Conductive behavior of cross-linked electropolymeric films formed by ‘star-shaped’ multifunctional precursors

Abstract

Electropolymeric films must simultaneously achieve high planarity and high conductivity to fully realize the advantages of their superior processing techniques for a wide range of semiconductor applications. In the promising electrodeposition organic light-emitting diode (OLED) technology, the primary hole transport layer, 4,4′,4′′-tri(N-carbazolyl)triphenylamine (TCTA) electropolymeric films, exhibits high planarity but hole mobility of 0.38 × 10⁻⁷  cm²  V⁻¹ s⁻¹, which constrains device brightness and efficiency. Investigations into the electrochemical, spectroelectrochemical, and electrical properties reveal that TCTA electropolymeric film consists of a crosslinked network formed by twisted, non-conjugated linkages between conjugated oligomer segments, rather than a long-range conjugated conductive polymer. TCTA represents a class of “star-shaped” multifunctional electropolymeric precursors, with the electropolymeric groups serving as the primary charge-transporting units. The twisted configurations of these electro-crosslinked polymers significantly impede carrier transport, despite the films' high planarity. However, these structures confer substantial electrochemical activity. For example, TCTA electropolymerized films exhibit a high specific capacitance of 349.8 F cm⁻³@15.2 A cm⁻³ and a high specific capacity of 19.4 mA h cm⁻³@15.2 A cm⁻³. Accordingly, such materials are not well-suited for use as functional layers in electrodeposited organic semiconductors, but may offer promise for applications in electrochemically active systems.

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Introduction

The unique processing method and inherent properties of electropolymeric films enable a wide range of potential applications. Among their key features, redox reversibility and conductivity are particularly important. Excellent redox reversibility, for instance, supports their use in energy storage,^1–3 electrochromism,^4,5 and electrochemical transistors.^6,7 To fully capitalize on the advantages of this processing method for broader semiconductor applications, the films must achieve both high charge transport capability and high planarity. Our group has developed expertise in fabricating organic light-emitting diodes (OLEDs) through electropolymerization techniques.⁸ By actively controlling the applied electrical signals, precursor polymerization is initiated, leading to the directional deposition of organic semiconductor films onto patterned electrodes. This mask-free, actively addressed deposition technique offers significant promise for the low-cost production of ultra-high-resolution OLEDs and holds promise for high-end applications, such as virtual reality and augmented reality, where extremely high resolution is required.^9–13

Although OLEDs with resolutions up to 2800 ppi have been successfully fabricated using electrodeposition, their brightness remains significantly below the levels required for practical applications.¹⁴ One major contributing factor is the inadequate optimization of the device structure. However, the creation of high-performance, highly planar interfacial layers that can effectively support the electrodeposition of emissive films remains a key challenge. Advancing this technology requires continued exploration and development of new interfacial materials tailored for electrodeposition. Currently, the most widely used interfacial layer is only the electropolymeric film of 4,4′,4′′-tri(N-carbazolyl)triphenylamine (TCTA, the chemical structure as shown in Fig. 1a).

Fig. 1 (a) Chemical structure of TCTA. (b) Schematic diagram of electrochemical dimerization of carbazoles.

The electrochemical properties of TCTA have been previously reported.¹⁵ Notably, the fabrication of high-planarity TCTA electropolymeric films and their application as hole transport layers in OLEDs have been explored.^14,16 In this study, we focus on the electrical characteristics of TCTA electropolymeric films. The measured hole mobility is 0.38 × 10⁻⁷  cm²  V⁻¹ s⁻¹, lower than that of vapor-deposited TCTA films (0.9 × 10⁻⁵ cm² V⁻¹ s⁻¹).¹⁷ The analysis of the electrochemical, spectroelectrochemical and electrical properties reveals that the aggregated structure of the TCTA crosslinked polymers inevitably includes large twisted conformations. These distortions disrupt the polymer's long-range conjugation and result in reduced film density compared to vapor-deposited films, leading to suboptimal electrical properties. Furthermore, the monovalent conjugated segments in the crosslinked films exhibit significantly enhanced charge transport capabilities compared to the multi-valent species. Ultimately, it is concluded that these electropolymeric films are unsuitable as charge transport layers. However, these conformations also confer substantial electrochemical activity on TCTA electropolymerized films, showcasing advantages in applications such as capacitors, characterized by a high specific capacitance of 349.8 F cm⁻³@15.2 A cm⁻³ and a high specific capacity of 19.4 mA h cm⁻³@15.2 A cm⁻³. For “star-shaped” multifunctional conjugated precursors such as TCTA, the functional groups that participate in electropolymerization also play a key role in facilitating charge transport. While the resulting twisted conformations impair charge transport, they concurrently facilitate the formation of ion-accessible channels that promote electrochemical doping.

Experimental

Materials

TCTA (99%) was purchased from Xi’an Yuri Solar Co., Ltd. Anhydrous acetonitrile (ACN) and dichloromethane (DCM) were purchased from J&K Scientific. Anhydrous propylene carbonate (PC) and tetrabutylammonium (TBAPF₆) were purchased from Energy Chemical. TBAPF₆ was recrystallized three times from ethanol and then dried at 120 °C for 24 hours before use. Glassy carbon, titanium, and platinum electrodes were purchased from Tianjin Aida Hengsheng Technology Development Co., Ltd. Indium tin oxide (ITO) coated glass slides with a thickness of 135 nm and sheet resistance of 15 Ω were obtained from South China Xiangcheng Technology Co., Ltd. Carbon paper was purchased from Thermo Fisher Scientific. PBFDO was purchased from Volt-Amp Optoelectronics Tech. Co., Ltd. The RE-7 non-aqueous reference electrode (Ag/Ag⁺ type) was purchased from ALS Co., Ltd, with the internal reference solution composed of 0.01 M AgNO₃ and 0.1 M TBAPF₆ in ACN.

Electrochemical experiments

All electrochemical experiments were conducted under a nitrogen atmosphere. A three-electrode system was employed with a CHI760E or Swiss Metrohm electrochemical workstation. For basic electrochemical measurements and analysis of TCTA, a glassy carbon electrode was used as the working electrode, a platinum wire electrode as the counter electrode, and Ag/Ag⁺ as the reference electrode. For the preparation of p-TCTA films for optical, electrical, and other measurements, ITO was employed as the working electrode, a titanium plate as the counter electrode, and Ag/Ag⁺ as the reference electrode. The polarographic potential-current convention was used, with oxidation currents defined as negative and reduction currents as positive. A mixed solvent of DCM, ACN, and PC (V/V/V = 2.5/0.6/1.9) was used, with TBAPF₆ as the supporting electrolyte to prepare a 0.1 M electrolyte solution. The reference electrode was calibrated with ferrocene prior to each electrochemical experiment. All potentials in this study are referenced to ferrocene. During electropolymerization, 0.4 × 10⁻³ M TCTA was added to the electrolyte solution. The potential range was from −0.8 to 1.07 V, with a scan rate of 0.3 V s⁻¹ and 30 cycles. Unless otherwise stated, all electropolymerization experiments for preparing p-TCTA films were conducted under these conditions. After electropolymerization, the p-TCTA films were washed three times with DCM and ACN to remove supporting electrolytes and unreacted precursors, followed by annealing at 100 °C for 60 minutes under a nitrogen atmosphere.

Device fabrication

Devices were fabricated using resistance evaporation coating equipment from Beijing Technol Science Co., Ltd. MoO₃ and Al were evaporated at a rate of 0.5 Å s⁻¹ and 0.7 Å s⁻¹, respectively, to deposit 10 nm and 100 nm films under a pressure of less than 2 × 10⁻⁵ Pa. The effective area of the devices is 0.05 cm². Current–voltage (J–V) curves were recorded using a Keithley 2450 source meter. Both device fabrication and measurements were carried out in a nitrogen atmosphere.

Characterization

Scanning electron microscopy was performed using a Hitachi Regulus 8100 with an accelerating voltage of 15 kV and a working distance of 11.8 mm. The thickness of the p-TCTA films was measured using a Bruker Dektak profilometer. The refractive index of the films was measured using a Mueller matrix ellipsometer from Wuhan Eoptics Technology Co., Ltd. In situ UV-Vis spectra were recorded on an Ocean Optics QE65000 spectrometer while in situ NIR spectra were collected using an AvaSpec XPNIR-512-2.5 spectrometer. The surface morphology of the samples was characterized using an atomic force microscope, Bruker Multimode 8 model from Bruker, Germany.

Results and discussion

Our investigation begins with the electropolymerization of TCTA and the electrochemical properties of its resulting films. For applications in organic semiconductor devices, a key consideration in selecting the electropolymerization conditions for TCTA is minimizing the surface roughness of the films while preserving their intrinsic physical and chemical properties. The optimization of these conditions has been thoroughly addressed in previous studies.¹⁶ Here, we follow the previously established protocol to fabricate highly planar polymer films on glassy carbon and ITO electrodes, achieving a root-mean-square roughness of less than 10 nm (see Fig. S1 and S3, ESI†).

The cyclic voltammogram (CV) for TCTA electropolymerization, shown in Fig. 2a, begins at an oxidation potential of 0.36 V and displays multiple distinct redox signals. With increasing numbers of voltammetric cycles, the current response intensifies, indicative of the deposition and sustained growth of the polymer p-TCTA on the electrode surface. CV experiments conducted over various potential scanning ranges (Fig. S2, ESI†) reveal that polymer formation and deposition occur only when the applied potential exceeds 1.0 V. Potential step and variable scan rate CV experiments (Fig. S4, ESI†) conclusively demonstrate that the first pair of redox peaks (0.51 V and 0.44 V) correspond to a thermodynamically reversible single-electron oxidation process, in which TCTA is oxidized to its monovalent cation. Furthermore, specialized voltammetry experiments (Fig. S5, ESI†) confirm that the second pair of redox peaks (0.81 V and 0.74 V) also represents a reversible single-electron oxidation process, whereby the monovalent cation is oxidized to its divalent form. Collectively, these findings reveal that TCTA, considered a unique oligomer, undergoes oxidative coupling (Fig. 1b) after losing three electrons, consistent with prior reports in the literature.¹⁵

Fig. 2 (a) CV curves for TCTA during electropolymerization. (b) CV curve for a p-TCTA film in monomer-free electrolytes, conducted at a scan rate of 50 mV s⁻¹.

The CV curve of p-TCTA films (Fig. 2b), measured in the monomer-free electrolyte, exhibits a broad redox plateau, with redox peaks corresponding to those observed during electropolymerization. The initial oxidation potential of p-TCTA is 0.36 V, from which the highest occupied molecular orbital (HOMO) level was estimated to be −5.16 eV (E_HOMO = −(4.8 + E_ox) eV). The lowest unoccupied molecular orbital (LUMO) level was estimated to be −1.78 eV, based on the optical bandgap (Fig. S6, ESI†). Analysis of the CV curves at various scan rates (Fig. S7, ESI†) shows that the peak currents of the redox peaks scale linearly with the scan rates, indicating that the charge transfer in the p-TCTA films is governed by the inherent redox characteristics of the film rather than by the transport of doping ions. These results indicate that the doping level in p-TCTA films can be precisely modulated by tuning the applied oxidation potential, providing a basis for subsequent investigations into the conductivity of p-TCTA under different doping conditions.

Following the investigation of TCTA's fundamental electrochemical properties, attention was turned to the charge transport characteristics of p-TCTA films. Due to the directional deposition of electropolymeric films onto conductive substrates, and their inability to be detached or transferred, conventional methods like field-effect transistors or Hall effect measurements are not applicable for evaluating the carrier mobility of p-TCTA. Consequently, the Mott–Gurney space charge limited current (SCLC) method was employed to determine the hole mobility of p-TCTA films, enabling a qualitative comparison between electrodeposited films and those prepared via vacuum evaporation.^18–21 The single-hole device structure consisted of ITO/PEDOT:PSS (40 nm)/p-TCTA (31 nm)/MoO₃ (10 nm)/Al (100 nm). In this configuration, PEDOT:PSS provides ohmic contact for effective hole injection at the anode, while the high work-function of Al and MoO₃ provides sufficient electron-blocking capability at the cathode.^22–25 The J–V characteristics of the device, shown in Fig. 3a, span a voltage range from −2 to 8 V. Fitting analysis reveals three distinct conductivity phases: n = 1.17 corresponds to the ohmic regime, 3.2 to the trap-filling SCLC regime, and 2.2 to the trap-free SCLC regime. According to the SCLC model:

where J is the current density, μ is the hole mobility, ε₀ is the vacuum permittivity (8.85 × 10⁻¹⁴ C V⁻¹ cm⁻¹), ε_r is the relative permittivity of the semiconductor, typically assumed to be around 3 for organic semiconductors, V is the applied voltage, and d is the film thickness of the active layer.

Fig. 3 Double logarithmic plot of the J–V curve for a hole-only device using (a) p-TCTA film and (b) TCTA vapor-deposited film. TCTA electropolymerization on ITO/PEDOT:PSS and details of the SCLC fitting are shown in Fig. S12 (ESI†). (c) J–V curves for p-TCTA films at various doping levels. (d) Conductivity and carrier mobility of p-TCTA films at different doping levels.

The hole mobility of p-TCTA films was extracted from the J^1/2–V characteristics (n = 2.2) of a single-hole device, yielding a value of 0.38 × 10⁻⁷ cm² V⁻¹ s⁻¹. In contrast, using the same device structure (Fig. 3b), the mobility of vacuum-deposited TCTA films was determined at 0.9 × 10⁻⁵ cm² V⁻¹ s⁻¹. Moreover, the J–V curves show that the electrodeposited film exhibits an additional trap-filling regime that is absent in the evaporated counterpart, implying a higher defect density in the electrodeposited TCTA film.²⁶

Similarly, techniques such as four-point probing or in situ conductivity measurements are not applicable for determining the conductivity of p-TCTA films at various levels of electrochemical doping. To qualitatively assess film conductivity, a sandwich structure (ITO/p-TCTA (doped, 61 nm)/Al (100 nm)) was employed.²⁷ The doping level of p-TCTA was modulated by varying the applied doping potential. Assuming that all electrochemically introduced charges function as carriers, the carrier mobility at different doping levels can be estimated in order-of-magnitude terms (as detailed in Section S4.2, ESI†). The electrical properties of doped p-TCTA films, as shown in Fig. 3c and d, reveal a conductivity below 10⁻⁵ S cm⁻¹ under approximate measurements. Consequently, TCTA electropolymeric films are found to be unsuitable as hole transport or injection layers.

The doping-induced spectral properties of p-TCTA were investigated to elucidate its structural characteristics and to identify the underlying factors limiting its charge transport capacity. Spectroelectrochemical experiments were carried out in a monomer-free electrolyte using an ITO substrate coated with a p-TCTA film as the working electrode. Potentials were applied via CV at a low scan rate of 5 mV s⁻¹ to ensure that the recorded spectra represented a quasi-steady state for each set potential. The differential spectra between the ionic and neutral states of p-TCTA at various potentials are shown in Fig. 4a. The correlation between changes in absorbance (ΔA) at specific wavelengths and the applied potentials is displayed in Fig. 4b. As the potential was scanned from the open-circuit to 1.07 V (not exceeding the maximum potential used during electropolymerization), the p-TCTA film underwent oxidative doping, manifesting a continuous decrease in the absorption peak at 332 nm associated with the neutral state. In the initial stages of doping, new absorption bands appeared and intensified between 400–500 nm, along with the emergence of a very broad absorption band spanning the visible to near-infrared (vis-NIR) range (centered around 1577 nm). As the doping level was further increased, a distinct new absorption peak emerged at 744 nm within the broad vis-NIR absorption band. The 1577 nm band reached a maximum intensity at 0.95 V and remained essentially unchanged at higher potentials.

Fig. 4 (a) Vis-NIR difference spectra of p-TCTA films at various potentials versus the neutral state. The original spectroelectrochemistry is shown in Fig. S13 (ESI†). (b) Variation of ΔA with applied potential at wavelengths of 332 nm, 412 nm, 744 nm, and 1577 nm. (c) Changes in ΔA at 332 nm, 412 nm and 1577 nm correlated with ΔA at 744 nm. (d) Refractive index curves comparing electrodeposited and vapor-deposited TCTA films. (e) Oxidative doping process of p-TCTA films.

Doped conductive polymers typically exhibit broad absorption in the NIR region, analogous to that of disordered metals, a feature commonly attributed to polarons—quasi-particles essential to their conductive behavior.^28,29 However, such broad NIR absorption is not exclusive to the doped states of conductive polymers. The ionic state of compounds comprising multiple identical (or structurally similar) redox centers conjugated together (viewed as oligomeric fragments of conductive polymers) also displays extensive broad absorption bands in the NIR spectrum.^30–35 These ionic state species are part of a unique class of donor–acceptor compounds, commonly known as organic mixed-valence compounds.³⁶ Generally, the shape of the polaron absorption bands undergoes continuous and subtle changes as the doping level of the conductive polymer increases, because the polymer chains at different doping levels essentially constitute different species, each with distinct electronic structures.^37–41 Conversely, redox processes in isolated oligomeric segments involve transitions between the neutral state and well-defined ionic states, resulting in the system's spectral behavior being characterized by transitions among several distinct absorption bands throughout the redox progression.

As shown in Fig. 4a, during the oxidative doping of p-TCTA, the shape of the absorption bands remains unchanged within a specific potential range, and no typical spectral changes associated with conductive polymer doping are observed. Analysis of ΔA at 774 nm as the independent variable reveals that the corresponding changes in ΔA at 332 nm, 412 nm, and 1577 nm (Fig. 4c) exhibit a linear correlation when ΔA@774 nm is less than 0.016. This linear relationship, as detailed in Section S7 of the ESI,† is indicative of a characteristic spectral transition between two species.

This analysis clearly indicates that p-TCTA does not behave as a long-range conjugated conductive polymer. We propose that p-TCTA consists of a crosslinked network of conjugated oligomeric segments, interconnected by larger twisted carbon–carbon or carbon–nitrogen bonds (as illustrated in Fig. 5a). These non-conjugated linkages keep the conjugated segments decoupled from each other, thereby preserving their individual properties. Thus, the doping of p-TCTA leads not to polaron formation; rather, it involves the oxidation of the conjugated segments into their cationic states, giving rise to the observed spectroelectrochemical features.

Fig. 5 (a) Schematic representation of twisted non-conjugated linkages (purple balls) of conjugated oligomer fragments (green olive balls) in p-TCTA. (b) Schematic comparison of density differences between electrodeposited (left) and vapor-phase deposited (right, blue olive balls) TCTA films.

As a crosslinked polymer derived from the electropolymerization of a multifunctional conjugated precursor, the presence of twisted conformations within the chains, rather than planar long-range conjugated configurations, is expected. These inherent twists reduce the compactness of the network film, as schematically illustrated in Fig. 5b. As shown in Fig. 4d, the refractive index of p-TCTA films is lower than that of vapor-deposited TCTA films, indicating that the electrodeposited films are less densely packed (see Section S8, ESI†). This structural configuration restricts charge transfer both within and between chains, typically resulting in suboptimal electrical properties in networks formed through the electropolymerization of multifunctional conjugated precursors.^42–46 Density functional theory calculations on the effect of torsional angles on charge transfer integrals between conjugated segments further corroborate the above discussion (see Section S9, ESI†).

However, these networks facilitate effective counter-ion doping channels, as evidenced by the linear relationship between peak currents and scan rates in the CV curves (Fig. S7, ESI†). This structural feature underpins the considerable capacitor performance of p-TCTA, which achieves a high specific capacitance of 349.8 F cm⁻³@15.2 A cm⁻³ and a high specific capacity of 19.4 mA h cm⁻³@15.2 A cm⁻³ (see Section S4, ESI†). Consequently, such crosslinked networks generally exhibit significant electrochemical redox activity (Table S2, ESI†), enabling enhanced energy storage and electrochromic performance.

Based on the preceding discussion, the spectroelectrochemical data of p-TCTA are re-evaluated. As shown in Fig. 4b, at approximately 0.36 V, a marked change occurs in the absorption spectrum, indicating the onset of oxidation. This change corresponds to the onset oxidation potential observed in Fig. 2b. In Fig. 4c, the linear correlation observed where ΔA@774 nm is less than 0.016 indicates that the redox transition between 0.36 V and 0.63 V involves only two species, that is, the oxidation of conjugated segments into their monovalent cations. The monovalent cation is characterized by absorption features in the 400–500 nm region and a broad band spanning the vis-NIR range.^42–44 The linear trend in Fig. 4c shifts when ΔA@774 nm exceeds 0.016, signaling the emergence of new species at around 0.63 V. This transition is consistent with the onset of the second oxidation peak in Fig. 2b, corresponding to the conversion of monovalent into divalent cations, which are marked by distinct absorption peaks at 744 nm.^47–49 As shown in Fig. 3d, the conductivity of doped p-TCTA films increases linearly up to 0.6 V, with relatively stable carrier mobility. However, a sharp decline in charge transport capabilities is observed beyond 0.65 V, coinciding with the oxidation of monovalent to divalent cations. This decline suggests that divalent cations, relative to monovalent ones, induce deeper potential wells (Fig. 6), thereby causing stronger carrier binding.^50,51 Altogether, the comprehensive alignment of electrochemical behavior, spectroelectrochemical signatures, and electrical properties conclusively supports the structural configuration of p-TCTA illustrated in Fig. 5 and clarifies the oxidative doping process proposed in Fig. 4e.

Fig. 6 Potential energy surfaces for charge transfer between conjugated fragments in p-TCTA at low (a) and high (b) doping levels. Hole transport from divalent to monovalent cations requires a higher activation energy ΔG* and recombination energy λ than the transition from monovalent cations to the neutral state, indicating that divalent cations create significantly deeper potential wells. The symbol [D] represents the conjugated oligomer fragment acting as the electron donor. The specific reaction schemes for charge transfer between conjugated fragments are shown in Fig. S15 (ESI†).

Conclusions

We have investigated the developmental challenges of electropolymeric interfacial layers for electrodeposition OLED technology, a promising approach for ultra-high-resolution display fabrication. Our study focuses on the structure and performance of TCTA electropolymeric films, which serve as the primary hole transport layer. These p-TCTA films demonstrate hole mobility, measuring at 0.38 × 10⁻⁷  cm²  V⁻¹ s⁻¹, which limits the brightness and efficiency of electrodeposited OLEDs. Spectroelectrochemical analysis reveals that p-TCTA exhibits spectral changes corresponding to transitions among several discrete species, markedly different from traditional conductive polymers. p-TCTA is a crosslinked polymer network consisting of twisted, non-conjugated linkages between conjugated oligomeric segments, rather than a long-range conjugated conductive polymer. This structural decoupling enables each conjugated segment to maintain its properties independently. Thus, the oxidative doping in p-TCTA fundamentally involves the oxidation of these segments into cations, rather than polaron formation. The consistency across the electrochemical, electrical, and spectroelectrochemical behaviors strongly supports the proposed structure and doping process of p-TCTA.

The study of p-TCTA provides a representative example of the structural and functional characteristics of electropolymeric films derived from a broad class of “star-shaped” precursors. These monomers typically feature multiple electropolymerizable groups that serve not only as reactive sites for film formation but also as the primary units for charge transport. Electropolymerization of such monomers generally leads to the formation of twisted, crosslinked networks, as observed in p-TCTA, which impede charge transport both within and between chains, resulting in limited electrical performance. Experimental data reveal that the monovalent conjugated segments in the crosslinked films exhibit significantly better charge transport than their multi-valent counterparts. While high-planarity, dopant-controlled electropolymeric films can be readily prepared from “star-shaped” precursors, their structural configuration renders them unsuitable as functional layers in semiconductor devices. Nevertheless, these configurations enable effective channels for counter-ion doping, thereby enhancing electrochemical activity. For instance, p-TCTA exhibits a high specific capacitance of 349.8 F cm⁻³@15.2 A cm⁻³ and a high specific capacity of 19.4 mA h cm⁻³@15.2 A cm⁻³. Consequently, the films achieve high doping levels, making them well-suited for applications like electrochromism and energy storage. The insights gained from this study provide valuable guidance for material selection in semiconductor applications, particularly in the development of interfacial layers for electrodeposited OLED technology.

Author contributions

Ying Wang: methodology, investigation, and writing – original draft. Bohan Wang: methodology, writing – review and editing, project administration. Lingyu Wang: investigation. Hanlin Gan: investigation. Wei Xiong: investigation. Yue Yu: methodology. Zhisheng Zhou: investigation. Shaohua Tong: investigation. Ning Li: resources. Yuguang Ma: conceptualization, writing – review and editing, supervision, and funding acquisition. All authors have given approval to the final version of the manuscript.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included as part of the ESI.†

Acknowledgements

The authors are grateful for the funding support from the National Key R&D Program of China (2020YFA0714604), the China Postdoctoral Science Foundation (2023M731163), the Fund of Guangdong Provincial Key Laboratory of Luminescence from Molecular Aggregates (2023B1212060003), South China University of Technology the Fundamental Research Funds of State Key Laboratory of Luminescent Materials and Devices (Skllmd-2023-09), the SSL Sci-tech Commissioner Program (20234383-01KCJ-G), and the National Nature Foundation (92463310).

Notes and references

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5tc00768b

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