Open Access Article
Yong-Rui Wanga,
Jui-Heng Wenga,
Shing-Jong Huanga,
Chun-Jen Su
b,
U-Ser Jeng
b,
Po-Ya Changb,
Wei-Tsung Chuang
*b and
Chien-Lung Wang
*a
aDepartment of Chemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan. E-mail: kclwang@ntu.edu.tw
bNational Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30092, Taiwan. E-mail: weitsung@nsrrc.org.tw
First published on 22nd January 2026
In supramolecular chemistry, higher structural complexity enables emergent functions in ordered soft matter. To construct structurally complex and functional Frank–Kasper (FK) phases, heterogeneity in supramolecular micelles is introduced by blending rigid aromatic dendrons (Ar2) with flexible aliphatic dendrons (D2). This approach creates micelles with surface concavities while preserving long-range periodicity of the FK σ lattice. The concave domains serve as enzyme-like pockets that accommodate guest molecules and facilitate photodimerization reactions. Structural analyses confirm that these features enhance complexity in hierarchical architecture and enable catalytic performance. This work presents a versatile strategy for designing FK phases that integrate molecular recognition, supramolecular precision, and catalytic function within an ordered framework.
One strategy to enhance complexity is the incorporation of aperiodicity within periodic lattices. In block copolymers, factors such as conformational asymmetry,4–7 volume asymmetry,8–10 compositional asymmetry,11–15 etc. have been applied to create symmetry breaking that leads to structural complexity in the spherical phases.16 Blending, in particular, provides a straightforward means of controlling both formation and stability of Frank–Kasper (FK) phases, where uneven interfacial curvature promotes non-spherical and multi-sized micellar motifs.11,12,17–23 However, blending-based polydispersity mainly alters micelle size and shape, and therefore offers only limited ways to introduce new structural features. Creating additional levels of complexity—such as spatially defined chemical environments, anisotropic interfaces, or directional binding sites—without disrupting the integration of the original FK lattice remains challenging. For example, although blending block copolymers can effectively shift the phase behavior of mixed systems, the resulting structures often retain a single pre-existing ordered phase, without generating finer structural features or new functional elements within that lattice.12 This highlights the difficulty of enhancing structural complexity while maintaining long-range order.
Dendrons and dendrimers offer a distinctive pathway to such complexity and structural features.24,25 Their generation-dependent shape evolution,26–28 precise molecular design,26,29–32 and versatile end-group modifications27,30,33,34 enable quasi-equivalent packing that relieves frustration and supports tetrahedrally close-packed FK lattices.35 Consequently, dendrons assemble into a remarkable diversity of structures—including cubic,27,29,30,35,36 tetragonal,28,31,35,37,38 quasicrystalline,28,37–39 hollow,33,34,37 and even chiral micelles34,39,40—surpassing what is typically achievable with block copolymers.31,37 In contrast, natural blended systems routinely exploit heterogeneity to generate structural multiplicity and dynamic functionality. Biological membranes, for instance, form compositionally heterogeneous microdomains such as lipid rafts, stabilized by cholesterol–sphingolipid interactions that enhance membrane responsiveness.41–44 Likewise, protein binding pockets provide concave hydrophobic cavities that couple structure to function, enabling selective guest recognition and catalysis by pre-organizing substrates and stabilizing transition states.45–48 These examples illustrate how blending-derived heterogeneity can simultaneously increase the complexity and functional adaptability of an assembly.
Motivated by these natural design principles—and by the ability of dendrons to introduce controlled heterogeneity—we sought to install designed concavities onto the surface of FK-phase supramolecular micelles. Our goal was to elevate the structural sophistication of the spherical assemblies while preserving the symmetry breaking and long-range integration of the FK lattice. As illustrated in Scheme 1, the diaryl amphiphiles (Ar2) are used as molecular rafts that create heterogeneity in supramolecular micelles formed by the amphiphilic di-dendron (D2). D2 molecule has been synthesized as the intermediate product of the Janus dendrimers for many research.49–59 In our previous study, D2 has demonstrated the ability to form FK σ phase with symmetry breaking.59 Since the Ar2 molecules are smaller and more rigid than D2, blending the Ar2 and D2 in the supramolecular micelles could create both heterogeneity and concavities in the supramolecular micelles of the FK phase. Catalytic functions mimic the natural hydrophobic pockets may also be added to the complex FK phase as the concavities on top of the Ar2 motifs could encapsulate guest molecules. Our characterization data indicated that on top of the symmetry breaking, the presence of the raft-inspired building blocks Ar2 in the supramolecular micelles of D2 created additional structural features and function to the FK σ phase. The overall integration of the synthetic self-assembly system is thus upgraded as the presence of the Ar2 advances both hierarchical complexity and functional adaptability of the spherical phase. This innovation aligns with Lehn's vision of progressive complexity,3 bridging the gap between structural sophistication and dynamic functionality in artificial self-assembly systems.
were obtained. The ordered phases of the mixtures were then prepared by heating to 150 °C—above the isotropization temperatures (Ti) of both D2 and Ar2 but below their decomposition thresholds (Fig. S16)—to ensure homogeneous mixing in the molten state. The resulting melts were cooled and annealed at 40 °C for 12 hours to facilitate self-assembly.
To confirm the uniform incorporation of molecular rafts into the ordered phase of D2, optical microscopy (OM) was employed for direct observation. As shown in Fig. 1a, macroscopic spherulitic structures were evident in the drop-cast samples of the Py2/D2 mixtures. With increasing Py2 content, the spherulitic morphology became increasingly disrupted. At
the emergence of dark aggregated domains suggests phase segregation of excess Py2. This conclusion is further supported by wide-angle X-ray scattering (WAXS) data (Fig. 1b), where distinct crystalline diffraction peaks attributed to Py2 are observed in the
sample. In contrast, WAXS profiles of samples with
display no sharp crystalline peaks, but instead feature a broad amorphous halo. This indicates that the spherulitic structures observed via OM do not originate from angstrom-scale crystalline ordering. The scattering profiles of varies of Ar2 are shown in Fig. S17.
To probe the internal aggregate structures within these spherulites, small-angle X-ray scattering (SAXS) analysis was conducted (Fig. 1c). The SAXS profiles revealed that self-assemble micellization of the Py2/D2 mixtures crystalizes into the FK σ phase. To further clarify how the SAXS data support the micellar assignment and FK σ phase formation, the primary and higher-order peaks were analyzed. The peak ratios (q/q0) are consistent with the reflection pattern of the FK σ lattice,60 and the comprehensive analysis of the σ-phase structure and its indexed diffraction peaks is provided in Table S1. The characteristic peaks q410, q330, and q002 were used to calculate the corresponding lattice parameters (a, b, c) by the standard geometric relations of tetragonal phase, shown in Table S2.38 Based on these lattice parameters, the diameter of the supramolecular micelles within the FK σ lattice (Dsphere) was estimated, also performed in Table S2. These results confirm that the incorporation of Py2 does not inhibit the ability of D2 to act as a cone-shaped motif and self-assemble into the FK σ phase. However, the presence of Py2 shifts the diffraction peaks to higher q values and broadens them, indicating that the inclusion of rigid, small Py2 molecules introduces heterogeneity within the micelles and compresses the σ-phase lattice.
The formation of this FK σ phase from cone-shaped motifs represents a thermodynamically stable self-assembly, further validated by differential scanning calorimetry (DSC). As shown in Fig. 1d, the Ti of the mixtures systematically decreases with increasing Py2 content. This phase behavior is consistent with the principle of colligative properties, where the incorporation of solute molecules (Py2) lowers the Ti of the host component (D2).61 This behavior also confirms that Py2 is well-dispersed within the D2-rich ordered domains for compositions with
At
however, the Ti does not decrease further, indicating that the excess Py2 exceeds the micelle's incorporation capacity and instead undergoes phase separation to form Py2-rich domains, as corroborated by both Fig. 1a and b. Additionally, the broadening of all (hkl) diffraction peaks in the SAXS profiles supports the DSC results, reinforcing the conclusion that Py2 molecules are randomly and uniformly distributed within the supramolecular micelles of D2, resulting in both a reduction in Ti and broadened diffraction features.
The miscibility of other Ar2 variants—Np2 and Bn2—with D2 was also assessed using the same protocol. The results, summarized in Fig. S18 and Tables S4–S9, confirm that both Np2 and Bn2 exhibit good miscibility with D2 up to
Moreover, increasing size mismatch between Ar2 and D2 leads to a greater suppression of Ti and more significant lattice contraction in the σ phase. This trend suggests that smaller molecular rafts introduce greater disruption to the micellar packing order, highlighting the influence of geometric compatibility on structural organization within FK σ phases.
The heterogeneity of the Py2/D2 micelles and the dynamic behavior of Py2 within the supramolecular micelles were further investigated by solid-state 13C–1H heteronuclear correlation (HETCOR) nuclear magnetic resonance (NMR) spectroscopy. For pure D2 in the FK σ phase, cross-polarization (CP) is relatively inefficient due to the high segmental mobility; therefore, the HETCOR spectrum was acquired using a prolonged CP contact time (tc) of 2 ms. In contrast, the HETCOR spectrum of Py2 was recorded with a short CP contact time of 200 µs to suppress undesired long-range polarization transfer.
As shown in Fig. 2a and b, the characteristic spectral features of D2 and Py2 are clearly distinguishable. For D2, only cross-peaks originating from the dodecyl chains are observed, appearing in the ranges of δC = 10–50 ppm and δH = 0–3 ppm. In contrast, the expected resonances from the O–CH2 units (δC ≈ 65–75 ppm),62 the pentaerythritol core (δC = 50–65 ppm and δH = 2–5 ppm), and the aromatic moieties (δC = 100–120 ppm and δH = 5–8 ppm) are absent. This behavior can be attributed to their significantly higher mobility, which leads to inefficient 1H–13C dipolar recoupling under the applied CP conditions, as discussed in detail in Fig. S19. For Py2, in addition to the signals originating from the pentaerythritol core, an additional broad resonance at approximately δC ≈ 120 ppm was observed, which can be attributed to the Py segments. The aromatic 1H signals of Py2 are widely distributed and predominantly broadened due to strong residual 1H–1H dipolar couplings that persist even under MAS conditions, as well as the heterogeneous local environments experienced by the Py2 segments within the micelles.63–65 For the Py2/D2 mixtures, the cross-peaks associated with Py2 are clearly observed in the HETCOR spectra for samples with
in the HETCOR spectra, acquired with a prolonged contact time of 5 ms, as shown in Fig. 2c and d. In contrast, the Py2 signals in the
mixture are too weak to be detected (Fig. S20) owing to the low Py2 concentration. To gain deeper insight into the location and orientation of the Py segments within the micelles, a 1H spin-diffusion (PSD) block was incorporated into the HETCOR pulse sequence, rather than further extending the CP contact time, in order to probe long-range intermolecular spatial correlations. This strategy was adopted for three main reasons. First, magnetization decay in the present approach is governed by T1 relaxation, whereas an extended CP contact time is limited by T1ρ relaxation, and T1 is typically much longer than T1ρ. Second, 1H–1H dipolar interactions play a crucial role in long-range intermolecular magnetization transfer; however, the spin-locking RF field ramped linearly from 40 to 50 kHz during CP may partially suppress these dipolar interactions and thus hinder spin diffusion. Third, excessively long CP contact times (>50 ms) may lead to power-handling issues in commercial MAS probeheads. As shown in Fig. 2e and f, at a spin-diffusion time (tSD) of 250 ms, magnetization from the 1H nuclei of the dodecyl chains is efficiently transferred to the Py2 segments. This effective magnetization transfers between the dodecyl chains and the Py segments indicates that the Py segments of the molecular rafts are primarily located within the hydrophobic shell of the supramolecular micelles, as schematically illustrated in Scheme 2a.
According to the previous work in our group,59 in the σ phase of D2, each supramolecular micelle is constructed with ca. 19 cone-like D2 molecules. Therefore, at
each supramolecular micelle of Py2/D2 mixtures has to accommodate ca. 4 and 6 Py2 molecules, respectively. Combining the ssNMR results in Fig. 2 and the SAXS, WAXS and OM data in Fig. 1, it was found that the presence of Py2 creates structural heterogeneity to the supramolecular micelles of D2, but the loading capacity of the micelles is limited, as 6 Py2 molecules in each micelle is effective enough to create crowded environment that slows down the dynamics of the molecular rafts. The maximum loading capacity of each micelle in the σ phase is about 6 Py2 molecules, as the higher molar ratio of Py2 in the mixture led to the phase-separated Py2-rich domains.
A comparable diffusion-based experiment was carried out for the Np2/D2 system at a molar fraction of 20%, following the same experimental strategy as used for the Py2/D2 mixtures. As shown in Fig. S21, distinct intermolecular magnetization transfer between the aliphatic region of D2 and the aromatic resonances of Np2 was observed, indicating efficient spin diffusion between these components. This result demonstrates that replacing Py2 with a different aromatic molecular raft (Ar2) leads to a similar spatial proximity between the aromatic segments and the dodecyl-chain-rich hydrophobic domains of the D2 supramolecular micelles. The Np2/D2 diffusion data therefore support the generality of aromatic raft incorporation within concaved σ-phase micelles, rather than a behavior specific to the Py2 system.
as illustrated in Scheme 2b.
To differentiate the dispersion environments, the An-loaded assemblies are denoted as An@σ for the assemble using simply D2 as the host (conventional micelles), and An@σ(Ar2) for those using Ar2/D2 mixtures as the hosts (concaved micelles).
SAXS profiles in Fig. 3a shows that guest loading perturbs the lattice of conventional micelles, causing more significant lattice contraction and peak broadening of the σ phase of D2, as shown in Table S11 and Table S12. The insignificant changes of the FK σ framework of σ(Ar2) indicate that the pre-organized concavities localize guest molecules and reduce the extent of global lattice distortion. Due to the size differences, the incorporation of Py2, Np2 and Bn2 results in concavities with difference depths in the micelles. Among the variants, σ(Np2) provides the optimal balance of geometric complementarity and interaction strength, stably encapsulating 2 – 3 eq. of An without phase-separation (Fig. S22 and S23). Collectively, these results establish that only concavities of suitable depth enable stable guest encapsulation, with σ(Np2) standing out by accommodating two An per concavity—precisely the stoichiometry for photodimerization—highlighting the unique role of geometry-tuned concavities in stabilizing and pre-organizing guests.
Since σ(Np2) exhibited the most favorable guest encapsulation, we next evaluated its impact on photoreactivity. As shown in Fig. 3b, crystalline An dimerized very slowly under UV irradiation (λ = 365 nm) due to the rigid packing of the lattice. In contrast, An dispersed in conventional micelles (An@σ) reached about 45% conversion within 2 h, consistent with the requirement for suitable intermolecular orientation;67 the modestly improved conversion can be attributed to the greater molecular mobility in the fluidic micellar environment. Remarkably, in σ(Np2) assemblies nearly complete photodimerization occurred within 1 h, demonstrating that the concavities not only stabilize guest encapsulation but also promote effective preorganization of the reactants. Collectively, these results show that concavity-engineered micelles enhance photoreactivity through the combined effects of confinement and spatial preorganization, thereby closely emulating the functional characteristics of enzymatic active sites.
Together, these findings establish σ(Np2) as the most effective architecture for promoting photoreactivity. More broadly, they highlight a generalizable strategy in which concavity confinement, molecular recognition, and dynamic guest exchange are embedded within a FK σ lattice, thereby functionally mimicking enzymatic active sites and advancing Lehn's vision of progressively complex soft materials.
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