Wide-range tunable circularly polarized luminescence in triphenylamine supramolecular polymers via charge-transfer complexation

Abstract

Circularly polarized luminescence materials with broad color tunability are highly valuable for applications in 3D display and photonic technologies. Here we show that incorporating intermolecular charge-transfer complexation into chiral supramolecular polymers is an efficient strategy to achieve this objective. Adjusting the charge-transfer strength between triphenylamine donors and naphthalenemonoimide acceptors enables tunable circularly polarized luminescence signals across the visible light spectrum. This includes blue-colored emission for the supramolecular donor polymers, as well as green, yellow, orange and red-colored emission for supramolecular donor–acceptor polymers. The donor–acceptor packing modes are further influenced by the presence or absence of acetylene linkages on the triphenylamine donors, resulting in ground- or excited-state charge transfer with varying luminescent lifetimes. Additionally, white-light circularly polarized luminescence is achieved by encapsulating blue- and orange-emitting species into surfactant-based micelles in a compartmentalized manner. Overall, manipulating charge-transfer complexation in supramolecular polymers provides an effective approach to wide-range tunable circularly polarized luminescence materials.

Circularly polarized luminescence materials with broad color tunability are highly valuable for applications in 3D display and photonic technologies. Here, the authors incorporate intermolecular charge-transfer complexation into chiral supramolecular polymers to enable tunable circularly polarized luminescence signals across the visible light spectrum.

Introduction

The practical application of circularly polarized luminescence (CPL) materials in 3D displays and photonic technologies requires broad color tunability spanning the entire visible light spectrum^1–8. Chiral π-aromatic luminophores present promising candidates to attain this objective owing to their well-defined structure, ease of modification, and ability to control multiscale chirality^9–15. A feasible method for adjusting CPL emission colors involves modulating the π-conjugation length of aromatic luminophores^16–21. Alternatively, designing D-π-A chiral luminophores with intramolecular charge-transfer interactions (ICT)^22–25, where D and A represent electron donor and acceptor, respectively, facilitates CPL wavelength variation. However, both approaches require tedious synthetic procedures, thus limiting their practicality. Intermolecular charge-transfer complexation^26–30 offers a viable approach to tackle this challenge. The donor and acceptor molecules interact non-covalently, eliminating the requirement to combine them into a single molecular entity in ICT systems. The emission signal is independent of the optical energy gap of individual compounds but relies on the HOMO–LUMO offset between donor and acceptor molecules. It leads to varying degrees of π-electron transfer, allowing for multi-color emission tunability by modulating the electronic characteristics of the donors or acceptors^31–34.

It is particularly appealing for integrating intermolecular charge-transfer complexes into single-handed nanostructures using the principles of supramolecular chemistry. The overall non-covalent binding strength stems from multiple synergistic processes by systematically incorporating various secondary interactions into charge–transfer complexes. This leads to the formation of long-range-ordered supramolecular polymers through the helical organization of charge-transfer complexes. The transition dipoles of adjacent donor–acceptor pairs couple together in the resulting supramolecular polymers, enhancing the dissymmetry factor for CPL materials^35–37. Additionally, these non-covalent polymers display excellent film-forming capability when drop-cast from solution, eliminating the need for external polymer matrices. Despite these promising prospects, controlling CPL emission behaviors in such supramolecular polymeric systems remains challenging. This is because intermolecular charge-transfer complexation depends not only on the electron-rich or electron-deficient properties of donor–acceptor pairs, but also on the molecular packing mode. Although the latter effect has been extensively investigated in the liquid crystalline or crystalline state^38–40, the dynamic nature of supramolecular systems^41–47 complicates the understanding of the relationship between donor–acceptor packing modes and CPL behaviors.

In this study, we sought to construct wide-range tunable CPL supramolecular systems through intermolecular charge-transfer complexation between triphenylamine donors and naphthalenemonoimide acceptors. Specifically, the triphenylamine compounds (R)−1 and (R)−2 (Fig. 1) form one-dimensional supramolecular homopolymers facilitated by tri-fold hydrogen bonds between adjacent amides. The helical bias of supramolecular polymers is governed by remote chirality transfer^48–52 from the alkyl stereogenic centers on (R)−1 [or (R)−2] to the inner triphenylamine core, leading to the emergence of blue-colored CPL signals. Upon mixing the triphenylamine donors with naphthalenemonoimide acceptor 3 or 4 (Fig. 1), the resulting donor–acceptor complexes display green, yellow, orange, and red-colored CPL at the supramolecular polymeric state. These color variations are achieved through minor structural modifications of the donor or acceptor units to adjust charge-transfer strength^53–55. Subtle structural alterations on the triphenylamine donor led to distinct donor–acceptor arrangements at the supramolecular level. Specifically, (R)-1, containing acetylene linkages, induces ground-state charge transfer⁵⁶ toward the naphthalenemonoimide guests. In comparison, (R)-2, devoid of acetylene linkages, facilitates excited-state charge transfer^57–59 under identical conditions, resulting in a difference in luminescent lifetimes. It is worth noting that since the pioneering work of Liu and Duan in 2019³⁶, several systems, ranging from supramolecular gels to covalently linked macrocycles³⁷, have demonstrated the generation of CPL via donor-to-acceptor charge transfer. However, these studies primarily focus on CPL with a single emission color. The combination of supramolecular donor–acceptor polymerization and intermolecular charge-transfer complexation, as exemplified in the current study, provides an efficient strategy for developing CPL materials with tunable properties across a broad range of emission colors.

Fig. 1. Schematic illustration for wide-range tunable circularly polarized luminescence of supramolecular donor–acceptor polymers via intermolecular charge-transfer complexation.

The chemical structures of the triphenylamine donor compounds (R)-1 or (R)−2, the naphthalenemonoimide acceptor compound 3 or 4, and the model compound 5 are shown in the frame.

Results

Chiral supramolecular polymerization of triphenylamine compound (R)−1

Three enantiopure N-[(1 R)-phenylethyl]benzamides are integrated into the peripheries of triphenylamine in (R)−1, facilitating the bias of single-handed helicity during one-dimensional supramolecular assembly. To investigate the distinction between monomeric and aggregated states, we perform solvent- and temperature-dependent spectroscopic measurements on a 20 μM solution of (R)−1. As widely documented, tetrahydrofuran and chlorinated solvents with high refractive index are benign for the π-conjugated systems in solution, whereas in aliphatic solvents with low refractive index such as methylcyclohexane (MCH) or decane, both hydrogen bonding and π–π stacking would be more favorable. In chloroform or tetrahydrofuran, (R)−1 shows a relatively weak circular dichromic (CD) signal below 300 nm (Supplementary Fig. 6). The enantiomer compound (S)-1 exhibits a mirror-imaged CD signal under the same condition. These CD signals hardly change upon varying the temperature from 293 K to 353 K (Supplementary Fig. 6), thus representing the intrinsic molecular chirality of (R)-1 originating from the (1 R or 1S)-phenylethyl stereogenic centers.

In sharp contrast, the CD signals hugely change in aliphatic solvents such as methylcyclohexane upon varying the temperature. At high temperatures, the chirality signals (Fig. 2a and Supplementary Fig. 6) are similar to those in chloroform or tetrahydrofuran. These phenomena support the dominance of molecularly dissolved species at high temperatures, reflecting the intrinsic molecular chirality signal. Lowering the temperature from 353 K to 293 K induced a hypochromic effect in the π − π* transition of triphenylamine (λ_max = 358 nm, Fig. 2a). The CD spectra simultaneously exhibited a bisignated Cotton signal in the triphenylamine’s absorption region, with a positive maximum at 346 nm (Δε = 92.1 L cm⁻¹ mol⁻¹, g value = 0.0014) and negative one at 378 nm (Δε = –161 L cm⁻¹ mol⁻¹, g value = –0.0029, Fig. 2a). These CD signals reflect the supramolecular chirality signals, denoting remote chirality transfer from the alkyl stereogenic centers to the inner triphenylamine cores. It is worthy to note that the chiral supramolecular arrangement of (R)-1 promotes anisotropic aggregation of triphenylamines with exciton coupling character, leading to amplified supramolecular chirality signals compared to the intrinsic molecular chirality signal.

Fig. 2. Supramolecular polymerization behaviors.

a CD (upper) and UV–Vis (bottom) spectra of (R)−1 and the enantiomer compound (S)-1 (c = 20 μM in MCH). b Normalized cooling curves (α_agg: degree of aggregation) of compounds (R)-1 and (R)−2 (c = 20 μM in MCH), acquired by monitoring the CD intensity changes at 378 nm and 372 nm, respectively. c FT–IR spectra of the N–H stretching vibration of (R)−1 at monomeric state (in chloroform, black line) and supramolecular polymeric state (in MCH, red line).

When transferring the MCH solution of (R)-1 to a quartz plate via spin-coating (thickness: 1.41 ± 0.10 μm, Supplementary Fig. 22), the Cotton effect in the film state retains the same shape as that in solution (Supplementary Fig. 26). It should be mentioned that macroscopic anisotropies may affect the CD profile through linear dichroism (LD) and linear birefringence (LB). Using diffuse reflection circular dichroism spectra (DRCD) with the rotation angle varied from 0° to 360° in 90° steps, the recorded five individual CD profiles show the same CD amplitudes (Supplementary Fig. 27). Additionally, the recorded CD profiles exhibit angular-independent properties. As the rotation angle varies from 0° to 360° in 90° step, the CD signals remain consistent (Supplementary Fig. 26). These results support that the film samples are generally isotropic, with a negligible effect of LD and LB on the CD signals.

Non-sigmoidal melting curves were further obtained by monitoring the temperature-dependent CD intensity changes of (R)-1 in MCH at 378 nm (Fig. 2b and Supplementary Fig. 7), confirming the involvement of a cooperative nucleation-elongation assembly mechanism (Supplementary Eqs. 1–5)^60–62. In a 20 μM MCH solution of (R)-1, the critical elongation temperature (T_e) was determined to be 322.2 K (Fig. 2b). The theoretical number-averaged degree of polymerization was 172 at 298 K (Supplementary Fig. 8), verifying the formation of long-range-ordered supramolecular polymers in MCH. This is reflected in the gelation tendency of (R)-1 in concentrated MCH [critical gelation concentration (CGC): 25.2 mg/mL], involving the entanglement of one-dimensional nanofibers (Supplementary Figs. 9–10).

DFT calculations were performed to elucidate the non-covalent complexation mode in the (R)-1 supramolecular polymers. The optimized geometry of (R)-1 shows twist angles between the benzene rings (37.35°, 32.47° and 31.22°), confirming the propeller-shaped structure of the central triphenylamine unit (Supplementary Fig. 11). Upon supramolecular assembly, the trimeric (R)-1₃ exhibits helical arrangements with a rotation angle of 6.5°. N–H···O bond lengths between neighboring amides range from 1.85 to 1.89 Å (Supplementary Fig. 11), illustrating the primary role of tri-fold intermolecular hydrogen bonds in the non-covalent polymerization process. Simultaneously, the average π–π distance between neighboring triphenylamines in (R)-1₃ is determined to be 3.77 Å (Supplementary Fig. 11). This indicates relatively weak π–π stacking interactions, possibly attributed to the propeller-shaped structure of the triphenylamine units. Loose packing of triphenylamines in supramolecular polymers results in a 1.4-fold enhancement of emission intensity compared to the monomeric state (Supplementary Fig. 12).

Taking advantage of the supramolecular chirality and fluorescent properties, the (R)-1 supramolecular polymers displayed a blue-colored CPL signal (λ_max: 472 nm, g_lum: −7.2 × 10^-3, Φ = 16.2%, Fig. 3a, Supplementary Figs. 19 and 23). Under identical conditions, a mirror-imaged CPL signal was observed for (S)-1 (Fig. 3a). Switching the solvent to chloroform weakened hydrogen bonding interactions, indicated by a shift in N–H stretching vibrations from 3274 cm⁻¹ to 3450 cm⁻¹ in FT–IR spectra (Fig. 2c). Consequently, this led to the absence of CPL signals for (R)-1 or (S)-1 (Supplementary Fig. 13). Accordingly, the chiral supramolecular polymerization driven by tri-fold hydrogen bonds is crucial for the emergence of CPL signals.

Fig. 3. CPL of supramolecular donor–acceptor polymers.

a Normalized CPL spectra of supramolecular donor polymers 1 and supramolecular donor–acceptor polymers 1·3 in the film state upon excitation at 365 nm. b Normalized CPL spectra of supramolecular donor polymers 2, together with supramolecular donor–acceptor polymers 2·3 and 2·4 in in the film state upon excitation at 365 nm. c The CIE coordinates of 1, 2, complexes 1·3, 1·4, 2·3 and 2·4 in supramolecular polymeric films.

CPL of supramolecular donor–acceptor polymers (R)-1·3

The presence of triphenylamines in (R)-1 supramolecular polymers facilitates non-covalent donor–acceptor complexation with the naphthalenemonoimide 3. As an initial step, we employed the model triphenylamine compound 5 (Fig. 1) to investigate charge-transfer behaviors. Compound 5 exhibited a blue-colored emission originating from the triphenylamine π–π* transitions (λ_max: 428 nm, Φ = 13.6%, Supplementary Figs. 15–16), while the naphthalenemonoimide acceptor 3 was almost non-emissive (Supplementary Fig. 15). An equimolar mixture of 5 and 3 resulted in a green-colored emission centered at 540 nm (Supplementary Fig. 16). Simultaneously, the emission lifetimes increased from 0.63 ns for 5 to 28.6 ns for 5 · 3 (Φ = 7.0%, Supplementary Fig. 17 and Supplementary Table 3). Density functional theory (DFT) calculations reveal that the highest occupied molecular orbital (HOMO) of 5 · 3 is entirely localized on the electron-donor 5, whereas the lowest unoccupied molecular orbital (LUMO) is spread across the acceptor 3 (Supplementary Fig. 18). This confirms electron transition from the HOMO of 5 to the LUMO of 3 upon light excitation, giving rise to red-shifted charge transfer emission between the triphenylamine donor and the naphthalenemonoimide acceptor.

Subsequently, we investigated charge-transfer complexation in the supramolecular donor–acceptor polymers (R)-1·3. Mixing equimolar amounts of (R)-1 and 3 resulted in green-colored emission, similar to the model system 5·3 (Supplementary Figs. 19 and 29). The emission lifetime of complex (R)-1·3 was 17.0 ns (Supplementary Fig. 21), shorter than that of 5·3 (28.6 ns, Supplementary Fig. 17 and Supplementary Table 3). The reduction in emission lifetimes can be primarily attributed to two reasons. Firstly, the peripheral alkyl chains on (R)-1 may enhance molecular vibration, thereby increasing the non-radiative decay rate. Secondly, the amides on (R)-1 form intermolecular hydrogen bonds, resulting in significant hindrance to triphenylamine-naphthalenemonoimide complexation. Consequently, a staggered packing mode was observed for (R)-1·3 (vide infra, Fig. 4e), which was distinct from the face-to-face packing in the model system 5·3 (Supplementary Fig. 18).

Fig. 4. Characterization of ground- and excited-state supramolecular charge-transfer polymers.

a Normalized fluorescence of the (R)-1·3 supramolecular polymeric films with the gradual increase of 3 molar ratios from 0% (blue line) to 100% (green line) (λ_ex = 365 nm). b Normalized fluorescent intensity of the (R)−2·3 supramolecular polymeric films with the gradual increase of 3 molar percentage from 0% (blue line) to 100% (orange line) (λ_ex = 365 nm). c Normalized excitation spectra of donors [(R)−1, (R)−2], acceptors (3, 4) and their CT complexes [(R)−1·3, (R)−2·3] in films, which were recorded at the maximum wavelength of their emission peaks, respectively. d Emission lifetime decay profiles of (R)−1·3 and (R)−2·3 excited at 365 nm. The tested wavelengths of (R)−1·3 and (R)−2·3 were 525 nm and 577 nm, respectively. e Top view of the geometry-optimized donor–acceptor–donor trimeric structures (R)−1·3 and (R)−2·3 based on dispersion-corrected PM6-D3H4 semi-empirical calculations via MOPAC software.

Green-colored CPL signals emerged for the supramolecular donor–acceptor polymers (R)-1·3 in the film state (λ_max: 538 nm, g_lum: –3.6 × 10^–3, Φ = 8.0%, Fig. 3a and Supplementary Fig. 24). As expected, (S)-1·3 displayed a mirror-imaged CPL signal (Fig. 3a and Supplementary Fig. 14). Although the direction of the CPL signals coincides, the binary complex (R)-1·3 [or (S)-1·3] displayed red-shifted signals compared to the individual species (R)-1 [or (S)-1], due to chirality transfer from stereoisomeric methyl units to the donor–acceptor charge-transfer complex at the supramolecular level. Rotation-dependent spectroscopic measurements of the (R)-1·3 [or (S)-1·3] film revealed consistent CPL characteristics (ϕ = 0°, 90°, 180°, 270°, and 360° with respect to the direction of excitation light, Supplementary Fig. 25). These findings eliminate artifacts resulting from macroscopic alignments, supporting the origin of CPL from intermolecular charge-transfer complexation.

It should be noted that the fluorescence quantum yield of supramolecular donor–acceptor polymers (R)-1·3 is relatively lower than that of the supramolecular homopolymers (R)-1 (8.0% versus 16.2%, Supplementary Table 3). This difference can be attributed to the energy-gap law, which states that non-radiative transitions increase as the energy gap decreases. As the luminous wavelength red-shifts, the vibrational coupling (non-radiative transition) between the zero vibrational level of the singlet state (ν₀) and the high vibrational level of the ground state is significantly enhanced, leading to lower fluorescence quantum yields for red-shifted luminophores. Nonetheless, the non-covalent packing of charge-transfer complexes in supramolecular polymers induces a rigidifying effect that reduces non-radiative processes. As a result of the delicate balance between these two factors, supramolecular donor–acceptor polymers (R)-1·3 still exhibit moderate emission and CPL intensities (Supplementary Fig. 19).

Wide-range tunable CPL upon varying the donor or acceptor structures

Furthermore, we aimed to modulate the CPL colors by varying the structure of either the triphenylamine donor or the naphthalenemonoimide acceptor. The donor compound (R)−2 exhibited a shortened π-conjugated structure compared to (R)−1 due to the removal of acetylene linkages. (R)-2 also tends to form single-handed supramolecular polymers in MCH (Supplementary Figs. 30–36). Significantly, (R)-2 exhibits higher thermo-stability than (R)−1 under identical conditions (T_e: 330.9 K versus 322.2 K at 293 K, Fig. 2b and Supplementary Fig. 32). It also exhibits a stronger gelation tendency (CGC: 20.6 mg/mL versus 25.2 mg/mL in MCH, Supplementary Fig. 35). We attribute these phenomena to the different twisting of the triphenylamine cores. According to DFT calculations, the rotation angles increase from 6.5° in the trimeric species (R)−1₃ to 11.9° in (R)-2₃, resulting in strengthened hydrogen bonding for the latter species (intermolecular N–H···O distances of adjacent amides: 1.85–1.89 Å in (R)−1₃ versus 1.82–1.86 Å in (R)−2₃, Supplementary Figs. 11 and 37). This finding aligns with the Gibbs free energy changes observed in the supramolecular polymerization process, indicating that (R)-2 is 2.3 kJ mol⁻¹ higher in energy compared to (R)−1 (–38.2 kJ mol⁻¹ versus –35.9 kJ mol⁻¹ at 298 K, Supplementary Figs. 7 and 32).

Supramolecular homopolymers of (R)-2 displayed blue-colored CPL at 453 nm (|g_lum | : 9.4 × 10^-3, τ: 2.07 ns, Φ = 14.1%, Fig. 3b, Supplementary Figs. 39 and 46). Non-covalent donor−acceptor polymerization takes place upon mixing compounds (R)-2 and 3, resulting in an orange-colored CPL signal centered at 558 nm (|g_lum | : 5.6 × 10^-3, τ: 62.6 ns, Φ = 5.9%, Fig. 3b, Supplementary Figs. 40 and 46). Although (R)-2 exhibited a 20 nm hypsochromic CPL emission signal compared to (R)−1 due to shortened π-conjugation, (R)-2 · 3 displayed a red-shifted CPL compared to (R)−1 · 3. DFT calculations (Supplementary Fig. 42) were employed to clarify the phenomena, revealing a significant increase in the HOMO energy level from –4.88 eV for (R)−1 · 3 to –4.78 eV for (R)-2 · 3. In the meantime, the LUMO energy level showed only a 0.02 eV increase. Thus, the red-shifted CPL of (R)-2 · 3 can be attributed to the elevation of the HOMO levels of the triphenylamine donor.

Besides, we investigated the impact of the naphthalenemonoimide acceptor structure (3 versus 4) on the circularly polarized luminescent colors. Regarding complex (R)-2·4, the CPL signals are bathochromic-shifted by 62 nm compared to that of (R)-2·3 under identical conditions, giving rise to a red-colored CPL signal centered at 620 nm (|g_lum | : 8.8 × 10⁻³, τ: 32.1 ns, Φ = 1.3%, Fig. 3b, Supplementary Figs. 43 and 46). Theoretical calculations (Supplementary Fig. 44) revealed comparable HOMO energy levels between (R)-2·4 and (R)-2 · 3 (–4.81 eV versus –4.78 eV), with a significant change in LUMO energy levels decreasing from –2.24 eV for the former complex to –2.44 eV for the latter one. This implies that the incorporation of bromine into the naphthalenemonoimide acceptor reduces molecular energy levels for 4, resulting in a diminished HOMO–LUMO bandgap for 2 · 4.

Overall, the triphenylamine donors (R)−1 and (R)-2 emit blue light at the supramolecular homopolymeric state. The charge-transfer complexes between triphenylamine and naphthalenemonoimide result in red-shifted circularly polarized luminescence, with the direction depending on the triphenylamine donor. Modifying the acetylene linkages on the triphenylamine donor to adjust the HOMO energy levels, together with attaching bromide to the naphthalenemonoimide acceptor to alter the LUMO energy levels, provides supramolecular donor–acceptor polymers displaying green, yellow, orange, and red circularly polarized luminescence signals for complexes 1·3, 1·4, 2·3, and 2·4, respectively (Fig. 3c, Supplementary Fig. 29 and Supplementary Figs. 45–46). Taken together, the current supramolecular polymeric systems provide a feasible way for achieving a broad spectrum of CPL spanning the entire visible light spectrum.

Ground- versus excited-state charge-transfer luminescence in supramolecular donor–acceptor polymers

Deeper insights into the luminescent properties were attained by adjusting the molar ratio between the triphenylamine donor and naphthalenemonoimide acceptor. For complex (R)−1·3, the emission signal of the resulting supramolecular polymeric films gradually red-shifted as the molar ratio of 3 to (R)−1 increased (from 0 to 100 mol%, Fig. 4a). In contrast, for (R)-2·3, the emission signals of (R)-2 showed an immediate decrease in intensity as the amount of 3 increased, accompanied by an enhancement of the low-energy emission centered at 572 nm (Fig. 4b). To further elucidate the origin of these distinctions, we investigated excitation spectra of prepared supramolecular polymeric films. In particular, with the addition of acceptor 3, the excitation spectrum of the (R)−1·3 complex exhibited a prominent red-shifted charge-transfer band compared to the donor (R)-1 alone (Fig. 4c), while the excitation spectra of (R)−2 and (R)-2·3 are generally identical (Fig. 4c). These variations were also observed in the absorption spectra (Supplementary Figs. 49–50). According to previous reports, the former phenomenon can be attributed to the charge-transfer interaction in the ground state, while the latter is associated with excited-state charge-transfer emission, known as an exciplex^{28,36,63–65}. Fluorescence lifetime measurements confirm this conclusion, showing a 3.7 times longer average lifetime for (R)-2·3 compared to (R)−1·3 (τ: 62.6 ns versus 17.0 ns, Fig. 4d). This phenomenon is attributed to the migration of excitons within the exciplex species, leading to an extended relaxation time of the excited state. Similarly prolonged emission lifetimes were observed in (R)-2·4 compared to (R)−1·4 (τ: 32.1 ns versus 4.28 ns, Supplementary Figs. 21 and 41).

The results underscore the significant impact of the donor’s acetylene linkages on the charge-transfer luminescent signals. This discrepancy arises from distinct donor–acceptor packing modes, as elucidated by DFT calculations on the donor–acceptor–donor trimeric structures of (R)−1·3 and (R)-2·3. In the optimized structure of (R)−1·3, acceptor 3 is arranged in a face-to-face stacking configuration with the diphenylacetylene moiety on (R)-1 (Fig. 4e and Supplementary Fig. 47), with an average donor–acceptor π-distance of 3.35 Å. The proximity between donor and acceptor molecules facilitates charge transfer interactions in the ground state. In contrast, 3 does not engage in face-to-face stacking in the (R)−2·3 trimer. Instead, it is positioned outside the stacking structure of (R)-2, maintaining non-covalent complexation through CH···π interactions (2.46–2.69 Å, Fig. 4e and Supplementary Fig. 48). The increased distance between the donor and acceptor in (R)-2·3 promotes exciplex formation over ground state charge transfer upon photo-excitation.

In addition to the ground-state structures, we have further calculated the optimized structures of (R)−1·3 and (R)-2·3 in the excited state (Supplementary Figs. 47–48). For (R)−1·3, the optimized excited-state structure is similar to its ground-state configuration. Although the average donor-acceptor π-distance slightly increases in the excited state compared to the ground state (3.36–3.52 Å versus 3.36–3.46 Å), this distance remains sufficient to facilitate charge-transfer interactions. In comparison, for (R)-2·3, the CH···π distance between 3 and (R)-2 decreases in the excited state compared to the ground state (2.55–2.69 Å versus 2.35–2.63 Å), yet 3 remains positioned outside the (R)-2 stacking structure (Supplementary Fig. 48). These phenomena are primarily attributed to the tighter packing of triphenylamines in (R)-2 compared to (R)−1 in the supramolecular polymeric state.

Time-dependent density functional theory (TD-DFT) calculations provided further evidence to support this conclusion. Similar to the model complex 5·3, the HOMO of (R)−1·3 is localized on the triphenylamine donor, while the LUMO is situated on the naphthalenemonoimide acceptor 3. The HOMO → LUMO transition of (R)-1·3 constituted 97.2% of the S₀ to S₁ transition. Conversely, the oscillator strength for the S₀ to S₁ transition of (R)−2·3 is significantly lower than that of (R)−1·3 (f: 0.0073 versus 0.0534, Supplementary Tables 1 and 2). As a result, (R)-2·3 exhibited weaker charge-transfer interactions in the ground state compared to (R)-1·3. Therefore, subtle structural alterations in the triphenylamine donor not only affect the CPL wavelength, but also regulate the CPL lifetimes for supramolecular donor–acceptor polymers through ground- versus excited-state charge transfer.

White-light CPL induced by compartmentalization

Given the broad tunability of circularly polarized emission in supramolecular donor–acceptor polymers, we sought to produce white-light CPL by adjusting the ratio of emissive species. Typically, white light emission comprises at least two complementary colors—blue and orange—without interfering with each other^66–68. In our supramolecular polymeric systems, high-energy blue emission originates from the triphenylamine donor, while low-energy emission arises from donor–acceptor charge-transfer complexation. Unfortunately, direct mixing of the blue-emitting species (R)-2 and the orange-emitting species (R)-2·3 in the film state did not yield white-light emission, because of the susceptibility of charge-transfer luminescence to donor–acceptor stoichiometries (vide supra, Fig. 4b and Supplementary Fig. 52).

We developed a compartmentalization^69,70 strategy to address this challenge (Fig. 5a). Specifically, 100 μL of tetrahydrofuran solutions containing the blue-emitting species (R)-2 and the orange-emitting species (R)-2·3 (c = 2.00 mM) were separately injected into a 5 mL aqueous solution of cetyl trimethyl ammonium bromide (CTAB) surfactant (c_CTAB = 1.00 mM). Each species underwent ultrasonication for 2 hours, followed by overnight stirring at 353 K to evaporate the organic solvent, resulting in the formation of spherical micelles (Supplementary Fig. 51). When (R)-2 and (R)-2·3 aqueous solutions were mixed together in various ratios, the emission signals of both (R)-2 at 413 nm and (R)-2·3 at 563 nm remained largely constant, despite fluctuations in the emission intensity ratios (Supplementary Figs. 53–54). Notably, white-light emission was produced at a mixture ratio of (R)-2: (R)-2·3 = 1: 1, resulting in a CIE coordinate at (0.32, 0.32) (Fig. 5b and Supplementary Fig. 53). Furthermore, (R)-2 /(R)-2·3 and (S)-2/(S)-2·3 encapsulated in CTAB exhibited mirror-imaged white-light CPL signals (|g_lum | : 4.2 × 10⁻³, Fig. 5c). These findings emphasize the crucial role of CTAB compartmentalization in achieving white-light CPL materials for charge-transfer luminescent species.

Fig. 5. Compartmentalization-induce white-light CPL.

a Schematic illustration of preparing white-light CPL via CTAB compartmentalization. The photograph shows white light luminescence of (R)−2/(R)−2·3 encapsulated in CTAB [λ_ex = 365 nm, (R)−2: (R)−2·3 = 1: 1]. b CIE coordinates of (R)−2/(R)−2·3 aqueous solutions encapsulated in CTAB upon varying the ratio of (R)−2·3 from 0 to 100 mol% (orange line). c Mirror-imaged CPL of white-light emissive (R)−2/(R)−2·3 (solid line) and (S)−2/(S)−2·3 (dotted line) aqueous solutions encapsulated in CTAB (λ_ex = 365 nm).

Discussion

In summary, we have successfully developed triphenylamine supramolecular polymers with intermolecular charge-transfer complexation towards naphthalenemonoimide acceptors. Subtle structural modifications to the triphenylamine donors or naphthalenemonoimide acceptors lead to varying charge-transfer strengths, allowing for tunable CPL signals across the visible light spectrum. This encompasses blue-colored CPL for supramolecular donor polymers (R)−1 or (R)-2, as well as green, yellow, orange and red-colored CPL for supramolecular donor–acceptor polymers (R)−1·3, (R)−1·4, (R)-2·3, and (R)-2·4, respectively. The donor–acceptor packing modes are influenced by the presence or absence of acetylene linkages on the triphenylamine donors, resulting in ground-state charge transfer for (R)−1·3 [or (R)−1·4] versus excited-state charge transfer for (R)−2·3 [or (R)-2·4]. Moreover, white-light CPL is attained by encapsulating the blue-emissive species (R)-2 and the orange-emissive species (R)-2·3 into CTAB surfactants in a compartmentalized manner. Overall, this study highlights how manipulating charge-transfer complexation in supramolecular donor–acceptor polymers provide an efficient approach to CPL materials with tunable emission properties.

Methods

Measurements

¹H NMR spectra were collected on a Bruker AscendTM 400 MHz spectrometer with TMS as the internal standard. ¹³C NMR spectra were recorded on a Bruker AscendTM 400 MHz spectrometer at 101 MHz. High-resolution mass spectrometer (MS) data were obtained by LTQ-Orbitrap XL from Thermo-Fisher. MALDI‒TOF measurements were recorded on a Bruker Autoflex Speed spectrometer with DCTB as the matrix. UV–Vis spectra were recorded on a UV−1800 Shimadzu spectrometer. Circular dichroism (CD) measurements were performed on a Jasco J−1500 circular dichroism spectrometer, equipped with a PFD-425S/15 Peltier-type temperature controller. Circular polarized luminescence (CPL) measurements were performed on a Jasco CPL-300 circularly polarized luminescence spectrophotometer. Steady-state emission spectra were recorded on FS5 spectrofluorometer from Edinburg Instruments. Emission lifetime studies were conducted with Fluorolog-3-Tau and Deltaflex (Horiba Scientific) with a semiconductor laser as the excitation source. Fourier transform-infrared (FT-IR) spectra were collected using a Nicolet 6700 FT-IR spectrometer. Atomic force microscope (AFM) measurements (tapping mode) were performed using a Bruker Dimension Icon with ScanAsyst system in air with silica cantilevers (RFESPA-75, Ohm-cm Antimony (n) doped Si) and a resonance frequency of ~ 75 kHz and a spring constant of ~ 3 N m⁻¹. The images were analyzed using the Pico Image processing program. Scanning electron microscope (SEM) measurements were performed using FEI Quanta FEG 250 Scanning Electron Microscope.

Theoretical calculations

Optimization of the structures were performed using the semi-empirical PM6-D3H4 method as implemented in the MOPAC package. Dispersion interactions were considered and all calculations were carried out in vacuum. The reliability of the optimized structures was checked via frequency calculations based on density functional theory (DFT, Gaussian 09 W B.01 software package). There are no imagery frequencies for the optimized geometries. The long side chains were substituted by H atoms to make the calculation feasible. The DFT functional ωB97XD was used, together with the basis set 6-31 G(d) was adopted. The molecular orbitals were visualized using the Gauss View 6.0 software. Time-dependent density functional theory (TD-DFT) calculations were performed at the same computational level without adding a solvation model.

Author contributions

F.W. and R.L. conceived the idea for this project. Y.G. performed the experiments, analyzed the data, and produced the artwork under the direction of F.W. J. M. performed the DSC and DRCD experiments. Y.Z. and R.L. contributed to the theoretical calculations. All authors contributed to the manuscript.

Peer review

Peer review information

Nature Communications thanks Subi George and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. A peer review file is available.

Data availability

The coordinates of optimized geometries are available in a separate Excel file as source data. All other data generated in this study, including experimental and synthetic procedures, compound characterization, theoretical calculations, UV-Vis, emission, emission lifetime, CD, CPL, NMR, FT-IR, MALDI-TOF and AFM analyses, are available within the article and its Supplementary Information or from the corresponding authors. Source data are provided with this paper.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1038/s41467-024-53297-z.