005–12011

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Manuskript erhalten: 16. April 2019Ver-nderte Fassung erhalten: 10. Juni 2019Akzeptierte Fassung online: 18. Juni 2019Endggltige Fassung online: 17. Juli 2019

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