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Antiaromatic Characteristic Analysis of 1,4-Diazapentalene Derivatives: A Theoretical Study Jie Zheng,†,‡ Xuhui Zhuang,†,‡ Li Qiu,†,‡ Yu Xie,†,‡ Xiaobo Wan,*,† and Zhenggang Lan*,† †

Key Laboratory of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, 266101 Shandong, People’s Republic of China ‡ University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China S Supporting Information *

ABSTRACT: 1,4-Diazapentalene heteroacenes are potential n-type semiconductors that could be used as a new type of material for organic field-effect transistors (OFETs), but their synthesis is still challenging due to their antiaromaticity. The study on their structure− stability relationship should provide useful guidance to the design of stable diazapentalenes. We examined the stability of several types of heteroacenes bearing the 1,4-diazapentalene core using NICS(1)zz calculations. The influence of the fusion pattern, the introduction of substituents, and the incorporation of other heterocycles on the antiaromaticity of the central 1,4-diazapentalene core was systematically studied. It was found that the linear fusion of aromatic rings to the antiaromatic core increases the stability of the heteroacene. The fusion of electron-poor heterocyclic rings also enhances the stability effectively, whereas the fusion of electron-rich heterocyclic rings destabilizes the system. In addition, the combination of the linear fusion pattern or introduction of electron-poor heterocyclic rings to the antiaromatic core reduces the reorganization energy for electron transport, suggesting a way to achieve better n-type semiconductors.

1. INTRODUCTION In last decades, conjugated aromatic heteroacenes with potential application in organic field-effect transistors (OFETs) have attracted great research interest, because of their stability, adjustable electronic-rich/poor character, and high charge-carrier mobility exceeding amorphous Si.1,2 On the contrary, the heteroacenes bearing an antiaromatic core was less studied due to their instability and synthetic challenges.3−6 Although scarcely reported, the example given by Takimiya5 showed that antiaromatic heteroacenes could be used as holetransporting materials, with the mobility up to 10−3 cm2 V−1 s−1. Therefore, the design of novel stable antiaromatic heteroacenes became an interesting research topic. Theoretically, it should be very important to study the structure− stability relationship of such antiaromatic systems, and to guide the synthesis toward antiaromatics with better stability for OFET materials.7,8 The antiaromaticity is directly related to the stability of a planar antiaromatic system. Normally, antiaromatic compounds tend to adopt a nonplanar conformation to diminish the destabilization effect of the 4nπ systems, just like cyclooctatetraene. However, in a compound that is forced to adopt planar conformation, the dilution of the antiaromaticity becomes important to improve the stability of the whole system. Different from the factors that govern the stability of a linear aromatic acenes (for example, the possibility of [4 + 2] cyclization or dimerization increases with the increase of the © XXXX American Chemical Society

conjugated length in aromatic acenes), we considered that whether the antiaromaticity could be diluted is a more important issue to determine the stability of a fused antiaromatic system. The acenes with a pentalene core display the typical antiaromatic characters (8π electrons),9 and a few studies were performed to improve the stability of such compounds.3,5,7,8,10 Besides these molecules, the syntheses of azapentalenes11−13 were sporadically reported in the literature. We envisioned that the replacement of the C atom with the N atom may endue them with the electron-deficient character and make them potential n-type antiaromatic semiconductors.14 Recently, we reported an improved synthesis toward antiaromatic heteroacenes bearing the 1,4-diazapentalene core, such as indolo[3,2-b]indole (II, A-1 in Scheme 1) and dibenzoindolo[3,2-b]indole (BBII, A-2 in Scheme 1). A-2 showed better stability than A-1 due to the linear expansion of the conjugated system; however, its angular isomer, iso-BBII (A-3 in Scheme 1), was too unstable to be synthesized.14 This indicates that the stability of the antiaromatic system is not only influenced by fusing more aromatic rings to dilute the antiaromatic character of the central core15−17 but also strongly depended on the ring-fusion pattern. We calculated the Received: January 7, 2015 Revised: March 26, 2015

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DOI: 10.1021/acs.jpca.5b00163 J. Phys. Chem. A XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry A

physical insight of NICS has been widely discussed in many previous works,25−27 we only shortly discuss its essential idea here. The significant electronic delocalization exists in aromatic system; thus the circle ring current should appear when the external magnetic field is presented. This causes the magnetic shielding effects at the chosen points in vicinity of ring center, further leading to the chemical shift in the NMR measurement for a virtual nucleus. Such absolute chemical shielding (magnetic shielding effect), reflected by the NICS value, provides the direct way to probe aromaticity of ring systems. In general, a more negative NICS value means a stronger aromaticity. As suggested by previous work,28−31 the NICS values at the position that is 1 Å above or below the geometrical center of rings, namely NICS(1), should be more reliable in the judgment of the aromatic/antiaromatic feature. Particularly, NICS(1)zz of the central five-membered heterocycle ring (Figure S1, Supporting Information) was selected as the criteria to evaluate the stability of all compounds containing the 1,4-diazapentalenes core. All the calculations were performed with the density functional theory (DFT) method using the GAUSSIAN 09 package.32 The ground-state geometries of all species were optimized using the B3LYP functional33−35 with the 6-31+G* basis set. To characterize the antiaromatic features, the NICS values were estimated by the inversion of isotropic shielding values. In this step, the large basis set 6-311++G** was employed to get the correct description of chemical shifts. The THF solvent was considered by the polarizable continuum model (PCM). For the compounds of group A, the calculations of their lowest excited states were performed with the TDDFT method at the B3LYP/6-31+G* level. The employment of organic semiconductors in OFET materials is strongly dependent on their charge-mobility efficiency. As a group of n-type semicondoctors, stable 1,4diazapentalene derivatives in principle retain the ability of electron conduction. Thus, as complementary studies, we also chose stable 1,4-diazapentalene derivatives, namely, the compounds of groups A, B, and D, to study their chargemobility features, particularly the electron-transfer properties. In principle, the electron-transfer rate between two stacked compounds is estimated by the Marcus theory:36,37

Scheme 1. Group A: Derivatives with Linear or Nonlinear Fused Benzene Rings

antiaromaticity of the center diazapentalene core, and the results matched well with the experimental ones. This further arouses our interests to investigate systematically the factors that might influence the stability of 1,4-diazapentalene heteroacenes. Thus, a series of compounds were designed theoretically to examine their structure−stability relationship, including the derivatives with linear or nonlinear fused benzene rings (A-1 to A-5 in Scheme 1), the derivatives with electrondonating or -withdrawing substituents (B-1 to B-4 in Scheme 2 and C-1 to C-10 in Scheme 3), and the derivatives with electron-rich or -poor heterocyclic rings (D-1 to D-12 in Scheme 4 and E-1 to E-12 in Scheme 5). Here, we report the theoretical study of the stability evolution of the 1,4-diazapentalene derivatives using the nucleus independent chemical shift (NICS) method23−25 and further evaluate their reorganization energy, which is an important parameter for OFETs. The current computational study provided useful clues to enhance the stability of the parent diazapentalene core. Two important designing ideas may be very useful: the first one is that the linear fusion of aromatic rings onto the antiaromatic core strongly enhances the overall stability, whereas the nonlinear fusion does not; the other one is that the introduction of electron-poor heterocyclic rings further enhances the stability. The calculation on the reorganization energy of the stable antiaromatic diazapetalenes shows that a linear fusion pattern could reduce the reorganization energy, which would favor the charge-transfer process. We expect that this work throws light on the understanding of the stability of antiaromatic systems and gives helpful ideas to synthesize useful compounds with potential employment in OFETs.

k≠ =

⎛ (λ + ΔG°)2 ⎞ 2π 1 Hn , i 2 exp⎜ − ⎟ 4λKbT ⎠ ℏ 4πλKbT ⎝

(1)

where K≠ is the transfer rate, Hn,i is the electron-transfer integral, ΔGo is the free-energy of the reaction, λ is the reorganization energy, Kb is the Boltzmann constant, and T is the temperature. In principle, the rigorous estimation of the reaction rate represents a big challenge due to many reasons.38 For instance, the electronic couplings (electron-transfer integral) show the strong dependence of stacked geometries that is not known for the present systems. In addition, the

2. COMPUTATIONAL DETAILS From the theoretical point of view, the electronic-structure calculations may provide a reliable clue on antiaromatic characters. In recent years, there are a few works focused on the stabilities of the aromatic heteropentalenes by theoretical means.18−24 In these studies, the NICS initially proposed by Schleyer25−27 and co-workers was widely used as a quantitative criterion to determine aromaticity/antiaromaticity. Since the

Scheme 2. Group B: Derivatives with Electron-Withdrawing Substituents

B


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The Journal of Physical Chemistry A Scheme 3. Group C: Derivatives with Electron-Donating Substituents

neutral state when going from the anionic to neutral geometry and the energy change in the anionic state when going from the neutral to anionic geometry, respectively.

Scheme 4. Group D: Derivatives with Fused Electron-Poor Heterocyclic Rings

3. RESULTS AND DISCUSSION 3.1. Antiaromaticity and Stability. Because only the 1,4diazapentalene core displays the antiaromatic character, the smaller NICS(1)zz values of this core should indicate the higher stability of the compound. The NICS(1)zz values of the diazapentelene core of groups A−E were calculated, and results are shown in Figure 1 and Table S1 in the Supporting Information. For easy comparison, the NICS(1)zz value of A-1 (30.70) was chosen as the reference because all the other compounds were designed on the basis of the A-1 geometry, and previous experimental work indicated its stability falls into the transition region between strong and weak antiaromatic systems.14 This implies that the compounds more stable than the A-1 might be obtained experimentally in suitable conditions. 3.1.1. Fusion Pattern of Aromatic Rings. Group A compares five derivatives (A-1 to A-5) with different fusion patterns. They could be divided into two subgroups: A-2 and A4 are the linear extension of A-1, while A-3 and A-5 are the angular extension of A-1. As shown in Figure 1, the NICS(1)zz value of A-2 is 20.61 and A-4 is 14.92, which decreases significantly compared with that of A-1 (30.70). This clearly indicates that the antiaromaticity of the diazapentalene core is effectively diluted with the increase of linear fusion of more benzene rings to the center aromatic core and will contribute to the overall stability. However, this statement holds true only when more linearly fused benzene rings would not lead to side reactions such as [4 + 2] cyclization or dimerization. In other

reorganization energy is decomposed as intramolecular and intermolecular ones. It is very difficult to estimate the contribution of the latter term that involves the solvent rearrangement and its associating polarization change during the electron-transfer processes. As a preliminary study, it should be reasonable to examine the intramolecular reorganization energy of all species and decide their relative charge-mobility feature qualitatively. Because the details of the calculations on the intramolecular reorganization energy were well discussed by previous work,39−41 we only outline the essential idea here. The intramolecular reorganization energy for the electron-transfer process describes the energy relaxation due to the geometry changes of individual molecules. This term is obtained by the sum of λe and λe−, which describe the energy change in the

Scheme 5. Group E: Derivatives with Fused Electron-Rich Heterocyclic Rings

C


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Figure 1. NICS(1)zz values of the left five-membered central ring of each compound.

diazapentalene moiety in A-3 showed the strongest antiaromatic character. Compound A-5 has six “semilocalized” aromatic sextets, in which the moiety in the elliptic curve resembles the structure of A-1. However, due to their semilocalized nature, the electronic coupling between the aromatic sextets at the periphery positions to the center aromatic sextet is not strong, which could not effectively increase the effective conjugated length. This explains why compound A-5 has an NICS(1)zz value similar to (but smaller than) that for A-1. The photoexcitation pattern also reflects the aromatic/ antiaromatic nature of the compounds in group A (Table S2, Supporting Information). Generally speaking, if the HOMO → LUMO transition is forbidden, the compound displays a typical antiaromatic character; on the contrary, if the HOMO → LUMO transition is allowed, the compound displays a typical aromatic character. Hence, we calculated the electronic transition of the compounds in group A. As shown in Figure 2, the HOMO → LUMO transitions of A-1 and the nonlinearly extended compounds (A-3 and A-5) are completely forbidden, consistent with their antiaromatic feature. In contrast, the HOMO → LUMO transitions of the linearly extended compounds (A-2 and A-4) are allowed, reflecting that their antiaromatic nature is highly diluted.

words, the number of the benzene rings that we can linearly fuse to this diazapentalene system has an upper limit. That is why in A group the maximum number of linearly fused benzene rings is 3 (the anthracene structure is quite stable toward [4 + 2] cyclization or dimerization at ambient conditions). In contrast, compound A-3 displays a very high NICS(1)zz value (54.90) and its synthesis should be almost impossible. This is in accordance with the experimental results.14 On the contrary, A5 with the “butterfly-shaped” fusion pattern to A-1 shows a slightly smaller NICS(1)zz value (28.01) than A-1. The different influence of the fusion patterns on the dilution of the antiaromatic character could be explained by the most stable resonance structure dictated by the so-called “Clar’s” rule.42 It indicates that the most stable structure of annulated benzenes is the one possessing the maximal number of the aromatic sextets separated by the entirely “empty” six-membered rings. In other words, the π-electrons tend to be “semilocalized” in disjoint πsextets, which form isolated aromatic islands surrounded by the π-electron “empty” rings. On the basis of this rule, the benzene rings at the terminal positions could be assigned to the aromatic sextets, as shown in Scheme 6, which correspond to the most stable resonance structures. The resonance structures of A-2 and A-4 are similar to each other, in which the central diazapentalene moiety does not present a typical structure of antiaromtic systems.14 In contrast, the central diazapentalene moiety of A-3 has two resonance structures (one shown in red), both resembling the antiaromatic annulene. Therefore, the Scheme 6. Stable Resonance Structures of A-1 to A-5

Figure 2. Energy diagrams of group A. “A” denotes the dipole-allowed transition, and“F” means the optically forbidden transition. D


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controversial effects on the stability. Generally, compounds in group C show stabilities similar to that of A-1 (if they are not less stable), with the exception of C-5 and C-10. A clear correlation between the electron-donating ability and the stability of the antiaromatic system was not observed, and it seems that the position of substitution might play an important role on the overall outcome. 3.1.3. Introduction of Electron-Poor or Electron-Rich Heterocyclic Rings. Pyridine and pyrazine are among the most common electron-poor heterocycles, and their introduction onto the diazapentalene core has a dramatic influence on the stability, which is summarized in group D. Generally speaking, the replacement of the benzene ring on the indolo[3,2-b]indole core by either pyridine or pyrazine ring increases the stability (from D-1 to D-8), with the only exception of D-4 (NICS(1)zz ∼ 33.78). It is obvious that the more electron-poor pyrazine stabilizes the diazapentalene core better than pyridine moiety, and the position of the N atom also plays a role. For example, D-2 (NICS(1)zz ∼ 26.61) and D3 (NICS(1)zz ∼ 24.27) are more stable than D-1 (NICS(1)zz ∼ 29.47), and a similar trend is observed when D-4, D-5, and D-6 are compared. Strikingly, the stability of D-6 (NICS(1)zz ∼ 23.45) is very close to that of A-2 (NICS(1)zz ∼ 20.61), implying the replacement of the benzene ring by the electronpoor heterocycles with the proper N position has similar stabilizing effects as the increase of the effective conjugated length. However, the combination of the introduction of the electro-poor heterocycles with the increase of the effective conjugated length does not have a linear addition effect on the stability. For instance, although a further improvement on the stability was observed from D-9 to D-12, the best result D-9 (NICS(1)zz ∼ 19.66) only shows a slightly better stability when compared with A-2 (NICS(1)zz ∼ 20.61), which has the same effective conjugated length. But it is noteworthy to point out that the combination of these two effects is still worthy because the introduction of electron-poor heterocycles will further increase the electron affinity of these antiaromatic systems, which might facilitate the electron-transfer process, and make them better n-type semiconductors. The direct fusion of five-membered electron-rich heterocycles to the 1,4-diazapentalene core largely enhances antiaromatic characters, because such fusion (1) adds more electron density in the central rings, and (2) forces the diazazpentalene core to adopt a typical antiaromatic resonance structure. As a result, all species from E-1 to E-6 are extremely unstable (their NICS(1)zz > 67.77), even less stable than bare diazapentalene.14 However, fusing five-membered electron-rich heterocyclic rings linearly to A-1 core structure (E-7 to E-9) does not have a dramatic impact on the stability [NICS(1)zz value between 28.65 and 31.49, similar to values for A-1], which could also be explained by Clar’s rule. On the contrary, the angular fusion of five-membered electron-rich heterocyclic rings (E-10 to E-12) decreases the stability (compared to that for A1), in accordance with the results discussed in section 3.1.1. Overall, compounds E1 to E6 seem to be too unstable to be synthesized; thus they should rather be ruled out from future experimental work. The stability of E10 to E12 is between the stability of A-1 and A-3, so they might be synthesized but their stability might be an issue. In the above discussion, we mainly considered the NICS(1)zz value of the central five-membered heterocycle ring, because it directly reflects antiaromaticity and is relevant to the stability of the whole systems. As a supplementary investigation, we also

The frontier orbitals of the compounds in group A give a visual explanation of the change of the orbital symmetry hence the possibility of photoinduced transitions, as shown in Figure 3. All compounds in group A belong to the C2h symmetry

Figure 3. Frontier orbitals (HOMO−1, HOMO, and LUMO) of group A.

group. Electronic structure calculations indicate that the symmetry of the HOMO and LUMO orbitals of A-1 are assigned as the Au and Au irreducible representations, respectively. Hence the HOMO → LUMO transitions are optically forbidden. In contrast, the HOMO−1 displays Bg symmetry leading to the optical allowed HOMO−1 → LUMO transition. Same symmetry arguments are held for the explanation of optical-transition intensity of the A-1 derivatives with the nonlinear extension (A-3 and A-5), which reflects their similarity. Interestingly, the LUMO orbital of A-5 is quite similar to that of A-1, indicating that the aromatic rings at the periphery positions contributes little to the LUMO. That is why A-5 shows an antiaromatic nature similar to that of A-1. On the contrary, the symmetries of the HOMO and LUMO orbitals of the linearly extension of A-1 (A-2 and A-4) become the Bg and Au, respectively, hence the corresponding transitions are optically allowed. 3.1.2. Introduction of Additional Functional Substituents in the Adjacent Aromatic Rings. The electron-withdrawing or electron-donating natures of the substituents attached in the aromatic six-membered rings of A-1 are compared. Halogens are chosen as typical electron-withdrawing substituents not only because of their electronegativity but also because of their large influence on the packing mode and the OFET performance of heteroacenes.31 Chlorination and fluorination on A-1 slightly increase the stability, as shown in Figure 1. Fluorination (B-3 and B-4) shows a better overall stabilization effect than chlorination (B-1 and B-2). However, the increase of the degree of halogenation does not lead to better stability, as similar NICS(1)zz values were found for B-1 and B-2 (29.88 vs 29.93), as well as for B-3 and B-4 (28.22 vs 28.09). We are not so sure about the reasons, but it might result from the delicate balance between the electronegativity of the halogens and the back-donating effects of their lone pairs. On the contrary, the inclusion of electron-donating substituents (group C) has E


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Figure 4. (a) Reorganization energy and (b) correlation between reorganization energy and NICS(1)zz values of compounds of groups A, B, and D.

open-shell singlet state, though all efforts show that the wave functions finally collapse into the closed-shell singlet state. Thus, the open-shell singlet state should not play any role here. 3.2. Reorganization Energy. In principle, a smaller reorganization energy implies a faster electron-transfer rate (eq 1).36,37 Because the previous discussions have already pointed out that the compounds in groups A, B, and D may be stable, the reorganization energy of these systems was examined and the results are shown in Figure 4 and Table S5 (Supporting Information). The increase of the effective conjugated length dramatically decreases the reorganization energy. For example, the reorganization energy of A-1 is 0.44 eV, which is decreased to 0.35 eV when one or more benzene rings are linearly fused to it (A-2), and further decreased to 0.29 eV when a naphthalene ring is linearly fused to it (A-4). On the contrary, angularly fusing a benzene ring to A-1 does not increase the effective conjugated length, so A-3 shows a reorganization energy (0.46 eV) similar to that of A-1. The introduction of electron-withdrawing substituents does not have an obvious influence on reorganization energy. All compounds in group B have reorganization energies (0.43− 0.47 eV) similar to that of A-1. However, the introduction of electron-poor heterocycles has an obvious influence on the reorganization energy. It is obvious that the reorganization energy increases when the benzene ring on the indolo[3,2-b]indole core (A-1) is replaced with pyridine or pyrazine rings (from D-1 to D-8), indicating that existence of more heteroatoms in the system might lead to a larger geometry distortion during the electron-transfer process. However, this effect might be canceled by increasing the effective conjugated length. For instance, D-9 shows a similar reorganization energy (0.49 eV) when compared with A-1, and compounds D-10 to D-12 exhibit reorganization energies similar to that of A-2. This again indicates that the combination of the introduction of electron-poor heterocycles and the increase of effective conjugated length might be an effective way to find better antiaromatic n-type semiconductors.

made additional calculation on the NICS(1)zz values of the aromatic ring adjacent to the central five-membered rings (Figure S1, Table S1 Supporting Information). Interestingly, two sets of NICS(1)zz values display a certain correlation (Figure S2, Supporting Information). When the central fivemembered heterocycle ring displays lower antiaromaticity, the adjacent ring becomes less aromatic. The reason is quite obvious: the dilution of antiaromaticity of the central ring is on the cost of the aromaticity of the adjacent aromatic rings. For consistency, the current work mainly focuses on the NICS value of the central five-membered heterocycle ring. As suggested by previous works, the isomerization energy (ISE)27,43 is an additional reasonable criterion to evaluate the stability of the aromatic systems due to the strong correlation between ISE and NICS.44−46 We chose a series of compounds with the same A-1 core to examine their ISE values. In this work, a methyl group is added into the six-membered rings adjacent to the central five-membered heterocycle ring (Figure S3, Supporting Information). It is reasonable to assume that such attachment should not significantly change the aromaticity/antiaromaticity of the whole system. The isomerization reactions of such structures were shown in Figure S3 (Supporting Information). The energy difference between the above two structures defines the ISE of the selected compounds (Table S3, Supporting Information). It is true that larger ISE values normally correspond to smaller NICS(1)zz values, implying the weaker antiaromaticity of the whole system (Figure S4, Supporting Information). This suggests that ISE originally proposed for the aromatic systems may also play as an additional criterion to determine the stability of antiaromatic systems. Because we mainly focus on the discussion of NICS(1)zz, here, more details on ISE can be found in the Supporting Information. To examine the possible involvement of other electronic states, we performed the wave function stability analysis of the closed-shell singlet states of all molecules. The results show that the ground-state closed-shell wave function are stable for all species. In addition, the triplet-state minimum-energy structures of all molecules were optimized at the B3LYP/6-31+g* level. The calculation results show that the triplet states are located higher than the singlet states for all studied compounds (Table S4, Supporting Information). The reason is possibly due to the fact that we do not have an extremely long conjugated system here. Although for a few of compounds (E1 to E6), the triplet energies are not much higher than the singlet energies, these compounds are not essential for the stability evaluation due to their extreme instability. We also tried to search the

4. CONCLUSIONS In this article, we systematically studied the structure−stability relationship of several types of heteroacenes bearing the 1,4diazapentalene core using NICS(1)zz calculation. For those stable derivatives, we also evaluated their reorganization energy while is an important parameter to determine the electrontransfer feature of OFETs. F


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Center, CAS, and the super computational center of CASQIBEBT for providing computational resources.

In summary, the fusion of aromatic ring to the 1,4diazapentalene core may dilute its antiaromatic feature, whereas the final stability is largely dependent on the fusion pattern. The linear pattern improves its stability and the nonlinear way leads to the opposite effect. Due to the attraction of electron density by electron-withdrawing substituents, the inclusion of such functional moieties or fused electron-poor heterocyclic rings generally enhances the stability of the compounds with a 1,4-diazapentalene core, and vice versa. In addition, the inclusion of fused rings displays a much larger impact on stability than the simple addition of functional substituents, because the fused rings are directly connected to the 1,4diazapentalenes core. The increase of the effective conjugated length dramatically decreases the reorganization energy. The introduction of electron-withdrawing substituents does not have an effective influence on reorganization energy. In contrast, the introduction of electron-poor heterocycles may modify the reorganization energy. The combination of the introduction of electronpoor heterocycles and the increase of effective conjugated length might be effective to improve the electron-conduction ability in antiaromatic n-type semiconductors. We expect that this work throws light on the understanding of the stability of antiaromatic systems and gives helpful ideas to design novel 1,4-diazapentalene based compounds with potential employment in OFETs.

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ASSOCIATED CONTENT

S Supporting Information *

The figure of the positions to measure NICS(1)zz; the table of NICS(1)zz values of each compound; the figure of the relationship between NICS(1)zz(A) and NICS(1)zz(B); the table of excited states of the compounds in group A; the figure of three possible pathways in the ISE calculations; the table of ISE (kcal/mol)and NICS(1)zz values of selected compounds; correlation diagram between ISE1, ISE2, ISE3, and NICS(1)zz(A) or NICS(1)zz(B); the table of energy differences between the triplet state at the triplet minimum and the closedshell singlet state at the ground-state minimum; the table of reorganization energy values of compounds in group A, group B, and group D; the figure of stacked (A-4)2 complex and relevant dimers. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*X. Wan. Fax: +86-532-80662778. Tel: +86-532-80662740. Email: [email protected]. *Z. Lan. Fax: +86-532-80662778. Tel: +86-532-80662630. Email: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the CAS 100 Talent Project, NSFC project (Grant Nos. 21103213, 21174157, and 91233106), and the Director Innovation Foundation of CAS-QIBEBT. The authors thank the support by Key Lab of Nanodevices and Nanoapplications, Suzhou Institute of Nano-Tech and NanoBionics, CAS (Funding No. 14HZ03). The authors also thank Supercomputing Center, Computer Network Information G


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Antiaromatic Characteristic Analysis of 1,4 ... - ACS Publications

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