Non-macrocyclic molecular design enables cavity-adaptive cocrystals with high elasticity and low-threshold lasing

Domain: physics
Published: 2026-02-12
Editorial outcome: major_revision

Abstract
The construction of cavity-adaptive cocrystals (CACs) based on linear non-macrocyclic π-conjugated hosts remains challenging due to their inherently weak and less predictable binding capabilities compared to conventional macrocyclic hosts. Here we overcome this limitation through the rational design and synthesis of CACs employing a structurally engineered non-macrocyclic host. This host combines a linear π-conjugated backbone with sterically hindered groups, allowing dynamic cavity modulation while maintaining its luminescent characteristics upon solvent and guest encapsulation. Heteroatom-modified guest molecules of similar size form molecular cavities with comparable dimensions yet exhibit different luminescence characteristics. Further tailoring the host’s π-backbone yields color-tailorable CACs. These systems exhibit relatively strong intralayer C−H···π interactions coupled with weak interlayer forces, leading to high elasticity and low-threshold lasing action in single crystals and microcrystals. This work establishes a non-macrocyclic host/guest platform with adaptive cavities, demonstrating its potential as flexible laser emitters.

Introduction
Supramolecular host-guest complexes have garnered significant interest due to their diverse applications in drug carriers, gas separation, molecular machines, and optics1–5. The field has evolved significantly since Pedersen’s pioneering discovery of crown ethers in the 1960s6, with subsequent development of diverse macrocyclic hosts including cyclodextrins7, cucurbiturils8, and pillararenes9–11. These systems demonstrate inherent molecular recognition capabilities through their preorganized molecular cavities. Among these, cyclophanes represent a particularly important class of macrocyclic receptors12,13. Notable examples include Stoddart’s positively charged ExBox⁴⁺(Fig.1a), which exhibit exceptional binding affinity for polycyclic aromatic hydrocarbons (PAHs)14, and Würthner’s neutral perylenediimide-based cyclophanes15. The latter was further extended to larger terrylene bisimide (TBI) systems with enhanced PAH binding capabilities16. While traditional host-guest chemistry has primarily focused on solution-phase guest binding and cavity modulation, with relatively few studies investigating solid-state photofunctional properties. Particularly, pillararene- and cyclophane-based complexes have demonstrated unusual phenomena such as solid-state lasing17 and thermally activated delayed fluorescence (TADF)18,19, due to the profound interplay between hosts and aromatic guests. The confined host cavity environment enables fluorescence enhancement and/or stabilization of triplet excitons, allowing precise modulation of excited-state optical properties.

Beyond these well-established structural frameworks in host-guest chemistry, recent studies have revealed exceptions where sterically hindered aromatic compounds featuring a central planar π-core and symmetric bulky terminal groups/ions act as non-macrocyclic hosts20,21. Through mediation by charge-transfer (CT) and/or hydrogen bonding interactions, these non-macrocyclic compounds can effectively encapsulate solvent molecules or small π-conjugated guests, leading to the formation of cavity-adaptive cocrystals (CACs). This approach has enabled advanced solid-state photofunctional properties, including tunable emissions20 and near-infrared room-temperature phosphorescence (RTP)21. Notably, Würthner’s group employed a C64 nanographene derivative with four imide substituents to construct CACs with PAHs and metal-organic compounds (e.g., coronene and platinum porphyrin), yielding multilayer nanographene assemblies22,23. Inspired by these discoveries, we propose a sterically hindered distyrylbenzene (DSB) derivative24–28 as an effective host for linear and planar PAHs. Our strategy leverages the weak C−H···π interactions to form photofunctional CACs, capitalizing on DSB’s large molecular dimensions and high fluorescence efficiency. This system holds promise as a versatile platform for the rational construction of CACs toward high-efficiency solid-state lasing and the unlocking of additional physicochemical properties.

Herein, we developed a linear DSB derivative decorated with terminal steric groups as a potential host for constructing CACs. Such a non-macrocyclic DSB-based compound dynamically encapsulates both solvent molecules and PAHs, forming host/guest microcrystals and single crystals with tunable molecular cavity sizes, i.e., CACs. The host binds smaller and larger guests in distinct 1:2 and 1:1 stoichiometric ratios through C−H···π and/or C−H···O interactions, while adjacent host molecules are stabilized by weak van der Waals forces between terminal groups. The resulting host/guest microcrystals maintain high-efficiency photoluminescence with only slight spectral shifts compared to the pristine host. Introducing heteroatoms into guests would not affect the cavity structures but would result in different luminescence behaviors. The emission colors of these CACs can be tailored by modifying the host’s central π-backbones. The synergistic intralayer and interlayer interactions endow the CAC single crystals with high elasticity, while high crystallinity and photoluminescence quantum yields (PLQYs) allow low-threshold lasering in microcrystals, even in elastic single crystals. This research provides deep insight into the development of CACs with flexible photonic properties.

Results
We chose linear 4,4’-bis[4-(di-p-tolylamino)styryl]biphenyl (1, Fig.1b) as a host for functional CACs based on two key advantages: (1) Its biphenyl-bridged DSB backbone with bulky p-tolyl terminals may potentially allow the accommodation of diverse PAH guests through extended π-conjugation length and confinement effect. (2) Such a type of π-backbones generally exhibits high PL efficiencies and crystallinity due to weak intermolecular C−H···π forces29,30. We initially investigated the crystalline assemblies of 1 obtained from different solvent mixtures (Fig.2a, see Supplementary Table 1 for details). Slow evaporation of 1 from a tetrahydrofuran/ethanol mixture (THF/EtOH; v/v=1:1, C =2.5mM) yielded well-defined cyan-emitting microribbons (MRs), as verified by fluorescence microscopy and SEM results (FM/SEM, Fig.2b,c). These MRs have hundreds of micrometers in length and tens of micrometers in width. Instead of MRs, slow evaporation of 1 from 1,4-dioxane/n-propanol (Dio/PA) and toluene/isopropanol (Tol/IPA) gave green-emitting rectangle and parallelogram microplates (MPs), respectively. After examining more solvent mixtures, we found that the luminescence color of the microcrystals is governed by the type of good solvent used in the preparation. The use of non-aromatic solvents generally yields cyan-emitting microcrystals, with the sole exception of Dio, which enables green-emitting microcrystals. Conversely, when aromatic solvents (e.g., chlorobenzene (CB) and p-xylene (PX)) were used, green-emitting MPs were consistently produced (Supplementary Figs. 1−3). These distinctly different assembled morphologies indicate the effect of solvents on the crystal structures of 1.

Centimeter-sized crystals of 1 suitable for single-crystal X-ray diffraction (SCXRD) analysis were grown from THF/EtOH, Dio/PA, and Tol/IPA, respectively. Crystallographic analysis revealed that both Dio and Tol solvent molecules are encapsulated within the flexible linear cavities of 1 in a 2:1 stoichiometry (denoted as 1·Dio and 1·Tol), whereas THF molecules are excluded (Fig. 2a and Supplementary Table 2 and Fig. 4). In its solvent-free form, the linear π-skeleton of 1 adopts a twisted configuration, stabilized by multiple C−H···π interactions (Supplementary Fig. 5). In contrast, the π-skeleton of host 1 in 1·Tol and 1·Dio undergoes planarization to facilitate solvent encapsulation, clearly confirming the formation of CACs. Although THF is structurally and dimensionally similar to both Dio and Tol, it features only a single ether oxygen atom. In contrast, Dio contains two such oxygen atoms, and Tol possesses a conjugated benzene ring. Crystallographic analysis reveals that the 1·Tol is stabilized primarily by weak C–H···π interactions between host 1 and Tol. In comparison, 1·Dio exhibits additional dual and cooperative C–H···O interactions, which further enhance its structural stability. Unlike Dio or Tol, THF lacks the capacity to provide sufficient interaction sites or binding driving forces, leading to its significantly weaker binding affinity for host 1. Powder X-ray diffraction (PXRD) patterns of these three assemblies also verify the presence or absence of solvent inclusion (Supplementary Fig. 6). These results imply that solvent inclusion within the host framework is a prerequisite for green emission, a process that occurs efficiently with aromatic solvents but is largely impeded with non-aromatic ones. Notably, host 1 exhibits no specific selectivity for the inclusion of non-aromatic Dio molecules, in stark contrast to its preferential selectivity for benzene-derived solvents.

Morphology predictions (Supplementary Fig. 7) reveal that the top/bottom planes of 1, 1·Dio, and 1·Tol microcrystals are predominantly stabilized by van der Waals forces between terminal steric groups, with preferential growth along the [100] directions. The single-crystalline nature of these assemblies was further corroborated by polarized optical microscopy (POM), TEM image, and selected-area electron diffraction (SAED) pattern (Supplementary Figs. 8 and 9).

The absence of face-to-face π-π interactions in compound 1 results in a modest PL red-shift (~15 nm) of its microcrystals (1 MRs) relative to the monomeric solution, along with a solid-state photoluminescence quantum yield (PLQY) of 36.30% (Supplementary Fig. 6 and Table 3)31. Apparently, aromatic solvent Tol has a larger molecular size compared to Dio, thus leading to a more expansive cavity space in 1·Tol. While both 1·Tol and 1·Dio microcrystals involve solvent encapsulation, the extent of red shift in their PL peaks differs slightly relative to pure host MRs. Moreover, PLQYs of 1·Tol and 1·Dio MPs are both significantly enhanced, accompanied by reduced PL decay lifetimes compared to the host 1 (Supplementary Fig. 10 and Table 3). The enhancement in luminescence efficiency is presumably due to the solvent inclusion-induced planarization of the π-backbone in host 1, which suppresses molecular vibrations and rotations, thus minimizing non-radiative decay pathways32. Specifically, 1·Tol MPs achieve an exceptionally high PLQY of 58.10% with a slightly short lifetime of 1.02 ns. Unfortunately, however, 1·Tol and 1·Dio MPs readily decompose within less than a day (Supplementary Fig. 11), due to solvent desorption. Driven by the phenomenon of solvent encapsulation, particularly the selective inclusion effect of aromatic solvents, we conceived that large linear π-conjugated compounds could serve as alternative guests to construct robust CACs.

Building upon the above strategy, we chose four π-conjugated molecules with variable linear dimensions involving styrene (ST), trans-stilbene (SB), DSB, and trans,trans-distyrylbiphenyl (BPDSB) as guest components (Fig. 3a and Supplementary Fig. 12). This selection enables a comprehensive evaluation of the correlation between cavity dimensions and guest molecular length. For comparative analysis, we initially synthesized ribbon- or plate-like microcrystals of the four guests, which exhibited emissions ranging from blue-purple to cyan (Supplementary Tables 4, 5 and Fig. 13). Subsequently, we performed equimolar cocrystallization of host 1 with each linear guest molecule from precursor solutions (Supplementary Table 6). FM/SEM observations (Fig. 3b, c) reveal that the resulting co-assemblies appear as similar ribbon- or plate-like microcrystals, but with green or cyan emission instead.

Crystallographic information demonstrates that host 1 maintains its dynamic binding capacity for all four guest molecules, forming the cocrystals termed as 1·ST, 1·SB, 1·DSBa, and 1·BPDSB (Fig. 3f, g and Supplementary Tables 7, 8). Notably, structural analysis uncovers distinct binding stoichiometries: each cavity of host 1 incorporates two ST molecules arranged with inversion symmetry, while SB, DSB, and BPDSB molecules exhibit 1:1 host/guest binding. In the 1·ST system, ST serves as both the solvent and the guest. The resulting cavity sizes follow the sequence: V 1·BPDSB ˃ V 1·DSB ˃ V 1·ST ˃ V 1·SB. Although longer along the b axis, guest molecules typically yield larger cavities, the larger cavity size in 1·ST compared to 1·SB arises from the accommodation of two shorter ST molecules per molecular cavity. Similar to 1·Dio and 1·Tol, the linear π-core of host 1 in all four cocrystals undergoes a conformational change and becomes planar upon complexation (Supplementary Fig. 14), thereby creating optimally sized cavities for guest accommodation. Molecular packing analysis reveals that these CACs are mainly stabilized by C−H···π interactions between 1 and each guest. Notably, the cavity size of 1 reaches its maximum when complexed with BPDSB, matching the fully extended π-core of host 1 (Fig. 3e). Unlike macrocyclic hosts with fixed intrinsic cavities8,33 or porous frameworks with predetermined voids34–36, host 1 presents exceptional cavity adaptability when complexation with guests of varying lengths, enabling the formation of guest-induced CACs.

Among the four host/guest microcrystals (1·ST, 1·SB, 1·DSBa, and 1·BPDSB) examined, all except 1·BPDSB utilized pure Dio or a THF/Dio mixture (v/v=3:2) during liquid-phase preparation. To exclude any contribution of Dio to the cavity dimensions of these CACs, we intentionally replaced this mixed solvent system. Notably, the use of pure THF as the good solvent for preparing microcrystals of 1·SB and 1·DSBa still affords similar assembled morphologies and luminescence colors (Supplementary Fig. 15). PXRD analysis confirmed that the host/guest microcrystals, whether prepared from pure THF or a THF/Dio mixture, possess identical crystal structures. These findings imply a competitive interplay between linear guest molecules (e.g., SB and DSB) and good solvents (e.g., Dio and Tol) during cocrystal growth. The stronger intermolecular interactions of the linear guests with host 1, however, dominate and effectively preclude the incorporation of solvent molecules into the host framework.

PXRD patterns of the four host/guest assemblies match well with their SCXRD patterns and the top/bottom crystal planes of all microcrystals are enclosed by (001) planes (Supplementary Fig. 16), as confirmed by predicted growth morphologies (Supplementary Fig. 17). POM images reveal their single-crystalline nature (Supplementary Fig. 18). In comparison to host 1 MRs, the PL peaks of 1·Tol, 1·SB, and 1·DSBa microcrystals show a slight red shift, while 1·Dio and 1·ST microcrystals exhibit a more pronounced red shift (Fig. 3d; Supplementary Figs. 6 and 19). Based on the distinct stacking modes of host molecules within these CAC systems, we infer that host–host interactions are stronger in 1·Dio and 1·ST, whereas they are relatively weaker in 1·Tol, 1·SB, and 1·DSBa (Fig. 3f and Supplementary Fig. 4). Absorption spectra of these four microcrystals (1·ST, 1·SB, 1·DSBa, and 1·BPDSB) closely resemble those of 1 MRs, indicating that host 1 dominates their optical properties. Compared to the pure 1 MRs, the PL lifetimes of the four microcrystals (Supplementary Fig. 20) either increase (1·ST and 1·SB) or decrease (1·DSBa and 1·BPDSB). While all four host/guest assemblies exhibit markedly enhanced PLQYs in the range of 62.85–95.36%, significantly exceeding the value of 36.30% observed for the pristine host 1 (Supplementary Table 9 and Fig. 21). By analogy with the solvated crystals of 1, we attribute this enhancement to the rigidification of the host’s π-system following PAH encapsulation, which suppresses non-radiative transition pathways and consequently boosts PL efficiency32. Notably, these CACs maintain structural integrity for six months in dark conditions, possibly due to their extended π-interaction surfaces compared to 1·Dio and 1·Tol.

Further decreasing the molar ratio of 1 to DSB in a Dio/EtOH mixture (e.g., 1:2) led to green-emitting MPs instead of cyan-emitting MRs, indicating the formation of another cocrystal (Supplementary Fig. 22). Crystallographic information confirms a cocrystal comprising 1 and DSB in a stoichiometric ratio of 2:3 (denoted as 1·DSBb), in which DSB molecules are selectively trapped within two distinct cavities of host 1. One molecular cavity accommodates only a single DSB molecule, while the other can simultaneously encapsulate two DSB molecules. These two types of cavities are arranged in an alternating fashion along the b axis, while the DSB molecules in both cavities adopt edge-to-face stacking along the a axis (Supplementary Fig. 23). The entire structure is stabilized by C−H···π interactions between the host framework and the enclosed DSB molecules. Morphological characterization reveals that 1·DSBb MPs preferentially grow along the [100] direction (Supplementary Figs. 24 and 25). The green emission at 505 nm for 1·DSBb MPs exhibits a slight red-shift compared to 1·DSBa MRs (Supplementary Fig. 26), probably due to enhanced intermolecular interactions.

To further investigate the effects of heteroatoms (e.g., N and S) on the cavities of host 1, we examined three linear PAH guests with comparable lengths: p-quaterphenyl (4P), 4,4-di(4-pyridyl)biphenyl (4PPy), and α-quarterthiophene (4S) (Fig. 4a and Supplementary Fig. 27). Host 1 still exhibits guest-dependent cavity adaptability, as evidenced by equimolar guest binding and nearly identical cavity sizes (Supplementary Fig. 28). Likewise, intermolecular C−H···π interactions act as a dominant force (Supplementary Fig. 29), which may endow these cocrystals with high PLQYs. Comparatively, 1·4P MRs exhibit cyan emission while both 1·4PPy and 1·4S MRs display yellow-green emissions (Fig. 4b and Supplementary Table 10, Fig. 30). Notably, the main PL peak of 1·4PPy MRs shows a 40 nm red-shift compared to 1·4P (Fig. 4c and Supplementary Fig. 31), probably due to additional CT interactions between the aniline groups of 1 and the pyridyl moieties of 4PPy. To verify this conclusion, we further conducted absorption, PL lifetime, and electron paramagnetic resonance (EPR) measurements of 1·4PPy MRs. The diffuse reflectance absorption spectrum displays a new long-wavelength absorption band that is absent in either pure host 1 or guest 4PPy. Compared to host 1 (τ=1.31 ns), the 1·4PPy MRs shows a prolonged PL lifetime of 2.26 ns. Additionally, an EPR signal with a g-value of 2.00526 (close to free electron) unambiguously indicates the presence of unpaired electrons and radical species in 1·4PPy, providing direct proof of a CT process37. The above results undoubtedly confirm the presence of weak CT interactions between host 1 and the guest 4PPy (Supplementary Fig. 32). While the yellow-green emission of 1·4S MRs likely arises from sulfur-rich 4S. POM data and morphology simulations indicate that the microcrystals exhibit single-crystalline characteristics with preferential growth along the [100] direction (Supplementary Figs. 33 and 34). While PXRD patterns and crystallographic information verify their nearly identical crystal structures despite heteroatom modifications (Fig. 4d; Supplementary Table 11 and Fig. 31). In contrast to 1·4PPy MRs, both 1·4P and 1·4S MRs exhibit similarly short fluorescence lifetimes (~1.2 ns, Supplementary Fig. 35).

Notably, PL lifetimes of 1-derived host/guest microcrystals either increase or decrease relative to that of pure host 1, with most values falling within the range of 1–2 ns (Supplementary Fig. 36). We attribute this variation to the synergistic interaction between the host and guest molecules, which collectively modulates the competition between radiative and non-radiative transition pathways in the CACs38. Specifically, guest encapsulation promotes planarization of the host molecular skeleton, enhancing host-guest interactions and thereby facilitating the radiative decay process. Concurrently, this synergistic effect may also suppress non-radiative pathways present in the pure host crystal by reducing lattice defects and restricting molecular vibrations and rotations. The short, nanosecond-scale PL lifetime promotes rapid radiative recombination, minimizing energy loss due to triplet accumulation and thereby establishing a favorable photophysical basis for low-threshold lasing. Furthermore, the host framework demonstrates versatile guest-binding capability, accommodating not only linear molecules but also planar π-conjugated systems such as anthracene (An), tetracene (Tc) and their halogenated derivatives (Supplementary Figs. 37 and 38).

The excited-state properties of the CAC systems were investigated using time-dependent density functional theory (TD-DFT). An analysis of the transition orbitals corresponding to the maximum oscillator strength in the absorption spectrum (Supplementary Table 12) shows that most cocrystals (e.g., 1·DSBa, and 1·4P) exhibit electron and hole densities primarily localized on host 1 (Supplementary Figs. 39 and 40). This indicates that the initial photoexcitation takes place within the host material, dominating the subsequent electronic transitions and emission. However, in rare cases like 1·4S, the PL spectrum exhibits the characteristic emission of the 4S guest molecule, which appears to contradict the host-dominated excitation. We propose that this is due to a highly efficient Förster resonance energy transfer (FRET) from the host 1 to the 4S guest, facilitated by the significant spectral overlap between the host’s emission and the guest’s absorption. Under periodic boundary conditions, TD-DFT calculations reveal that the key electronic transition associated with the low-energy absorption band in 1·4PPy is characterized by a shift of electron density from the π-conjugated backbone of host 1 to the pyridine ring of guest 4PPy. The spatial separation of this CT pathway is visually confirmed by the plotted hole and electron density distributions (Supplementary Fig. 40b). Such distinct separation of the frontier orbitals is a hallmark of CT excitation. Additionally, energy decomposition analysis (EDA) using the sobEDA method revealed that both electrostatic and dispersion interactions play crucial roles in stabilizing the CAC systems (Supplementary Fig. 41). To identify the dominant structural origins of the dispersion contributions, we performed a systematic sobEDA analysis on a representative 1:1 host/guest structure, strategically fragmenting host 1 into two components: terminal substituents and π-backbone (Supplementary Figs. 42 and 43). The results demonstrate that dispersion interactions primarily occur between the host’s π-backbone and guest molecule (π-surface interactions), with negligible contributions from terminal substituents. This conclusively establishes adjacent π-surface interactions as the key stabilizing factor in these CACs.

The linear π-backbone of host 1 plays a pivotal role in determining the cavity structures and luminescent performances of the resulting CACs. To systematically explore the influence of π-backbones, we strategically devised and synthesized additional host molecules: N4,N4,N4”‘,N4”‘-tetra-p-tolyl-[1,1’:4’,1”:4”,1”‘-quaterphenyl]−4,4”‘-diamine and 4,4’-(1,4-phenylenedivinyl)bis[N,N-di(p-tolyl)aniline] (2 and 3 for short, respectively; Fig. 5a), both possessing linear π-backbones. Similar to their solution-state behavior, the 1D crystalline assemblies of 2 and 3 display blue and cyan emissions, respectively (Fig. 5c; Supplementary Table 14 and Figs. 44−46), resulting from the differences in π-backbones. Crystallographic information reveals that molecular geometries and packing of 2 and 3 are analogous to those of 1 (Fig. 5b; Supplementary Table 15 and Figs. 47, 48), suggesting they share similar guest encapsulation capabilities.

As anticipated, host 2 forms well-defined molecular cavities that enable 1:1 stoichiometric binding with 4P during cocrystallization (Fig. 5c, d; Supplementary Table 16 and Figs. 49, 50). Intriguingly, however, the π-backbone of host 2 exhibits reduced planarity upon guest complexation compared to host 1, presumably due to weakened C−H···π interactions in 2·4P. Within these cavities, the 4P guest molecules adopt an nearly parallel arrangement, creating 1D molecular channels. Similarly, host 3 bearing a DSB-based π-backbone gave analogous cavity and crystal structures when complexed with DSB (3·DSB), while retaining significant backbone distortion (Fig. 5a, b, d). 2·4P and 3·DSB were assembled into blue- and green-emitting MPs, respectively, exhibiting prolonged PL lifetimes compared to pure host microcrystals (Fig. 5c; Supplementary Figs. 51−55 and Table 17). Perversely, 4,4’-(anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(N,N-di-p-tolylaniline) (4) featuring an extended π-backbone (Fig. 5a, b) allows the inclusion of 9,10-diphenylanthracene (DPA) but only forms small cavity structures near its terminal groups (Fig. 5d and Supplementary Fig. 49). The resulting 4·DPA MPs exhibit red emission with a relatively high PLQY of 34.21%, caused by the slippage of adjacent 4 molecules along their long molecular axes in 4·DPA (Fig. 5c, d and Supplementary Table 17).

In the 1-derived CAC systems, C−H···π interactions serve as the dominant force between 1 and guests, while additional weak interlayer C−H···π interactions resulting from 1’s bulky substituents occur orthogonally. This combination of intermolecular forces creates favorable conditions for the formation of flexible crystalline materials39. As demonstrated, a centimeter-sized 1·ST single crystal was initially examined, demonstrating pronounced elastic properties. When subjected to axial mechanical stress, the ribbon-shaped crystal, mounted on a glass coverslip, underwent giant macroscopic bending (a maximum bending angle of ~180°) while maintaining both high-efficiency green emission and crystallinity. This crystal shows excellent reversibility through multiple deformation cycles (Fig. 6b and Supplementary Movie 1). Significantly, five additional ribbon-shaped single crystals (1·SB, 1·DSBa, 1·4P, 1·4PPy, and 1·4S) also exhibit macroscopic elasticity with each capable of being bent into stable U-shaped configurations without fracture (Supplementary Movies 2–6).

To quantitatively assess the mechanical properties of CACs, we performed uniaxial tensile tests on their single crystals using a laboratory-built instrument (Supplementary Fig. 56)40. The average tensile modulus was determined as follows: 1·ST (0.152 GPa), 1·SB (0.277 GPa), 1·DSBa (0.514 GPa), and 1·4PPy (0.662 GPa) (Supplementary Figs. 57 and 58). Control experiments further confirmed the effect of crystals thickness; for instance, thinner 1·ST crystals (23 μm) displayed greater bending flexibility than thicker ones (49 μm), consistent with classical mechanical expectations (Supplementary Fig. 59 and Movies 7–9). Molecular packing motifs of these six cocrystals when viewed down the b axis (Fig. 6a and Supplementary Figs. 60 and 61) reveal that multiple terminal substituents form interlocked hinge structures avoiding long-range interlayer slippage. Within the layers, the host and guest molecules form an extensive C–H···π interaction network, which tightly locks adjacent molecules and allows for immediate structural recovery upon the removal of external stress. As the guest size increases, the layer-confined host/guest interactions strengthen, leading to a corresponding rise in tensile modulus. Notably, 1·ST exhibits a comparatively low modulus, which can be attributed to its distinctive herringbone-like packing. This molecular arrangement enables the crystal to accommodate and sustain substantial deformation over a wide strain range under applied stress. Similar to single-component molecular crystals40–43, these CACs all display great elasticity, showcasing their superior potential for designing flexible crystalline materials.

Noticeably, the combination of high PLQYs and short fluorescence lifetime is highly favorable for achieving amplified spontaneous emission (ASE) and lasing44–47, suggesting that these well-crystallized host/guest microcrystals may function effectively as both microscale gain media and optical cavities. Comparative studies of the optically pumped characteristics of 1, 1·Dio, and 1·Tol microcrystals using a 400 nm femtosecond pulsed laser (Supplementary Fig. 62) revealed intense green emissions from their tips and lateral facets at higher pumping densities, accompanied by significantly enhanced PL intensity and markedly narrowed PL linewidth (Fig. 6c; Supplementary Figs. 63 and 64). The characteristic S-shaped nonlinear dependence of both PL intensity and linewidth on pump fluence clearly indicates the transition from spontaneous emission to ASE or lasing. Moreover, this confirms that microcrystals of 1 and 1·Tol exhibit ASE, while 1·Dio MPs show clear lasing action. The ASE/lasing thresholds (Eth) for 1, 1·Dio, and 1·Tol microcrystals were estimated to be 30.7, 8.04, and 7.01 μJ·cm-2, respectively. The solvated microcrystals of 1 exhibit significantly reduced lasing thresholds compared to the pristine host MRs, which may be attributed to their extrinsic cavity structures. However, both pristine host MRs and solvated microcrystals of 1 suffer from rapid degradation in luminescence and lasing properties upon exposure to air, thereby limiting their practical application in photonic devices.

Notably, all seven host/guest microcrystals based on host 1 demonstrated wavelength-tunable lasing actions under identical testing conditions and their lasing thresholds were 2 to 15 times lower than that of pure host 1 MRs (Table 1 and Supplementary Figs. 65–72). Among these, the best-performing system, 1·BPDSB MPs, achieves an ultralow threshold of 2.61 μJ/cm². The CAC system outperforms both pure host 1 and previously reported DSB-based crystals by achieving a significantly lower lasing threshold (Supplementary Table 18), confirming the efficacy of this strategy for enhanced lasing performance. The effective reduction in the lasing threshold of this cocrystal system is primarily attributed to a significant increase in the radiative decay rate (kr), which is influenced by cavity structure, size, and the degree of guest conjugation. As described above, structural analysis reveals that the cavity size of 1-derived CACs (1·SB, 1·ST, 1·DSBa, 1·BPDSB) is effectively modulated by the linear length of the styryl-functionalized guest. Evidently, a clear negative correlation between the lasing threshold and the cavity size is observed: The lasing threshold shows a progressive decrease with increasing cavity size (Supplementary Fig. 73). This trend is consistent with the observation that 1·BPDSB, which has the largest cavity size, also has the lowest lasing threshold. For similar cavity sizes, the lasing threshold is governed by the guest conjugation degree. Despite the structural similarity, 1·DSBa exhibited a significantly lower lasing threshold than 1·4P and 1·4PPy (Eth, 1·DSBa = 4.14 μJ/cm²; Eth, 1·4P = 7.55 μJ/cm²; Eth, 1·4PPy = 13.90 μJ/cm²). We attribute this to the extended π-conjugation length in DSB, which features a double-bond linkage versus the single bond in 4P and 4PPy (Supplementary Fig. 73). This trend holds for styryl-modified guests, where an increased conjugation degree consistently leads to a lower lasing threshold in their cocrystals. We propose that a larger size and greater conjugation in the guest strengthen host/guest intermolecular interactions. This, in turn, facilitates superior electronic coupling and accelerates kr, thereby improving lasing performance.

Fundamentally, the formation of the CACs substantially alters the molecular packing, and the resulting confined cavity structure results in a significant PLQY enhancement of CACs. Notably, despite some variation, the PL lifetime (τ) of the host/guest microcrystals remains within the 1–2 ns range, which is consistent with that of pristine host 1 (Supplementary Fig. 36). According to the relation Kr = Φ/τ, the significant improvement in Φ contributes to an increase in the kr value of the CACs (Table 1 and Supplementary Figs. 21 and 74)28. For instance, 1·BPDSB MPs exhibit a lower lasing threshold due to their higher kr, whereas 1·4S MRs, with a lower kr, show no lasing activity. This difference is attributed to the larger conjugation degree of the BPDSB guest. Although SB has a longer conjugation length than ST, the molecular cavity of 1·SB is smaller than that of 1·ST, which leads to a reduced kr and an increased lasing threshold in its microcrystals. Additionally, the extra CT interaction between 1 and 4PPy results in an extended fluorescence lifetime, thereby reducing kr and leading to an increased threshold in 1·4PPy MRs relative to that of 1·4P MRs. We also found that pristine microcrystals of hosts 2, 3, and 4 exhibited no ASE or lasing even at high pump energies (Supplementary Fig. 75). Upon guest encapsulation, however, the resulting 2·4P and 3·DSB microcrystals showed low-threshold lasing with thresholds of 9.26 and 7.28 μJ/cm², respectively (Supplementary Fig. 76). This demonstrates that guest encapsulation enhances the system’s gain, activating lasing in otherwise inactive host materials and thereby expanding the material toolbox for flexible lasers. However, no laser performance was observed in the 1·4S and 4·DPA microcrystals (Supplementary Fig. 77), which indicates their unsuitability as optical gain media.

Specifically for the 1·DSBb MRs, the laser mode spacing follows the Fabry-Perot (FP) resonance relationship, Δλ = λ² / 2Lng, where λ is the wavelength, L is the optical path length, and ng is the group refractive index (Supplementary Fig. 78). The mode spacing decreases with increasing cavity length and exhibits a linear dependence on the reciprocal cavity length (1/L). Similar FP-type lasing characteristics are observed in 1·BPDSB MPs (Supplementary Fig. 79). Based on the flexible nature of CAC single crystals and their microcrystals’ lasing ability, we studied how bending affects their lasing. When a 400 nm fs laser was pointed at the surfaces of three ribbon-like 1·DSBa single crystals in both straight and bent states, each showed bright PL spots (Fig. 6d, e). The straight crystal only produced ASE, with no clear laser peaks. However, the bent crystals exhibited high-resolution, fine PL peaks, confirming significant laser action (Supplementary Fig. 80). The more the crystal was bent, the lower the energy needed to start lasing. This is likely because the straight crystal cannot guide light effectively for waveguide feedback, while bending helps create distributed feedback and curved resonant cavities. This initial application case demonstrates the significant advantages of CACs in the field of flexible photonics. The inclusion of large π-conjugated guests significantly improves the stability of the host crystals, demonstrating promising application potential. After four months of air exposure at room temperature, six of the seven microcrystals maintain stable lasing thresholds (E'th), showing only a minor increase (Supplementary Table 19 and Fig. 81). This enhanced durability further undercover the additional advantage of CACs in boosting material stability.

Methods
Chemicals
Host compounds involving 4,4-bis[4-(di-p-tolylamino)styryl]biphenyl (1, 98%) and 4,4’-(1,4-phenylenedivinyl)bis[N,N-di(p-tolyl)aniline] (3, 99%) were purchased from Meryer and used without further purification. N4,N4,N4”‘,N4”‘-tetra-p-tolyl-[1,1’:4’,1”:4”,1”‘-quaterphenyl]−4,4”‘-diamine (2, 98%) and 4,4’-(anthracene-9,10-diylbis(ethyne-2,1-diyl)) bis(N,N-di(p-tolylaniline) (4, 98%) were synthesized following the reported methods.

Guest compounds involving styrene (ST, 98%), trans-stilbene (SB, 98%), trans,trans-1,4-distryrylbenzene (DSB, 98%), p-quaterphenyl (4P, 98%), 4,4-di(4-pyridyl)biphenyl (4PPy, 98%), and α-quaterthiophene (4S, 98%), 9,10-diphenylanthracene (DPA, 98%) were purchased from TCI, and used without further purification. And 4,4’-di((E)-styryl)−1,1’-biphenyl (BPDSB, 98%) was synthesized following the reported methods.

Organic solvents involving tetrahydrofuran (THF, A.R.), 1,4-dioxane (Dio, A.R.), toluene (Tol, A.R.), dichloromethane (DCM, A.R.), acetone (AC, A.R.), N,N-dimethylformamide (DMF, A.R.), dimethyl sulfoxide (DMSO, A.R.), limonene (Lim, A.R.), chlorobenzene (CB, A.R.), α-methylstyrene (α-MST, A.R.), p-xylene (PX, A.R.), cyclohexane (CHX, A.R.), hexane (A.R.), n-propanol (PA, A.R.), isopropanol (IPA, A.R.), ethanol (EtOH, A.R.), methanol (MeOH, A.R.) were purchased from Beijing Chemical Agent Ltd., China. All solvents were directly used without further purification.

Synthesis of host and guest compounds
The detailed synthetic procedures of 2, 4, and BPDSB are described in Supplementary Section 1.

Solution assembly of four host materials
As a representative example, pure 1 MRs was performed by slow evaporation of a drop of 1 in a THF/EtOH mixture (v/v=1:1, C =2.5 mM) on a silicon or a quartz substrate at room temperature. Similarly, 2 MRs were prepared by slow evaporation of its monomer solution in a THF/EtOH mixture (v/v=1:1, C =0.5 mM) on a silicon or a quartz substrate at room temperature. And 2 MRs were obtained by slow evaporation of a drop of 3 in a Dio/EtOH mixture (v/v=1:1, C =5 mM) on a silicon or a quartz substrate at room temperature. 4 MRs were prepared by slow evaporation from THF/EtOH (v/v=1:2, C =0.8 mM) on a silicon or a quartz substrate at room temperature, as shown in Supplementary Table 13.

Preparation of large-sized single crystals of four host materials
Single crystals of 1 or 4 were synthesized by slow evaporation of their monomer solution in THF/EtOH (v/v=1:1, C =1 mM or C =0.5 mM) in a sealed glass bottle. Similarly, a single crystal of 3 was formed by slow evaporation of a stock solution of 3 in Dio/EtOH (v/v=1:1, C =1 mM). A single crystal of 2 was obtained via an anti-solvent diffusion method combined with solvent-evaporation induced crystallization. Typically, 2 mL of a stock solution of 2 in THF (C =0.5 mM) was sealed in a 50 mL weighing bottle that contained an unsealed weighing bottle loaded with 6 mL of ethanol. EtOH vapor acted as an anti-solvent and was crucial to the growth of large-sized crystals of 2.

Preparation of 1·Dio and 1·Tol MPs
Typically, 1·Dio MPs were achieved by slow evaporation of a drop of a precursor solution of 1 in Dio/PA (v/v=1:1, C =1 mM) on a silicon or a quartz substrate. Similarly, 1·Tol MPs were prepared by slow evaporation of 1 from Tol/IPA (v/v=1:1, C =2.5 mM).

Preparation of large-sized single crystals of 1·Dio and 1·Tol
Single crystals of 1·Dio were synthesized by direct evaporation of a monomer solution of 1 in Dio/PA (v/v=1:1, C =2.5 mM) in a sealed glass bottle. Similarly, single crystals of 1·Tol were formed by slow evaporation of a stock solution of 1 in Tol/IPA (v/v=1:1, C =2.5 mM).

Preparation of the microcrystals of pure guests
Typically, SB MPs were achieved by slow evaporation of a drop of a precursor solution of SB in DCM/EtOH (v/v=1:1, C =50 mM) on a silicon or a quartz substrate. Similarly, DSB MRs were prepared by slow evaporation from a Dio/CHX mixture (v/v=1:1, C =2.67 mM). 4P MPs were synthesized through slow evaporation from Dio (C =2 mM), while 4S MPs were acquired by slow evaporation from a Dio/EtOH mixture (v/v=1:1, C =1.25 mM). DPA MRs were prepared from a DCM/EtOH mixture (v/v=1:1, C =1.5 mM), as detailed in Supplementary Table 4.

In contrast, BPDSB MPs were obtained by uniformly mixing 1 mL of a monomer solution of BPDSB in THF with 1 mL EtOH and the mixture was allowed to stand for 30 min at 25 °C. While 4PPy MPs were synthesized on a hot plate by a microspacing physical vapor transport (PVT) technique. Prior to sublimation, a drop of a monomer solution of 4PPy in THF (C =2 mM) was spin-coated on a glass coverslip and then slowly evaporated. The resulting microparticles were used as the precursor source for vapor-phase growth. The sublimation temperature and time were set at 230 °C and 40 s, respectively.

Preparation of host/guest microcrystals
Host/guest microcrystals derived from hosts 1−4 were synthesized following two different synthetic procedures (Methods I and II), and the detailed experimental parameters are shown in Supplementary Table 7.

Method Ⅰ. 1·SB, 1·ST, 1·DSBa, 1·DSBb, 1·4S, 2·4P, 3·DSB, and 4·DPA microcrystals were prepared by a facile solution co-assembly route. For 1·SB, solid powders of host 1 and guest SB with 1:3 molar ratio were first dispersed in a THF/Dio mixture (v/v=3:2, C =5 mM, C =15 mM). After the addition of an equal volume of IPA, such a ternary mixture (THF/Dio/IPA, v/v/v=3:2:5) was allowed to evaporate slowly, in which IPA acts as an anti-solvent. Finally, 1·SB MRs were deposited on a silicon or a quartz substrate at room temperature. To enable the complete binding of 1 to SB, an excess of SB molecules was used to enhance the intermolecular interactions between them. Similarly, 1·ST MRs were obtained using THF, ST, and IPA as co-solvents. Specifically, solid powders of host 1 were initially dissolved in a THF/ST mixed solution (v/v=3:2, C₁=5 mM), and an equal volume of IPA was then added as an anti-solvent to induce crystallization. The ternary mixture (THF/ST/IPA, v/v/v=3:2:5) was allowed to evaporate slowly at ambient temperature, yielding 1·ST MRs deposited on silicon or quartz substrates. Note that ST is a liquid at room temperature and was used directly as a solvent component in the initial solution. 1·DSBa MRs and 1·DSBb MPs were obtained at different host/guest molar ratios. Specifically, 1·DSBa MRs were obtained by slow evaporation of a Dio/EtOH mixture (v/v=1:1, C =C =0.5 mM), while 1·DSBb MPs were prepared at a host/guest molar ratio of 1:2 using a Dio/PA mixture (v/v=1:1, C =0.5 mM, C =1 mM). Following the aforementioned approach, 1·4S MRs were prepared from a Dio/EtOH mixture (v/v=1:1, C =C =2.5 mM), while 2·4P MPs were synthesized by employing THF as the good solvent and EtOH as the anti-solvent under slow evaporation conditions (v/v=1:1, C =C =0.5 mM). For 3·DSB MPs, a ternary solvent system (THF/Dio/IPA, v/v/v=3:2:15, C =C =0.4 mM) was utilized, where IPA served as the anti-solvent during slow evaporation. In the case of 4·DPA MPs, a binary mixture (Dio/MeOH, v/v=1:1, C =C =1 mM) was gradually evaporated, with MeOH serving as the anti-solvent during crystallization.

Method Ⅱ. 1·BPDSB, 1·4P, and 1·4PPy microcrystals were prepared by a solution-phase coprecipitation method. For 1·BPDSB MPs, solid powders of host 1 and guest BPDSB with a 2:1 molar ratio were firstly dispersed in a THF/Tol mixture, and then EtOH was introduced as an anti-solvent (v/v/v=3:2:5, C =0.5 mM). The mixture solution was transferred into a petri dish, which was placed on a hot plate to allow for slow evaporation at 50 °C. Shortly afterwards, the clear solution became turbid and crystalline precipitates of 1·BPDSB were collected by centrifugation. For 1·4P MRs, solid powders of host 1 and guest 4P in a 1:1 molar ratio were initially dissolved in Dio to prepare a precursor solution (C =1 mM). An equal volume of EtOH was then added as an anti-solvent. After approximately 1 min, a large quantity of 1·4P MRs precipitated. In contrast, 1·4PPy MRs were obtained without the use of an anti-solvent to induce crystallization. Specifically, equimolar amounts of host 1 and guest 4PPy were co-dissolved in THF, and the solution was allowed to stand at room temperature for about 3 h, after which a large quantity of 1·4PPy MRs precipitated spontaneously.

Preparation of large-sized host/guest single crystals
Large-sized host/guest single crystals suitable for single-crystal XRD analysis (SCXRD) were obtained following three different preparation procedures (Methods i−iii), and the detailed experimental parameters are shown in Supplementary Table 7.

Method I. Centimeter- or millimeter-sized single crystals of 1·ST, 1·SB, 1·DSBa, 1·4PPy, 1·4S, and 4·DPA were prepared via solution-phase evaporation. Take 1·SB as an example, its single crystals were obtained by slow evaporation of a monomer solution of 1 in THF/Dio/PA containing a certain amount of SB (v/v/v=3:2:1, C =2.5 mM, C =7.5 mM) in a sealed glass bottle. Single crystals of 1·ST were grown by slow evaporation from a ST/IPA mixture (v/v=1:1, C =1 mM) in a sealed plastic centrifuge tube. 1·DSBa and 1·4S single crystals were both obtained via slow evaporation from a Dio/EtOH mixture (C =C =0.5 mM; v/v=1:1, C =C =1 mM). For 1·4PPy, its single crystals were obtained by slow evaporation from a THF solution (C =C =1 mM). Single crystals of 4·DPA were grown by slow evaporation from a Dio/MeOH mixture (C =C =1 mM).

Method II. For poorly soluble guests, CAC single crystals were obtained via thermal evaporation-induced crystallization. As a representative example, for 1·DSBb, a mixture of host 1 and guest DSB in a 1:2 molar ratio was dissolved in a THF/Tol/EtOH mixture (v/v=1:1:2), with an initial concentration of C =2C =0.25 mM. The resulting dilute solution was transferred to a petri dish and slowly evaporated at 60 °C on a hot plate. After complete solvent removal, large single crystals of 1·DSBb were deposited on the bottom of the dish. Similarly, single crystals of 1·BPDSB suitable for X‑ray diffraction analysis were prepared using a 1:1 molar ratio of host 1 and guest BPDSB in a THF/Tol/EtOH mixture (v/v/v=3:2:5) under identical concentration and temperature conditions.

Method III. Centimeter- or millimeter-sized single crystals of 1·4P were obtained via an anti-solvent diffusion method combined with solvent-evaporation induced crystallization. Specifically, solid powders of host 1 and guest 4P with a 1:1 molar ratio were first dispersed in Dio (C =C =0.5 mM), and then 2 mL of a mixed solution was sealed in a 50 mL weighing bottle that contained an unsealed glass bottle loaded with 6 mL of EtOH. After one week, large-sized single crystals of 1·4P were formed at the bottom of the weighing bottle. Similarly, high-quality single crystals of 2·4P and 3·DSB were also realized by the above cocrystallization route. In detail, host 2 and guest 4P were dissolved in THF at equal concentrations (C =C =0.5 mM). Then, 2 mL of this mixture was placed into a 50 mL weighing bottle that contained an unsealed glass bottle with 6 mL of EtOH. After about one week, large-sized single crystals of 2·4P had formed at the bottom of the weighing bottle. In the case of 3·DSB, an equimolar mixture of host 3 and guest DSB was initially dissolved in a THF/Dio mixture (v/v=3:2, C =C =0.5 mM). And then, 2 mL of this solution was placed into a 50 mL weighing bottle containing an unsealed glass bottle filled with 6 mL of IPA, and high-quality crystals of 3·DSB were formed at the bottom of the weighing bottle over a period of one week.

Sample characterization
1H and 13C NMR spectra were recorded on a JEOL JNM-A500/ECZ400S instrument with chemical shifts being referenced against tetramethylsilane as the internal standard. The morphologies and sizes of a variety of host/guest microcrystals and their constituent materials were examined using field-emission scanning electron microscopy (FESEM, Apreo S LoVac) at an acceleration voltage of 5 kV. Prior to observation, the samples were deposited with a thin gold layer using an Edwards Sputter Coater. TEM images were obtained using a JEOL-2100 electron microscope operated at 80 kV. Each of the as-prepared samples was transferred onto a carbon-coated copper grid and dried at room temperature. The X-ray diffraction (XRD) patterns were measured on a D/max 2400 X-ray diffractometer with Cu Kα radiation (λ=1.54050 Å) operated in the 2θ range from 3 to 40°, by using the samples spin-coated on the surface of a quartz substrate. The photoluminescence (PL) spectra of the samples were measured on a HORIBA JOBTNYVON FLUOROMAX-4 spectrofluorimeter with a slit width of 1 nm. The PL decay measurements were performed by a steady-state and transient-state fluorescence spectrometer (FLS-1000). The samples were both deposited on the surface of a quartz substrate. The fluorescence microscopy (FM) images were obtained using an Olympus bx53 fluorescence microscope with a spot-enhanced charge-coupled device (CCD). Each of the host/guest microcrystals dispersed on a glass substrate was excited locally by variable pumping pulses via a home-built micro-PL system. A fs laser system (Pharos, Light Conversion) delivered laser pulses at 800 nm (50 fs, 1 KHz), which were then sent to an optical parametric amplifier to generate the pump pulses (400 nm). The fs laser spot, with a diameter of ~50 µm, is focused onto the samples through a 40x objective lens. The PL spectra were collected using an optical spectrometer (Princeton Instruments) with a spectral resolution of 0.2 nm.

Theoretical calculations
The geometries of the crystals were optimized using density functional theory (DFT) under periodic boundary conditions in the CP2K software package48,49. The PBE exchange-correlation functional and GTH pseudopotentials with the DZVP-MOLOPT-GTH basis set were employed. The convergence criteria of minimization for the maximum geometry change and force difference were set at 3×10-3 Bohr and 4.5×10-4 Hartree/Bohr, respectively. The vertical electron excitations were calculated using time-dependent density functional theory (TD-DFT) at the PBE/TZVP-GTH theoretical level. The energy decomposition analysis was performed at the B3LYP-D3(BJ)/6-311+G(2d,p) theoretical level in Gaussian 09 software, in combination with the sobEDA approach50,51. In addition, the electron and hole density distributions were visualized using the Multiwfn software package52,53.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript reports the design and synthesis of non-macrocyclic host–guest cocrystals with cavity-tunable structures, demonstrating elasticity and lasing behavior. The work is conceptually innovative and potentially impactful in the field of supramolecular photonic materials. The systematic exploration of π-conjugated hosts and diverse aromatic guests provides valuable insights into the correlation between molecular packing, cavity adaptability, and photophysical properties. However, despite the novelty, the manuscript has several weaknesses in mechanistic explanation, and discussion depth. Specifically, the role of solvents in crystal formation, the origins of PL spectral shifts, the mechanistic interpretation of energy transfer, and the quantification of elasticity and lasing thresholds require substantial improvement.\n\nMajor comments\n1. The authors propose that the elastic properties of the crystals are correlated with cavity size and guest structure; however, crystal thickness and shape may also play important roles in influencing the elastic behavior. The current explanation lacks quantitative support. It is recommended that systematic data, such as those obtained through mechanical testing or simulations, be provided to strengthen the argument regarding \"cavity-dependent elasticity.\"\n2. The lasing thresholds of different crystals are reported, but a systematic comparison under identical conditions between the pristine host and host–guest crystals is missing. Establishing a clear quantitative relationship between lasing thresholds, cavity size, and guest conjugation degree would greatly strengthen the study.\n\nMinor comments\n1. In the first paragraph of Results and Discussion, only the morphological differences induced by different solvents are described, without further mechanistic explanation (e.g., possible solvent encapsulation or selective inclusion effects).\n2. In the second paragraph of Results and Discussion, it is stated that Dio and Tol molecules can be encapsulated in a 2:1 stoichiometry within host 1’s flexible cavities, whereas THF is excluded. However, the reason for THF’s exclusion is not discussed.\n3. In the second paragraph of Results and Discussion, the reported PLQY value (36.30%) is mentioned without contextual significance or comparison with analogous systems. It would be better to relocate this discussion to later sections and highlight the emission enhancement relative to the pristine host.\n4. On page 5, In the section Synthesis of cavity-expandable host-guest microcrystals via complexation host 1 and PAH guests, the cavity sizes of 1·ST, 1·SB, 1·DSBa, and 1·BPDSB are compared. Since some of these crystals were grown in solvents containing dioxane, clarification is needed on how the influence of different solvent molecules on cavity formation and size is excluded.\n5. On page 5, third paragraph, the PL peak of 1·DSBa microcrystals is nearly identical to pristine 1, whereas others show slight red shifts. The reasons for this discrepancy are not addressed.\n6. On page 6, first paragraph, line 2, “Host” is not capitalized.\n7. On page 6, first paragraph, line 7, the 40 nm red-shift of 1·4PPy compared to 1·4P is attributed to additional CT interactions, but no theoretical calculations or literature evidence are provided.\n8. On page 8, first paragraph, the statement that “electrons and holes are localized on the guest but emission originates from the host” (in 1·DSBa and 1·BPDSB) lacks mechanistic clarity. This phenomenon requires a clearer mechanistic explanation (e.g., whether Förster or Dexter energy transfer is involved).\n9. The manuscript repeatedly mentions shorter or longer PL lifetimes of host–guest crystals compared to the host, but does not explain the origins of these changes or their implications for photophysical performance.\n\nIn summary, the manuscript introduces an interesting and novel concept of cavity-expandable non-macrocyclic host–guest crystals with elastic and lasing properties. However, the current version lacks sufficient mechanistic explanations, systematic comparisons, and quantitative analyses to support the claims. I recommend minor revision.", "reviewer_2": "Meng, Zhao, Lei, and coworkers reported organic cocrystals as potential materials for organic solid-state lasers (OSSLs). OSSLs, which employ organic gain media, offer several advantages, including facile processing, mechanical flexibility, and biocompatibility. Accordingly, the development of efficient organic gain media, particularly those with low threshold energies, is of significant importance. The authors’ study may therefore attract interest from the broader community. However, the present work does not appear to overcome the intrinsic drawbacks of organic crystals as gain media for OSSLs, such as photophysical losses and limited large-area processability. Although the authors emphasize that their materials exhibit very low threshold energies, the reported values are merely comparable to or higher than those previously reported. While the elasticity of the cocrystals is indeed intriguing, it does not seem to represent a decisive breakthrough in the field. Moreover, the description of “host–guest” cocrystals involving non-macrocyclic molecules is potentially misleading and remains debatable. Taken together, this work does not appear suitable for publication in this journal. Detailed comments are as follows.\n\n1. The definitions of key terms such as “cavity” and “host–guest” should first be established in a precise and consistent manner, as their meanings differ across research fields. For instance, in the context of lasers, a “cavity” refers to the optical resonator responsible for light amplification, whereas in molecular crystals, the same term denotes an internal void or pore capable of accommodating guest molecules. Given that the intended application of the present work lies in lasers, the use of the term “cavity” requires particular caution. However, the manuscript appears to employ this terminology without sufficient care, which may lead to confusion or misinterpretation.\n2. Similarly, the term “host–guest” should be employed with greater precision. In the field of optoelectronics, it typically refers to doping, where guest molecules are incorporated as dopants (impurities) to modulate optoelectronic properties. In contrast, within supramolecular chemistry, the term specifically denotes the encapsulation of a guest molecule within the cavity of a host. Given these distinct usages, the manuscript should apply the term with more caution to avoid conceptual ambiguity.\n3. The manuscript describes cocrystals involving non-macrocyclic molecules as “host–guest” systems, but this usage could be misleading. Numerous organic crystals are known to trap solvent molecules, and many cocrystals form in defined stoichiometric ratios such as 1:1 or 1:2; however, not all of these are classified as “host–guest” cocrystals. The observation that solvent desorption leads to decomposition of the crystals strongly suggests that a stable “cavity” capable of reversible adsorption and desorption of guest molecules is not maintained. To substantiate the claim that the reported cocrystals are indeed of the host–guest type, the authors should provide further evidence—for example, demonstrating reversible adsorption/desorption of guest molecules and the persistence of the cavity structure after desorption. Without such evidence, the materials should more appropriately be regarded as general cocrystals rather than host–guest systems.\n4. The lasing behavior observed from various cocrystal combinations is intriguing, and it was demonstrated that the threshold energy can be reduced. However, since lowering the threshold energy is of critical importance in organic lasers, a more detailed discussion on why certain combinations lead to lower threshold energies would greatly benefit the readers.\n5. The current manuscript appears to rely heavily on data presented in the Supporting Information, which makes it difficult for readers to follow the main text. While the cartoons and schematic representations are certainly helpful, it would be preferable to include more of the relevant scientific data from the Supporting Information in the main manuscript.", "reviewer_3": "This research group developed non-macrocyclic receptors with molecular cleft capable of binding aromatic guests in a crystalline state, and the host-guest cocrystals exhibited efficient fluorescence, high elasticity, and low-threshold lasing. Host 1 showed good adaptability to a series of guests of different shapes and sizes. The whole experiments and calculations have been well done, and the manuscript is well organized. However, I am reluctant about the recommendation of this work for publication in Nature Communications because of the luck of an impact and competitive advantage as compared with others; because benchmark studies and data are unclear, the readers cannot know how impactful and advanced this work is. It may be natural that similar host and guest molecules get together in a crystalline state. Clear demonstration of practical application might be effective for the enhancement of the quality of this work. Minor things are listed below.\n(1) Data for compound 1 without guests should be added to Fig. 6.\n(2) Compound numbers, 1, 2 and 3, need to be added to the structures in Fig. 1 and 5, respectively.\n(3) The caption of (e) in Fig. 3 seems to be missing.\n(4) The association constants in a solution would facilitate the readers to grasp binding strengths in the present host-guest systems."}, "author_response": "We are grateful to the referee for their positive assessment and insightful comments, which have greatly enhanced the quality of our work. In our revised manuscript, we have provided more in-depth mechanistic explanations and discussions. Specific improvements include elucidating the solvent's role in crystal formation, clarifying the origin of the luminescence spectral shifts, detailing the energy transfer mechanism, and offering quantitative descriptions of the elastic and lasing properties.\n\nMajor Comments:\n1. The authors propose that the elastic properties of the crystals are correlated with cavity size and guest structure; however, crystal thickness and shape may also play important roles in influencing the elastic behavior. The current explanation lacks quantitative support. It is recommended that systematic data, such as those obtained through mechanical testing or simulations, be provided to strengthen the argument regarding \"cavity-dependent elasticity.\"\nResponse:\nThanks for the valuable comments provided by the referee, which have been very helpful for our in-depth understanding of the elastic properties of organic cocrystals based on host 1. Following the referee’s suggestion, we performed uniaxial tensile tests using a self-built mechanical testing system and obtained the corresponding tensile modulus. Based on this, we again evaluated the elastic deformation capability of these organic cocrystals and confirmed that they all exhibit a pronounced U-shaped deformation. Notably, the mechanical testing results further indicate that the elastic behavior of the rod-like organic cocrystals shows no direct correlation with the cavity size or the guest structure. In the revised manuscript, we have updated the relevant figures and conclusions and added corresponding descriptions.\nAs demonstrated, centimeter-sized 1·ST single crystals were initially examined, demonstrating remarkable elastic properties. When subjected to axial mechanical stress, a rod-like crystal of 1·ST mounted on a glass coverslip underwent giant macroscopic bending (a maximum bending angle of ~180°) while maintaining both high-efficiency green emission and crystallinity. This crystal shows excellent reversibility through multiple deformation cycles (Fig. 6b and Supplementary Movie 1). Significantly, five additional rod-like host-guest crystals (1·SB, 1·DSBa, 1·4P, 1·4PPy, and 1·4S) also exhibit remarkable elasticity with each capable of being bent into stable U-shaped configurations without fracture (Supplementary Movies 2–6).\nFig. 6 Elastic and lasing performances of CACs. a Local interlayer molecular packing schematic diagram of CACs when viewed down the b axis and its schematic diagram of the corresponding single crystal elastic response. b Elastic bending behavior of six ribbon-like single crystals: 1·SB, 1·ST, 1·DSBa, 1·4P, 1·4PPy, 1·4S. Scale bar, 5 mm. c PL images of 1 and nine host/guest microcrystals under 400 nm fs-laser excitation. Scale bar, 25 μm. d Corresponding photophysical parameters. e Schematic illustration of fs-laser vertical excitation at the maximum curvature points of the (001) facet of 1·DSBa single crystals in both straight and bent states. The insets show the corresponding side-view FM images excited by UV light. Scale bar, 5 mm. f Low- and high-resolution PL spectra of the straight and bent 1·DSBa crystals recorded above the lasing thresholds. The insets show the corresponding top-view FM images. Scale bar, 200 μm.\nTo quantitatively assess the mechanical properties of CACs, we performed uniaxial tensile tests on their single crystals using a laboratory-built instrument (Supplementary Fig. 56). The average tensile modulus was determined as follows: 1·ST (0.152 GPa), 1·SB (0.277 GPa), 1·DSBa (0.514 GPa), and 1·4PPy (0.662 GPa) (Supplementary Fig. 58). Control experiments further confirmed the effect of crystals thickness; for instance, thinner 1·ST crystals (23 μm) displayed greater bending flexibility than thicker ones (49 μm), consistent with classical mechanical expectations (Supplementary Fig. 59 and Movies 7–9). Molecular packing motifs of these six cocrystals when viewed down the b axis (Fig. 7a and Supplementary Figs. 60, 61) reveal that multiple terminal substituents form interlocked hinge structures avoiding long-range interlayer slippage. Within the layers, the host and guest molecules form an extensive C–H···π interaction network, which tightly locks adjacent molecules and allows for immediate structural recovery upon the removal of external stress. As the guest size increases, the layer‑confined host/guest interactions strengthen, leading to a corresponding rise in tensile modulus. Notably, 1·ST exhibits a comparatively low modulus, which can be attributed to its distinctive herringbone‑like packing. This molecular arrangement enables the crystal to accommodate and sustain substantial deformation over a wide strain range under applied stress. Similar to single-component molecular crystals, these CACs all display great elasticity, showcasing their superior potential for designing flexible crystalline materials.\nSupplementary Figure 56. (a) Schematic representation of tensile testing used to quantitatively study the mechanical properties of CAC single crystals. (b) Schematic diagram of a typical stress-strain curve obtained from a tensile test.\nTo quantitatively analyze and compare the mechanical behavior of the CAC single crystals, we conducted uniaxial tensile tests on the crystals using a laboratory-built tensile instrument to obtain stress-strain curves. The specific parameters were: tensile speed of 0.005 mm/s, and force sensor units in mN. To accurately calculate the engineering stress, we observed the cross-section of the fractured crystals using SEM results and measured the approximate area (S) at the fracture point of the samples using image processing software (Photoshop). The strain was calculated using the formula σ = F/S, where F is the applied tension force. The tensile modulus (E) of the crystals was obtained by calculating the slope of the initial linear region (strain range 0-0.01) of the stress-strain curve.\nSupplementary Figure 57. SEM images of the fracture cross-section of the CAC single crystals involving (a) 1·ST, (b) 1·SB, (c) 1·DSBa, and (d) 1·4PPy from the tensile test.\nSupplementary Figure 58. Stress-strain curves of the CAC single crystals involving (a) 1·ST, (b) 1·SB, (c) 1·DSBa, and (d) 1·4PPy obtained from tensile tests.\nSupplementary Figure 59. Maximum bending amplitudes of 1·ST crystals with different thicknesses under external force. (a , b , c ) Schematics illustrating the maximum bending extent. 1 1 1 (a , b , c ) Corresponding FM images in straight and bent states as well as low- and 2 2 2 high-magnification SEM images of the fractured crystals along the thickness plane. All samples were excited by UV light. Scale bar, 5 mm.\nSupplementary Figure 60. Packing motifs of (a) 1∙SB, (b) 1∙ST, and (c) 1∙DSBa viewed down the b axis.\nSupplementary Figure 61. Packing motifs of (a) 1∙4P, (b) 1∙4PPy, and (c) 1∙4S viewed down the b axis.\n\n2. The lasing thresholds of different crystals are reported, but a systematic comparison under identical conditions between the pristine host and host–guest crystals is missing. Establishing a clear quantitative relationship between lasing thresholds, cavity size, and guest conjugation degree would greatly strengthen the study.\nResponse:\nWe sincerely thank the referee for the valuable suggestions. As rightly pointed out by the referee, we also find that a systematic comparison of the lasing performance between the pristine host crystal and the resulting host/guest crystals under the same conditions as well as the establishment of quantitative structure-property relationships are crucial for deepening the impact of this work. Following the referee's suggestion, we conducted a systematic evaluation of the lasing performance for the pristine host 1 MRs and seven host/guest microcrystals under strictly identical experimental conditions using our home-built optical pumping setup (Supplementary Figs. 62–72). For each type of microcrystal, five samples were selected and systematically characterized to evaluate their lasing performance. As outlined in the manuscript, the lasing thresholds of a series of host/guest microcrystals based on steric-hindrance-functionalized host molecules are significantly reduced compared with those of the pristine host microcrystals. The new data have been incorporated into the revised manuscript and have significantly strengthened our conclusions. Our specific responses and new findings are as follows:\nComparative studies of the optically pumped characteristics of 1, 1·Dio, and 1·Tol microcrystals using a 400 nm femtosecond pulsed laser (Supplementary Fig. 62) revealed intense green emissions from their tips and lateral facets at higher pumping densities, accompanied by significantly enhanced PL intensity and markedly narrowed PL linewidth (Fig. 6c; Supplementary Figs. 63 and 64).\nRemarkably, all seven host/guest microcrystals based on host 1 demonstrated wavelength-tunable lasing actions under identical testing conditions and their lasing thresholds were 2 to 15 times lower than that of pure host 1 MRs (Supplementary Figs. 65–72). Among these, the best-performing system, 1·BPDSB MPs, achieves an ultralow threshold of 2.61 μJ/cm². These results clearly demonstrate the general efficacy of CACs in improving laser performance. The effective reduction in the lasing threshold of this cocrystal system is primarily attributed to a significant increase in the radiative decay rate (k), which is influenced by cavity structure, size, r and the degree of guest conjugation (Supplementary Fig. 73). As described above, structural analysis reveals that the cavity size of 1-derived CACs (1·SB, 1·ST, 1·DSBa, 1·BPDSB) is effectively modulated by the linear length of the styryl-functionalized guest. Remarkably, a clear negative correlation between the lasing threshold and the cavity size is observed: The lasing threshold shows a progressive decrease with increasing cavity size. This trend is consistent with the observation that 1·BPDSB, which has the largest cavity size, also has the lowest lasing threshold. For similar cavity sizes, the lasing threshold is governed by the guest conjugation degree. Despite the structural similarity, 1·DSBa exhibited a significantly lower lasing threshold than 1·4P and 1·4PPy (E a = 4.14 μJ/cm²; E = 7.55 μJ/cm²; E = 13.90 μJ/cm²). th, 1·DSB th, 1·4P th, 1·4PPy\nWe attribute this to the extended π-conjugation length in DSB, which features a double-bond linkage versus the single bond in 4P and 4PPy. This trend holds for styryl-modified guests, where an increased conjugation degree consistently leads to a lower lasing threshold in their cocrystals. We propose that a larger size and greater conjugation in the guest strengthen host/guest intermolecular interactions. This, in turn, facilitates superior electronic coupling and accelerates k, r thereby improving lasing performance.\nSupplementary Figure 62. Schematic demonstration of the transmittance optical path in the micro-PL setup for the laser or ASE characterization.\nSupplementary Figure 63. (a) PL spectra of single typical 1 MR (a) with increasing pumping power density of a 400 nm fs laser. The inset shows the corresponding FM image. Scale bar, 25 μm. (b, c, d, e, f) Correlation between PL intensity or fwhm of five 1 MRs at 492 nm and the incident laser power density.\nSupplementary Figure 65. (a) PL spectra of single typical 1∙SB MR (a) with increasing pumping power density of a 400 nm fs laser. The inset shows the corresponding FM image. Scale bar, 25 μm. (b, c, d, e, f) Correlation between PL intensity or fwhm of five 1∙SB MRs at 508 nm and the incident laser power density.\nSupplementary Figure 66. (a) PL spectra of single typical 1∙ST MR (a) with increasing pumping power density of a 400 nm fs laser. The inset shows the corresponding FM image. Scale bar, 25 μm. (b, c, d, e, f) Correlation between PL intensity or fwhm of five 1∙ST MRs at 509 nm and the incident laser power density.\nSupplementary Figure 67. (a) PL spectra of single typical 1∙DSBa MR (a) with increasing pumping power density of a 400 nm fs laser. The inset shows the corresponding FM image. Scale bar, 25 μm. (b, c, d, e, f) Correlation between PL intensity or fwhm of five 1∙DSBa MRs at 493 nm and the incident laser power density.\nSupplementary Figure 68. (a) PL spectra of single typical 1∙DSBb MP (a) with increasing pumping power density of a 400 nm fs laser. The inset shows the corresponding FM image. Scale bar, 25 μm. (b, c, d, e, f) Correlation between PL intensity or fwhm of five 1∙DSBb MPs at 507 nm and the incident laser power density.\nSupplementary Figure 69. (a) PL spectra of single typical 1∙BPDSB MP (a) with increasing pumping power density of a 400 nm fs laser. The inset shows the corresponding FM image. Scale bar, 25 μm. (b, c, d, e, f) Correlation between PL intensity or fwhm of five 1∙BPDSB MPs at 502 nm and the incident laser power density.\nSupplementary Figure 70. (a) PL spectra of single typical 1∙4P MR (a) with increasing pumping power density of a 400 nm fs laser. The inset shows the corresponding FM image. Scale bar, 50 μm. (b, c, d, e, f) Correlation between PL intensity or fwhm of five 1∙4P MRs at 493 nm and the incident laser power density.\nSupplementary Figure 71. (a) PL spectra of single typical 1∙4PPy MR (a) with increasing pumping power density of a 400 nm fs laser. The inset shows the corresponding FM image. Scale bar, 50 μm. (b, c, d, e, f) Correlation between PL intensity or fwhm of five 1∙4PPy MRs at 533 nm and the incident laser power density.\nSupplementary Figure 72. Comparison of the average lasing thresholds (Eₜₕ) between host 1 MRs and its host/guest microcrystals (1·SB, 1·ST, 1·DSBa, 1·DSBb, 1·BPDSB, 1·4P, and 1·4PPy).\nSupplementary Figure 73. (a) Bar graphs of E and k for 1∙SB, 1∙ST, 1∙DSBa, and 1∙BPDSB as th r a function of cavity size. (b) Bar graphs of E and k for 1∙DSBa, 1∙4P, and 1∙4PPy as a function th r of guest conjugation extent.\n\nMinor Comments:\n1. In the first paragraph of Results and Discussion, only the morphological differences induced by different solvents are described, without further mechanistic explanation (e.g., possible solvent encapsulation or selective inclusion effects).\nResponse:\nWe thank the referee for this insightful comment. To address this point, we have provided further mechanistic explanation regarding the observed morphological differences induced by various solvents in the revised manuscript. Crucially, we have now unambiguously distinguished between mere solvent encapsulation and selective guest inclusion within our CACs system. Solvent encapsulation refers to the passive entrapment of solvent molecules within the voids or channels of a host crystal during crystal growth. This process is primarily driven by spatial accommodation and serves to stabilize the crystal structure, without significant selectivity. In such cases, the encapsulated solvent is usually the one present in large excess during crystallization. In contrast, selective inclusion involves the active and specific recognition of certain guest molecules by the host through complementary intermolecular interactions, such as hydrogen bonding, π–π stacking, or van der Waals forces. This process depends on the geometric and functional complementarity between the host and guest. We therefore employed a wider variety of solvents to elucidate the primary mechanism (solvent encapsulation vs. selective inclusion) governing the crystallization of host 1.\nAfter examining more solvent mixtures, we found that the luminescence color of the microcrystals is governed by the type of good solvent used in the preparation. The use of non-aromatic solvents generally yields cyan-emitting microcrystals, with the sole exception of Dio, which enables green-emitting microcrystals. Conversely, when aromatic solvents (e.g., CB and PX) were used, green-emitting MPs were consistently produced (Supplementary Figs. 1–3). These distinctly different assembled morphologies indicate the effect of solvents on the crystal structures of 1.\nSupplementary Figure 1. Chemical structures of the twelve solvents selected to examine the effect of solvents on the crystal structures of 1.\nSupplementary Figure 2. FM images of microcrystals of 1 formed by slow evaporation from different solvent mixtures (C = 2.5 mM) involving (a) THF/CHX (v/v = 1:1), (b) THF/EtOH (v/v 1 = 1:1), (c) THF/Dio/IPA (v/v/v = 1:1:2), (d) THF/DCM/EtOH (v/v/v = 1:1:2), (e) THF/AC/EtOH (v/v/v = 1:1:2), (f) THF/DMF/EtOH (v/v/v = 1:1:2), (g) THF/DMSO/EtOH (v/v/v = 1:1:2), (h) THF/Lim/EtOH (v/v/v = 1:1:2), (i) THF/Tol/EtOH (v/v/v = 1:1:2), (j) THF/CB/EtOH (v/v/v = 1:1:2), (k) THF/α-MST/EtOH (v/v/v = 1:1:2), and (l) THF/PX/EtOH (v/v/v = 1:1:2), respectively. All samples were excited by UV light. Scale bar, 100 μm.\nSupplementary Figure 3. FM images of (a) 1∙Dio, (b) 1∙Tol, (c) 1∙CB, and (d) 1∙PX MPs. All samples were excited by UV light. Scale bar, 100 μm.\nThese results imply that solvent inclusion within the host framework is a prerequisite for green emission, a process that occurs efficiently with aromatic solvents but is largely impeded with non-aromatic ones. Notably, host 1 exhibits no specific selectivity for the inclusion of non-aromatic Dio molecules, in stark contrast to its preferential selectivity for benzene-derived solvents.\nThese new supporting data has been added into the revised Results and Discussion section to clarify the mechanistic basis for the solvent-dependent morphological differences.\n2. In the second paragraph of Results and Discussion, it is stated that Dio and Tol molecules can be encapsulated in a 2:1 stoichiometry within host 1’s flexible cavities, whereas THF is excluded. However, the reason for THF’s exclusion is not discussed.\nResponse:\nWe sincerely thank the referee for their insightful comment. We have now provided a more detailed explanation in the revised manuscript regarding the inability of THF to be incorporated into host 1.\nAlthough THF is structurally and dimensionally similar to both Dio and Tol, it features only a single ether oxygen atom. In contrast, Dio contains two such oxygen atoms, and Tol possesses a conjugated benzene ring. Crystallographic analysis reveals that the 1·Tol is stabilized primarily by weak C–H···π interactions between host 1 and Tol. In comparison, 1·Dio exhibits additional dual and cooperative C–H···O interactions, which further enhance its structural stability. Unlike Dio or Tol, THF lacks the capacity to provide sufficient interaction sites or binding driving forces, leading to its significantly weaker binding affinity for host 1 (Supplementary Fig. 5).\nSupplementary Figure 5. (a, c, f) Molecular configurations of (a) 1, (c) 1·Dio, and (f) 1·Tol as well as the dihedral angles between two adjacent benzene rings. (b, d, e, g) Typical C‒H···π interactions (black lines) or C‒H···O interactions (red lines) as well as intermolecular distances (Å) between adjacent two molecules in (b) 1 or between host 1 and solvent molecules in (d, e) 1·Dio, and (g) 1·Tol, respectively.\n3. In the second paragraph of Results and Discussion, the reported PLQY value (36.30%) is mentioned without contextual significance or comparison with analogous systems. It would be better to relocate this discussion to later sections and highlight the emission enhancement relative to the pristine host.\nResponse:\nWe sincerely thank the referee for your valuable suggestion. We agree that reporting the PLQY without adequate context or comparison to relevant systems diminished the data's clarity and impact. In light of this, we have moved the PLQY discussion to the section on the photophysical properties of the solvated crystals of 1, which now features a systematic comparison among the 1·Tol MPs, 1·Dio MPs, and the pristine host 1 MRs. Moreover, a comparative analysis of the luminescence efficiency was performed for the 1∙SB, 1∙ST, 1∙DSBa, 1∙DSBb, 1∙BPDSB microcrystals, and the pristine host 1.\nThe absence of face-to-face π-π interactions in compound 1 results in a modest PL red-shift (~15 nm) of its microcrystals (1 MRs) relative to the monomeric solution, along with a solid-state photoluminescence quantum yield (PLQY) of 36.30% (Supplementary Fig. 6 and Table 3). Apparently, aromatic solvent Tol has a larger molecular size compared to Dio, thus leading to a more expansive cavity space in 1·Tol. While both 1·Tol and 1·Dio microcrystals involve solvent encapsulation, the extent of red shift in their PL peaks differs slightly relative to pure host MRs. Moreover, PLQYs of 1·Tol and 1·Dio MPs are both significantly enhanced, accompanied by reduced PL decay lifetimes compared to the host 1 (Supplementary Table 3 and Figs 10, 21a). The enhancement in luminescence efficiency is presumably due to the solvent inclusion-induced planarization of the π-backbone in host 1, which suppresses molecular vibrations and rotations, thus minimizing non-radiative decay pathways. Specifically, 1·Tol MPs achieve a high PLQY of 58.1% with a remarkably short lifetime of 0.35 ns. Unfortunately, however, 1·Tol and 1·Dio MPs readily decompose within less than a day (Supplementary Fig. 8), due to solvent desorption. Driven by the phenomenon of solvent inclusion, particularly the selective inclusion effect of aromatic solvents, we conceived that large linear π-conjugated compounds could serve as alternative guests to construct robust CACs.\nSupplementary Table 3. Summarized photophysical parameters of host 1 microcrystals as well as its solvated microcrystals (1·Dio and 1·Tol)\nWhile all four host-guest assemblies exhibit markedly enhanced PLQYs in the range of 62.85–95.36%, significantly exceeding the value of 36.30% observed for the pristine host 1 (Supplementary Fig. 73). By analogy with the solvated crystals of 1, we attribute this enhancement to the rigidification of the host's π-system following PAH encapsulation, which suppresses non-radiative transition pathways and consequently boosts PL efficiency.\nSupplementary Figure 21 (a) Histogram comparing the PLQYs of host 1 MRs with 1∙Dio and 1∙Tol MPs. (b) Histogram comparing the PLQYs of host 1 MRs with host/guest microcrystals involving 1∙SB, 1∙ST, 1∙DSBa, 1∙DSBb, 1∙BPDSB. (c) Histogram comparing the PLQYs of host 1 MRs with 1∙4P and 1∙4PPy MRs.\n4. On page 5, In the section Synthesis of cavity-expandable host-guest microcrystals via complexation host 1 and PAH guests, the cavity sizes of 1·ST, 1·SB, 1·DSBa, and 1·BPDSB are compared. Since some of these crystals were grown in solvents containing dioxane, clarification is needed on how the influence of different solvent molecules on cavity formation and size is excluded.\nResponse:\nWe sincerely thank the referee for the insightful comments and valuable questions regarding our manuscript. The point raised concerning the potential influence of different solvent molecules on the host-guest cavity sizes is indeed critical. We fully agree that a rigorous comparison of cavity dimensions requires elimination of any possible solvent templating effects. To address this point, we performed a series of control experiments. The results clearly demonstrate that the observed differences in cavity size are primarily dictated by the intrinsic sizes of the PAH guests, rather than by the solvent molecules used in the crystallization process. Below, we provide a detailed explanation along with supporting data.\nAmong the four host/guest microcrystals (1·ST, 1·SB, 1·DSBa, and 1·BPDSB) examined, all except 1·BPDSB utilized pure Dio or a THF/Dio mixture (v/v = 3:2) during liquid-phase preparation. To exclude any contribution of Dio to the cavity dimensions of these CACs, we intentionally replaced this mixed solvent system. Remarkably, the use of pure THF as the good solvent for preparing microcrystals of 1·SB and 1·DSBa still affords similar assembled morphologies and luminescence colors (Supplementary Fig. 15). PXRD analysis confirmed that the host/guest microcrystals, whether prepared from pure THF or a THF/Dio mixture, possess identical crystal structures. These findings imply a competitive interplay between linear PAH molecules (e.g., SB and DSB) and good solvents (e.g., Dio and Tol) during cocrystal growth. The stronger intermolecular interactions of the linear PAHs with host 1, however, dominate and effectively preclude the incorporation of solvent molecules into the host framework.\nSupplementary Figure 15. (a, b) FM images and (c, d) PXRD patterns of (a, c) 1∙SB and (b, d) 1∙DSB MRs. All samples were formed from pure THF. For comparison, PXRD patterns of 1∙SB MRs obtained from THF/Dio and 1∙DSB MRs obtained from pure Dio as well as SCXRD patterns of 1∙SB and 1∙DSB are also involved. The samples were excited by UV light. Scale bar, 100 μm.\nWe have re-determined the single-crystal structure of 1 and DSB obtained from a Dio/EtOH mixture at a 1:2 molar ratio. The new structure reveals that no solvent molecules (Dio) are incorporated in the lattice of 1 and DSB (1·DSBb), in which the stoichiometric ratio of 1 to DSB was found to be 2:3. Unexpectedly, the SCXRD data exhibits excellent agreement with the previously reported PXRD pattern of the corresponding MPs. Therefore, whether solvent molecules are included in the host framework depends on subtle differences in the preparation conditions. Accordingly, we have updated the description of the crystal structure of 1·DSBb in the revised manuscript (Supplementary Table 8 and Fig. 24).\nSupplementary Table 8. Crystallographic data of 1-derived CACs involving 1·SB, 1·ST, 1·DSBa, 1·DSBb, and 1·BPDSB\nSupplementary Figure 24. (a) Predicted growth morphology of 1∙DSBb simulated from its crystallographic data using Materials Studio software. (b) PXRD pattern of 1∙DSBb MPs. For comparison, SCXRD pattern of 1∙DSBb and PXRD patterns of its constituent materials are also involved.\nCrystallographic information confirms a cocrystal comprising 1 and DSB in a stoichiometric ratio of 2:3 (denoted as 1·DSBb), in which DSB molecules are selectively trapped within two distinct cavities of host 1. One cavity accommodates only a single DSB molecule, while the other can simultaneously encapsulate two DSB molecules. These two types of cavities are arranged in an alternating fashion along the b axis, while the DSB molecules in both cavities adopt edge-to-face stacking along the a axis (Supplementary Fig. 23). The entire structure is stabilized by C−H···π interactions between the host framework and the enclosed DSB molecules.\nSupplementary Figure 23. (a) Molecular configuration of 1 molecule in 1∙DSBb as well as the dihedral angles between two adjacent benzene rings. (b, d) Packing motifs of 1∙DSBb. (b) Front view and (d) side view. (c) Typical C‒H···π (black lines) interactions and distances (Å) between 1 and DSB molecules.\nIn the 1·ST system, ST serves as both the solvent and the guest. Given its relatively small molecular size, a pair of ST molecules are co-encapsulated within the cavity of host 1 (Fig. 3f, g).\nFig. 3f, g Packing motifs of 1∙ST. (a) Front view and (b) side view.\n5. On page 5, third paragraph, the PL peak of 1·DSBa microcrystals is nearly identical to pristine 1, whereas others show slight red shifts. The reasons for this discrepancy are not addressed.\nResponse:\nWe thank the referee for his/her kind reminder. As noted, the emission spectrum of 1·DSBa microcrystals closely resembles that of the pure host 1, while the microcrystals of 1·SB, 1·ST, and 1·BPDSB exhibit a slight red shift compared to host 1. We have carefully analyzed this phenomenon and attribute it primarily to the specific cavity structures formed in the CACs and the associated alterations in the molecular packing of the host.\nTD-DFT calculations have confirmed that the luminescence originates from the radiative transition of the host molecule, which exhibits intrinsic intramolecular charge-transfer (ICT) character, where electron density shifts from the peripheral steric hindrance groups to the central π-conjugated core. Crystal structure analysis reveals that the CACs exhibit two distinct packing motifs, denoted as Type A and Type B, as illustrated in Fig. R1.\nFigure R1. Two typical packing motifs involving (a) Type A and (b) Type B packing in 1-derived CACs.\nCrystal structure analysis reveals that 1·Tol, 1·SB, and 1·DSBa adopt similar type A packing motifs. As the cavity size increases among these structures, their emission maxima progressively approach that of host 1, occurring at 508 nm, 503 nm, and 495 nm, respectively (Fig. R2). In the cocrystals with smaller cavity sizes, the peripheral groups of adjacent host molecules can spatially overlap with the π-core of another host molecule (Fig. R3). This enhances intermolecular interactions and contributes to the observed red shift.\nFigure R2. (a) PL spectra of 1∙DSB MRs, 1∙Tol MPs and 1∙SB MRs. The insets show the corresponding FM images. Scale bar, 25 μm.\nFigure R3. (a , b , c ) Molecular configurations of 1 molecules in (a ) 1∙DSBa, (b ) 1∙Tol, and (c ) 1 1 1 1 1 1 1∙SB as well as the dihedral angles between two adjacent benzene rings. Packing motifs of 1∙DSBa, 1∙Tol, and 1∙SB in (a , b , c ) front view and (a , b , c ) side view.\n2 2 2 3 3 3\nFurthermore, the herringbone packing structure adopted by the host molecules (Type B) increases the π-orbital overlap between adjacent molecules, leading to a more substantial red shift, as exemplified by 1·Dio (518 nm) and 1·ST (509 nm). Additionally, the formation of CACs can induce a more planar conformation in the host molecule, effectively extending the π-conjugation length, which may also contribute to the red-shifted emission (Figs. R4 and R5).\nFigure R4. PL spectra of 1∙Dio MPs and 1∙ST MRs. The insets show the corresponding FM images. Scale bar, 25 μm.\nFigure R5. (a , b ) Molecular configurations of 1 molecules in (a ) 1∙Dio and (b ) 1∙ST as well as 1 1 1 1 the dihedral angles between two adjacent benzene rings. Packing motifs of 1∙Dio and 1∙ST in (a , 2 b ) front view and (a , b ) side view.\n2 3 3\nIn comparison to host 1 MRs, the PL peaks of 1·Tol, 1·SB, and 1·DSBa microcrystals show a slight red shift, while 1∙Dio and 1∙ST microcrystals exhibit a more pronounced red shift (Fig. 3d; Supplementary Figs. 6 and 19). Based on the distinct stacking modes of host molecules within these CAC systems, we infer that host–host interactions are stronger in 1∙Dio and 1∙ST, whereas they are relatively weaker in 1·Tol, 1·SB, and 1·DSBa (Fig. 3f and Supplementary Fig. 4). This difference in interaction strength likely accounts for the varying degrees of red shift observed in the emission peaks across the different systems. We plan to further investigate the underlying mechanism of the PL red shift in future work.\n6. On page 6, first paragraph, line 2, “Host” is not capitalized.\nResponse:\nWe are grateful to the referee for their insightful feedback. The corresponding revisions have been made.\n7. On page 6, first paragraph, line 7, the 40 nm red-shift of 1·4PPy compared to 1·4P is attributed to additional CT interactions, but no theoretical calculations or literature evidence are provided.\nResponse:\nWe appreciate the referee's constructive and helpful feedback. As the referee correctly pointed out, in our previous submission we ascribed the notable PL red shift of 1·4PPy MRs relative to 1·4P to CT interactions between the aniline groups of 1 and the pyridyl moieties of 4PPy. Nevertheless, there is a lack of detailed evidence to clarify such intermolecular interactions. As described in the manuscript, crystallographic information reveals that 1·4P and 1·4PPy possess nearly identical packing modes and unit cell parameters. The substitution of both ends of quaterphenyl with pyridine groups yields an electron-deficient 4PPy. Concurrently, host molecule 1 incorporates an electron-rich N, N-diphenylmethyl unit. Its complexation with 4PPy promotes the formation of a CT complex 1·4PPy. Furthermore, due to the substantial steric hindrance imposed by this electron-donating substituent, the resulting donor-acceptor complex does not adopt the conventional planar, alternating stacked architecture. We have therefore revised the manuscript to provide a more thorough and compelling experimental justification for the assignment of the CT interaction in the 1·4PPy cocrystal.\nTo verify this conclusion, we further conducted absorption, PL lifetime, and electron paramagnetic resonance (EPR) measurements of 1·4PPy MRs (Supplementary Fig. 32). The diffuse reflectance absorption spectrum displays a new long-wavelength absorption band that is absent in either pure host 1 or guest 4PPy. Compared to host 1 (τ = 1.31 ns), the 1·4PPy MRs shows a prolonged PL lifetime of 2.26 ns. Additionally, a EPR signal with a g-value of 2.00526 (close to free electron) unambiguously indicates the presence of unpaired electrons and radical species in 1·4PPy, providing direct proof of a CT process (Angew. Chem. Int. Ed. 2017, 56, 7831–7835). The above results undoubtedly confirm the presence of weak CT interactions between host 1 and the guest 4PPy.\nUnder periodic boundary conditions, TD-DFT calculations reveal that the key electronic transition associated with the low-energy absorption band in 1·4PPy is characterized by a shift of electron density from the π-conjugated backbone of host 1 to the pyridine ring of guest 4PPy. The spatial separation of this CT pathway is visually confirmed by the plotted hole and electron density distributions (Supplementary Fig. 40b). Such distinct separation of the frontier orbitals is a hallmark of CT excitation.\nSupplementary Figure 32. (a) ESR spectra and (b) electron spin ESR result of 1∙4PPy MRs at 298 K. (c) Diffuse-reflectance absorption spectra of 1 MRs, 4PPy MPs, and 1∙4PPy MRs. (d) Time-resolved fluorescence decay curves of 1 and 1∙4PPy MRs.\nSupplementary Figure 40. Electron and hole orbital distributions in (a) 1‧4P, (b) 1‧4PPy, and (c) 1‧4S based on TD-DFT calculations.\n8. On page 8, first paragraph, the statement that “electrons and holes are localized on the guest but emission originates from the host” (in 1·DSBa and 1·BPDSB) lacks mechanistic clarity. This phenomenon requires a clearer mechanistic explanation (e.g., whether Förster or Dexter energy transfer is involved).\nResponse:\nThanks for the referee’s insightful comment regarding the need for greater mechanistic clarity on the emission process in the 1·DSBa and 1·BPDSB cocrystals. We agree that the initial statement was not sufficiently supported. In our initial approach, analyzing an isolated host/guest pair without considering the crystalline environment was indeed an oversight, which led to an incomplete interpretation. To address this, we have revised our computational strategy. We now performed TD-DFT calculations on the full crystal structure to model the excited state more accurately and added new calculation results into the Supplementary Information.\nSupplementary Figure 39. Electron and hole orbital distributions in (a) 1‧SB, (b) 1‧DSBa, and (c) 1‧BPDSB based on TD-DFT calculations.\nAn analysis of the transition orbitals corresponding to the maximum oscillator strength in the absorption spectrum (Supplementary Table 12) shows that most cocrystals (e.g., 1·DSBa and 1·4P) exhibit electron and hole densities primarily localized on host 1 (Supplementary Figs. 39 and 40). This indicates that the initial photoexcitation takes place within the host material, dominating the subsequent electronic transitions and emission. However, in rare cases like 1·4S, the PL spectrum exhibits the characteristic emission of the 4S guest molecule, which appears to contradict the host-dominated excitation. We propose that this is due to a highly efficient Förster resonance energy transfer (FRET) from the host 1 to the 4S guest, facilitated by the significant spectral overlap between the host's emission and the guest's absorption.\nSupplementary Figure 40. Electron and hole orbital distributions in (a) 1‧4P, (b) 1‧4PPy, and (c) 1‧4S based on TD-DFT calculations.\n9. The manuscript repeatedly mentions shorter or longer PL lifetimes of host–guest crystals compared to the host, but does not explain the origins of these changes or their implications for photophysical performance.\nResponse:\nThanks for the referee's meticulous observation. As the referee noted, the PL lifetimes of these host/guest microcrystals are either extended or shortened compared to host 1. Following the referee's suggestion, we have added a brief discussion on the origin of these changes.\nNotably, PL lifetimes of 1-derived host/guest microcrystals either increase or decrease relative to that of pure host 1, with most values falling within the range of 1–2 ns (Supplementary Fig. 36). We attribute this variation to the synergistic interaction between the host and guest molecules, which collectively modulates the competition between radiative and non‑radiative transition pathways in the CACs. Specifically, guest encapsulation promotes planarization of the host molecular skeleton, enhancing host/guest interactions and thereby facilitating the radiative decay process. Concurrently, this synergistic effect may also suppress non‑radiative pathways present in the pure host crystal by reducing lattice defects and restricting molecular vibrations and rotations. The short, nanosecond-scale PL lifetime promotes rapid radiative recombination, minimizing energy loss due to triplet accumulation and thereby establishing a favorable photophysical basis for low-threshold lasing.\nSupplementary Figure 36. Plots of PL lifetimes of host 1 and host/guest microcrystals involving 1·SB, 1·ST, 1·DSBa, 1·DSBb, 1·BPDSB, 1·4P, and 1·4PPy.\n\nComment:\nIn summary, the manuscript introduces an interesting and novel concept of cavity-expandable non-macrocyclic host–guest crystals with elastic and lasing properties. However, the current version lacks sufficient mechanistic explanations, systematic comparisons, and quantitative analyses to support the claims. I recommend minor revision.\nResponse:\nWe extend our sincere gratitude to the referee for his/her constructive comments and positive recognition of our work. We have carefully addressed all of the detailed and valuable suggestions in the revision. We believe these modifications have further strengthened the quality of the paper."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have comprehensively addressed all the concerns raised in my initial review. They have supplemented detailed mechanistic explanations (e.g., solvent effects, PL spectral shift origins, energy transfer mechanisms), provided quantitative data for elasticity (uniaxial tensile test results) and lasing thresholds (systematic comparisons under identical conditions), and clarified ambiguous terminology (renaming to \"cavity-adaptive cocrystals\" and defining \"molecular cavity\"). The additional experimental evidence, revised figures, and improved discussion have significantly strengthened the manuscript’s scientific rigor and clarity. The work’s novelty in integrating elasticity and low-threshold lasing in non-macrocyclic cocrystals remains compelling, with broad implications for supramolecular photonic materials. Given the thorough revisions and the high quality of the updated work, I recommend accepting the manuscript for publication.", "reviewer_2": "The authors have addressed concerns raised by the reviewers in a thorough, constructive, and scientifically sound manner. In particular, the newly added experiments and expanded datasets substantially strengthen the photophysical/laser-performance claims and improve the overall rigor and clarity of the manuscript. The revised version now provides a more balanced positioning relative to prior OSSL gain media and clarifies the conceptual description of the cocrystal system (including the terminology around “host–guest”), thereby eliminating the main sources of ambiguity raised in my initial review.\n\nOverall, I find that the manuscript has been significantly improved and now meets the standard for publication in this journal, and I recommend acceptance.", "reviewer_3": "Non-macrocyclic receptors capable of binding guests in a crystalline state have been developed. Host 1 showed cavity adaptability upon complexation with guests of varying lengths to form guest-induced cavity-adaptive cocrystals (CACs). The host-guest cocrystals exhibited efficient fluorescence, high elasticity, and low-threshold lasing. This revised work may be acceptable for publication in Nature Communications after further revision.\n\nThe association constants in solutions will facilitate the readers to grasp the binding strengths required for the unique behaviors reported herein. Based on Figures 3d and 4c, this reviewer strongly believes that it will be possible to monitor the binding events by UV-vis or FL spectral changes. Even if the solubilities of the guests are poor, the mixing of the host and guest (in a powder) in solvent will give a homogeneous solution because Figures 3d and 4c were successfully obtained; how were these UV-vis or FL spectra measured? The binding isotherms should be given at least in the Supporting Information even when only straight lines rather than saturation curves are obtained."}, "author_response": "We are delighted to learn that the revisions have been acknowledged by the reviewer, and we sincerely appreciate his/her valuable suggestions as well as the careful review of this manuscript.\n\nWe are pleased to hear that our responses and modifications address the reviewer’ concerns. We would also like to express our sincere appreciation for the constructive feedback and the considerable effort invested in reviewing our manuscript.\n\nWe are grateful to the reviewer for valuable feedback on our manuscript. The suggestion regarding the determination of binding constants and spectral monitoring is indeed crucial for a deeper and quantitative understanding of the present no-macrocyclic cocrystal systems. We fully agree with the reviewer’s perspective and have systematically supplemented the relevant experimental data and analysis as advised. The details are provided below:\nFirst, to clarify the complexation behavior of the host and guest molecules in solution, we recorded the ¹H NMR spectra of the individual host (1), the individual guest (SB, DSB, or 4PPy), and an equimolar mixture of the two (Figs. R1-R3). Regrettably, no significant changes were observed in the chemical shifts of characteristic proton signals. To further investigate, we conducted a ¹H NMR titration experiment by incremental addition of guest 4PPy to a solution of host 1. Similarly, no significant chemical shift perturbations were detected (Fig. R3). We speculate that this may be due to the relatively weak binding affinity between the host and guest, or because the binding mode does not significantly alter the electron density or magnetic anisotropy around the relevant protons.\nFigure R1. (a) 1H NMR spectra (400 M, CDCl ) of 1, SB, and their equimolar mixture; (b) Local 3 magnification of (a) in the chemical shift range of δ 6.90-7.65 ppm, showing the characteristic peak in detail.\nFigure R2. (a) 1H NMR spectra (400 M, CDCl ) of 1, DSB, and their equimolar mixture; (b) 3 Local magnification of (a) in the chemical shift range of δ 6.90-7.50 ppm, showing the characteristic peak in detail.\nFigure R3. (a) 1H NMR spectra (400 M, CDCl ) titration for 4PPy was added into host 1 sulution; 3 (b) Local magnification of (a) in the chemical shift range of δ 6.90-8.70 ppm, showing the characteristic peak in detail.\nFor the host/guest systems exhibiting significant changes in UV-Vis absorption or fluorescence spectra, we systematically performed spectroscopic titration experiments (Figs. R4-R7). Despite the limited solubility of some guest molecules, we acquired comprehensive spectral data within the feasible concentration range and attempted to estimate the binding constants of 1·SB, 1·DSB, 1·4P, and 1·4PPy using the Benesi–Hildebrand (B–H) equation. Considering the complexity of fluorescence measurements in organic compound solutions and their susceptibility to various interfering factors, this study employed UV-Vis absorption spectroscopy for titration experiments and subsequent determination of binding constants to ensure more reliable and reproducible quantitative analysis results. The experimental results showed clear and reproducible changes in the UV-Vis absorption spectra, which directly confirmed the presence of effective interactions between the host and guest molecules. Typically, for 1·SB, an SB solution (C = 30 mM) was SB gradually titrated into 3 mL of a host 1 solution with a concentration of 1.0×10⁻⁵ M until the absorbance change reached saturation. Fitting the data with the B–H equation yielded a binding constant K of 14.97 ± 0.22 M⁻¹ for this system. Using the same method, we further determined a the binding constants for 1·DSB, 1·4P, and 1·4PPy to be 16.22 ± 0.35 M⁻¹, 242 ± 2.2 M⁻¹, and 315.43 ± 2.39 M⁻¹, respectively (Figs. R4-R7). These results indicate that the chemical structure of the guest significantly influences the binding strength with the host, particularly guests with pyridine groups exhibit stronger complexation ability.\nDue to the relatively weak host/guest interactions and the solubility limitations of some guest molecules in the present non-macrocyclic cocrystal systems, the determined binding constants exhibit a measurable degree of uncertainty. To ensure the rigor of the reported data, these values are provided for reference only and have not been included in the main manuscript or supplementary materials.\nFigure R4. (a) UV-Vis absorption spectra of host 1 (C = 10-5 M) upon titration with guest SB in 1 THF/Dio (v/v = 3:2, C = 3×10-2 M). (b) Benesi-Hildebrand equation was used to calculate the SB binding constant of 1 and SB as K = 14.97±0.22 M-1.\na\nFigure R5. (a) UV-Vis absorption spectra of host 1 (C = 10-5 M) upon titration with guest DSB in 1 Dio (C = 3×10-3 M). (b) Benesi-Hildebrand equation was used to calculate the binding constant DSB of 1 and DSB as K = 16.22±0.35 M-1.\na\nFigure R6. (a) UV-Vis absorption spectra of host 1 (C = 10-5 M) upon titration with guest 4P in 1 Dio (C = 1.5×10-3 M). (b) Benesi-Hildebrand equation was used to calculate the bonding 4P constant of 1 and 4P as K = 242±2.2 M-1.\na\nFigure R7. (a) UV-Vis absorption spectra of host 1 (C = 10-5 M) upon titration with guest 4PPy 1 in THF (C = 3×10-3 M). (b) Benesi-Hildebrand equation was used to calculate the binding 4PPy constant of 1 and 4PPy as K = 315.43±2.39 M-1.\na"}, {"round": 3, "reviewer_comments": {"reviewer_3": "The binding constants of compound 1 for SB, DSB, 4P, and 4PPy were determined by UV-Vis titrations. Although those for SB and DSB appear to be less reliable because of the large baseline deviation and little or no spectral changes, respectively, those for 4P and 4PPy (Figures R6 and R7) looks reliable, judging from the remarkable spectral changes and small standard deviation values. In addition, Figure R6 has an isosbestic point at 355 nm, which strongly suggests a 1:1 association. The information that these systems have binding constants of around 300 M-1 is quite useful for the readers. UV-Vis titrations were more sensitive to the host-guest interactions than NMR titrations, which sounds reasonable and meaningful."}, "author_response": "We sincerely appreciate his/her positive feedback and agree that the determination of binding constants is meaningful for readers to understand the CACs system. We are truly grateful for his/her valuable comments and careful review of the manuscript."}]

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