Synergistic 3D π–π networks enforce persistent foldamer configuration with tunable full-color circularly polarized luminescence

Abstract

Achieving molecular chirality with enantiostability in purely π-conjugated foldamers remains a substantial challenge due to inherently weak π-π stacking interactions and facile racemization. Herein, we introduce a novel design strategy employing synergistic intramolecular 3D π–π stacking networks within a 1,8-diarylnaphthalene framework, enabling foldamers to exhibit extraordinary configurational stability. A systematic series of quinoxaline- and phenazine-based foldamers incorporating carbazole (CZ) and diphenylamine (DPA) donors were synthesized, with chiral configurations stabilized through complementary face-to-face and laterally offset π–π stacking interactions. Single-crystal X-ray analyses and computational studies confirmed the formation of complex intramolecular π-networks, providing exceptional racemization barriers (ΔG^‡ up to 26.06 kcal mol^-1), exceeding conventional atropisomers. Additionally, the modular donor-acceptor design facilitates full-color circularly polarized luminescence (469–684 nm), maintaining high dissymmetry factors (|g_lum | > 10^-3) across solution and solid-state environments. This work establishes a generalizable principle for constructing chiral foldamers with enantiostability and tunable optical properties through tailored 3D aromatic interactions, offering significant advances in chiral optoelectronics and responsive materials.

Achieving molecular chirality with enantiostability in π-conjugated foldamers is challenging due to weak π-π interactions and easy racemization. Here, the authors employ a 3D π–π stacking strategy within a 1,8-diarylnaphthalene framework, achieving exceptional configurational stability and tunable optical properties.

Introduction

Foldamers are synthetic oligomers designed to adopt predictable and stable three-dimensional conformations^1–8. They have emerged as a central research area in supramolecular chemistry and materials science, with profound implications spanning from molecular recognition and catalysis to advanced optoelectronic and photonic applications^9–13. Aromatic foldamers, in particular, have attracted substantial attention owing to their intrinsic ability to form stable secondary structures through π–π stacking interactions^14–18. Unlike hydrogen bonding or metal coordination, π–π stacking provides an intrinsically reversible, dynamic, yet relatively weak stabilizing force, posing significant challenges in achieving molecular chirality with enantiostability^14–18. Thus, while aromatic stacking interactions can drive the initial formation of chiral folds, maintaining long-term structural integrity and enantiopurity under ambient conditions remains a formidable scientific and synthetic challenge.

To date, a variety of strategies have been explored to enhance the configurational stability of chiral aromatic foldamers. Notably, approaches such as bulky substituent incorporation, macrocyclization, and the introduction of additional covalent interactions have been employed to elevate the energetic barrier of racemization^19–25. For example, previous reports on ortho-phenylene oligomers demonstrated controlled helical folding mediated by offset face-to-face aromatic interactions^26–29. However, these systems typically suffer from rapid conformational interconversion, limiting their practical applications in chiral optoelectronic technologies. Similarly, chiral aromatic oligoamide foldamers incorporating pyrene excimers or macrocyclic aggregates demonstrated stable chiroptical properties but generally lacked broad tunability in their emission colors^30–34. Achieving foldamers with both exceptionally high racemization barriers and modularly tunable chiroptical properties like full-color circularly polarized luminescence (CPL) remains relatively unexplored and represents an urgent frontier in advanced functional materials.

Li et al. recently developed a novel class of multilayer 3D chiral architectures that show particular promise for resolving the aforementioned issues^7,8,35–46. Building upon this, we envisioned an innovative approach based on the strategic construction of intramolecular 3D π–π stacking networks within a modular, π-conjugated aromatic foldamer scaffold. Specifically, we report herein a series of novel 1,8-diarylnaphthalene-derived foldamers featuring quinoxaline (Qx) and phenazine (Pz) acceptor units coupled with carbazole (CZ) or diphenylamine (DPA) donors, carefully designed to leverage the cooperative interplay of diverse π–π stacking motifs (Fig. 1). Unlike traditional foldamers that typically rely on a single dominant stacking interaction or planar stacking interface^46–48, our design systematically integrates multiple complementary stacking geometries, including co-facial, offset, and T-shaped interactions^49,50. This synergistic combination establishes a robust 3D aromatic network, dramatically enhancing configurational stability and raising the racemization energy barriers (ΔG^‡ up to 26.06 kcal mol⁻¹) beyond conventional atropisomerization thresholds. Crucially, single-crystal X-ray crystallography clearly demonstrates that our foldamers adopt stable, inherently chiral configurations stabilized by a complex intramolecular 3D network of π–π interactions involving both electron-rich and electron-poor aromatic components. Comprehensive structural and computational analyses, including interaction region indicator (IRI) and energy decomposition analyses (EDA), reveal the origin of this configurational persistence as arising from a delicate balance between directional van der Waals interactions, steric effects from strategically placed tert-butyl substituents, and optimal overlap of complementary electron-donor and acceptor π-surfaces. Remarkably, these analyses uncover how subtle changes in stacking geometry or substituents can profoundly influence enantiostability, thereby providing fundamental insight into the rational molecular design of configurationally stable foldamers. Beyond achieving exceptional stereochemical control, our design platform simultaneously enables precise tuning of the foldamers’ optoelectronic properties. By modulating donor-acceptor pairs and substituent electronic effects, we successfully achieved modular full-color photoluminescence spanning from blue to deep red (469–684 nm), with pronounced intramolecular charge-transfer (ICT) transitions clearly verified by extensive spectroscopic and theoretical studies. Significantly, chiral foldamers exhibited robust CPL both in solution and solid states, characterized by high dissymmetry factors (|g_lum | > 10^-3), thereby positioning our foldamer series as promising candidates for emerging chiral photonic applications such as circularly polarized OLED displays, chiral sensing, bio-imaging, and optically active security inks^51–54. Therefore, this work advances the foldamer concept by presenting a fundamentally novel strategy—exploiting synergistic intramolecular 3D π–π stacking networks—to achieve molecular chirality with enantiostability and versatile optical functionality in fully organic π-systems. Through careful design, we deliver simultaneously enhanced configurational stability, sophisticated structural complexity, and finely adjustable optoelectronic performance within a single chiral architecture. This integrated design principle not only provides a profound advancement in foldamer chemistry but also lays critical groundwork for future generations of chiral functional materials, where stability, versatility, and tunability are of paramount importance.

Fig. 1. Conceptual model.

a conceptual model of the synergistic 3D π–π network that stabilizes the chiral foldamer configuration, b building blocks constituting the 3D π–π network.

Results and Discussion

Design and synthesis of 3D π-network foldamers

Consistent with our molecular design strategy outlined in the introduction, to investigate the synergistic effects of intramolecular π-π interaction, we designed and synthesized two novel foldamer series featuring C₂-symmetric architectures, quinoxaline-based (Qx) and phenazine-based (Pz). In this molecular framework, the quinoxaline (Qx) and phenazine (Pz) moieties served as electron-accepting units, while carbazole (CZ) and diphenylamine (DPA) derivatives were incorporated as the elongated electron-donating units, which were widely used as the advanced D-A type luminescent emitters^55–57. Naphthalene served as π-conjugated linkers between donor and acceptor moieties. These racemic compounds were synthesized via Pd-catalyzed Suzuki-Miyaura cross-coupling under the optimized conditions, achieving isolated yields of 87-94% (Fig. 2a and synthetic details in Supplementary Information-section 2). Systematic substitution generated six derivatives: Qx-CZ, Qx-CZ-tBu, Qx-DPA-tBu, Pz-CZ, Pz-CZ-tBu and Pz-DPA-tBu (Fig. 2b, c), where t-Bu groups increase steric hindrance and further enhance the electron-donating effect (full characterization by NMR, HR-MS data in Supplementary Information-section 3). Chiral HPLC resolution using a Daicel CHIRALPAK IF column (n-hexane/CH₂Cl₂) successfully separated all racemic mixtures into enantiopure forms (The highest e.e. up to 99%, verified by analytical HPLC in Fig. S35-S40; proportion of mobile phase and retention times in Tables S1, S2). Thermal analysis revealed exceptional stability across the series, with 5% weight-loss temperatures (T_d) ranging from 469 °C to 496 °C (Fig. S78-S83).

Fig. 2. Synthesis and structures.

a key synthetic steps, structural formulas of b Qx foldamers and c Pz foldamers.

Single-crystal structure of chiral foldamers

To verify structural assumptions from the synthesis and ensure molecular chirality, single crystals of enantiopure Qx-CZ-tBu were grown by slow diffusion from a solution in CH₂Cl₂ to methanol. X-ray crystallographic analysis (CCDC: 2393433 and 2393434) unambiguously confirmed the mirror-image relationship (Fig. 3a, b and Supplementary Data 1 and 2) between the two enantiomers, as evidenced by their flack parameters of 0.204 and 0.037 (Tables S3 and S4). Both enantiomers of Qx-CZ-tBu adopt a chiral folded configuration devoid of symmetry planes or inversion centers (Fig. 3a, b). Taking the single crystal of Qx-CZ-tBu (Fig. 3b) as an example, the central quinoxaline (R₄) engages in nearly coplanar stacking with two benzene rings (R₂ and R₆), exhibiting interplanar distances of 3.5 Å (R₂-R₄, dihedral angle 27.9 °) and 3.6 Å (R₄-R₆, dihedral angle 24.5 °). This face-to-face alignment of the R₂-R₄-R₆ triad establishes a through-space conjugation network mediated by π-π stacking interactions. Notably, offset π-π stacking interactions were observed between naphthalene moieties (R₁ and R₇) and carbazole units (R₃ and R₅), with interlayer distances/dihedral angles of 4.5 Å/7.5 ° (R₃-R₇) and 4.2 Å/19.8 ° (R₁-R₅). Crystallographic packing analysis revealed the absence of intermolecular π-stacked arrays (Fig. 3c). Under analogous crystallization conditions, racemic compounds Qx-CZ, Qx-CZ-tBu, Qx-DPA-tBu and Pz-CZ (Supplementary Data 3-6) were obtained and found to exhibit similar intramolecular π-stacking motifs. Alternatively, in the single crystal of Qx-DPA-tBu (Figure. S45 and Supplementary Data 5), the laterally offset π-π stacking interactions between naphthalene moieties and diphenylamine units were remarkably weakened, with interlayer distances/dihedral angles of 5.7 Å/61.8 ° and 4.6 Å/50.1 °. From the perspective of stacking categories and geometries, these various short-range π-π stacking oriented in different directions synergistically form the intramolecular 3D π-networks of the entire foldamers.

Fig. 3. Single-crystal structures and intramolecular non-covalent interactions.

Single crystal structures of the enantiomers of Qx-CZ-tBu, a peak 1 in HPLC, b peak 2 in HPLC, and c packing of Qx-CZ-tBu (peak 2 in HPLC). d IRI maps of Qx-CZ, Qx-CZ-tBu, Qx-DPA-tBu, Pz-CZ, Pz-CZ-tBu, and Pz-DPA-tBu, sign(λ₂)ρ is mapped on IRI isosurfaces according to the color bar.

To systematically investigate the π-stacking modulation of noncovalent interactions, we performed Interaction Region Indicator (IRI) analyses to quantify key parameters, including hydrogen bonding, van der Waals (vdW) forces, and steric effects⁵⁸. As shown in Fig. 3d, all six compounds exhibited prominent vdW interactions within their central three-layer and edge dual-layer regions. Notably, systems with planar carbazole (CZ) moieties (Pz-CZ, Qx-CZ, Pz-CZ-tBu, and Qx-CZ-tBu) demonstrated more remarkable vdW interactions between CZ units and naphthalene groups in laterally dual-layer regions. In contrast, the nonplanar diphenylamine (DPA)-containing analogs (Pz-DPA-tBu and Qx-DPA-tBu) showed attenuated vdW interactions in edge dual-layer regions accompanied by enhanced steric repulsions. The chiral configurational stability of intramolecular 3D π-networks may be influenced by the energetic compensation between vdW and steric forces.

With these results in hand, we proceeded to determine the absolute configuration of chiral foldamers. As shown in Fig. 3b, it reveals that the structure possesses two chiral axes independently located at R₁-R₄ and R₇-R₄, enabling the formation of (R_a, R_a) or (M, M) configurations based on the Cahn-Ingold-Prelog (CIP) rules^59,60, which is analogous to previously reported multi-axially chiral naphthalene oligomers⁶¹. Simultaneously, this structure exhibits planar chirality⁶², reminiscent of classical ansa-type architectures^63,64. However, unlike the ansa chains that completely rely on covalent bridging motifs, the planar chirality here arises from a hybrid strategy combining dual-layer π-π stacking interactions (R₁/R₅ and R₃/R₇) and covalent cross-linkings (R₁-R₄-R₇-R₆-R₅ and R₇-R₄-R₁-R₂-R₃). As a result, it generates two unsealed yet conformationally strained macrocyclic chains, which may suppress racemization by restricting free rotation of the prochiral face (R₄), thereby enabling the formation of (S_p, S_p) or (M, M) configurations. Hence, the enantiomers of these foldamers harbor two chiral fragments, which overlap both axial and planar chirality. Their meso-isomer (P, M) is unstable and was not detected in HPLC and NMR due to significant steric hindrance between the top and bottom layers.

Enantiostability mechanism of chiral foldamers

Building upon structural insights from X-ray crystallography, to elucidate clearly the relationship between the synergistic differences of these π-network foldamers and their enantiostability, we conducted the quantitative assessment through dynamic HPLC analyses monitoring enantiomeric excess (e.e.) decay in CH₂Cl₂ at 293 K (Figs. S47–S52, Tables S9–S14). The resulting data, including rate constants (k), half-lifetimes (t₁_/₂), and racemization energy barriers (ΔG^‡), are summarized in Table 1. All chiral foldamers exhibited exceptionally available racemization barriers (ΔG^‡ = 22.93–26.06 kcal mol⁻¹), surpassing the typical atropisomerization threshold (ΔG^‡ = 22.2 kcal mol⁻¹) and confirming room-temperature stereochemical integrity⁶⁵. Furthermore, the variation in foldamer enantiostability originates from the distinct stacking and steric effects between the extended donor groups and the naphthalene rings, whereas the extension of the central electron-acceptor group does not alter the enantiostability. Consequently, their stability falls into three distinct gradients. The lowest ΔG^‡ values were provided by the DPA-tBu-modified Qx-DPA-tBu and Pz-DPA-tBu, at 22.99 and 22.93 kcal mol⁻¹, respectively. The stability of the CZ-modified foldamers was enhanced, with ΔG^‡ values of 23.34 and 23.35 kcal mol^-1 for Qx-CZ and Pz-CZ. Notably, introducing tert-butyl groups to CZ significantly boosted stability, the ΔG^‡ values for Qx-CZ-tBu and Pz-CZ-tBu increased to 26.06 and 25.78 kcal mol⁻¹, respectively, and the corresponding t_1/2 at room temperature extended from the order of hours to days (Table 1).

Table 1.

Summary of k, t_1/2 and ΔG^‡ of enantioenriched Qx-CZ, Qx-CZ-tBu, Qx-DPA-tBu, Pz-CZ, Pz-CZ-tBu and Pz-DPA-tBu

	Qx-CZ	Qx-CZ-tBu	Qx-DPA-tBu	Pz-CZ	Pz-CZ-tBu	Pz-DPA-tBu
ka (s−1)	2.38 × 10−5	2.23 × 10−7	4.33 × 10−5	2.34 × 10−5	3.62 × 10−7	4.84 × 10−5
ΔG‡ (kcal mol−1)	23.34	26.06	22.99	23.35	25.78	22.93
t1/2a	242.5 min	18 day	133.3 min	247.2 min	11 day	119.3 min

^aRecorded in CH₂Cl₂ (c = 0.1 mg mL⁻¹) at 293.15 K.

Next, we employed theoretical calculations using Hirshfeld-partitioned Independent Gradient Model (IGMH) analyses coupled with electrostatic potential (ESP) mapping and energy decomposition analysis (EDA)^66–69 to deconvolute the contributions to configurational locking. IGMH analyses revealed that dominant intramolecular interactions, including π-π interactions, C–H···π interactions, and N···H interactions, stabilize the foldamers (Figs. S106–S111). It is important to note that, in addition to the π-π interactions formed between the central three layers, the planar CZ groups can form significant additional π-π interactions with the naphthalene rings. In contrast, the π-π interactions between the non-planar DPA-tBu groups and the naphthalene rings are significantly weakened or even absent due to their flexible conformations, leaving primarily C–H···π interactions (Fig. S108). Complementary ESP maps demonstrated charge complementarity between the π-surfaces (negative planar regions vs. positive edges), consistent with directional π-stacking geometries driven by co-facial π-π interactions in the central core and laterally offset π-π stacking (Figs. S99–S104). EDA further quantified steric effects, showing that introducing tert-butyl groups, replacing carbazole with diphenylamine, or extending the central core all increase molecular steric hindrance (Fig. S112). For instance, Pauli repulsion energies increased slightly from 1286.19 kcal mol^-1 (Pz-CZ) to 1292.05 kcal mol^-1 (Pz-CZ-tBu) upon tert-butyl substitution. We can infer that further increasing steric effects on the premise of establishing favorable lateral π-π stacking effectively enhances enantiostability. In contrast, steric hindrance alone is insufficient to enhance stability. For example, the increased steric hindrance from extending the central electron-acceptor fails to translate into better enantiostability because the stacking geometry—characterized by an open dihedral angle—remains unchanged and fails to improve the effectiveness of configurational locking. These analyses reveal that the enantiostability of chiral foldamers arises from a synergistic interplay of multiple π-π stacking interactions in a 3D π-network: directional co-facial and offset π-π stacking lock the chiral configuration, whereas only when positioned within a geometry conducive to π-π stacking can sterically hindering tert-butyl groups further restrict changes in the local conformation and enhance the configurational stability of the entire molecule, underscoring the prerequisite role of the stacking geometry.

Photoluminescence properties of chiral foldamers

Given the structural stability confirmed above, we further explored how intramolecular π–π interactions influence luminescence behaviors^70–72, it encouraged us to investigate the photoluminescence properties of foldamers in different solutions and solid conditions. The UV-vis absorption profiles of six chiral foldamers exhibited structure-dependent variations in CH₂Cl₂ (Fig. 4a, b; Table 2). Characteristic π-π transitions dominated the 300–330 nm region, while intramolecular charge-transfer (ICT) transitions appeared at 350-430 nm⁷³. Notably, tert-butyl functionalization of carbazole donors induced a 6 nm bathochromic shift in Qx-CZ-tBu (348 nm vs. 342 nm for Qx-CZ), consistent with enhanced electron-donating capacity. Extended π-conjugation in phenazine-containing systems (e.g., Pz-CZ at 425 nm) generated low-energy absorption tails, as corroborated by TD-DFT simulations (Fig. S105) revealing donor-to-acceptor spatial charge transfer.

Fig. 4. Photophysical characterization.

Absorption and emission spectra of a Qx foldamers and b Pz foldamers in CH₂Cl₂ (c = 10 μM), λ_ex = 330 nm for Qx-CZ, λ_ex = 335 nm for Qx-CZ-tBu, λ_ex = 350 nm for Qx-DPA-tBu, λ_ex = 345 nm for Pz-CZ, λ_ex = 350 nm for Pz-CZ-tBu, and λ_ex = 370 nm for Pz-DPA-tBu. c Emission photographs under 365 nm UV irradiation and d CIE color coordinates of foldamers in CH₂Cl₂ (c = 10 μM). e Emission spectra of foldamers in PMMA doped film (w.t.=1%) and f emission photographs under 365 nm UV irradiation.

Table 2.

Summary of Optical Properties of Qx-CZ, Qx-CZ-tBu, Qx-DPA-tBu, Pz-CZ, Pz-CZ-tBu and Pz-DPA-tBu

	λabsa (nm)	λema (nm)	λemb (nm)	Φc (%)	τaved (ns)	EHOMOe (eV)	ELOMOe (eV)	ΔEDFTe (eV)	EHOMOf (eV)	ΔEopticalg (eV)
Qx-CZ	294,342	469	450	1.1	1.09	-5.425	-2.179	3.25	-5.487	2.94
Qx-CZ-tBu	298,348	506	457	4.9	2.52	-5.267	-2.161	3.11	-5.335	2.96
Qx-DPA-tBu	302,340	572	518	5.8	21.53	-4.922	-2.117	2.81	-4.985	2.88
Pz-CZ	294,342,425	546	525	0.8	1.07	-5.410	-2.693	2.72	-5.488	2.47
Pz-CZ-tBu	298,348,425	595	535	2.1	3.15	-5.231	-2.671	2.56	-5.316	2.47
Pz-DPA-tBu	301,352,425	684	605	2.0	20.69	-4.887	-2.620	2.27	-4.961	2.45

^a Recorded in CH₂Cl₂ (c = 10 μM) at 298 K. ^b Recorded in PMMA doped films (w.t. = 1%) at 298 K. ^c Emission quantum yields using an integrating sphere, recorded in CH₂Cl₂ (c = 10 μM). ^d Emission lifetime in PMMA doped films. ^e DFT calculations (B3LYP-D3(BJ)/6-311 G(d,p)) for MM-enantiomers, E_gap(DFT) = E_LUMO − E_HOMO. ^f Measured by cyclic voltammetry (CV) in CH₂Cl₂. ^g E_gap(optical): optical energy gap obtained from the absorption spectra onset in CH₂Cl₂.

Photoluminescence spectra demonstrated pronounced polarity-responsive redshifts by ICT effect, with Qx-CZ-tBu exhibiting a 68 nm bathochromic shift from hexane (452 nm) to DMF (520 nm) (Fig. S56, Table S15). Systematic donor and acceptor variation enabled full-color emission tuning (blue to red) in CH₂Cl₂ through electronic-donating strength modulation (wavelength: DPA-tBu > CZ-tBu > CZ) and acceptor π-extension (wavelength: Pz > Qx), which is shown in Fig. 4a, d and summarized in Table 2. Taking the Qx-CZ as an example, tert-butyl substitution redshifted emission to Qx-CZ-tBu by 37 nm (469 → 506 nm), while phenazine incorporation induced a 77 nm shift (469 → 546 nm from Qx-CZ to Pz-CZ). Frontier orbital analysis revealed the HOMO and LUMO are mainly distributed on the donor and acceptor fragments, respectively, whereas the naphthyl linkers hardly participate in the HOMO and LUMO distribution, leading to a weak overlap between the D and A electronic clouds, and this effect becomes more pronounced with enhanced electron donors (D) and acceptors (A), resulting in barely any HOMO-LUMO overlap in Pz-DPA-tBu (Fig. 5). It suggested the possibility of through-space charge-transfer (TSCT) from donor to acceptor.

Fig. 5. Frontier molecular orbital plots.

Spatial distributions of HOMOs and LUMOs of Qx-CZ, Qx-CZ-tBu, Qx-DPA-tBu, Pz-CZ, Pz-CZ-tBu, and Pz-DPA-tBu. ΔE is energy gap between HOMO and LUMO.

In addition, the AIEE phenomenon was prominently observed in DMF/H₂O mixtures. For example, Qx-CZ exhibits a 14-fold fluorescence enhancement and a 15 nm hypsochromic shift from pure DMF to 50% water content (Fig. S54), underscoring the structural dependence of emission behavior on microenvironmental changes. Dynamic light scattering confirmed nanoparticle formation (d = 99 nm), due to restricted intramolecular rotation in aggregates suppressed nonradiative decay. Based on this result, we performed the solid-state emission of six compounds, tuning persisted in PMMA doped films, maintaining full-color region (Fig. 4e, f). Transient fluorescence analyses revealed donor-dependent lifetime modulation, with DPA systems exhibiting about 20-fold longer lifetimes (21.53 ns for Qx-DPA-tBu) versus carbazole analogs (1.09 ns for Qx-CZ) (Table S16).

Cyclic voltammetry (CV) measurements also revealed systematic modulation of frontier orbital energies across the foldamer series. Based on the oxidation curve of cyclic voltammetry (Fig. S72–S77, Table 2), the HOMO energy level of the six foldamers were estimated to be −5.487, −5.335, −4.985, −5.488, −5.316 and −4.961 eV with the equation of E_HOMO = -[E_ox - E_(Fc/Fc+) + 4.8] eV, which agreed with the theoretically calculated E_HOMO. This indicated that the stronger donor (DPA-tBu > CZ-tBu > CZ) resulted in a higher E_HOMO. In addition, the level gap (ΔE_opt) from the UV/Vis absorption spectrum of the six foldamers was also agreed with calculated ΔE_DFT data, and the LUMO energy level were estimated to be −2.547, −2.375, −2.105, −3.018, −2.846 and −2.511 eV with the equation of E_LUMO = E_HOMO + ΔE_opt which indicated that the extended conjugated acceptor (Pz > Qx) resulted in the lower E_LUMO. Based on calculated emission process and optical experiments, it was deduced that ICT emissions of six foldamers arose from S₁ → S₀ deactivation (Tables S19–S30).

Chiroptical properties of foldamers

Having thoroughly characterized the structural and emission properties, we sought to investigate whether the structure induces chiroptical properties, including those in the solid state. As shown in Fig. 6a, b, the circular dichroism (CD) spectra of six enantiomeric pairs in CH₂Cl₂ exhibited mirror-symmetric Cotton effects across their UV-vis absorption regions (230-430 nm), with absorption dissymmetry factors (|g_abs | ) (g_abs = Δε/ε) ranging from 10⁻³ to 10⁻² (Figure. S84), whose trends agreed with the calculated |g_abs|^cal data (Table 3 and Fig. S119). For (P,P)-Qx-CZ-tBu/(M,M)-Qx-CZ-tBu (Fig. 6a), two distinct Cotton effect regions were observed: a short-wavelength region (300-330 nm) attributed to exciton coupling within the stacked aromatic layers arising from π-π transitions, and long-wavelength charge-transfer bands (350-430 nm) corresponding to intramolecular donor-to-acceptor interactions. Furthermore, the CD spectra of all enantiomers in PMMA doped films were consistent with the Cotton effects observed in solution (Figs. S85–S90). These CD signatures validate the chiral character originating from exciton coupling between π-stacked parallel layers. Theoretical simulations (TD-DFT/B3LYP-D3(BJ)/6-311 G) successfully reproduced both the spectral line shapes and Cotton effect polarities (Fig. 6c, d), enabling unambiguous assignment of the chiral HPLC elution order (Fig. S35–S40): peak1 corresponds to (P,P)-configured enantiomers, while peak2 represents (M,M)-configured counterparts.

Fig. 6. CD spectra.

Experimental CD spectra of enantiomers for a Qx foldamers and b Pz foldamers in CH₂Cl₂ (c = 10 µM). The calculated CD spectra of c Qx foldamers and d Pz foldamers in CH₂Cl₂.

Table 3.

Summary of Chiroptical Properties of Qx-CZ, Qx-CZ-tBu, Qx-DPA-tBu, Pz-CZ, Pz-CZ-tBu and Pz-DPA-tBu

	CDa		S0 − S1 transitionb				CPLa	S1 − S0 transitionb
	λ [nm]	|gabs |	|μ | c	|m | d	θ [degree]	|gabs|cal	|glum |	|μ | c	|m | d	θ [degree]	|glum|cal
Qx-CZ	302	7.7 × 10−3	372	1.20	125.3	7.5 × 10−3	<10−3	590	0.78	111.7	2.0 × 10−3
Qx-CZ-tBu	305	16.8 × 10−3	146	0.43	42.7	8.6 × 10−3	2.9 × 10−3	555	0.71	109.0	1.7 × 10−3
Qx-DPA-tBu	298	9.2 × 10−3	175	0.93	83.7	2.3 × 10−3	2.0 × 10−3	161	1.07	74.9	7.0 × 10−3
Pz-CZ	324	4.5 × 10−3	348	0.60	127.4	4.2 × 10−3	<10−3	507	0.48	123.2	2.1 × 10−3
Pz-CZ-tBu	306	4.7 × 10−3	342	0.52	129.3	3.8 × 10−3	3.8 × 10−3	503	0.41	126.9	2.0 × 10−3
Pz-DPA-tBu	304	7.4 × 10−3	81	0.35	50.4	11.0 × 10−3	4.3 × 10−3	75	0.36	65.2	8.1 × 10−3

^aMeasured in CH₂Cl₂ solutions (c = 10 μM). ^bCalculated by TD-DFT at B3LYP-D3(BJ)/6-311 G(d,p) level of theory for MM-enantiomers. ^c | μ | [10⁻²⁰ esu cm]. ^d | m | [10⁻²⁰ erg G⁻¹].

Subsequently, we explored the potential of the foldamers as chiral emitters by measuring their circularly polarized luminescence (CPL) under various conditions. As shown in Fig. 7, the mirror-image CPL spectra of the enantiomers confirmed their chiroptical properties in the excited state. Consistent with the fluorescence emission spectral trends, the CPL spectra of each enantiomer also exhibited wavelength shifts dictated by structural modifications, enabling full-color CPL tunability from blue to red light simply by altering the donor and acceptor units. Under solution conditions, Qx-CZ and Pz-CZ exhibited notably fluctuating CPL signals with reduced intensities compared to the other four compounds, displaying opposite signs for the same configuration, their luminescence dissymmetry factor (|g_lum | ) were all below 10^-3 (Figs. 7a, b and S91-S94). In contrast, Qx-CZ-tBu, Qx-DPA-tBu, Pz-CZ-tBu and Pz-DPA-tBu achieved |g_lum| of 2.9 × 10^-3, 2.0 × 10^-3, 3.8 × 10^-3 and 4.3 × 10^-3, respectively. Based on the formula: g_lum = 2(I_L–I_R)/(I_L + I_R), where I_L and I_R represent the intensities of left and righthanded CPL, precise measurement of I_L and I_R is essential, the low experimental signal-to-noise ratio observed for Qx-CZ and Pz-CZ in CPL measurements may originate from their weak solution-state emission (low PLQY, see Table S17). Consistent with reports suggesting modulation of the CPL sign by controlling ICT emission^74,75, we anticipate that the stronger donor effects of DPA-tBu and CZ-tBu relative to CZ, modulating the overall electronic structure of molecules, correlate with their distinct CPL signs. Indeed, when Qx-CZ and Pz-CZ were dispersed in PMMA doped films (w.t. = 1%) to form solidstate conditions or aggregated in mixed solvents (DMF/H₂O), their CPL signals and g_lum curves became relatively smooth and recognizable, exhibiting aggregation induced CPL enhancement (Figs. 7c, d and S95-S98). Other foldamers with stronger ICT (Qx-CZ-tBu, Qx-DPA-tBu, Pz-CZ-tBu and Pz-DPA-tBu) exhibited notable CPL emission with g_lum values similarly on the order of 10⁻³ in dilute solutions, aggregated states or PMMA doped films (Figs. S91–S98). It is noteworthy that, because the enantiomeric purity of some compounds could not be maintained over extended periods, the experimentally determined g_lum values for the four compounds other than Qx-CZ-tBu and Pz-CZ-tBu (which were perfectly optically pure) are likely underestimated relative to the actual values due to enantiomeric decay reducing the enantiomeric excess.

Fig. 7. CPL spectra.

a, b CPL spectra of the enantiomers of Qx foldamers and Pz foldamers in CH₂Cl₂ (c = 10 µM), λ_ex = 330 nm for Qx-CZ, λ_ex = 335 nm for Qx-CZ-tBu, λ_ex = 350 nm for Qx-DPA-tBu, λ_ex = 345 nm for Pz-CZ, λ_ex = 350 nm for Pz-CZ-tBu and λ_ex = 370 nm for Pz-DPA-tBu. c, d CPL spectra of the enantiomers of Qx foldamers and Pz foldamers in PMMA doped film.

According to theory, the luminescence dissymmetry factor is described as: g_lum = 4 ×|μ|×|m|× cosθ / (μ|²+|m|²), where μ and m are the transition electric dipole moment (TEDM) and transition magnetic dipole moment (TMDM) vectors, respectively, and θ is the angle between μ and m. The TEDM of organic molecules is typically several hundred times larger than the TMDM; therefore, the equation simplifies to g_lum = 4 × cosθ × | m | /|μ | . This simplified equation indicates that the key to obtaining higher g_lum values is the large ratio of |m | /|μ| and a large |cos θ | . To explain the variations in the dissymmetry factors, TD-DFT calculations were performed at the B3LYP/6-31 G level to obtain the |μ | , |m| and θ values for the excited states (S₁ → S₀ transition) of each enantiomeric compound (Fig. 8 and Table 3). As shown in Fig. 8 and Table 3, markedly, the foldamers using diphenylamine as the electron donor exhibit significantly smaller |μ| values (161 × 10⁻²⁰ esu cm for Qx-DPA-tBu and 75 × 10⁻²⁰ esu cm for Pz-DPA-tBu), whereas those employing carbazole as the electron donor all possess |μ| values exceeding 500 × 10⁻²⁰ esu cm. Concurrently, the variations in |m| values across the compounds are relatively minor. Furthermore, while the foldamers with diphenylamine donors display acute θ angles and those with carbazole donors exhibit obtuse θ angles, this difference exerts minimal influence on the |cosθ| values. Consequently, the larger calculated |g_lum|^cal values for Qx-DPA-tBu (7.0×10^-3) and Pz-DPA-tBu (8.1 × 10⁻³) are primarily attributed to their smaller |μ| values. In contrast, the carbazolemodified foldamers achieve |g_lum|^cal values of approximately 2.0 × 10⁻³. Overall, based on experimental and theoretical analysis, the |g_lum| of the foldamers is influenced by both electronic effects and geometries—stronger ICT and greater π-extension are more favorable for enhanced CPL performance.

Fig. 8. Theoretical calculation of the dissymmetry factors.

The transition electric dipole vectors (μ) and magnetic dipole vectors (m) in the S₁ → S₀ transition processes for a Qx-CZ, b Qx-CZ-tBu, c Qx-DPA-tBu, d Pz-CZ, e Pz-CZ-tBu, and f Pz-DPA-tBu. θ is the angle between μ and m.

Conclusions

This study demonstrates a strategy for constructing chiral foldamers with enantiostability through synergistic intramolecular 3D π-networks, advancing stereochemical control driven by π-π interactions. By integrating central cofacial and laterally offset π-stacking modes within a 1,8-diarylnaphthalene scaffold, we designed foldamers with enhanced configurational stability, achieving racemization barriers (ΔG^‡ up to 26.06 kcal mol⁻¹) that exceed conventional atropisomers. Crystallographic and dynamic HPLC analyses reveal that this stability originates from a cooperative triplexπ-stacking network, where face-to-face interactions enforce structural rigidity, while offset donor-acceptor stacking generates torsional asymmetry to lock planar chirality. Peripheral van der Waals interactions and steric enforcement further stabilize the folded architecture. The modular design enables simultaneous control over stereochemical persistence and photoluminescence properties. By tuning donor-acceptor pairs, emission wavelengths are systematically modulated across the broad spectrum (469–684 nm) through intramolecular charge-transfer transitions, while retaining robust circularly polarized luminescence (|g_lum | > 10⁻³) in both solution and solid states. This dual functionality, stereochemical stabilization coupled with emissive tunability, resolves the common compromise between structural rigidity and electronic adaptability in chiral materials. Combined experimental and theoretical analyses establish a design framework that correlates π-stacking geometries (co-facial vs. offset) and energy contributions to stereochemical outcomes. These results not only highlight the importance of orchestrated aromatic interactions in stabilizing functional folds but also pave the way for new applications in chiral photonics, sensing, and advanced material science.

Methods

General characterization methods

400 MHz ¹H and 100 MHz ¹³C spectra were recorded on a Bruker spectrometer. High-resolution mass spectral data were obtained on Mass spectra were recorded on a LCMS-IT-TOF or MALDI-TOF MS. Single-crystal X-ray diffraction data were collected on Bruker APEX-I CCD diffractometer. UV-vis spectra were recorded on a SHIMADZU UV-2600. Steady state and transient fluorescence spectra were recorded on HORIBA Fluorolog-3. Fluorescent quantum efficiencies were determined using a Hamamatsu Quantaurus-QY spectrometer (C11347-11). Particle sizes were recorded on Zetasizer nano ZS90.

Electrochemical and thermogravimetric measurements

Cyclic voltammetry (CV) measurements were carried out on a CHI660E (CH Instruments, USA) in a three-electrode cell in an anhydrous CH₂Cl₂ solution of tetrabutylammonium hexafluorophosphate (n-Bu₄NPF₆, 0.1 M) with a scan rate of 100 mV/s at room temperature. All potentials were further calibrated against ferrocene/ferrocenium (Fc/Fc⁺). Thermogravimetric analysis was performed with a NETZSCH STA 409 PC/PG thermogravimetric analyzer under nitrogen, heating from 30 °C to 800 °C at a rate of 10 °C/min.

HPLC analysis and racemization kinetics

The separation of isomers with chiral configurations was performed by chiral HPLC and Analytical HPLC was performed on a Waters 2695 instrument equipped with a photodiode array detector and CHIRALPAK columns (4.6 mm × 250 mm, 5 μm) from Daicel Chiral Technologies. Column temperature was maintained at 35 °C. The racemization kinetics experiments were carried out at 20 °C.

Preparation of PMMA films

PMMA (20 mg) and enantiomer (0.2 mg) was dissolved in 1 ml of CH₂Cl₂ in a 2 cm diameter culture dish. The resulting mixture is vaporized at room temperature in a well-ventilated environment to obtain a uniform film that can be used to characterize CD and CPL spectra.

CD and CPL measurements

The CD spectra were measured using a Circular Dichroism spectrometer (Chirascan V100). CPL measurements of solutions and PMMA films were performed with a circularly polarized luminescence spectrometer (CPL-300, Jasco). The solution is measured as soon as it was configured to prevent the effects of racemization.

Crystal growth

The single crystals of Rac-Qx-CZ, Rac-Qx-CZ-tBu, and Rac-Pz-CZ were grown by slow diffusion from a solution in CH₂Cl₂ to n-hexane. The single crystals of PP-Qx-CZ-tBu, MM-Qx-CZ-tBu, and Rac-Qx-DPA-tBu were grown by slow diffusion from a solution in CH₂Cl₂ to methanol.

Theoretical Calculations

All of the simulation calculations were carried out with Gaussian 16 program package⁷⁶. The geometry optimization of all molecules in ground state (S₀) at the level of B3LYP-D3(BJ)/6-311 G(d,p) has been evaluated using the density functional theory (DFT) method. The polarizable continuum model (PCM) was used, with dichloromethane as the solvent. The simulated UV-Vis and ECD spectra were performed by time-dependent density functional theory (TD-DFT) calculations at the CAM-B3LYP-D3(BJ)/6-311 G(d,p) level, and the lowest 100 vertical singlet electronic excited states were formulated. The S₁ geometry of all molecules were optimized at the level of CAM-B3LYP-D3(BJ)/6-311 G(d,p) using the TD-DFT method. The electrostatic potential (ESP) surfaces and independent gradient model based on Hirshfeld partition (IGMH)^66,67 were calculated using the Multiwfn⁶⁸ program based on the wavefunction information obtained at the B3LYP-D3(BJ)/6-311 G(d,p) level. The isosurface maps of interaction region indicator (IRI) and Energy Decomposition Analysis (EDA)⁶⁹ were calculated at the (B3LYP/6-31 G*) level of theory. The transition electronic and magnetic dipole moments of all enantiomers were calculated by Multiwfn program. All orbitals and isosurfaces were visualized by Visual Molecular Dynamics (VMD) program⁷⁷. The transition electronic/magnetic dipole vectors of all enantiomers were magnified by a factor of 8 to facilitate observation. The transition electronic/magnetic dipole moments (µ, m) and dissymmetry factors (g) were calculated based on the literature methods^78,79.

Author contributions

All authors have given approval to the final version of the manuscript. †These authors contributed equally, H.H. conducted organic synthesis and performed the characterizations; Q.Z. conducted theoretical calculations. CRediT: H.H. investigation, methodology, visualization, data curation, formal analysis, writing – original draft; Q.Z. software, data curation, writing – original draft; Z.W. data curation; H.L. data curation; J.X. visualization, data curation; Z.W. data curation; W.C. software; J.L. supervision, conceptualization, writing – review & editing, funding acquisition; C.J. supervision, methodology, conceptualization, writing – review & editing, funding acquisition.

Peer review

Peer review information

Communications Chemistry thanks Scott Hartley and the other anonymous reviewer(s) for their contribution to the peer review of this work. A peer review file is available.

Data availability

All the data and methods are present in the main text, the Supplementary Information and Supplementary Data files. The crystallographic data for structures reported in this article have been deposited at the Cambridge Crystallographic Data Centre (CCDC), under deposition number CCDC 2393434 for PP-Qx-CZ-tBu [Supplementary Data 1], CCDC 2393433 for MM-Qx-CZ-tBu [Supplementary Data 2], CCDC 2393430 for Rac-Qx-CZ [Supplementary Data 3], CCDC 2393432 for Rac-Qx-CZ-tBu [Supplementary Data 4], CCDC 2393661 for Rac-Qx-DPA-tBu [Supplementary Data 5], CCDC 2393431 for Rac-Pz-CZ [Supplementary Data 6]. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary Data 7 provides all numerical source data underlying the graphs. Supplementary Data 8 to 13 provide the Cartesian coordinates in the ground state for MM-Qx-CZ, MM-Qx-CZ-tBu, MM-Qx-DPA-tBu, MM-Pz-CZ, MM-Pz-CZ-tBu, and MM-Pz-DPA-tBu, respectively. Comprehensive details on the syntheses, NMR and mass spectrometry characterization, chiral HPLC analysis, crystallographic analysis (including crystallographic tables), determination of racemization barriers, characterization of photophysical properties, electrochemical properties, thermogravimetric analysis, chiroptical properties, and theoretical calculations are provided in the Supplementary Information.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1038/s42004-025-01855-x.