English

• Expanded porphyrins are attractive targets because of their excellent NIR optical and multi-electronic donating and accepting properties [1-5]. In contrast to classical porphy-rin(1.1.1.1) [6, 7], most expanded porphyrins exhibit more flexible molecular structures and powerful metal complexation abilities [1-3, 6-8]. Furthermore, the variable topologies of expanded porphyrins are ideal platforms for investigating the aromaticity conversion [9-12]. Among the expanded porphyrins, hexaphyrins (Fig. 1) which consist of six pyrrolic units and methine carbons are typical expanded porphyrins and offer advantages such as good isolated yields, conformational flexibility, ability to metalate with a range of metals, and new skeleton construction by replacement of the pyrrolic subunits or methine carbon atoms [13, 14].

  Figure 1

  

  Figure 1.  [26]Hexaphyrin(1.1.1.1.1.1) and various hex-aphyrins(2.1.2.1.2.1), all aryl groups at meso-positions are omitted for clarity.

  DownLoad: Full-Size Img PowerPoint

  In this context, we focused on C₂ (two carbons linkage) methine-bridged hexaphyrins(2.1.2.1.2.1) and their complexes to discover novel molecular geometries, aromaticity, and optical and electronic properties. From 2019, Yamada group and we have developed diphenylvinylene-/dimethylvinylene-/vinylene-bridged hexaphyrins(2.1.2.1.2.1) (Fig. 1) [15-17]. Among these, C₂ methine-bridged hexaphyrin(2.1.2.1.2.1) [15], diphenyl-vinylene bridged hexaphyrin(2.1.2.1.2.1) copper complexes [16], have aromatic figure-of-eight Hückel topologies, vinylene bridged hexaphyrin(2.1.2.1.2.1) [17] with planar aromatic topologies. The figure-of-eight vinylene-bridged hexaphyrins(2.1.2.1.2.1) free base has not yet been obtained (Fig. 1), and the demetalization of diphenyl-vinylene-bridged hexaphyrin(2.1.2.1.2.1) copper complexes gave a twisted conformation similar to that of the diphenyl-vinylene-bridged hexaphyrin(2.1.2.1.2.1) free base [16, 18-20]. The fusion of aromatic units, such as benzo, can potentially increase the π-conjugation of expanded porphyrins [21]. The extended fusion of benzo unit acts as contributors where the Clar's sextet [22, 23] shifts from one side to another, with enough power to interfere with the electronic structure and global aromaticity [21]. Increased π-conjugation also results in rich aromaticity and NIR optical properties [1-3, 9-14]. However, the fusion of the benzo units in hexaphyrins has not yet been reported.

  Herein, we report the first synthesis of a novel benzo-bridged figure-of-eight hexaphyrin(2.1.2.1.2.1) free base (Hex) and its copper complex (HexCu) with three benzo units embedded into hexaphyrin(1.1.1.1.1.1), however both Hex and HexCu showed figure-of-eight molecular structures and non-aromatic properties. The structure, optical and electronic properties, and aromaticity of Hex and HexCu were investigated using high resolution mass spectrometry (HR-MS), electron paramagnetic resonance spectroscopy (EPR), nuclear magnetic resonance spectroscopy (NMR), X-ray crystallography, UV–vis absorption, electrochemistry, harmonic-oscillator model for an aromaticity (HOMA), nucleus independent chemical shift (NICS), anisotropy of the induced current density (ACID) and electron density of delocalized bonds (EDDB).

  The synthesis scheme is depicted in Scheme S1 (Supporting information). The key building blocks, 1, 2-di(1H-pyrrol-2-yl)benzene (DPB) and 1, 2, 4, 5-tetra(pyrrol-2-ly)benzene (TPB), were synthesized via an established method [24-30]. Our previous work revealed the treatment of DPB and pentafluorobenzaldehyde with 3 mol% boron trifluoride ethyl ether complex (BF₃·OEt₂) in CH₂Cl₂ for 3 h, followed by oxidation with 2, 3-dichloro-5, 6-dicyanobenzo-quinone (DDQ) and metalation with Cu(OAc)₂·H₂O, only gave a porphyrin(2.1.2.1) copper PorCu as the product (Scheme S1a) [24-27]. We attempted to synthesize the benzo-fused porphyrin(2.1.2.1) dimer (Fig. S1 in Supporting information) through DPB and TPB as building blocks. Interestingly, our hypothetical benzo-fused porphyrin(2.1.2.1) dimer DiPorCu was observed as a trace product; however, the HexCu was isolated in ideal 15% yield together with porphyrin(2.1.2.1) copper in 11% yield upon treatment of 1 equiv. DPB, 1 equiv. TPB, and 1 equiv. pentafluorobenzaldehyde with 3 mol% BF₃·OEt₂ in CH₂Cl₂ for 3 h, followed by oxidation with DDQ and metalation with Cu(OAc)₂·H₂O (Scheme S1b).

  To further understand this acid-condensation reaction and evaluate the role of TPB, we did a series of reactions with different reaction conditions (Table S1 in Supporting information). Our previous work indicated the longer reaction time (12 h) and larger amount of the acid catalyst BF₃·OEt₂ (70 mol%) are key points for higher isolated yield of porphyrin(2.1.2.1) nanobelt PorNB from TPB as only building block, therefore, we chose different reaction times and amount of BF₃·OEt₂ to evaluate the construction and distribution of obtained products PorCu, DiPorCu and HexCu under these condensation reactions. Considering our obtained results from a series of condensation reactions in Table S1, we found that longer time and larger amount of acid are not good for yield of HexCu, most of DPB and TPB were consumed and form insoluble polymers (for example, for entry 8, we observed large amount of black solids in reaction mixture). However, we can isolate the HexCu under shorter condensation time and small amount of acid, but yields are low (entries 1–5 in Table S1). Therefore, due to complicated acid-condensation reactions and multiple pyrrolic-building blocks in this work, we concluded that the acceptable yield of HexCu needs moderate conditions (entries 3 and 4 in Table S1). Under these reaction conditions, reaction time, the amount of BF₃·OEt₂ and TPB are crucial for the synthesis of HexCu. Although TPB is not directly involved in the molecular framework, considering the previous works about porphyrin(2.1.2.1)s and hexaphyrin(2.1.2.1.2.1)s, the possible reaction mechanism was presented (Scheme S2 in Supporting information) [15-17, 24-27, 31]. The demetalization of HexCu performed to obtain Hex in 92% yield. The APCI-HR-MS spectra of Hex and HexCu exhibited corresponding molecular ion peaks at m/z = 1153.2080 (calcd. for C₆₃H₂₈F₁₅N₆ = 1153.2130 [M+H]⁺) and m/z = 1214.1255 (calcd. for C₆₃H₂₅CuF₁₆N₆ = 1214.1270 [M]⁺), respectively (Figs. S2 and S3 in Supporting information).

  Due to the open-shell structure of HexCu, the EPR spectrum was obtained in CH₂Cl₂ at 110 K to investigate its magnetic properties (Fig. 2a). The spectrum of HexCu was typical for axially symmetric Cu(Ⅱ) compound. A rather good estimate of the g-values and of A(Cu) can be obtained [[32], [33]]. The nitrogen hyperfine couplings are not well resolved. By including the nitrogen couplings in the simulation, the fit could most likely be improved. However, the rather featureless character of the spectrum makes it difficult to assign quantitatively and confidently precise values to the different interactions, as all of these additional parameters only contribute to field-dependent line broadening in the present case. Further details on the parameters are given in the Fig. S4 (Supporting information). The spin density of HexCu was delocalized on both the copper ion and the coordinated nitrogen atoms of its backbone (Fig. 2b), as determined by density functional theory (DFT) calculations. In our previous work, we did not investigate the magnetic property of the figure-of-eight shaped vinylene-bridged hexaphyrin(2.1.2.1.2.1) using NMR spectroscopy; therefore, the NMR spectra of Hex were obtained to investigate the molecular structures. The ¹H NMR spectrum of Hex clearly reflects its non-global aromaticity (Fig. 2c and Fig. S5 in Supporting information). The Hex displays two broad peaks of three NH resonances, and six sets of β-H resonances for the pyrrole units between 6.90 ppm and 5.85 ppm. These β-H resonances of benzo-bridged figure-of-eight hexaphyrin (2.1.2.1.2.1) Hex are attributed to its non-aromaticity [15-21, 34]. The ¹⁹F NMR spectrum of Hex exhibits three sets of signals assigned to the o-F, m-F, and p-F of the three C₆F₅ groups at meso-positions (Fig. S6 in Supporting information).

  Figure 2

  

  Figure 2.  (a) Experimental (black) and simulated (red) ESR spectra of HexCu. (b) spin density distribution for HexCu at an isovalue of 0.0004. (c) ¹H NMR spectrum of Hex in CDCl₃, 298 K.

  DownLoad: Full-Size Img PowerPoint

  Single crystals of Hex and HexCu suitable for X-ray crystallography were obtained through slow diffusion of hexane into a dichloromethane solution (Fig. 3). Both Hex and HexCu are composed of figure-of-eight structures, in contrast to the distorted structure of the diphenylvinylene-/dimethylvinylene-bridged hexaphyrins(2.1.2.1.2.1) free base [15-17]. The bond lengths of the meso-carbon and the adjacent pyrrole α-carbons of Hex show clear bond alternations (BLA): 1.421, 1.363, 1.432, 1.346, 1.407, 1.386 Å, which contributes to its non-aromatic property. The copper(Ⅱ) ion of HexCu is coordinated to four nitrogen atoms in a distorted square planar geometry. The bond lengths of the meso-carbon and the adjacent pyrrole α-carbons of HexCu show almost no bond alternations: 1.419, 1.390, 1.401, 1.387, 1.400, 1.391 Å; this result is similar to our findings on the aromatic figure-of-eight diphenyl-vinylene bridged hexaphyrin(2.1.2.1.2.1) copper complexes [10]. However, the bond lengths of the benzo bridges and the adjacent pyrrole α-carbons in HexCu (1.465, 1.469, 1.468, 1.472, 1.469, 1.462 Å) are similar to those in Hex (1.483, 1.446, 1.468, 1.467, 1.458, 1.459 Å), consistent with the typical C-C single bond distance [15-17, 35-37]. Therefore, the crystal data suggest that Hex and HexCu have non-aromatic properties, even figure-of-eight structures exist [9-12].

  Figure 3

  

  Figure 3.  Single crystal structures of (a) Hex and (b) HexCu with selected bond distances (Å). Thermal ellipsoids are shown at 40% probability. Aryl groups in side view have been omitted for clarity.

  DownLoad: Full-Size Img PowerPoint

  In order to assess and interpret the aromaticity of Hex and HexCu, HOMA [38], NICS [39], ACID [40, 41], and EDDB [42] values and isosurface maps were calculated and characterized in details. The HOMA values of Hex and HexCu, calculated along the annulene pathway and based on the crystal structures are 0.24 and 0.28, respectively, which are indicative of globally non-aromatic characteristics (Fig. S8 in Supporting information) [15-17]. The NICS probes inside the macrocycle of Hex also suggest the lack of global (anti)aromaticity (Fig. 4a and Fig. S9 in Supporting information) [9-12, 24-30]. The ACID plots of Hex and HexCu display no global ring current along the bridged-annulene pathway, however they clearly show local diatropic circulations in the bridged benzo units (Fig. 4, Fig. 4) [28-30, 40]. The EDDB analysis (Fig. 4d and Figs. S10 and S11, and Videos 1–4 in Supporting information) of Hex and HexCu confirms significant cyclic delocalization of π-electrons in the benzo units. Interestingly, some of the pyrrolic rings in HexCu appear to feature slightly more locally aromatic character than the corresponding ones in Hex. This, however, has no effect on the global picture of electron delocalization as revealed by the EDDB_H(r) function, which predicts on average about 0.80 |e| and 0.79 |e| per atom (excluding hydrogen atoms) to be delocalized in Hex and HexCu; for comparison, the corresponding EDDBH value for benzene is 0.92 |e| peer carbon atom. In turn, the EDDB_P(r) function in both systems predicts less than 0.07 |e| and 0.12 |e| per atom to be delocalized along the bridge-annulene pathway, which is less than 10% of the corresponding effectiveness of cyclic delocalization in benzene. Thus, the EDDB analysis predicts a clear and detailed picture of electron delocalization that supports local aromaticity in the benzo units and predicts no macrocyclic/global π-aromaticity in both Hex and HexCu. Above all, unlike our previous reported aromatic figure-of-eight diphenyl-vinylene bridged hexaphyrins(2.1.2.1.2.1) copper complexes, these NMR, crystal data, HOMA, NICS, ACID, and EDDB results indicated that the strong aromatic bridges, benzo units cut the global ring current circuit of Hex and HexCu even they are typical figure-of-eight Hückel topologies.

  Figure 4

  

  Figure 4.  (a) NICS(0) values calculated in points a–f of Hex, aryl groups at meso-positions are omitted for clarity. (b, c) ACID plots (isovalue = 0.03) of Hex and HexCu. (d) Isovalue contours of the global EDDBp(r) function of Hex determined for the Vogel's bridged-annulene pathway (marked red); the electron populations refer to the EDDB-based averaged atomic contributions to global (EDDB_H).

  DownLoad: Full-Size Img PowerPoint

  The UV–vis absorption spectra of Hex and HexCu were measured in CH₂Cl₂ (Fig. S12 in Supporting information). Hex exhibited a main absorption band at 508 nm associated with a broadened band at approximately 700 nm. HexCu exhibited a main absorption band at 554 nm and a shoulder band at 485 nm [43]. These absorption spectra reflect their non-aromaticity, in contrast with the absorption of aromatic diphenyl-vinylene-bridged hexaphyrin(2.1.2.1.2.1) copper complexes [16]. The redox properties of Hex and HexCu were measured using CV in CH₂Cl₂ (Fig. S13 in Supporting information). Hex showed multi-oxidation/reduction potential at 1.70, 1.22, 1.00, –1.10, –1.33, and –1.73 V (vs. SCE). The HexCu showed multi-oxidation and reduction potentials at 1.57, 1.37, 1.29, 0.92, –0.64, –1.24, and –1.80 V (vs. SCE), respectively. The HexCu gave a narrower 1^st Ox. to 1^st Red. gap (1.56 eV) than that in Hex (2.10 eV), which is consistent with the absorption features of the two compounds.

  DFT and time-dependent DFT (TD-DFT) calculations of Hex and HexCu were performed to better understand their optical properties (Figs. S14-S17, Tables S2 and S3 in Supporting information). The coordination of copper ion to Hex results in a narrower highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap than that in Hex alone, which is consistent with the absorption features of Hex and HexCu. The HOMO-LUMO gap in HexCu was larger than that in the diphenyl-vinylene bridged hexaphyrin(2.1.2.1.2.1) copper complexes because of the non-aromatic nature of HexCu [16, 44]. TD-DFT calculations of HexCu indicated its ICT absorption; the HOMO of HexCu is located on the fours coordinated pyrroles side, whereas the LUMO is mainly located on free pyrroles [25, 45, 46]. Therefore, the optical and redox properties, and DFT calculations support the non-aromatic properties of Hex and HexCu. Despite their non-aromaticity, Hex and HexCu contain degenerate HOMO and LUMO levels, contributing to their multielectron donating and accepting properties [30].

  In summary, we prepared the first benzo-bridged hex-aphyrin(2.1.2.1.2.1) free base Hex and its copper complex HexCu containing three bridged benzo units between the dipyrrin units. The single-crystal structures of Hex and HexCu clearly show figure-of-eight molecular structure. NMR, crystal structure, NICS(0), HOMA, ACID, and EDDB analyses revealed the non-aromatic resonance electronic structures of Hex and HexCu, in which the strong local aromatic benzo rings cut the global aromatic ring of hexaphyrin(2.1.2.1.2.1), contrast to our previously reported aromatic figure-of-eight diphenyl-vinylene bridged hexaphyrin(2.1.2.1.2.1) copper complexes. The redox properties of Hex and HexCu showed multi-oxidation/reduction potentials, indicating their multielectron donating and accepting properties, supported by their degenerated MO levels.

  Declaration of competing interest

  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.

  CRediT authorship contribution statement

  Xiaojuan Lv: Investigation, Data curation. Yuting Dong: Investigation, Data curation. Hongliang Huang: Supervision. Dariusz W. Szczepanik: Investigation. Naoki Aratani: Investigation. Takahisa Ikeue: Investigation. Feng Chen: Investigation, Data curation. Tao Zhang: Investigation, Data curation. Fengxian Qiu: Supervision, Funding acquisition, Data curation. Toshiharu Teranishi: Supervision. Songlin Xue: Supervision, Funding acquisition.

  Acknowledgments

  This work was partly supported by the National Natural Science Foundation of China (No. 22301108) and the Project Startup Foundation for Distinguished Scholars of Jiangsu University (Nos. 4111310026 and 5501310014).

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2024.110435.

  
  
• 1. [1]

     T. Tanaka, A. Osuka, Chem. Rev. 117 (2017) 2584–2640. doi: 10.1021/acs.chemrev.6b00371

  2. [2]

     A.S. Hazari, S. Chandra, S. Kar, B. Sarka, Chem. Eur. J. 28 (2022) e2021045. doi: 10.1002/chem.202104550

  3. [3]

     T. Soya, H. Mori, A. Osuka, Angew. Chem. Int. Ed. 57 (2018) 16108–16112. doi: 10.1002/ange.201811433

  4. [4]

     M. Sun, Y. Xie, G. Baryshnikov, et al., Chem. Sci. 15 (2024) 2047–2054. doi: 10.1039/d3sc05473j

  5. [5]

     C. Li, Q. Li, J. Shao, et al., J. Am. Chem. Soc. 142 (2020) 17195–17205. doi: 10.1021/jacs.0c09572

  6. [6]

     J. Mack, Chem. Rev. 117 (2017) 3444–3478. doi: 10.1021/acs.chemrev.6b00568

  7. [7]

     M. Umetani, T. Tanaka, T. Kim, D. Kim, A. Osuka, Angew. Chem. Int. Ed. 55 (2018) 8095–8099.

  8. [8]

     Y. Tanaka, J. Shin, A. Osuka, Eur. J. Org. Chem. 2008 (2008) 1341–1349. doi: 10.1002/ejoc.200701132

  9. [9]

     J.Y. Shin, K.S. Kim, M.C. Yoon, et al., Chem. Soc. Rev. 39 (2010) 2751–2767. doi: 10.1039/b925417j

  10. [10]

      A. Osuka, S. Saito, Chem. Commun. 47 (2011) 4330–4339. doi: 10.1039/c1cc10534e

  11. [11]

      V. Roznyatovskiy, C. Lee, J. Sessler, Chem. Soc. Rev. 42 (2013) 1921–1933. doi: 10.1039/c2cs35418g

  12. [12]

      Y.M. Sung, Y., J. Oh, W.Y. Cha, et al., Chem. Rev. 117 (2017) 2257–2312. doi: 10.1021/acs.chemrev.6b00313

  13. [13]

      C. Bruckner, E. Sternberg, R. Boyle, D. Dolphin, Chem. Commun. (1997) 1689–1890.

  14. [14]

      J. Shin, H. Furuta, K. Yoza, S. Igarashi, A. Osuka, J. Am. Chem. Soc. 123 (2001) 7190–7191. doi: 10.1021/ja0106624

  15. [15]

      S. Xue, D. Kuzuhara, N. Aratani, H. Yamada, Angew. Chem. Int. Ed. 58 (2019) 12524–12528. doi: 10.1002/anie.201906946

  16. [16]

      S. Xue, D. Kuzuhara, N. Aratani, H. Yamada, Inorg. Chem. 57 (2018) 9902–9906. doi: 10.1021/acs.inorgchem.8b00977

  17. [17]

      S. Xue, N. Liu, P. Mei, et al., Inorg. Chem. 60 (2021) 16070–16073. doi: 10.1021/acs.inorgchem.1c02609

  18. [18]

      M. Stępień, L. Latos-Grażyński, N. Sprutta, et al., Angew. Chem. Int. Ed. 46 (2007) 7869–7873. doi: 10.1002/anie.200700555

  19. [19]

      Z. Yoon, A. Osuka, D. Kim, Nature Chem. 1 (2009) 113–122. doi: 10.1038/nchem.172

  20. [20]

      N. Jux Priv. -Doz. Angew. Chem. Int. Ed. 47 (2008) 2543–2546.

  21. [21]

      K. Bartkowski, M. Pawlicki, Angew. Chem. Int. Ed. 60 (2021) 9063–9070. doi: 10.1002/anie.202011848

  22. [22]

      C.H. Suresh, S. Gadre, J. Org. Chem. 64 (1999) 2505–2512.

  23. [23]

      M. Bendikov, H. Duong, K. Starkey, et al., J. Am. Chem. Soc. 126 (2004) 7416–7417. doi: 10.1021/ja048919w

  24. [24]

      N. Liu, R. Osterloh, H. Huang, et al., Inorg. Chem. 61 (2022) 3563–3572. doi: 10.1021/acs.inorgchem.1c03596

  25. [25]

      S. Xue, X. Lv, N. Liu, et al., Inorg. Chem. 62 (2023) 1679–1685. doi: 10.1021/acs.inorgchem.2c04097

  26. [26]

      Y. Dong, L. Qian, F. Chen, et al., Chem. Commun. 60 (2024) 3986–3989. doi: 10.1039/d4cc00267a

  27. [27]

      X. Lv, Y. Dong, J. Wu, et al., Dalton Trans. 53 (2024) 5979–5984. doi: 10.1039/d4dt00143e

  28. [28]

      N. Liu, H. Morimoto, F. Wu, et al., Org. Lett. 24 (2022) 3609–3613. doi: 10.1021/acs.orglett.2c01147

  29. [29]

      S. Xue, N. Tkachenko, F. Wu, et al., Inorg. Chem. 63 (2024) 11494–11500. doi: 10.1021/acs.inorgchem.4c01781

  30. [30]

      S. Xue, D. Kuzuhara, N. Aratani, H. Yamada, Org. Lett. 21 (2019) 2069–2072. doi: 10.1021/acs.orglett.9b00329

  31. [31]

      K.S. Anju, S. Ramakrishnan, A. Srinivasan, Org. Lett. 13 (2011) 2498–2501. doi: 10.1021/ol200668a

  32. [32]

      L. Ye, Z. Ou, Y. Fang, et al., RSC Adv. 5 (2015) 77088–77096.

  33. [33]

      H. Gao, F. Wu, Y. Zhao, et al., J. Am. Chem. Soc. 114 (2022) 3458–3467. doi: 10.1021/jacs.1c11716

  34. [34]

      K. Wang, B. Xiao, L. Xu, et al., Chin. Chem Lett. 33 (2022) 4545–4548.

  35. [35]

      Y. Ishigaki, T. Shimajiri, T. Takeda, R. Katoono, T. Suzuki, Chem 4 (2018) 795–806.

  36. [36]

      D.R. Lide Jr, Tetrahedron 17 (1962) 125–134.

  37. [37]

      F.H. Allen, O. Kennard, D.G. Watson, et al., J. Chem. Soc. Perkin Trans. 2 (1987) S1–S19. doi: 10.1039/P298700000S1

  38. [38]

      T.M. Krygowski, J. Chem. Inf. Model. 33 (1993) 70–78. doi: 10.1021/ci00011a011

  39. [39]

      P. Schleyer, C. Maerker, A. Dransfeld, H. Jiao, E. Hommes, J. Am. Chem. Soc. 119 (1997) 12669–12670. doi: 10.1021/ja960582d

  40. [40]

      D. Geuenich, K. Hess, F. Köhler, R. Herges, Chem. Rev. 105 (2005) 3758–3772. doi: 10.1021/cr0300901

  41. [41]

      Q. Li, M. Ishida, Y. Wang, et al., Angew. Chem. Int. Ed. 62 (2023) e202212174.

  42. [42]

      D.W. Szczepanik, M. Andrzejak, J. Dominikowska, et al., Phys. Chem. Chem. Phys. 19 (2017), 28970–28981.

  43. [43]

      J. Chen, L. Liu, Y. Rao, et al., Angew. Chem. Int. Ed. 136 (2024), e202407340.

  44. [44]

      Q. Li, C. Li, G. Baryshnikov, et al., Nat. Commun. 11 (2020) 5289. doi: 10.1038/s41467-020-19118-9

  45. [45]

      S. Das, H. Bhat, N. Balsukuri, et al., Inorg. Chem. Front. 4 (2017) 618–638.

  46. [46]

      G.B. Maiya, V. Krishnan, J. Phys. Chem. 89 (1985) 5225–5235. doi: 10.1021/j100270a022

• 

  Figure 1  [26]Hexaphyrin(1.1.1.1.1.1) and various hex-aphyrins(2.1.2.1.2.1), all aryl groups at meso-positions are omitted for clarity.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  (a) Experimental (black) and simulated (red) ESR spectra of HexCu. (b) spin density distribution for HexCu at an isovalue of 0.0004. (c) ¹H NMR spectrum of Hex in CDCl₃, 298 K.

  下载: 全尺寸图片 幻灯片
  

  Figure 3  Single crystal structures of (a) Hex and (b) HexCu with selected bond distances (Å). Thermal ellipsoids are shown at 40% probability. Aryl groups in side view have been omitted for clarity.

  下载: 全尺寸图片 幻灯片
  

  Figure 4  (a) NICS(0) values calculated in points a–f of Hex, aryl groups at meso-positions are omitted for clarity. (b, c) ACID plots (isovalue = 0.03) of Hex and HexCu. (d) Isovalue contours of the global EDDBp(r) function of Hex determined for the Vogel's bridged-annulene pathway (marked red); the electron populations refer to the EDDB-based averaged atomic contributions to global (EDDB_H).

  下载: 全尺寸图片 幻灯片
•