Self-template Synthesis of Nanoporous Carbons from π-conjugated Ionic Liquids with Aromatic Functionalities

doi:10.21203/rs.3.rs-5001490/v1

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Self-template Synthesis of Nanoporous Carbons from π-conjugated Ionic Liquids with Aromatic Functionalities

https://doi.org/10.21203/rs.3.rs-5001490/v1

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Ionic liquids (ILs) are liquids composed of pure ionic components with melting points near room temperature that exhibit unique properties. They are also known as designer solvents. In particular, π-conjugated functional ILs demonstrate photoluminescent properties, making them promising for new applications. In addition, the organic moieties of ILs can function as precursors for carbon materials, facilitating efficient polymerization reactions at high temperatures.

In this paper, we present the structural aspects of nanoporous carbon materials derived from π-conjugated ILs, revealing that the domain structure of these ILs plays a crucial role in the carbonization process, as observed from the florescence spectroscopy of the precursor π-conjugated IL. This paper proposes a synthesis process for nanoporous carbon from π-conjugated ILs, demonstrating the thermal stability of ILs with mesoscopic domain structures, thereby promoting carbonization reactions while pore formation occurs simultaneously. This study expands the potential applications of π-conjugated ILs across various fields, and contributes to a deeper understanding of their unique properties from microscopic observations.

π-conjugated ionic liquid

fluorescence

domain structure

self-template synthesis

nanoporous carbon

Ionic liquids (ILs) are pure ionic components with a melting point at approximately room temperature (Freemantle 2010; Armand et al. 2009; Rogers and Seddon 2003). Owing to their pure ionic components in the liquid state, ILs have several unique properties that molecular liquids do not exhibit (i.e., negligible vapor pressures, high ionic conductivities, and high electrochemical and thermal stabilities). ILs are also known as designer solvents because they can be synthesized with the desired properties and compositions (Earle and Seddon 2000; Nasirpour et al. 2020). For example, magnetic ILs composed of anions with magnetic moments, such as FeCl₄⁻, have been reported to exhibit paramagnetic responses to magnetic fields in the liquid state (Hayashi and Hamaguchi 2004; Joseph et al. 2016; Futamura et al. 2020).

The new design of ILs with π-conjugated organic functionalities, such as aromatic rings, can widen the potential applications of ILs, including optical devices and porous liquids with permanent porosity, as liquid functional materials (Yao et al. 2018; Tao et al. 2014; Ogoshi et al. 2012). One example of π-conjugated ILs is 1-(2-naphthylmethyl)-3-methylimidazolium bis-[(trifluoromethane)sulfonyl]imide (NMMI-TFSI) (Yao et al. 2018; Tao et al. 2014). The organic NMMI cation has a naphthylmethyl group, which is a π-conjugated functional group attached to the nitrogen atom of imidazole. This can be achieved using a simple synthetic method with high production yields (Scheme 1). NMMI-TFSI exhibits photoluminescence, which is derived from the naphthyl functionality, even in a pure liquid state without any solvents, suggesting that applications, such as mechanoresponsive photoluminescent ink, can be realized (Li et al. 2014).

Another possibility for the application of ILs with π-conjugated functional groups is a precursor for the synthesis of functional carbon materials (Zhou et al. 2019; Liu et al. 2018; Sun et al. 2018; Qu et al. 2022; Kong and Chen 2015). As with typical organic compounds, the organic moieties of ILs might act as carbon sources (Ryoo et al. 1999; Ma et al. 2002; Li and Xue 2012). In particular, the polymerization reaction between the organic functionalities of ions can occur efficiently in ILs at high temperatures because ILs show high thermal stability up to the decomposition temperature in the condensed phase at the reaction temperature between organic moieties. However, the carbon yield is low for general imidazolium-type ILs, such as 1-ethyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]imide (EMI-TFSI).

This situation can be considerably improved by the introduction of the π-conjugated functionality into IL frameworks, as reported by Zhou et al. (Zhou et al. 2019; Tao et al. 2014). Furthermore, the carbon materials produced from these ILs have high volumes of nanopores, despite the absence of a template removal process followed by the pyrolysis of precursors, as observed in other nanoporous carbon syntheses (Ryoo et al. 1999; Ma et al. 2002; Li and Xue 2012). This suggests that the π-conjugated functionalities and mesoscopic domain formation of ILs (Triolo et al. 2007) play an important role in the carbonization and pore network formation processes. Although these unique processes for the synthesis of nanoporous carbons from π-conjugated ILs are related to π-conjugated IL structures and properties, the detailed relationships remain unclear.

Here, we report the structural aspects of nanoporous π-conjugated-IL-derived carbon (π-ILDCs), which can be obtained via the heat treatment of π-conjugated ILs without subsequent template removal treatments. Furthermore, the fluorescence measurements revealed an important relationship between the domain structure of the π-conjugated ILs and the carbonization process, suggesting that the mesoscopic heterogeneity of the π- conjugated IL structure facilitates carbonization. This study illustrates the use of ILs as functional materials for future generations.

2.1.　Synthesis of p-conjugated ILs

In this study, 1-methylimidazole (99.0%) and Li-TFSI (98.0%) were procured from Tokyo Chemical Industry (TCI) Co., Ltd. Moreover, 2-bromomethylnaphthalene (92%), toluene (99.5%), and benzyl bromide (97.0%) were purchased from FUJIFILM Wako Pure Chemical Co. Milli-Q water was obtained from Milli-Q Lab (Millipore Japan Co.). These chemicals were used as received without further purification. The synthetic procedure for the p-conjugated ILs is shown in Scheme 1. The π-conjugated ILs were synthesized in two steps: the Menshutkin reaction and subsequent anion exchange reaction (Tao et al. 2014). The detailed synthetic procedures for NMMI-TFSI and 1-benzyl-3-methylimidazolium bis-[(trifluoromethane)sulfonyl]imide (BzMI-TFSI) are shown in the Supplementary Information (SI). The chemical structures of the products were confirmed using proton nuclear magnetic resonance (¹H NMR, JNM-ECA500, JEOL Ltd.) and Mass spectroscopy (Autoflex III TOF/TOF, Bruker Daltonics Inc.), as shown in the SI.

Scheme 1 Synthesis of p-conjugated ILs

2.2. Characterization of p-conjugated ILs

2.2.1. Fluorescence spectroscopy

The fluorescence spectra of the pure NMMI-TFSI and NMMI-TFSI solutions with a solvent of dichloromethane (99.5%, FUJIFILM Wako Pure Chemical Co.) were measured using RF-5300 PC (Shimadzu Co., Ltd.). The fluorescence spectra of the binary IL mixtures of NMMI-TFSI and EMI-TFSI (98%, TCI) with several molar ratios were measured using RF-6000 (Shimadzu Co., Ltd.). The excitation wavelength was 280 nm.

2.2.2. Thermal properties of p-conjugated ILs

The thermal stabilities of the p-conjugated ILs and EMI-TFSI were measured using thermogravimetry/differential thermal analysis (TG/DTA, Shimadzu Co., Ltd.) under N₂ flow at 250 mL min^-1. The temperature and heating rate were 303–823 K and 1 K min^-1, respectively. Aluminum pans were used for the measurement and reference cells.

The freezing and melting behavior of the p-conjugated ILs was analyzed via differential scanning calorimetry (DSC) using a DSC6100 (Hitachi High-tech. Co.). p-conjugated ILs were introduced into the Al pans, and the temperature was decreased from 333 K to 123 K by cooling and then increased from 123 K to 333 K by heating at a rate of 2 K min^-1 under a dry N₂ flow of 50 mL min^-1. The interval between the heating and cooling processes was 30 min, to maintain the temperature at 123 K. The melting behavior of NMMI-TFSI in the initial state as a solid was also analyzed from 298 K to 333 K by heating at a rate of 2 K min^-1 under a dry N₂ flow of 50 mL min^-1. Alumina powder was used as a reference for the DSC measurements.

2.3. Synthesis of p-ILDCs

p-ILDCs were synthesized via the heat treatment of p-conjugated ILs in an electric tubular furnace under N₂ gas flow (250 mL min^-1). The p-conjugated ILs that were placed on ceramic boats were set in the center of the heat zone of the furnace. Heat treatment was performed from 298 K to 823 K at a rate of 3 K min^-1, and the temperature was maintained at 823 K for 10 min, followed by natural cooling to 298 K.

2.4. Characterization of p-ILDCs

2.4.1. XRD measurements

The p-ILDCs powders were placed in glass capillaries with an inner diameter of 0.7 mm (0.01 mm wall thickness), and then, the capillaries were sealed after heat treatment at 393 K under vacuum for 1 h to avoid the adsorption of water vapor by humidity. The X-ray diffraction (XRD) profiles of the p-ILDCs were measured using a Rapid II diffractometer (Rigaku Co. CuKa, 40 kV, 30 mA) equipped with a 2D imaging plate as a detector.

2.4.2. Raman spectroscopy

The Raman spectra of the p-ILDCs were measured with a Raman spectrometer (NRS-3100, JASCO Co.) using a 532 nm-wavelength laser at 298 K.

2.4.3. N₂ adsorption isotherms

The N₂ adsorption isotherms of the p-ILDCs were measured at 77 K using an Autosorb iQ2 (Anton Paar Co. Inc.). The surface areas A, micropore volumes V_mic, and average micropore width were determined from the α_s plots. The mesopore volumes V_mes were evaluated by subtracting the micropore volume from the total pore volume V_tot, which was determined from the adsorption volume at P/P₀ =0.95 with liquid nitrogen density at 77 K.

2.4.4. X-ray photoelectron spectroscopy

The chemical composition of the p-ILDCs was determined using X-ray photoelectron spectroscopy (XPS) measurements (JPS-9010TR JEOL co.) with an MgKα (10 kV, 10 mA) source.

3.1 Properties of p-conjugated ILs

Fig. 1 shows the DSC results of NMMI-TFSI measured in the initial state as a solid at 298 K. The DSC measurements showed an endothermic peak at 316 K during the first heating process (black), indicating the melting of NMMI-TFSI within the IL. However, freezing and melting transitions were not observed during the subsequent cooling and heating processes (red). Instead, changes in the baseline, indicating the glass transition of the liquid, were observed at 233 and 236 K during the cooling and heating processes, respectively. As reported by Tao et al. (Tao et al. 2014), the liquid state of NMMI-TFSI is stable at room temperature without crystallization for a long time (at least during the experimental time window). Even in this study, the synthesized NMMI-TFSI was observed to form a liquid at room temperature, and the supercooled liquid state was sufficiently stable to be used at room temperature without much concern for crystallization. The stability in the liquid state may be related to the bulky naphthylmethyl substrate of the NMMI cations. In this study, unless otherwise stated, we mainly focused on the liquid state of NMMI-TFSI at room temperature.

Fig. 1 DSC curve of NMMI-TFSI

For BzMI-TFSI, we only observed a baseline change in glass transition without freezing and melting transitions, suggesting that the liquid state was further stabilized by the change in functionality from naphthalene to benzene (Fig. S5).

NMMI-TFSI exhibits fluorescence emission derived from the naphthalene functional group. Fig. 2 shows the fluorescence spectra of NMMI-TFSI in the presence and absence of CH₂Cl₂. NMMI-TFSI diluted with 1 vol.% of CH₂Cl₂ solution showed sharp fluorescence spectra with a maximum at 338 nm, indicating monomer emission at the low concentration of NMMI-TFSI (Berlman 1971). In contrast, a broader peak with a maximum at a lower wavelength (407 nm) was observed for neat NMMI-TFSI. This indicates the dimerization of naphthyl groups within the excited state derived from the p-p interaction between the p-conjugated moieties, called “excimer emission” (Kołaski et al. 2012). Although Coulombic repulsive interactions can occur between NMMI cations, the formation of dimers between naphthyl groups is of considerable interest.

Fig. 2 Fluorescence spectra of NMMI-TFSI (red) and 1 vol.% NMMI-TFSI solution with CH₂Cl₂ (green)

The thermal stabilities of the p-conjugated ILs were determined via TG analysis under inert gas flow conditions (Fig. 3 (a)). NMMI-TFSI (red) did not show any weight change until approximately 570 K, indicating its high thermal stability as a general IL, similar to EMI-TFSI (black). Notably, 18 wt.% of residue remained at a higher temperature than the decomposition temperature of 640 K, whereas EMI-TFSI was thermally decomposed with a small amount of residue under the same heat-treatment conditions (i.e., 1.6 wt.%). Furthermore, the residual weight was comparable to the weight percentage of the naphthyl group in the formula mass of NMMI-TFSI (27%). In addition, we obtained 21 wt.% of residue for BzMI-TFSI (blue) via TG measurements under the same conditions, indicating the characteristics of the p-conjugated ILs upon heat treatment. The residues were black solids for both NMMI-TFSI and BzMI-TFSI, indicating the carbonization of the p-conjugated ILs by heating (Fig. 3 (b)). A similar tendency was reported by several researchers for ILs with p-conjugated functionalities (Zhou et al. 2019; Tao et al. 2014), indicating that p-conjugated moieties are effective carbonization sources.

Fig. 3 (a) TG profiles of NMMI-TFSI (red), BzMI-TFSI (blue), and EMI-TFSI (black) (b) Photograph of p-ILDC prepared from NMMI-TFSI as a precursor

3.2. Properties of p-ILDCs

To characterize the properties of the residual material obtained via the heat treatment of p-conjugated ILs, we mass-produced p-ILDCs from NMMI-TFSI and BzMI-TFSI in an electric furnace under N₂ gas flow. A photograph of the product obtained using NMMI-TFSI is shown in Fig. 3 (b). The yield of the glossy black powders was similar to the residual amount obtained from the TG results (i.e., 112 mg of solid was obtained from 484 mg of NMMI-TFSI, and 293 mg of solid was obtained from 1.45 g of BzMI-TFSI).

The XRD profiles of the obtained p-ILDCs are shown in Fig. 4. The horizontal axis represents the scattering parameter q (= 4psin q /l). The XRD profiles of the p-ILDCs prepared from NMMI-TFSI (red) and BzMI-TFSI (blue) show three broad peaks located at q = 17.5, 30.5, and 53.3 nm^-1. These correspond to the 002, 10, and 11 diffractions of graphitic materials, respectively. Table 1 lists the crystal structures of the p-ILDCs obtained using Scherrer’s equation. Here, d_hkl and D_hkl denote the interplanar spacing and crystallite size of the hkl plane, respectively. Some nanometer-order structural developments in the stacking of graphene sheets and the graphene basal plane were observed, revealing the formation of a micrographite structure in the p-ILDCs. Furthermore, the intensive small-angle X-ray scattering of the p-ILDCs over 0.5 nm^-1 < q < 5 nm^-1 indicates the existence of a considerable volume of nanopores in the p-ILDCs (insets of Fig. 4).

The Raman spectra of both the p-ILDCs show broad G and D bands located at 1580 and 1350 cm^-1, respectively, which are characteristic of amorphous carbon (Fig. S6). The D/G ratios of the p-ILDCs prepared from NMMI-TFSI and BzMI-TFSI are 0.91 and 0.92, respectively. The results from both the XRD and Raman scattering measurements suggest that the p-ILDCs are high-surface-area materials composed of aggregated micrographite.

Fig. 4 XRD profiles of the p-ILDCs

Table 1 Crystallinities of the p-ILDCs evaluated using XRD

Fig. 5 shows the N₂ adsorption isotherms of the p-ILDCs at 77 K. The shapes of the isotherms for both p-ILDCs were hybrids of Type I and Type IV isotherms according to the IUPAC classification, suggesting the existence of micro- to meso-porosities. The type H4 adsorption–desorption hysteresis for these isotherms indicates that larger mesopores are connected to the bottleneck of micropores (Thommes et al. 2015). Table 2 lists the porosities of the p-ILDCs obtained from the N₂ adsorption isotherms. The specific surface areas and microporosities (i.e., average micropore widths and micropore volumes) were determined via a_s analysis (Kaneko et al. 1992). The mesopore volumes were evaluated by subtracting the micropore volume from the total pore volume, which was obtained from the N₂ adsorption amounts at P/P₀ =0.95, following the Gurvich rule (Rouquerol et al. 2014). The specific surface areas of both the p-ILDCs were approximately 1000 m²g^-1, indicating that they are high-surface-area materials because of the nanoporosities. For both the p-ILDCs, the micropore volumes were larger than those of the mesopores, although the mesopore volumes were almost similar. These porosities are related to the characteristics of the precursor ILs. The higher surface area of the p-ILDCs prepared from NMMI-TFSI than those prepared from BzMI-TFSI can be attributed to the more developed aromatic structure of the naphthalene moiety, resulting in a lower D/G ratio and higher crystallite size of D₁₁ for the p-ILDCs obtained from NMMI-TFSI, despite the small differences. Interestingly, the average micropore widths of both the p-ILDCs are c.a. 0.9 nm, and the pore sizes are comparable to the dimension of the TFSI anions (Futamura et al. 2017).

Fig. 5 N₂ adsorption isotherms of the p-ILDCs obtained from NMMI-TFSI (red) and BzMI-TFSI (blue) at 77 K. The open and closed circles show adsorption and desorption, respectively.

Table 2 Porosities of the p-ILDCs evaluated from N₂ adsorption isotherm measurements

The chemical composition of the p-ILDCs was determined using XPS measurements. The wide-scan spectra for both the p-ILDCs detected signals from carbon, oxygen, and nitrogen elements, but the signals of fluorine and sulfur elements, which originate from the TFSI anion of the precursor-conjugated ILs, were not detected (Fig. S7). Table 3 lists the compositions of C, O, and N in both the p-ILDCs from the XPS results. In both the p-ILDCs, 6-7% of N atoms were included in their structure. Fig. 6 shows the XPS narrow scans for N1s of the p-ILDCs. These profiles were deconvoluted into two components, C-N and C=N, which indicate imidazole-type nitrogen atoms originating from the cations of the p-conjugated ILs (Yan et al. 2005). These XPS results suggest that organic cation structures, including aromatic moieties, mainly form a carbon framework, despite the combustion of inorganic anions by heat treatment, resulting in the formation of nanopores.

Fig. 6 XPS narrow scans for N1s of the p-ILDCs obtained from (a) NMMI-TFSI, and (b) BzMI-TFSI. Deconvoluted C-N (pink) and C=N (yellow) peaks and the total (black) are also shown.

Table 3 Compositions of C, O, and N elements for both p-ILDCs from XPS results

3.3 Relationship between carbonization and the liquid structures of p-conjugated ILs

Here, we discuss the relationship between the micro- to mesoscopic structures of the p-ILDCs and the liquid structures of the precursor-conjugated ILs. Fig. 7 shows the X-ray scattering profiles of NMMI-TFSI (red) and BzMI-TFSI (blue) in the liquid state. The X-ray scattering profile of BzMI-TFSI shows three peaks located at 3.4, 8.7, and 13.4 nm^-1 for q < 20 nm^-1, which are attributed to the periodicity of the interionic structures in the liquid state. In NMMI-TFSI, the peak observed at 8.7 nm^-1 in BzMI-TFSI became a shoulder, which indicates the loss of specific periodicity because of the bulky naphthylmethyl groups compared with the benzyl group, but the other two peaks at 3.6 and 12.7 nm^-1 were similarly observed. In particular, the first peak shows that the mesoscopic structure exists in both ILs (i.e., c.a. 1.6 nm and 1.7 nm periodic structures for BzMI-TFSI and NMMI-TFSI in the d-spacing, respectively). The peak located at the small-angle scattering region (< 5 nm^-1) is called a pre-peak, indicating the existence of the mesoscopic anisotropy of ILs called a domain structure (Triolo et al. 2007). Lopes et al. showed that the anisotropy of ILs can be attributed to a structure in which the nonpolar part, composed of organic groups, and the polar part, composed of inorganic groups, are separated (Lopes and Pádua 2006). The formation of the domain structure in both the p-conjugated ILs indicates the presence of neighboring aromatic functionalities. The proximity between the aromatic functionalities in the p-conjugated ILs is also supported by the excimer emission of NMMI-TFSI in the neat liquid state in the fluorescence spectrum, despite the monomer emission in the diluted solution (Fig. 2).

Fig. 7 X-ray scattering profiles of the p-conjugated ILs in the liquid state

To clarify the influence of neighboring aromatic functionalities in the p-conjugated ILs on the carbonization process, we investigated the effect of the dilution of NMMI-TFSI with EMI-TFSI as a solvent on the neighboring naphthyl groups and its relationship with the carbon yield by pyrolysis. Here, we assessed the neighboring naphthyl groups in the dilute NMMI-TFSI solutions by excimer emission from fluorescence measurements.

Fig. 8 (a) shows the fluorescence spectra of the binary IL mixtures of NMMI-TFSI and EMI-TFSI. Neat EMI-TFSI (black) did not show fluorescence over this wavelength region, despite the broad excimer emission of neat NMMI-TFSI (red), as shown in Fig. 2. The maximum intensity of the broad peak exhibited its highest value at an NMMI-EMI molar ratio of 3:1 (orange) and then continuously decreased with decreasing NMMI-TFSI content. Moreover, the wavelength at which the maximum intensity of the broad peak was observed exhibited a continuous blue shift as the proportion of NMMI-TFSI decreased. In contrast, the intensity of the monomer emission at l = 338 nm gradually increased with decreasing NMMI-TFSI content without any peak position shifts. These results indicate that the neighboring NMMI cations in the organic domain structures are maintained even at considerably low contents of the NMMI-TFSI solution (at least in NMMI:EMI = 1:9), despite the environment surrounding the adjacent states of the organic groups within the domain changing with the composition.

Fig. 8 (b) shows the NMMI-TFSI molar fraction (i.e., f _NMMI) dependence of I_ex/(I_mono+ I_ex), where I_ex and I_mono are the intensities of the excimer and monomer emissions, respectively. As the fluorescence intensity depends on the amount of fluorescent species, this value indicates whether the excimer or monomer species is the predominant component in the solution. In Fig. 8 (b), this value becomes less than 0.5, at f _NMMI = 0.1, indicating that the neighboring NMMI cations are minor in the solution, less than the molar fraction of NMMI-TFSI.

Fig. 8 (c) shows the TG curves for the binary IL mixtures of NMMI-TFSI and EMI-TFSI with different compositions. The residual weight after heating at 773 K decreased gradually with decreasing NMMI-TFSI content. However, this trend was not linear with respect to the NMMI-TFSI content. Fig. 8 (d) shows the f _NMMI dependence of the residual carbon yields. A flexion point can be observed at f _NMMI = 0.1, and the residual weight rapidly decreases at f _NMMI < 0.1. The correspondence at the f _NMMI of 0.1, where the monomer emission becomes dominant and the residual amount decreases rapidly, indicates that the neighboring aromatic rings are crucial in carbonization; this study is the first to elucidate this at a microscopic level.

Fig. 8 (a) Fluorescence spectra for the binary IL mixtures of NMMI-TFSI and EMI-TFSI with several compositions. The colors of the curves correspond to those of the molar ratios in the legend. (b) NMMI-TFSI molar fraction dependence of I_ex/(I_mono+ I_ex). Here, I_ex and I_mono are the intensities of the excimer and monomer emissions, respectively. (c) TG curves for the binary IL mixtures of NMMI-TFSI and EMI-TFSI with several compositions. The colors of the curves correspond to those of the molar ratios in the legend. (d) NMMI-TFSI molar fraction dependence of the residual weight from the TG results.

Finally, we propose a plausible synthesis mechanism for nanoporous carbon from p-conjugated ILs via heating (Fig. 9). In π-conjugated ILs, a domain structure, in which π-conjugated functional groups and inorganic components are mesoscopically separated and adjacent to each other, is formed. As ILs are thermally stable without evaporation, their domain structure is maintained up to the decomposition temperature. The carbonization reactions between π-conjugated functionalities can frequently occur in p-conjugated ILs at the decomposition temperature because of the highly condensed environments of aromatic moieties (i.e., cationic domain) while micropore formation occurs simultaneously, in which inorganic anions decompose via heat treatment. The average micropore size (0.9 nm) is comparable to that of the TFSI anion. The mesopores in the p-ILDCs could be derived from the mesoscopic aggregate structure of the anions (i.e., anionic domain).

Nanoporous carbons obtained from p-conjugated ILs can maintain the structural characteristics of the precursor ions (i.e., carbon framework structure and pore sizes), and we expect to investigate the synthesis of new porous carbons using characteristic ions with unique functional groups, such as the hooped macrocycle structure of benzene rings, in future studies (Bennett et al., 2021; Ogoshi et al. 2012; Takaba et al. 2019).

In this paper, we reported a new aspect of ILs with p-conjugated functionalities for the synthesis of nanoporous carbon materials. Micro- to mesoporous carbon materials can be obtained by heating p-conjugated ILs at their combustion temperatures without a subsequent temperate removal process. Furthermore, we clarified the relationship between the mesoscopic liquid structure and the carbonization process using fluorescence spectroscopy. In the heterogeneous domain structure, in which π-conjugated functional groups and inorganic components are mesoscopically separated and adjacent to each other, the polymerization reaction can frequently occur near the decomposition temperature because of the condensed environments of aromatic moieties without evaporations, while anions simultaneously decompose as nanopores. Our study widens the applications of p-conjugated ILs as functional materials, and deepens our knowledge of their unique properties from a microscopic viewpoint.

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Acknowledgements

This research was supported by Grant-in-Aid for Scientific Research (B) (No. 22H01905, 23K23173). We also would like to thank Editage (www.editage.com) for English language editing.

Author Contributions

R.F. is in main charge of this research. T.S., Y.M. and K.N. carried out the experiments. R.S. supported the interpretation of NMR spectra and measured Mass spectroscopies. R.F., T.S. and T.I. discussed the results and edited the paper.

Competing financial interests

The authors declare no competing financial interests.

Electronic supplementary material

The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Competing interests

The authors declare no competing interests.

Ethical Approval

Not applicable.

Funding:

This work was financially supported by JSPS KAKENHI Grant Numbers JP23K23173, JP22H01905.

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Scheme 1 is available in the Supplementary Files section.

No competing interests reported.

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Scheme 1 Synthesis of p-conjugated ILs
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Self-template Synthesis of Nanoporous Carbons from π-conjugated Ionic Liquids with Aromatic Functionalities

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Supplementary Files

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