Theoretical Research of Substituted Bay Region with Helical Chirality: Structures and Enantiomerization

Theoretical Research of Substituted Bay Region with Helical Chirality: Structures and Enantiomerization | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Theoretical Research of Substituted Bay Region with Helical Chirality: Structures and Enantiomerization Huimin Zhou, Yijian Ma, Jiaxin Shi, Na Yang, Chengshuo Shen This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8431401/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 13 Apr, 2026 Read the published version in Structural Chemistry → Version 1 posted 7 You are reading this latest preprint version Abstract We systematically investigated the chirality of substituted bay regions in polycyclic aromatic hydrocarbons (PAHs) via density functional theory (DFT) calculations, focusing on effects of substituents, π -conjugation extension, heterocycles, and π -skeleton curvature. Most bay-substituted PAHs form non-planar helical structures. As the steric hindrance of the substituents increases, the enantiomerization barriers of the phenanthrene derivatives increase. Similarly, π -conjugation extension can also increase the enantiomerization barriers. Heterocycles could also modulate the enantiomerization barriers of the PAHs by tuning the identity of the central heteroatom, and specifically, heterocyclic PAH derivatives incorporating heteroatoms with larger atomic radii exhibit higher enantiomerization barriers. Hexa[7]circulene ( PAH8 ), which contains a central heptagonal ring, is already non-planar, with an enantiomerization barrier of 15.9 kcal mol −1 . When the bay region of PAH8 is substituted, the enantiomerization barrier increases (up to 80.1 kcal mol −1 ). This work elucidates bay-region enantiomerization rules, providing theoretical guidance for designing functional chiral π -conjugated molecules. chirality enantiomerization barrier bay region Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1 Introduction Chiral polycyclic aromatic hydrocarbons (PAHs) with distorted chiral π -conjugation systems typically exhibit prominent chiroptical properties including electronic circular dichroism (ECD) and circularly polarized luminescence (CPL). 1 – 4 The most famous examples are helicenes 5 – 14 , which display significant ECD signals with Δ ε in the 10 2 L mol − 1 cm − 1 range, and CPL with a dissymmetry factor | g ₗ u ₘ| up to the 10 − 2 range. Aside from helicenes, another class of PAHs termed twistacenes also displays similar intense chiroptical properties. 15 – 23 The superior chiroptical properties of these PAHs, compared to centrally chiral molecules, likely stem from their chiral π -systems providing larger magnetic transition dipole moments. 24 – 28 A common strategy to construct chiral π -systems from planar π -systems is to create steric effects. For example, [4]helicene, composed of four ortho -fused benzenoid rings, adopts a non-planar, helical conformation due to steric repulsion between its terminal moieties. 29 – 33 Similarly, the twistacenes benefit from the steric hindrance imposed by side substituents, which induces twisting of their π -conjugated frameworks. 16 , 17 Recent studies on nanographenes have also revealed that the bay region—a structural motif comprising three contiguous benzenoid rings—can also exhibit helical chirality upon substitution. 34 , 35 Compared with unsubstituted phenanthrene adopting a planar structure, the phenanthrene with the bay region substituted with functional groups is no longer planar and exhibits a helical geometry. In 1996, Grimme and Peyerimhoff theoretically investigated the enantiomerization barriers of dimethyl substituted phenanthrene. 36 In 2021, we reported a series of nanographenes containing tert-butyl-substituted bay regions, where the conformation exert significant influence on the chiroptical properties. 37 Further examples have demonstrated that increased steric crowding could further enhance the stability of the bay region chirality, leading to chiroptical responses. 38 – 40 However, the inversion process (i.e., enantiomerization) of these chiral bay regions has not yet been systematically explored. In this paper, we aim to investigate the substituent effect on the geometric distortion of the bay region via density functional theory (DFT) calculations. Additionally, we investigate the enantiomerization process and calculate the inversion barrier of these chiral bay regions. We anticipate such study will provide a new idea in constructing novel chiral π -molecules with outstanding chiroptical properties. 2 Results and discussions All calculations have been conducted using Gaussian 09 software. 41 Geometry optimizations have been carried out at the PBE0-D3(BJ)/def2-TZVPP level of theory without imposing any symmetry constraints. 42 - 44 Harmonic vibrational frequency analysis was performed on the optimized geometries to determine the energy local minima with no imaginary frequency and the transition states with only one imaginary frequency. Phenanthrene ( Phen ) is chosen as the model system to evaluate substituent effects. A series of Phen derivatives, mono-substituted at the 4-position or bis-substituted at the 4,5-position with halogen atoms ( F, Cl, Br, I ), have been studied. To establish a connection between the structure and enantiomerization barriers (Δ G ‡ ) of Phen , we first use the dihedral angle of the four carbon atoms in the bay region, denoted as (5-4b-4a-4, ∠A), to measure the degree of distortion (Fig. 1a). After geometry optimization, we found that the monofluorine derivative ( Phen F,H ) retains a planar structure, ∠A is 0°, similar to the unsubstituted Phen . In contrast, all other mono-substituted derivatives adopt non-planar, helical conformations. ∠A increases with the increasing steric bulkiness of the halogen substituent in mono-substituted derivatives: Phen Cl,H (9.4°), Phen Br,H (13.8°), and Phen I,H (17.2°) (Fig. 1c). Similarly, for bis-substituted derivatives they also follow the same pattern: as the steric size increases, ∠A increases. All bis-substituted Phen exhibit chirality, and the smallest one is Phen F,F with ∠A of 22.4°; the largest one is Phen I,I with ∠A of 35.8°. Additionally, we calculated the enantiomerization barriers (corresponding to the inversion from P -helicity to M -helicity) of these helically shaped molecules by optimizing the geometry of the transition state of these Phen derivatives. For the transition state Phen Cl,H ‡ adopts a fully planar geometry, and the enantiomerization barrier is calculated as 1.1 kcal mol −1 . Similarly, the transition states Phen Br,H ‡ and Phen I,H ‡ are also fully planar, with calculated barriers of 1.2 and 1.5 kcal mol −1 , respectively. Notably, increasing the number of substituents leads to a significant elevation in enantiomerization barriers: Phen F, F (2.3 kcal mol −1 ), Phen Cl, Cl (16.2 kcal mol −1 ), Phen Br, Br (22.2 kcal mol −1 ), and Phen I, I (28.9 kcal mol −1 ) (Fig. 1c). The enantiomerization barriers of the remaining bis-substituted compounds are shown in Table 1. Furthermore, we investigated the relationship between the enantiomerization barrier and ∠A (Fig. 2). The barrier rises slowly at small ∠A but increases sharply when ∠A exceeds ca. 30°. Therefore, the larger the ∠A, the more significant the increase in the enantiomerization barrier. Table 1 . Enantiomerization barriers of phenanthrene derivatives in kcal mol −1 . Type Energy Type Energy Type Energy Phen H,H 0 Phen F,H 0 Phen Cl,H 1.1 Phen Br,H 1.2 Phen I , H 1.5 Phen F,F 2.3 Phen Cl,F 7.0 Phen Br,F 8.3 Phen I,F 9.3 Phen Cl,Cl 16.2 Phen Br,Cl 18.6 Phen I,Cl 20.8 Phen Br,Br 22.2 Phen I,Br 25.2 Phen I,I 28.9 In addition, we use the rotary angle (∠B) 45 , between two C-C bonds (C8a-C4b and C10a-C4a) of Phen , to establish a connection between the structure and enantiomerization barriers (Fig. 1b). For both mono- and bis-substituted derivatives, ∠B in the local minimum increases with the increase of the atomic size: Phen Cl, H (57.0°), Phen Br, H (57.3°), Phen I, H (57.7°), Phen F,F (56.9°), Phen Cl, Cl (59.9°), Phen Br,Br (60.2°), and Phen I, I (60.4°). Meanwhile, ∠B in the transition state is roughly diminishes with the increase of the atomic size. Therefore, we define the difference between ∠B in the transition state and ∠B in the local minimum as Δ∠B. In Phen Cl, H , Δ∠B is 0.4°. Similarly, Δ∠B is 1.5°for Phen I, H , 6.8°for Phen Cl, Cl , and 8.1°for Phen I, I , which is well accord to the increase of enantiomerization barrier (Fig. 1c). Then we investigated the enantiomerization barrier of methyl-, tert-butyl-, and phenyl-substituted Phen . We found that mono-substituted Phen exhibit ∠B ranging from 56.9° to 58.5°, and Δ∠B ranging from 0.4° to 3.3°with similar enantiomerization barriers of ca. 1 kcal mol −1 . On the other hand, the bis-substituted analogues show much higher enantiomerization barriers. For example, Phen Me,Me shows an enantiomerization barrier of 16.2 kcal mol −1 and Δ∠B is 6.7°. Notably, Phen tBu, tBu exhibits an extremely high enantiomerization barrier of 54.2 kcal mol −1 and Δ∠B also exhibits a large value of 11.7° (Fig. 3). Compared with the mono-substituted derivatives, the bis-substituted Phen derivatives exhibit higher enantiomerization barriers and the difference indicates that the two substituents might have a synergistic effect, thus augmenting the enantiomerization barriers. Overall, alkyl/aryl-substituted Phen derivatives have similar properties to halogen-substituted Phen derivatives, and the greater the change in Δ∠B, the higher the energy barrier for transition state. Subsequently, we explored the effect of π -conjugation extension and constructed a series of molecules with π -conjugated skeletons ( PAH1 to PAH7 ) (Fig. 4). For PAH1 , we added an additional benzenoid ring to the central ring, giving a triphenylene skeleton. The enantiomerization barriers for mono-tert-butyl-, bis-methyl-, and bis-bromo-derivatives PAH1 tBu,H , PAH1 Me,Me , and PAH1 Br,Br are 7.1, 20.2 and 25.1 kcal mol −1 , respectively (Table 2). These results are obviously larger than the unsubstituted Phen derivatives (1.1, 16.2 and 22.2 kcal mol −1 ). Similarly, by fusing two additional benzenoid rings to form a perylene-based skeleton, the three derivatives PAH2 tBu,H , PAH2 Me,Me , and PAH2 Br,Br display the enantiomerization barriers of 7.5, 26.7 and 31.1 kcal mol −1 , respectively. This increase may stem from the constrained deformation of ∠B by the extended π -system during the enantiomerization (Fig. S4). Analogous trends were observed for the subsequent PAHs ( PAH3 to PAH7 ). Notably for PAH5 , although the two additional benzenoid rings are fused to the two terminal rings, the enantiomerization barriers also increase significantly. Table 2 . Enantiomerization barriers of PAH1–PAH7 derivatives in kcal mol −1 . Type Energy Type Energy Type Energy PAH1 tBu,H 7.1 PAH1 Me,Me 20.2 PAH1 Br,Br 25.1 PAH2 tBu,H 7.5 PAH2 Me,Me 26.7 PAH2 Br,Br 31.1 PAH3 tBu,H 5.5 PAH3 Me,Me 23.9 PAH3 Br,Br 28.6 PAH4 tBu,H 7.3 PAH4 Me,Me 27.0 PAH4 Br,Br 30.6 PAH5 tBu,H 5.1 PAH5 Me,Me 21.1 PAH5 Br,Br 26.9 PAH6 tBu,H 9.4 PAH6 Me,Me 26.2 PAH6 Br,Br 31.6 PAH7 tBu,H 12.1 PAH7 Me,Me 25.0 PAH7 Br,Br 30.2 Furthermore, with increased π -extension forming a hexabenzocoronene PAH6 , the enantiomerization barriers exhibit no further obvious increase (vs. PAH3 , Fig. S5), suggesting that the distant benzenoid rings might bring negligible influence for the enantiomerization barriers (Fig. S8). Notably, PAH7 (the reduced product of Phen) exhibits a significantly higher enantiomerization barrier than unsubstituted Phen. The three derivatives, PAH 7 tBu,H , PAH 7 Me,Me , and PAH 7 Br,Br display the enantiomerization barrier of 12.1, 25.0 and 30.2 kcal mol −1 , respectively. It is likely due to the elongation of C–C bonds upon reduction, enlarging ∠B in PAH7 . To gain a deeper understanding of the relationship between ∠B and the enantiomerization, we systematically investigated the influence of Phen with the central benzenoid ring replaced by heterocycles ( H3X , X = C, Si, Ge, Sn, N, P, As, Sb, O, S, Se, and Te). We first calculated these heterocycle-substituted Phen compounds with mono-tert-butyl-substitution, and we found that ∠B values at the local minimum range from 29.5° to 59.3° depending on the different heterocycles (vs. 58.5° of Phen ). Among this series, only H3Sn tBu ,H shows a helical structure and its enantiomerization barrier is 1.2 kcal mol −1 . The other derivatives all show a fully planar π -skeleton. (Fig. 5) When switching to the bis-methyl- and bis-bromo-substituted derivatives (Fig. 6), we found that only H3O Me,Me and H3N Me,Me are fully planar, while the rest compounds possess helical geometry. If the central heteroatom is from the second period, ∠B are smaller and the enantiomerization barriers are relatively low. In contrast, heteroatoms from the fifth-period lead to a larger ∠B and higher enantiomerization barriers. Overall, we found a strong positive correlation between the enantiomerization barriers and ∠B (Fig. 6), indicating that the type of aromatic ring at the bay region exerts a significant influence on the enantiomerization barrier. We finally examined the impact of skeleton curvature and used hexa[7]circulene ( PAH8 ; Fig. 7) as an example 46 , which contains a central heptagonal ring and adopts negative curvature. Compared with PAH3 , PAH8 shows an additional benzenoid ring on the skeleton, resulting in the central hexagonal ring to be heptagonal. This aggravates the crowdedness of the bay region. Notably, even the unsubstituted PAH8 H,H already becomes non-planar, with the enantiomerization barrier of 15.9 kcal mol −1 (for comparison, PAH3 H,H is fully planar). Then we studied the enantiomerization barriers of mono-substituted and bis-substituted PAH8 derivatives, and the corresponding data, together with those of a series of halogen-substituted PAH8 derivatives, are summarized in Table 3. When PAH3 and PAH8 have the same substituents, for example the bis-bromo derivatives have barriers of 28.6 kcal mol⁻¹ ( PAH3 Br,Br , Fig. S5) and 56.7 kcal mol⁻¹ ( PAH8 Br,Br , Table 3), and the bis-methyl derivatives have barriers of 23.9 kcal mol⁻¹ ( PAH3 Me,Me , Fig. S5) and 51.5 kcal mol⁻¹ ( PAH8 Me,Me , Table 3), the enantiomerization barriers of PAH8 are always higher than PAH3 . Besides, we found that the enantiomerization barrier of PAH8 tBu,tBu reach up to 80.1 kcal mol −1 . Table 3 . Enantiomerization barriers of PAH 8 derivatives in kcal mol −1 . Type Energy Type Energy Type Energy PAH8 H,H 15.9 PAH8 F,H 20.0 PAH8 Cl,H 26.6 PAH8 Br,H 27.9 PAH8 I,H 29.3 PAH8 F,F 33.3 PAH8 F,Cl 41.2 PAH8 F,Br 42.4 PAH8 F,I 42.8 PAH8 Cl,Cl 52.0 PAH8 Cl,Br 54.2 PAH8 Cl,I 55.4 PAH8 Br,Br 56.7 PAH8 Br,I 58.5 PAH8 I,I 61.2 PAH8 Me,H 27.4 PAH8 tBu,H 36.0 PAH8 Ph,H 25.9 PAH8 Me , Me 51.5 PAH8 tBu , tBu 80.1 PAH8 Ph , Ph 51.1 3 Conclusion In summary, we have investigated the chirality for the substituted bay region in a rich array of PAHs with different substituents, π -conjugation extension, heterocyclic substitution and π -skeleton curvature. Most PAHs substituted at the bay region exhibit a steric effect, resulting in a non-planar π -skeleton, forming helical structures. The enantiomerization barriers of these PAHs are predominantly influenced by the steric bulk of the substituents. We found that the enantiomerization barriers of iodine-substituted and tert-butyl-substituted derivatives are always high, with respective values of Phen I,H (1.5 kcal mol − 1 ), Phen tBu,H (1.1 kcal mol − 1 ), Phen I,I (28.9 kcal mol − 1 ), and Phen tBu,tBu (54.2 kcal mol − 1 ). Furthermore, our investigations into heterocycle-incorporated PAH derivatives reveal that ∠B also exerts a significant influence on the enantiomerization barriers: the larger ∠B, the higher the corresponding enantiomerization barriers. Besides the π -conjugation on the phenanthrene moiety could also increases the enantiomerization barrier. Lastly, we studied a unique class of PAHs with negatively curved molecular π -skeleton—the hexa[7]circulene ( PAH8 ), which contains a central heptagonal ring. Such geometry shows the central bay region is much more crowded compared with the hexagonal derivatives PAH3 . In this work we aimed to investigate the geometry angle of the bay region by the substituents and discovered the rules for enantiomerization. We anticipate that this theoretical work will guide the design of large π -conjugated aromatic systems by incorporating chiral bay regions to enhance their chiroptical properties, and expect to use the chirality of the bay region to enrich the skeleton versatility of the functional PAHs. Declarations Acknowledgements I would like to express my sincere gratitude to the Zhejiang Sci-Tech University – School of Chemistry and Chemical Engineering for providing the ideal scientific environment that supported the completion of this research. Supplementary Information The online version contains supplementary material available at . Author contributions All authors contributed to the study. Chengshuo Shen and Na Yang conceived this project and undertook the theoretical calculations for the molecules under investigation. Huimin Zhou was responsible for data processing and article proofreading, Yijian Ma handled manuscript polishing and detail correction, and Jiaxin Shi was in charge of the organization of supporting materials. All authors have read and agreed to the published version of the manuscript. Funding This work was financially supported by the Zhejiang Provincial Natural Science Foundation, China (LY23B040003), and the National Natural Science Foundation of China (22561160131). Data availability Not applicable. Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Corresponding author : Chengshuo Shen References Anderson, HV., Gois, ND., Chalifoux, WA.: New advances in chiral nanographene chemistry. Org. Chem. Front. 10(16), 4167-4197 (2023). 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Additional Declarations No competing interests reported. Supplementary Files SCSupplementaryMaterials.pdf Cite Share Download PDF Status: Published Journal Publication published 13 Apr, 2026 Read the published version in Structural Chemistry → Version 1 posted Editorial decision: Revision requested 29 Dec, 2025 Reviews received at journal 28 Dec, 2025 Reviewers agreed at journal 24 Dec, 2025 Reviewers invited by journal 24 Dec, 2025 Editor assigned by journal 24 Dec, 2025 Submission checks completed at journal 24 Dec, 2025 First submitted to journal 23 Dec, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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10:19:58","extension":"html","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":127701,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8431401/v1/9a0388586ab01bf42208a0b8.html"},{"id":99036528,"identity":"766479c7-2e64-4a36-bb92-c670e9888a7c","added_by":"auto","created_at":"2025-12-26 10:19:58","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":186568,"visible":true,"origin":"","legend":"\u003cp\u003eOptimized structures of halogen-substituted phenanthrene derivatives (both energy local minimum and transition state), as well as their distortion angle (∠A), rotary angle (∠B), difference in rotary angles between the local minimum and transition state (Δ∠B) and enantiomerization barriers (in kcal mol\u003csup\u003e−1\u003c/sup\u003e).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8431401/v1/6c59a546cc02f539004f5bec.png"},{"id":99314391,"identity":"8f306b6e-216e-4aa1-8bc9-cf9af55f966b","added_by":"auto","created_at":"2025-12-31 16:21:20","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":74663,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation between halogen substitution patterns and enantiomerization barriers of phenanthrene derivatives.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8431401/v1/f361c2ac163d827d42953ede.png"},{"id":99036531,"identity":"d2388f2f-7ced-4122-a64a-e7d2c29f92e3","added_by":"auto","created_at":"2025-12-26 10:19:58","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":223942,"visible":true,"origin":"","legend":"\u003cp\u003eOptimized structures of alkyl/aryl-substituted phenanthrene derivatives, along with their rotary angle (∠B), and the difference in rotary angles between the local minimum and transition state (Δ∠B) and enantiomerization barriers (in kcal mol\u003csup\u003e−1\u003c/sup\u003e).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8431401/v1/7e52a9f8e2ed80cd3908f211.png"},{"id":99313055,"identity":"7a95aed4-66a8-47f3-94c5-14ab442be567","added_by":"auto","created_at":"2025-12-31 16:19:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":70548,"visible":true,"origin":"","legend":"\u003cp\u003eChemical structures of \u003cstrong\u003ePAH1–PAH7\u003c/strong\u003e.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8431401/v1/1da9bd62960ea90611525505.png"},{"id":99313303,"identity":"6637a1e9-3d35-4c9f-b869-e69a87645308","added_by":"auto","created_at":"2025-12-31 16:19:58","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":191802,"visible":true,"origin":"","legend":"\u003cp\u003eOptimized structures of a \u003cstrong\u003eH3X\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003etBu,H\u003c/strong\u003e\u003c/sub\u003e, as well as their rotary angles (∠B) and \u003cstrong\u003eH3Sn\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003etBu,H\u003c/strong\u003e\u003c/sub\u003e enantiomerization barriers (in kcal mol\u003csup\u003e−1\u003c/sup\u003e).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8431401/v1/96378c2ccee4bb6f2ec54230.png"},{"id":99036538,"identity":"45712cd7-da6b-4a84-8f04-c3204f383b5d","added_by":"auto","created_at":"2025-12-26 10:19:58","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":81608,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation between rotary angles (∠B) and enantiomerization barriers of bis-substituted \u003cstrong\u003eH3X\u003c/strong\u003ederivatives. (Red line: bis-methyl, black line: bis-bromo.)\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8431401/v1/26ee664cc06ace52d3af5f02.png"},{"id":99313697,"identity":"1fa21eed-b672-456b-b29f-f31cd94204c7","added_by":"auto","created_at":"2025-12-31 16:20:25","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":61434,"visible":true,"origin":"","legend":"\u003cp\u003eThe structures of \u003cstrong\u003ePAH8\u003c/strong\u003e derivatives and the enantiomerization barrier of \u003cstrong\u003ePAH8\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003eH,H\u003c/strong\u003e\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8431401/v1/9c4e97589ea2d30b49d3fd1a.png"},{"id":107352190,"identity":"000f1260-f407-4fca-bf0c-9a4dcaf203e6","added_by":"auto","created_at":"2026-04-20 16:13:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1403868,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8431401/v1/19fcb9ad-4829-4006-b0e8-fd161cfc2828.pdf"},{"id":99036555,"identity":"8c1ae2b9-4c18-448a-8ec0-b90fe7b0aef9","added_by":"auto","created_at":"2025-12-26 10:19:58","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":11658886,"visible":true,"origin":"","legend":"","description":"","filename":"SCSupplementaryMaterials.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8431401/v1/ef88f4256687e8fea6ab288a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Theoretical Research of Substituted Bay Region with Helical Chirality: Structures and Enantiomerization","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eChiral polycyclic aromatic hydrocarbons (PAHs) with distorted chiral \u003cem\u003eπ\u003c/em\u003e-conjugation systems typically exhibit prominent chiroptical properties including electronic circular dichroism (ECD) and circularly polarized luminescence (CPL).\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e The most famous examples are helicenes\u003csup\u003e\u003cspan additionalcitationids=\"CR6 CR7 CR8 CR9 CR10 CR11 CR12 CR13\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, which display significant ECD signals with Δ\u003cem\u003eε\u003c/em\u003e in the 10\u003csup\u003e2\u003c/sup\u003e L mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e range, and CPL with a dissymmetry factor |\u003cem\u003eg\u003c/em\u003eₗ\u003csub\u003eu\u003c/sub\u003eₘ| up to the 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e range. Aside from helicenes, another class of PAHs termed twistacenes also displays similar intense chiroptical properties.\u003csup\u003e\u003cspan additionalcitationids=\"CR16 CR17 CR18 CR19 CR20 CR21 CR22\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e The superior chiroptical properties of these PAHs, compared to centrally chiral molecules, likely stem from their chiral \u003cem\u003eπ\u003c/em\u003e-systems providing larger magnetic transition dipole moments.\u003csup\u003e\u003cspan additionalcitationids=\"CR25 CR26 CR27\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e A common strategy to construct chiral \u003cem\u003eπ\u003c/em\u003e-systems from planar \u003cem\u003eπ\u003c/em\u003e-systems is to create steric effects. For example, [4]helicene, composed of four \u003cem\u003eortho\u003c/em\u003e-fused benzenoid rings, adopts a non-planar, helical conformation due to steric repulsion between its terminal moieties.\u003csup\u003e\u003cspan additionalcitationids=\"CR30 CR31 CR32\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e Similarly, the twistacenes benefit from the steric hindrance imposed by side substituents, which induces twisting of their \u003cem\u003eπ\u003c/em\u003e-conjugated frameworks.\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e Recent studies on nanographenes have also revealed that the bay region\u0026mdash;a structural motif comprising three contiguous benzenoid rings\u0026mdash;can also exhibit helical chirality upon substitution.\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e Compared with unsubstituted phenanthrene adopting a planar structure, the phenanthrene with the bay region substituted with functional groups is no longer planar and exhibits a helical geometry. In 1996, Grimme and Peyerimhoff theoretically investigated the enantiomerization barriers of dimethyl substituted phenanthrene.\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e In 2021, we reported a series of nanographenes containing tert-butyl-substituted bay regions, where the conformation exert significant influence on the chiroptical properties.\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e Further examples have demonstrated that increased steric crowding could further enhance the stability of the bay region chirality, leading to chiroptical responses.\u003csup\u003e\u003cspan additionalcitationids=\"CR39\" citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e However, the inversion process (i.e., enantiomerization) of these chiral bay regions has not yet been systematically explored.\u003c/p\u003e \u003cp\u003eIn this paper, we aim to investigate the substituent effect on the geometric distortion of the bay region via density functional theory (DFT) calculations. Additionally, we investigate the enantiomerization process and calculate the inversion barrier of these chiral bay regions. We anticipate such study will provide a new idea in constructing novel chiral \u003cem\u003eπ\u003c/em\u003e-molecules with outstanding chiroptical properties.\u003c/p\u003e"},{"header":"2 Results and discussions","content":"\u003cp\u003eAll calculations\u0026nbsp;have been conducted using Gaussian 09\u0026nbsp;software.\u003csup\u003e41\u003c/sup\u003e Geometry optimizations have been carried out at the PBE0-D3(BJ)/def2-TZVPP level of theory without imposing any symmetry constraints.\u003csup\u003e42\u003c/sup\u003e\u003csup\u003e-\u003c/sup\u003e\u003csup\u003e44\u003c/sup\u003e Harmonic vibrational frequency analysis was performed on the optimized geometries to determine the energy local minima with no imaginary frequency and the transition states with only one imaginary frequency.\u003c/p\u003e\n\u003cp\u003ePhenanthrene (\u003cstrong\u003ePhen\u003c/strong\u003e) is chosen as the model system to evaluate substituent effects. A series of \u003cstrong\u003ePhen\u003c/strong\u003e derivatives, mono-substituted at the 4-position or bis-substituted at the 4,5-position with halogen atoms (\u003cstrong\u003eF, Cl, Br, I\u003c/strong\u003e), have been studied.\u003c/p\u003e\n\u003cp\u003eTo establish a connection between the structure and enantiomerization barriers (\u0026Delta;\u003cem\u003eG\u003c/em\u003e\u003csup\u003e\u0026Dagger;\u003c/sup\u003e) of \u003cstrong\u003ePhen\u003c/strong\u003e, we first use the dihedral angle of the four carbon atoms in the bay region, denoted as (5-4b-4a-4,\u0026nbsp;\u0026ang;A), to measure the degree of distortion (Fig. 1a). After geometry optimization, we found that the monofluorine derivative (\u003cstrong\u003ePhen\u003csub\u003eF,H\u003c/sub\u003e\u003c/strong\u003e) retains a planar structure, \u0026ang;A is 0\u0026deg;, similar to the unsubstituted \u003cstrong\u003ePhen\u003c/strong\u003e. In contrast, all other mono-substituted derivatives adopt non-planar, helical conformations. \u0026ang;A increases with the increasing steric bulkiness of the halogen substituent in mono-substituted derivatives: \u003cstrong\u003ePhen\u003csub\u003eCl,H\u003c/sub\u003e\u003c/strong\u003e (9.4\u0026deg;), \u003cstrong\u003ePhen\u003csub\u003eBr,H\u003c/sub\u003e\u003c/strong\u003e (13.8\u0026deg;), and \u003cstrong\u003ePhen\u003csub\u003eI,H\u003c/sub\u003e\u003c/strong\u003e (17.2\u0026deg;) (Fig. 1c). Similarly, for bis-substituted derivatives they also follow the same pattern: as the steric size increases, \u0026ang;A increases. All bis-substituted \u003cstrong\u003ePhen\u003c/strong\u003e exhibit chirality, and the smallest one is \u003cstrong\u003ePhen\u003csub\u003eF,F\u003c/sub\u003e\u003c/strong\u003e with \u0026ang;A of 22.4\u0026deg;; the largest one is \u003cstrong\u003ePhen\u003csub\u003eI,I\u003c/sub\u003e\u003c/strong\u003e with \u0026ang;A of 35.8\u0026deg;. Additionally, we calculated the enantiomerization barriers (corresponding to the inversion from \u003cem\u003eP\u003c/em\u003e-helicity to \u003cem\u003eM\u003c/em\u003e-helicity) of these helically shaped molecules by optimizing the geometry of the transition state of these \u003cstrong\u003ePhen\u003c/strong\u003e derivatives.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor the transition state\u0026nbsp;\u003cstrong\u003ePhen\u003csub\u003eCl,H\u003c/sub\u003e\u003csup\u003e\u0026Dagger;\u003c/sup\u003e\u003c/strong\u003e adopts a fully planar geometry, and the enantiomerization barrier is calculated as 1.1 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e. Similarly, the transition states \u003cstrong\u003ePhen\u003csub\u003eBr,H\u003c/sub\u003e\u003csup\u003e\u0026Dagger;\u003c/sup\u003e\u003c/strong\u003e and \u003cstrong\u003ePhen\u003csub\u003eI,H\u003c/sub\u003e\u003csup\u003e\u0026Dagger;\u003c/sup\u003e\u003c/strong\u003e are also fully planar, with calculated barriers of 1.2 and 1.5 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively. Notably, increasing the number of substituents leads to a significant elevation in enantiomerization barriers:\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eF,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eF\u0026nbsp;\u003c/sub\u003e\u003c/strong\u003e(2.3 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e), \u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eCl,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eCl\u0026nbsp;\u003c/sub\u003e\u003c/strong\u003e(16.2 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e), \u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eBr,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eBr\u0026nbsp;\u003c/sub\u003e\u003c/strong\u003e(22.2 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e), and \u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eI,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eI\u0026nbsp;\u003c/sub\u003e\u003c/strong\u003e(28.9 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e) (Fig. 1c).\u0026nbsp;The\u0026nbsp;enantiomerization\u0026nbsp;barriers of the remaining\u0026nbsp;bis-substituted\u0026nbsp;compounds are shown in Table 1. Furthermore, we investigated the relationship between the enantiomerization barrier and\u0026nbsp;\u0026ang;A (Fig. 2). The barrier rises slowly at small \u0026ang;A but increases sharply when \u0026ang;A exceeds ca. 30\u0026deg;.\u0026nbsp;Therefore, the larger the\u0026nbsp;\u0026ang;A,\u0026nbsp;the\u0026nbsp;more significant the increase in the\u0026nbsp;enantiomerization barrier.\u003c/p\u003e\n\u003ch3\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e Enantiomerization barriers of phenanthrene derivatives in kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e.\u003c/h3\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eEnergy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eEnergy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003eEnergy\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eH,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eF,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eCl,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eBr,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eI\u003c/sub\u003e,\u003csub\u003eH\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eF,F\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eCl,F\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e7.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eBr,F\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e8.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eI,F\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e9.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eCl,Cl\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e16.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eBr,Cl\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e18.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eI,Cl\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e20.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e22.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eI,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e25.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 16px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhen\u003csub\u003eI,I\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e28.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eIn addition,\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ewe use the rotary angle (\u0026ang;B)\u003csup\u003e45\u003c/sup\u003e, between two C-C bonds (C8a-C4b and C10a-C4a) of \u003cstrong\u003ePhen\u003c/strong\u003e, to establish a connection between the structure and enantiomerization barriers (Fig. 1b).\u0026nbsp;For both mono- and bis-substituted derivatives,\u0026nbsp;\u0026ang;B in the local minimum increases with the increase of the atomic size:\u003cstrong\u003e\u0026nbsp;Phen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eCl,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eH\u003c/sub\u003e\u003c/strong\u003e (57.0\u0026deg;),\u003cstrong\u003e\u0026nbsp;Phen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eBr,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eH\u003c/sub\u003e\u003c/strong\u003e (57.3\u0026deg;),\u003cstrong\u003e\u0026nbsp;Phen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eI,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eH\u003c/sub\u003e\u003c/strong\u003e (57.7\u0026deg;),\u0026nbsp;\u003cstrong\u003ePhen\u003csub\u003eF,F\u003c/sub\u003e\u003c/strong\u003e (56.9\u0026deg;),\u0026nbsp;\u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eCl,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eCl\u003c/sub\u003e\u003c/strong\u003e (59.9\u0026deg;),\u003cstrong\u003e\u0026nbsp;Phen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e (60.2\u0026deg;), and\u0026nbsp;\u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eI,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eI\u003c/sub\u003e\u003c/strong\u003e (60.4\u0026deg;).\u0026nbsp;Meanwhile,\u0026nbsp;\u0026ang;B in the transition state is roughly diminishes with the increase of the atomic size. Therefore, we define the difference between\u0026nbsp;\u0026ang;B in the transition state and\u0026nbsp;\u0026ang;B in the local minimum as\u0026nbsp;\u0026Delta;\u0026ang;B. In\u0026nbsp;\u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eCl,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eH\u003c/sub\u003e\u003c/strong\u003e,\u0026nbsp;\u0026Delta;\u0026ang;B\u0026nbsp;is 0.4\u0026deg;. Similarly,\u0026nbsp;\u0026Delta;\u0026ang;B is\u0026nbsp;1.5\u0026deg;for\u0026nbsp;\u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eI,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eH\u003c/sub\u003e\u003c/strong\u003e,\u003cstrong\u003e\u003csub\u003e\u0026nbsp;\u003c/sub\u003e\u003c/strong\u003e6.8\u0026deg;for\u0026nbsp;\u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eCl,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eCl\u003c/sub\u003e\u003c/strong\u003e,\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eand\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e8.1\u0026deg;for\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eI,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eI\u003c/sub\u003e\u003c/strong\u003e, which is well accord to the increase of enantiomerization barrier\u0026nbsp;(Fig. 1c).\u003c/p\u003e\n\u003cp\u003eThen we investigated the enantiomerization barrier of methyl-, tert-butyl-, and phenyl-substituted \u003cstrong\u003ePhen\u003c/strong\u003e. We found that mono-substituted \u003cstrong\u003ePhen\u003c/strong\u003e exhibit \u0026ang;B ranging from 56.9\u0026deg; to 58.5\u0026deg;, and \u0026Delta;\u0026ang;B ranging from 0.4\u0026deg; to 3.3\u0026deg;with similar enantiomerization barriers of ca. 1 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e. On the other hand, the bis-substituted analogues show much higher enantiomerization barriers. For example, \u003cstrong\u003ePhen\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e shows an enantiomerization barrier of 16.2 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e and \u0026Delta;\u0026ang;B is 6.7\u0026deg;. Notably, \u003cstrong\u003ePhen\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003etBu,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003etBu\u003c/sub\u003e\u003c/strong\u003e exhibits an extremely high enantiomerization barrier of 54.2 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e\u003csup\u003e\u0026nbsp;\u003c/sup\u003eand \u0026Delta;\u0026ang;B also exhibits a large value of 11.7\u0026deg; (Fig. 3).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCompared with the mono-substituted derivatives, the\u0026nbsp;bis-substituted \u003cstrong\u003ePhen\u003c/strong\u003e derivatives\u0026nbsp;exhibit higher enantiomerization barriers and the\u0026nbsp;difference indicates\u0026nbsp;that the two substituents might have\u0026nbsp;a synergistic effect, thus augmenting the enantiomerization barriers.\u0026nbsp;Overall, alkyl/aryl-substituted\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ePhen\u0026nbsp;\u003c/strong\u003ederivatives\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ehave similar properties to halogen-substituted \u003cstrong\u003ePhen\u0026nbsp;\u003c/strong\u003ederivatives, and the greater the change in \u0026Delta;\u0026ang;B, the higher the energy barrier for transition state.\u003c/p\u003e\n\u003cp\u003eSubsequently, we explored the effect of \u003cem\u003e\u0026pi;\u003c/em\u003e-conjugation extension and constructed a series of molecules with \u003cem\u003e\u0026pi;\u003c/em\u003e-conjugated skeletons\u0026nbsp;(\u003cstrong\u003ePAH1\u003c/strong\u003e to \u003cstrong\u003ePAH7\u003c/strong\u003e) (Fig. 4). For \u003cstrong\u003ePAH1\u003c/strong\u003e, we added an additional benzenoid ring to the central ring, giving a triphenylene skeleton. The enantiomerization barriers for mono-tert-butyl-, bis-methyl-, and bis-bromo-derivatives \u003cstrong\u003ePAH1\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e,\u003cstrong\u003e\u0026nbsp;PAH1\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e,\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eand\u003cstrong\u003e\u0026nbsp;PAH1\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e are 7.1, 20.2 and 25.1 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively (Table 2). These results are obviously larger than the unsubstituted \u003cstrong\u003ePhen\u003c/strong\u003e derivatives (1.1, 16.2 and 22.2 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e). Similarly, by fusing two additional benzenoid rings to form a perylene-based skeleton, the three derivatives \u003cstrong\u003ePAH2\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e, \u003cstrong\u003ePAH2\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e, and \u003cstrong\u003ePAH2\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e display the enantiomerization barriers of 7.5, 26.7 and 31.1 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively. This increase may stem from the constrained deformation of \u0026ang;B by the extended \u003cem\u003e\u0026pi;\u003c/em\u003e-system during the enantiomerization (Fig. S4). Analogous trends were observed for the subsequent PAHs (\u003cstrong\u003ePAH3\u003c/strong\u003e to \u003cstrong\u003ePAH7\u003c/strong\u003e). Notably for \u003cstrong\u003ePAH5\u003c/strong\u003e, although the two additional benzenoid rings are fused to the two terminal rings, the enantiomerization barriers also increase significantly.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003cstrong\u003e.\u0026nbsp;\u003c/strong\u003eEnantiomerization barriers of \u003cstrong\u003ePAH1\u0026ndash;PAH7\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ederivatives in kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e.\u003c/h3\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"79%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 77px;\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 46px;\"\u003e\n \u003cp\u003eEnergy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 80px;\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 46px;\"\u003e\n \u003cp\u003eEnergy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 76px;\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 46px;\"\u003e\n \u003cp\u003eEnergy\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH1\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e7.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 80px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH1\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e20.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH1\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e25.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH2\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 80px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH2\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e26.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH2\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e31.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH3\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e5.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 80px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH3\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e23.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH3\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e28.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH4\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e7.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 80px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH4\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e27.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH4\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e30.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH5\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e5.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 80px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH5\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e21.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH5\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e26.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH6\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e9.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 80px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH6\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e26.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH6\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e31.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 77px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH7\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e12.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 80px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH7\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e25.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH7\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 46px;\"\u003e\n \u003cp\u003e30.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eFurthermore, with increased \u003cem\u003e\u0026pi;\u003c/em\u003e-extension forming a hexabenzocoronene \u003cstrong\u003ePAH6\u003c/strong\u003e, the enantiomerization barriers exhibit no further\u0026nbsp;obvious increase (vs. \u003cstrong\u003ePAH3\u003c/strong\u003e,\u0026nbsp;Fig. S5), suggesting that the distant benzenoid rings might bring negligible influence for the enantiomerization barriers\u0026nbsp;(Fig. S8).\u0026nbsp;Notably, \u003cstrong\u003ePAH7\u0026nbsp;\u003c/strong\u003e(the reduced product of Phen)\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eexhibits a significantly higher enantiomerization barrier than unsubstituted\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ePhen.\u003c/strong\u003e The three derivatives, \u003cstrong\u003ePAH\u003c/strong\u003e\u003cstrong\u003e7\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e, \u003cstrong\u003ePAH\u003c/strong\u003e\u003cstrong\u003e7\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e, and \u003cstrong\u003ePAH\u003c/strong\u003e\u003cstrong\u003e7\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e display the enantiomerization barrier of 12.1, 25.0 and 30.2 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e, respectively. It is likely due to the elongation of C\u0026ndash;C bonds upon reduction, enlarging \u0026ang;B in \u003cstrong\u003ePAH7\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eTo gain a deeper understanding of the relationship between \u0026ang;B and the enantiomerization, we systematically investigated the influence of \u003cstrong\u003ePhen\u003c/strong\u003e with the central benzenoid ring replaced by heterocycles (\u003cstrong\u003eH3X\u003c/strong\u003e, X = C, Si, Ge, Sn, N, P, As, Sb, O, S, Se, and Te). We first calculated these heterocycle-substituted\u003cstrong\u003e\u0026nbsp;Phen\u003c/strong\u003e compounds with mono-tert-butyl-substitution, and we found that \u0026ang;B values at the local minimum range from 29.5\u0026deg; to 59.3\u0026deg; depending on the different heterocycles (vs. 58.5\u0026deg; of \u003cstrong\u003ePhen\u003c/strong\u003e). Among this series, only \u003cstrong\u003eH3Sn\u003csub\u003etBu\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003e,H\u003c/sub\u003e\u003c/strong\u003e shows a helical structure and its enantiomerization barrier is 1.2 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e. The other derivatives all show a fully planar \u003cem\u003e\u0026pi;\u003c/em\u003e-skeleton. (Fig. 5)\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWhen switching to the bis-methyl- and bis-bromo-substituted derivatives (Fig. 6), we found that only \u003cstrong\u003eH3O\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e and \u003cstrong\u003eH3N\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e are fully planar, while the rest compounds possess helical geometry. If the central heteroatom is from the second period, \u0026ang;B are smaller and the enantiomerization barriers are relatively low. In contrast, heteroatoms from the fifth-period lead to a larger \u0026ang;B and higher enantiomerization barriers. Overall, we found a strong positive correlation between the enantiomerization barriers and \u0026ang;B (Fig. 6), indicating that the type of aromatic ring at the bay region exerts a significant influence on the enantiomerization barrier.\u003c/p\u003e\n\u003cp\u003eWe finally examined the impact of skeleton curvature and used hexa[7]circulene (\u003cstrong\u003ePAH8\u003c/strong\u003e; Fig. 7) as an example\u003csup\u003e46\u003c/sup\u003e, which contains a central heptagonal ring and adopts negative curvature. Compared with \u003cstrong\u003ePAH3\u003c/strong\u003e, \u003cstrong\u003ePAH8\u003c/strong\u003e shows an additional benzenoid ring on the skeleton, resulting\u0026nbsp;in the central hexagonal ring to be heptagonal. This aggravates the crowdedness of the bay region. Notably, even the unsubstituted \u003cstrong\u003ePAH8\u003csub\u003eH,H\u003c/sub\u003e\u003c/strong\u003e already becomes non-planar, with the enantiomerization barrier of 15.9 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e (for comparison, \u003cstrong\u003ePAH3\u003csub\u003eH,H\u003c/sub\u003e\u003c/strong\u003e is fully planar).\u0026nbsp;Then we studied the\u0026nbsp;enantiomerization barriers of mono-substituted and\u0026nbsp;bis-substituted\u0026nbsp;\u003cstrong\u003ePAH8\u003c/strong\u003e derivatives, and the corresponding data, together with those of a series of halogen-substituted \u003cstrong\u003ePAH8\u003c/strong\u003e derivatives, are summarized in Table 3. When \u003cstrong\u003ePAH3\u003c/strong\u003e and \u003cstrong\u003ePAH8\u003c/strong\u003e have the same substituents, for example the bis-bromo derivatives have barriers of 28.6 kcal mol⁻\u0026sup1; (\u003cstrong\u003ePAH3\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e, Fig. S5) and 56.7 kcal mol⁻\u0026sup1; (\u003cstrong\u003ePAH8\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e, Table 3), and the bis-methyl derivatives have barriers of 23.9 kcal mol⁻\u0026sup1; (\u003cstrong\u003ePAH3\u003csub\u003eMe,Me\u003c/sub\u003e,\u003csub\u003e\u0026nbsp;\u003c/sub\u003e\u003c/strong\u003eFig. S5) and 51.5 kcal mol⁻\u0026sup1; (\u003cstrong\u003ePAH8\u003csub\u003eMe,Me\u003c/sub\u003e\u003c/strong\u003e, Table 3), the\u0026nbsp;enantiomerization barriers of\u0026nbsp;\u003cstrong\u003ePAH8\u003c/strong\u003e are always higher than \u003cstrong\u003ePAH3\u003c/strong\u003e. Besides, we found that the\u0026nbsp;enantiomerization barrier\u0026nbsp;of \u003cstrong\u003ePAH8\u003csub\u003etBu,tBu\u003c/sub\u003e\u003c/strong\u003e reach up to 80.1 kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e Enantiomerization barriers of \u003cstrong\u003ePAH\u003c/strong\u003e\u003cstrong\u003e8\u003c/strong\u003e derivatives in kcal mol\u003csup\u003e\u0026minus;1\u003c/sup\u003e.\u003c/h3\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 59px;\"\u003e\n \u003cp\u003eEnergy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 96px;\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 59px;\"\u003e\n \u003cp\u003eEnergy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003eType\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 56px;\"\u003e\n \u003cp\u003eEnergy\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eH,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e15.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eF,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e20.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eCl,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e26.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eBr,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e27.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eI,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e29.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eF,F\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e33.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eF,Cl\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e41.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eF,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e42.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eF,I\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e42.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eCl,Cl\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e52.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eCl,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e54.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eCl,I\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e55.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eBr,Br\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e56.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eBr,I\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e58.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003csub\u003eI,I\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e61.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eMe,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e27.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003etBu,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e36.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003ePh,H\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e25.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eMe\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003e,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003e\u0026nbsp;Me\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e51.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003etBu\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003e,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003e\u0026nbsp;tBu\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e80.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePAH8\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003ePh\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003e,\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003e\u0026nbsp;Ph\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e51.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"3 Conclusion","content":"\u003cp\u003eIn summary, we have investigated the chirality for the substituted bay region in a rich array of PAHs with different substituents, \u003cem\u003eπ\u003c/em\u003e-conjugation extension, heterocyclic substitution and \u003cem\u003eπ\u003c/em\u003e-skeleton curvature. Most PAHs substituted at the bay region exhibit a steric effect, resulting in a non-planar \u003cem\u003eπ\u003c/em\u003e-skeleton, forming helical structures. The enantiomerization barriers of these PAHs are predominantly influenced by the steric bulk of the substituents. We found that the enantiomerization barriers of iodine-substituted and tert-butyl-substituted derivatives are always high, with respective values of \u003cb\u003ePhen\u003c/b\u003e\u003csub\u003e\u003cb\u003eI,H\u003c/b\u003e\u003c/sub\u003e (1.5 kcal mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), \u003cb\u003ePhen\u003c/b\u003e\u003csub\u003e\u003cb\u003etBu,H\u003c/b\u003e\u003c/sub\u003e (1.1 kcal mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), \u003cb\u003ePhen\u003c/b\u003e\u003csub\u003e\u003cb\u003eI,I\u003c/b\u003e\u003c/sub\u003e (28.9 kcal mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and \u003cb\u003ePhen\u003c/b\u003e\u003csub\u003e\u003cb\u003etBu,tBu\u003c/b\u003e\u003c/sub\u003e (54.2 kcal mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Furthermore, our investigations into heterocycle-incorporated PAH derivatives reveal that \u0026ang;B also exerts a significant influence on the enantiomerization barriers: the larger \u0026ang;B, the higher the corresponding enantiomerization barriers. Besides the \u003cem\u003eπ\u003c/em\u003e-conjugation on the phenanthrene moiety could also increases the enantiomerization barrier. Lastly, we studied a unique class of PAHs with negatively curved molecular \u003cem\u003eπ\u003c/em\u003e-skeleton\u0026mdash;the hexa[7]circulene (\u003cb\u003ePAH8\u003c/b\u003e), which contains a central heptagonal ring. Such geometry shows the central bay region is much more crowded compared with the hexagonal derivatives \u003cb\u003ePAH3\u003c/b\u003e. In this work we aimed to investigate the geometry angle of the bay region by the substituents and discovered the rules for enantiomerization. We anticipate that this theoretical work will guide the design of large \u003cem\u003eπ\u003c/em\u003e-conjugated aromatic systems by incorporating chiral bay regions to enhance their chiroptical properties, and expect to use the chirality of the bay region to enrich the skeleton versatility of the functional PAHs.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e I would like to express my sincere gratitude to the Zhejiang Sci-Tech University – School of Chemistry and Chemical Engineering for providing the ideal scientific environment that supported the completion of this research.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary Information\u003c/strong\u003e The online version contains supplementary material available at \u0026nbsp;.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e All authors contributed to the study. Chengshuo Shen and Na Yang conceived this project and undertook the theoretical calculations for the molecules under investigation. Huimin Zhou was responsible for data processing and article proofreading, Yijian Ma handled manuscript polishing and detail correction, and Jiaxin Shi was in charge of the organization of supporting materials. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e This work was financially supported by the Zhejiang Provincial Natural Science Foundation, China (LY23B040003), and the National Natural Science Foundation of China (22561160131).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding author\u003c/strong\u003e: Chengshuo Shen\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAnderson, HV., Gois, ND., Chalifoux, WA.: New advances in chiral nanographene chemistry. Org. Chem. 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Chem. 45(8), e27252 (2023).\u003c/li\u003e\n\u003cli\u003eYu, W., Yang, C., Feng, X., Shen, C.: Scholl cyclization of [6]helicenes into negatively curved hexa[7]circulenes. Chin. Chem. Lett. 36(11), 110939 (2025).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"structural-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"stuc","sideBox":"Learn more about [Structural Chemistry](https://www.springer.com/journal/11224)","snPcode":"11224","submissionUrl":"https://submission.nature.com/new-submission/11224/3","title":"Structural Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"chirality, enantiomerization barrier, bay region","lastPublishedDoi":"10.21203/rs.3.rs-8431401/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8431401/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWe systematically investigated the chirality of substituted bay regions in polycyclic aromatic hydrocarbons (PAHs) via density functional theory (DFT) calculations, focusing on effects of substituents, \u003cem\u003eπ\u003c/em\u003e-conjugation extension, heterocycles, and \u003cem\u003eπ\u003c/em\u003e-skeleton curvature. Most bay-substituted PAHs form non-planar helical structures. As the steric hindrance of the substituents increases, the enantiomerization barriers of the phenanthrene derivatives increase. Similarly, \u003cem\u003eπ\u003c/em\u003e-conjugation extension can also increase the enantiomerization barriers. Heterocycles could also modulate the enantiomerization barriers of the PAHs by tuning the identity of the central heteroatom, and specifically, heterocyclic PAH derivatives incorporating heteroatoms with larger atomic radii exhibit higher enantiomerization barriers. Hexa[7]circulene (\u003cstrong\u003ePAH8\u003c/strong\u003e), which contains a central heptagonal ring, is already non-planar, with an enantiomerization barrier of 15.9 kcal mol\u003csup\u003e−1\u003c/sup\u003e. When the bay region of \u003cstrong\u003ePAH8\u003c/strong\u003e is substituted, the enantiomerization barrier increases (up to 80.1 kcal mol\u003csup\u003e−1\u003c/sup\u003e). This work elucidates bay-region enantiomerization rules, providing theoretical guidance for designing functional chiral \u003cem\u003eπ\u003c/em\u003e-conjugated molecules.\u003c/p\u003e","manuscriptTitle":"Theoretical Research of Substituted Bay Region with Helical Chirality: Structures and Enantiomerization","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-26 10:19:53","doi":"10.21203/rs.3.rs-8431401/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-12-29T08:56:56+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-29T02:32:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"99518618704974370550178042828509255412","date":"2025-12-24T10:32:26+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-24T09:52:29+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-24T09:49:07+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-24T05:22:37+00:00","index":"","fulltext":""},{"type":"submitted","content":"Structural Chemistry","date":"2025-12-23T07:23:56+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"structural-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"stuc","sideBox":"Learn more about [Structural Chemistry](https://www.springer.com/journal/11224)","snPcode":"11224","submissionUrl":"https://submission.nature.com/new-submission/11224/3","title":"Structural Chemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e8b271c5-43af-48f7-837a-589f511e7f1f","owner":[],"postedDate":"December 26th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-04-20T16:11:09+00:00","versionOfRecord":{"articleIdentity":"rs-8431401","link":"https://doi.org/10.1007/s11224-026-02748-y","journal":{"identity":"structural-chemistry","isVorOnly":false,"title":"Structural Chemistry"},"publishedOn":"2026-04-13 15:58:07","publishedOnDateReadable":"April 13th, 2026"},"versionCreatedAt":"2025-12-26 10:19:53","video":"","vorDoi":"10.1007/s11224-026-02748-y","vorDoiUrl":"https://doi.org/10.1007/s11224-026-02748-y","workflowStages":[]},"version":"v1","identity":"rs-8431401","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8431401","identity":"rs-8431401","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}