Quantitative analysis of zigzag and armchair edges of carbon

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Quantitative analysis of zigzag and armchair edges of carbon materials with/without pentagons using infrared spectroscopy Tatsuya Sasaki, Yasuhiro Yamada, and Satoshi Sato Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b00949 • Publication Date (Web): 06 Aug 2018 Downloaded from http://pubs.acs.org on August 6, 2018

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Analytical Chemistry

Quantitative analysis of zigzag and armchair edges on carbon materials with/without pentagons using infrared spectroscopy Tatsuya Sasaki, † Yasuhiro Yamada,*†Satoshi Sato† Graduate School of Engineering, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan

†

KEYWORDS Zigzag Edge, Armchair Edge, Infrared Spectroscopy, Density Functional Theory Calculation

ABSTRACT: Edge structures of carbon materials such as zigzag and armchair edges are known to affect their chemical and electronic properties. Although infrared spectroscopy (IR) has been known to be capable of identifying such edge structures, quantitative analysis using IR spectra has been conducted using only out-of-plane sp2C-H bending vibration and the estimation of the percentage of edges is still challenging. In this work, a novel two-dimensional method to quantify edge structures of carbon materials with/without pentagons was developed by analyzing both out-of-plane sp2C-H bending and in-plane sp2CH stretching vibration. Calibration factors of sp2C-H on each type of edge were obtained from experimental and simulated IR spectra of various reference compounds. Using the calibration factors, the edge structures of carbonized aromatic compounds with zigzag edges such as tetracene, armchair edges such as chrysene, and zigzag-like edges such as coronene were estimated quantitatively. From tetracene carbonized at 893 K, chrysene carbonized at 933 K, and coronene carbonized at 873K, carbon materials with 20% of zigzag edges, 38% of armchair edges, and 67% of other edges were prepared, respectively. This method can be utilized as quantitative analysis to determine edge structures of various carbon materials prepared below 933 K at lowest.

1. INTRODUCTION Carbon materials such as graphene and carbon nanotube1-5 have been recently attracting attention because of their mechanical strength, light weight, chemical reactivities, and electrical and thermal conductivity.6-11 Especially, electrical and chemical properties of carbon materials have been reported to be relevant to the edge structures such as zigzag and armchair edges (Figure 1a).1218 These controlled edge structures are expected to be applied to electrical devices, gas sensors, and catalysts.611,19,20

Synthesis methods of graphene and graphene nanoribbon with controlled edge structures such as zigzag and armchair edges have been reported.21-26 But, it is difficult to introduce one type of edges using conventional techniques for preparing carbon materials because other types of edges are also introduced,27,28 unless techniques of organic synthesis using catalysts are applied.29,30 Thus, it is necessary to evaluate edge structures quantitatively in addition to qualitatively. Microscopes such as aberration-corrected transmission electron microscopes and scanning tunneling microscope, spectroscopy techniques such as infrared spectroscopy (IR), Raman spectroscopy, and temperatureprogrammed desorption have been reported as methods to determine the edge structures.29-31 Microscopes are effective to analyze edge structures at atomic scale, but the analysis is limited to small region with basically flat surface. Raman spectroscopy is a well-known analytical method to determine the number of layers of graphene,32,33 chirality of

carbon nanotubes,34,35 graphitic (G) band, and disordered (D) band,36-40 and this method has also been utilized as a method to determine zigzag edges at 1450 cm-1 and armchair edges at 1250 cm-1.41 However, their quantitative analysis of edges are still under debate.42,43 IR is one of conventional analytical methods for determination of functional groups on carbon materials. Although this method can clarify edge structures, especially sp2C-H, of carbon materials, this conventional method attracted less attention until recent years.44-46 Out-of-plane sp2C-H bending vibrations on four types of edge structures were assigned as SOLO (860-910 cm-1) , DUO (810-860 cm1), TRIO (750-810 cm-1), and QUATRO (730-770 cm-1)47 (Figures 1b and 2a). These assignments between 730 and 910 cm-1 were utilized to quantify such four types of edge structures of carbon materials using the calibration factors obtained from seven reference aromatic compounds with various functional groups such as one methyl group and one five-membered ring.48 However, seven reference compounds are insufficient and the presence of functional groups may shift the peak positions. In addition, utilization of peaks only between 730 and 910 cm-1 is insufficient to determine the edge structure quantitatively because these peaks originated from each edge may overlap each other depending on the edge structures. From the different aspect, it has been reported that edge structures of zigzag (ca. 3155-3165 cm-1) and armchair edges (ca. 3190-3215cm-1) can be clearly determined by in-plane sp2C-H stretching vibration as results of calculated spectra (Figures 1b and 2b).49

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However, the reported work determines the peak positions by only calculation, and the experimental peak positions are not mentioned. It is necessary to compare the calculated peak positions with experimental peak positions and determine the amount of edges quantitatively. In addition, for quantitative analysis, analysis of edge sctuctures from two aspects such as out-of-plane sp2C-H bending vibration and in-plane sp2C-H stretching vibration is essential to ensure validity of the presence of specific edge structures.

Following twenty-two aromatic compounds (Figure 3) were used as reference compounds to obtain peak positions of edges and intensities of the peaks for qualitative analyses. Abbreviations of each structures are written above each structure in Figure 3. Purities and companies of these compounds are described in the section S1.1 of supporting information (SI).

Figure 2. Reported peak positions for various vibration modes of sp2C-H. (a) Out-of-plane sp2C-H bending vibration. The experimental wavenumbers for each edge shown below each structure were obtained from the figures in a reference.47 (b) In-plane sp2C-H stretching vibration. The calculated wavenumbers for each edge below each structure were obtained from the figures in a reference.49 The asterisk in this figure indicates an armchair-like edge.

Figure 1. Edge structures of carbon materials and a procedure of this work to determine the edge structures quantitatively. (a) Example of definition of edge structures in this work. (b) An example of quantitative analysis of edge structures using geometric mean of peak areas of DRIFT spectra corrected by the calibration factors in two ranges between 730 and 910 cm-1 (left) and between 3000 and 3100 cm-1 (right). In this work, we determined the peak position and calibration factors of each edges by analyzing twenty-two reference aromatic compounds composed of either only hexagonal rings without side chain or hexagonal and pentagonal rings without side chain in two regions such as out-of-plane sp2C-H bending vibration and in-plane sp2C-H stretching vibration using infrared spectroscopy. By applying these positions and calibration factors of reference samples, we further experimentally quantified edge structures of carbon materials, which were prepared by heat treatment of aromatic compounds. 2. EXPERIMENTAL 2.1 Reference compounds for quantitative analysis

2.2 Quantitative analysis of edges by DRIFT spectra 2.2.1 Adjustment of peak areas by calibration factors For quantitative analysis, the presence of specific edges and the amount of specific edges have to be clarified. The quantitative analyses were previously conducted using only out-of-plane sp2C-H bending vibration.48 However, the quantitative analyses using only one type of vibration may lead to incorrect results, which will be explained later. By combining these two types of vibrations and conducting two dimensional analyses (Figure 1b), it is possible to obtain proper results for quantitative analyses. Thus, these compounds (Figure 3) were analyzed by diffuse reflectance infrared Fourier spectroscopy (DRIFTs) (FT-IR4200, JASCO, Japan) at room temperature. Calibration factors of each peak for out-of-plane sp2C-H bending vibration and in-plane sp2C-H stretching vibration were obtained from the slope of calibration curve (eq. S1). The detailed method to obtain calibration factors is explained in S1.2 of SI. 2.2.2 Definition of edge structures and calculation of geometric mean Reported definitions of edge structures for out-ofplane sp2C-H bending47 and in-plane sp2C-H stretching vibration49 are mostly different. For example, SOLO contains zigzag edges and armchair-like edges (eq. S3), and


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Analytical Chemistry DUO contains zigzag-like and armchair edges (eq. S4). Thus, SOLO and zigzag edges are partially difference, and also DUO and armchair edges are partially different. Thus, for out-of-plane sp2C-H vibration, armchair edges and zigzaglike edges were separately defined (Tables 2, 3, and Figure S29). It is essential to unify the definition of edge structures for these two types of vibrations as much as possible as shown in the section S1.3 in order to obtain the quantitative information two dimensionally and more accurately than before. For this purpose, the geometric mean (eq. 1 and the section S1.4), which has abilities to combine two types of different vibrations and to quantify the edge structures twodimensionally (Figure 1b), was calculated. Mainly three types of edges such as zigzag, armchair, and others with/without pentagons were classified in addition to bay edges as shown in Figure 3 and Tables 1-4. For two-dimensional analyses using combination of two types of vibrations, a geometric mean, Pn_edge (bending*stretching) (eqs. 1 and S19) obtained by multiplying Pn_edge (bending) and Pn_edge (stretching) (eq. S18), is more suitable than summation, because the geometric mean (Figure 1b) can cancel out the presence of misleading peaks. Pn_edge (bending) and Pn_edge (stretching) are percentages of calibrated peak area of one type of edges, An_edge (eq. S2), which is an experimental peak area of a certain edge (an_edge) divided by calibration factor of kn_edge. Detailed definition of these edge structures and calculation methods for geometric mean are explained in the section S1.3 in SI.

decided by adjusting experimental wavenumber to calculated one (Figure 4). The detailed method to obtain the scaling factor is explained in S2.1 of SI.

P𝑛𝑒𝑑𝑔𝑒 (𝑏𝑒𝑛𝑑𝑖𝑛𝑔∗𝑠𝑡𝑟𝑒𝑡𝑐ℎ𝑖𝑛𝑔) [%] = 2√P𝑛_𝑒𝑑𝑔𝑒 (𝑏𝑒𝑛𝑑𝑖𝑔𝑛𝑔) × P𝑛_𝑒𝑑𝑔𝑒 (𝑠𝑡𝑟𝑒𝑡𝑐ℎ𝑖𝑛𝑔)

eq. 1

, where Pn_edge (bending) is the percentage of out-of-plane sp2CH bending vibration on one type of edges. Pn_edge (stretching) is the percentage of in-plane sp2C-H stretching vibration on one type of edges. Pn_edge (bending*stretching) is the percentage of a geometric mean for bending and stretching vibration of sp2C-H on the edges. 2.3 Preparation of carbon material Coronene was placed in glass tube and sealed after being dried at 353 K for 2 h under reduced pressure (Figure S31). The ampoule tube including coronene was carbonized at 873 K for 1 h. Tetracene and chrysene were prepared similarly, and they were heated at 893 K for 2 h and 933 K for 2 h in our previous work, respectively.50 933 K for chrysene and 873 K for coronene were selected because these temperatures are the lowest carbonized temperature of each compound. 893 K was used for tetracene because tetracene form sp3C-H during carbonization and the sp3C-H can be mostly eliminated and only sp2C-H was present at 893 K.50 2.4 Simulation of IR spectra Density functional theory (DFT) calculation was conducted to obtain IR spectra and vibration mode using b3lyp/6-31g(d) in Gaussian 09.51 After lengths and angles of structures were optimized, vibrational analysis was conducted using keyword of freq. Scaling factors for adjusting simulated spectra to experimental spectra were

Figure 3. Structures of reference aromatic compounds to obtain calibration factors and the definition of edge structures. (a) Anthracene. (b) Tetracene. (c) Benz[a] anthracene. (d) Benzo[a]pyrene. (e) Dibenzo[b,def] chrysene. (f) Naphto[2,3-a]pyrene. (g) Pyrene. (h) Benzo [ghi]perylene. (i) Coronene. (j) Phenanthrene. (k) Chrysense. (l) Picene. (m) Triphenylene. (n) Perylene. (o) Dibenzo[g,p]chrysene. (p) Hexabenzocoronene. (q) Quaterrylene. (r) Indeno[1,2,3-cd]fluoranthene. (s) Benzo [k]fluoranthene. (t) Benzo[b]fluoranthene. (u) Indeno [1,2,3-cd]pyrene. (v) Fluoranthene. Abbreviations of each structure are written above each structure. Other than this figure, Tetra-Zigzag and Graph-Zigzag or Chry-Armchair and Graph-Armchair were basically marked as Zigzag or Armchair, respectively. Marks of each edge, that are not shown as structures in this figure, are also explained at the bottom of this figure for clarity of definition (See the section S1.3 in SI for detail).



3. RESULTS AND DISCUSSION 3.1 Assignment of peaks for various edges using experimental and simulated spectra Figure 4 shows DRIFT spectrum of naphto[2,3a]pyrene as one of examples for assignments. The assignment was conducted by comparing the peaks of sp2CH in simulated spectrum and experimental spectrum (Figures S1-S22 in SI). Twenty-two reference compounds were analyzed with a similar method. In case of out-ofplane sp2C-H bending, it was experimentally and theoretically proved that peak positions of various edge structure did not have dependence on the molecular weight (Figure S23). Thus, assignments of edge structures using aromatic compounds in this work can be applied to those of various carbon materials.

Figure 4. Peak assignment of DRIFT spectrum of naphto[2,3-a]pyrene (Na) using DFT calculation. (a) Out-ofplane sp2C-H bending vibration. (b) In-plane sp2C-H stretching vibration. Top spectrum: calculated spectrum. Bottom spectrum: experimental spectrum. Colored marks are same as those used in Figure 3f. Table 1. Assignment of peak positions for zigzag edges. Types of Zigzag edges*1

Peak positions*2/ cm-1 Out-of-plane sp2CH bending

In-plane sp2C-H stretching

Tetra-Zigzag (SZigzag)

889 (882-904: experimental)

Graph-Zigzag (SZigzag)

874 (874-901: experimental) (886-900: calculated)*3

3007 (30013014: experimen tal)

Names in parentheses indicate definitions of edges for out-of-plane sp2C-H bending explained in S1.3 in SI. *2 Experimental peak positions were averaged using numbers in Figures S23a and S27. *3 Calculated peak positions were obtained from Figure S24.

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peak positions,49 this work clearly showed the experimental peak positions. Zigzag edges can be divided into (1) zigzag edges on linear compounds such as anthracene and tetracene (Tetra-Zigzag) and (2) zigzag edges on graphene (Graph-Zigzag). Tetra-Zigzag means that benzene rings fused together in one line with zigzag edges similar to tetracene. Graph-Zigzag indicates that linear aromatic compounds fused together in two or more lines with zigzag edges on aromatic compounds, graphene nanoribbon, and graphene. Table 2. Assignment of peak positions for armchair edges. Types of Armchair edges*1


In-plane sp2CH stretching

Armchair-like (Chry-Armchairlike) (SArmchair-like)

817 (813-839: experimental) vibrated together with a peak of armchair


Armchair-like (Graph-Armchairlike) (SArmchair-like)

817 (N. A.: experimental) (808-834: calculated)*3 vibrated together with a peak of armchair

5ring-Armchairlike (S5ring-Armchairlike)



Armchair, 5ringrelated-Armchair (Chry-Armchair) (QArmchair, TArmchair, DArmchair, Q5ringrelated-Armchair, T5ringrelated-Armchair, D5ringrelated-Armchair)



Armchair, 5ringrelated-Armchair (Graph-Armchair) (QArmchair, TArmchair,

817 (811-831: experimental) (808-834: calculated)*3

*1

Tables 1-4 show representative peak positions for each edge, which were obtained from experimental peak positions in this work (Figures S1-S22). Detailed definition of edges are explained in sections 2.2.2 and S1.3. Contrary to the reported work, which exhibited only the calculated

DArmchair) 5ring-Armchair (Q5ring-Armchair, T5ring-Armchair, D5ringArmchair)



Same as *1,2 in Table 1. *3 Calculated peak positions were obtained from Figure S26. *1,2


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Table 3. Assignment of peak positions for others edges. Types of edges*1

Others

Zigzag-like (QZigzaglike, TZigzag-like, DZigzaglike)




3028 (3009-3047: experimenta l Zigzaglike, 3023-3042: 5ringZigzag-like)

5ring-Zigzag-like, 5ring-relatedZigzag-like (Q5ringT5ring-ZigzagZigzag-like, D5ring-Zigzag-like, like, Q5ring-related-Zigzag-like, T5ring-related-Zigzag-like, D5ring-relatedZigzag-like) Other (QOther, Q5ring-Other, Q5ring-related-Other)

Other (TOther, T5ringOther, T5ring-related-Other)

*1,2

745 (QUATRO and 5ring-QUATRO) (725-773: experimental QUATRO, 728755: experimental 5ring-QUATRO) 757 (TRIO) (748765: experimental) 770 (5ring-TRIO) (748-777: experimental)

3048 (3022-3067: experimenta l Other, 3050-3063: experimenta l 5ringOther)

Same as *1,2 in Table 1.

As shown in Table 2, armchair edges can be mainly divided into (1) Armchair, (2) Armchair-like, (3) 5ringArmchair, and (4) 5ring-Armchair-like edges. Other armchair-related edges such as 5ring-related-Armchair showed in Figure 3 and 5ring-related-Armchair-like (not shown) were excluded from Table 2 because of the lack of data in this work. (1) The Armchair edges can be further divided into Chry-Armchair and Graph-Armchair edges, where Chry-Armchair edges indicate that benzene rings fused together in one line with armchair edges similar to chrysene. Graph-Armchair edges mean that linear aromatic compounds fused together in two lines or more lines with armchair edges. (2) The Armchair-like edges can be further divided into Chry-Armchair-like and Graph-Armchair-like edges, where Chry-Armchair-like edges indicate armchairlike edges in a chrysene-like structures such as chrysene and picene and Graph-Armchair-like edges mean armchairlike edges on graphene-like structure. (3) 5ring-Armchair edges indicate armchair edges next to pentagon(s). (4) 5ring-Armchair-like edges indicate armchair-like edges next to pentagon(s). Edges of “Others” can be divided into (1) zigzag-like edges (Zigzag-like) and (2) the other edges (Other). Zigzaglike is the edges of aromatic compounds such as pyrene and

coronene, whereas other edges include the rest of all edges except for bay edges. Zigzag-like edges can be further divided into Zigzag-like and 5ring-related-Zigzag-like edges, where Zigzag-like indicates Zigzag-like edges without pentagons and 5ring-related-Zigzag-like means that Zigzaglike edges influenced by pentagons. These ranges of peak positions in Tables 1-4 were determined by Figures S23 and S27. Table 4. Assignment of peak positions for bay edges. Types of Bay edges*1

Peak positions/ cm-1 Out-of-plane sp2C-H bending


Bay (Qbay, Tbay, Dbay, Sbay)

Unclear (ca. 796: experimental) (Peak positions could not be determined clearly because of the only one experimentally analyzed spectrum of D[g,p].)

Unclear (ca. 3096: experimental) (3086 and 3106: from two experimental peak positions of D[g,p]) ca. 3212-3222 (from reported calculated results)49

*1

Same as *1 in Table 1.

3.2 Calibration factors for each type of edges Twenty-two kinds of PAHs were diluted to 3 wt.% in KBr and analyzed by DRIFTs to obtain calibration factor from the slopes of calibration curves (Figure S29 for 700950 cm-1 and Figure S30 for 2950-3150 cm-1). The calibration curves were obtained by plotting area of corresponding peaks versus the amount of hydrogen in 1g of KBr. Depending on the types of edges, the slopes were different, indicating that the calibration factors (eq. S1) are different depending on the types of edges. The calibration factor of out-of-plane sp2C-H bending vibration for zigzag edges was 33 (Figure S29a), that for zigzag-like (Zigzag-like and 5ring-related-Zigzag-like) edges was 10 (Figure S29b), that for armchair edges was 17 (Figure S29c), that for TRIO was 4.4 (Figure S29d), that for QUATRO (QUATRO and 5ring-QUATRO) was 22 (Figure S29e), that for 5ring-TRIO was 16 (Figure S29f), that for 5ring-Armchair was 13 (Figure S29g), and that for 5ringArmchair-like was 29 (Figure S29h). The correlation coefficients, “R”, in the equation of Figure S29 were 0.74 for zigzag, 0.77 for Zigzag-like and 5ring-related-Zigzag edges, 0.29 for armchair, 0.79 for TRIO, and 0.72 for QUATRO and 5ring-QUATRO, 0.47 for 5ring-TRIO, 0.45 for 5ringArmchair, and -0.04 for 5ring-Armchair-like edges. Correlations were relatively high for zigzag and zigzaglike edges, whereas those were low for armchair, TRIO, and QUATRO. The low correlation is probably because of the coupled vibration.52 Because of the coupled vibration, the difference between TRIO and QUATRO was not clear enough. Thus, calibration factors of 4.4 for TRIO and 22 for



QUATRO were averaged and one calibration factor of 9.4 for both TRIO and QUATRO was utilized for quantitative analysis of both TRIO and QUATRO. The calibration factors of in-plane sp2C-H stretching vibration for zigzag edges, zigzag-like edges, armchair edges, other edges, 5ring-Armchair edges, and 5ringArmchair-like edges were 2.3 (Figure S30a), 4.7 (Figure S30b), 5.3 (Figure S30c), 6.9 (Figure S30d), 6.3 (Figure S30e), and 6.4 (Figure S30f), respectively. The correlation coefficients, “R”, in the equation of Figure S30 for zigzag edges, zigzag-like edges, armchair edges, 5ring-Armchair edges, 5ring-Armchair-like edges, and other edges were 0.62, 0.78, 0.72, 0.77, 0.78, and 0.53, respectively. It indicates that correlation was relatively high and these calibration factors can be applied to quantitative analysis. Intensities of peaks for out-of-plane sp2C-H bending vibration were higher than those for in-plane sp2C-H stretching vibration. Thus, peaks originated from the bending vibration can be utilized to classify the presence of each edge structure clearly, but correlation coefficients for out-of-plane sp2C-H bending vibration is lower than those for in-plane sp2C-H stretching vibration as explained in Figures S29 and S30 because of the coupled vibration52 for out-of-plane sp2C-H bending vibration. Thus, these two vibrations have to be combined, because the combination can improve the reliability of quantitative analysis. Correlation coefficients of extrapolation lines in parenthesis of Figure S29d and e were negative, but positive correlation coefficients were obtained by excluding the values of B[a]p in Figure S29d and An, Ph, and Tr in Figure S29e. Thus, slopes of the extrapolation lines with positive correlation coefficient were utilized to obtain the calibration factors. Calibration curve and calibration factor for armchair-like edges could not be obtained because of the lack of available standards. However, the peak positions of armchair-like edges in Na and B[a]a were close to the extrapolation line for armchair edges (Figure S30c). Thus, 5.3, which is the calibration factor for armchair edges, was applied to that for armchair-like edges. The slope of 5ring-related-Zigzag-like edge was close to that of Zigzag-like edge. Thus, these results were plotted together in Figure S29b. The slope of 5ring-QUATRO edge was also close to that of QUATRO. Thus, these results were plotted together in Figure S29e. 3.3 Quantitative analysis of edge structures of carbon materials Figures S42-S44 show experimental DRIFT spectra of as-received and carbonized tetracene, chrysene, and coronene. Peak positions of as-received compounds were assigned as results of DFT calculation, whereas averaged peak positions of each edge in Tables 1-4 were applied to experimental spectra of carbonized materials. Calculation method of eq. 1 was utilized to obtain the percentage of edge structures of as-received compounds and carbonized materials (Table 5). The detailed explanation for peak positions is written in section S5 in SI. For the estimated carbonized structures, the percentage of one type of edge was obtained in Table 5 using eq. 2 by counting the number of sp2C-H on each edge,

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based on the structures without pentagon in Figure S35. For more detailed analysis of carbonization, percentages of structural control, which show the percentages of remaining specific edges after carbonization,27 were also calculated in Table 5 using eq. S20. P𝑛_𝑒𝑑𝑔𝑒 (𝑛𝑢𝑚𝑏𝑒𝑟) [%] N𝑛_𝑒𝑑𝑔𝑒 × 100 = N𝑍𝑖𝑔𝑧𝑎𝑔 + N𝐴𝑟𝑚𝑐ℎ𝑎𝑖𝑟 + N𝑂𝑡ℎ𝑒𝑟𝑠

eq. 2

, where Nn_edge is the number of sp2C-H on one type of edges. Table 5 Percentages of edges structures of three reference compounds and their carbonized samples using the calibration factors. Samp le name

Temp eratu re /K

Component/% Zigz ag

Others

Tetra cene

298 893

893*1

22 20 (91 )*2 33

298 933

0 5

70 57 (81) *2

933*1

0

30

298 873 873*1

0*1

Chrys ene

Coro nene

0 0

Ziglike

Armchair Oth er

Withou t 5ring*3

5rin g*4

78 48 (62) *2

0 13

0 19

25

25

0

30 29 (97)*2 40

0 9

0*1

0 0 0

17

30

100 67 (67)*2 80 0

33 20

0

Estimated structures without pentagons in Figure S35 were utilized to obtain the percentage of edge structures. *2 The number in parenthesis is a percentage of structural control calculated using eq. S20. *3 Armchair edges without pentagon include Armchair and Armchair-like edges without influence of pentagon. *4 5ring includes 5ring-related-Armchair, 5ring-Armchair, and 5ring-Armchair-like edges. *1

By combining the results of Figure S42a and b, it was revealed that carbonized tetracene contained 20% of zigzag edges and 13% of armchair edges (Table 5). The percentage of structural control of zigzag edges in carbonized tetracene was 91% (Table 5), but the types of zigzag edges changed from tetracene-like zigzag edges to graphene-like zigzag edges. From these results, it is estimated that sp2C-H on zigzag edges in tetracene reacted each other by dehydrogenation reaction53 and carbonization reactions proceeded, generating armchair edges (Figure S35a). In addition, pentagon (5ring in Table 5) increased from 0 to 19%. The formation of pentagon was proposed in our previous work.50 This carbonization


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Analytical Chemistry process of linear aromatic compounds such as pentacene has been reported54 and the carbonization of pentacene in the reported work showed the same tendency with carbonization of tetracene in this work. By combining the results of Figure S43a and b, it was revealed that carbonized chrysene contained 29% of armchair edge and 5% of zigzag edges (Table 5). The percentage of structural control of armchair edges in carbonized chrysene was 97%. The high percentage of structural control of armchair edges is partly because new armchair edges can be formed by bonding two chrysene molecules, in addition to the elimination of existing armchair edges. The increment and the decrement of armchair edges depend on the positions of dehydrogenation reaction between chrysene molecules (Figure S35b). Another reason is that the unreacted chrysene is remaining in the sample. By combining the results of Figure S44a and b in addition to the Raman spectra (Figure S34c), it was revealed that carbonized coronene contained 67% of others edges including zigzag-like edges and 33% of armchair edges. The percentage of structural control of other edges including zigzag-like edges was 67%. Especially, the narrow full width at half maximum of newly formed peaks of Raman spectra of carbonized coronene indicates the well-ordered structure compared with carbonized tetracene and chrysene. Thus, the increment of armchair edges in Table 5 can be explained from the point of view of both experimental and calculated spectra. In addition, formation of armchair edges by reacting coronene have also been mentioned in the previous works,55 which can support the analytical method of this work. 4. Conclusion This work developed a novel method to quantify the edge structures such as zigzag, armchair, and other edges of carbon materials with/without pentagons using IR by combining peaks originated from out-of-plane sp2C-H bending vibration and in-plane sp2C-H stretching vibration. This method could determine edge structures much more accurately than conventional methods using only peaks of out-of-plane sp2C-H bending vibration because twenty-two reference compounds with various edges and density functional theory calculation to simulate spectra were used to determine the calibration factor of peaks originated from specific edge structures in this work. Through this quantification of edge structures, this work also clarified the unreported experimental peak positions of in-plane sp2C-H stretching vibration on zigzag, zigzag-like, other, armchairlike, and armchair edges at 3001-3014, 3009-3047, 30223067, 3064-3069, and 3060-3097 cm-1, respectively.

ASSOCIATED CONTENT Supporting Information. (i) Detailed methods for quantitative analysis of edges by DRIFT spectra, (ii) Calculated IR spectra and experimental DRIFT spectra of aromatic compounds, (iii) calculated IR spectra, Raman spectra, and experimental DRIFT and Raman spectra of estimated carbonized tetracene, chrysene, and coronene, (iv) dependence of molecular weight

and wavenumber, and (v) detailed preparation method of carbon materials. These materials are available free of charge via the Internet at http://pubs.acs.org.”

AUTHOR INFORMATION Corresponding Author * Tel/Fax: +81-43-290-3376. E-mail address: [email protected] (Y. Yamada).

CONFLICT OF INTEREST Funding Source. This work was supported by JSPS KAKENHI Grant Number JP18K04833.

ACKNOWLEDGMENTS This work was supported by JSPS KAKENHI Grant Number JP18K04833.

ABBREVIATIONS IR, infrared spectroscopy; DRIFTs, diffuse reflectance infrared Fourier spectroscopy; DFT, density functional theory; An, anthracene; Te, tetracene; Ch, chrysense; B[a]a, benz[a]anthracene; D[g,p], dibenzo[g,p]chrysene; B[ghi], benzo[ghi]perylene; D[b,def], dibenzo[b,def]chrysene; Na, naphto[2,3-a]pyrene; Pi, picene; Co, coronene; Ph, phenanthrene; Py, pyrene; B[a]p, benzo[a]pyrene; Tr, triphenylene; Pe, perylene; He, hexabenzocoronene; Qu, quaterrylene; Bbf, benzo[b]fluoranthene; Bkf, benzo[k]fluoranthene; Inp, indeno[1,2,3-cd]pyrene; Inf, indeno[1,2,3-cd]fluoranthene; Fl, fluoranthene; TCI, Tokyo Chemical Industry; Zig, zigzag; TetraZigzag, tetracene-like zigzag; Graph-Zigzag, graphene-like zigzag; Arm, armchair; Chry-Armchair-like, chrysene-like armchair-like; Graph-Armchair-like, graphene-like armchair-like; Chry-Arm, chrysene-like armchair; Graph-Armchair, graphenelike armchair; Zigzag-like, zigzag-like; 5ring-Armchair-like, armchair-like edges next to pentagon; 5ring-Armchair, armchair edge next to pentagon; 5ring-related-Other, other edges influenced by pentagon; 5ring-TRIO, TRIO next to pentagon; 5ring-QUATRO, QUATRO next to pentagon; 5ring-related-Zigzag-like, zigzag-like edges influenced by 5-membered ring

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Quantitative analysis of zigzag and armchair edges on carbon materials with/without pentagons using infrared spectroscopy


Quantitative analysis of zigzag and armchair edges of carbon

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