AbstractA series of meso‐trifluoromethyl‐substituted expanded porphyrins, including N‐fused [24]pentaphyrin 3, [28]hexaphyrin 4, [32]heptaphyrin 5, [46]decaphyrin 6, and [56]dodecaphyrin 7, were synthesized by means of an acid‐catalyzed one‐pot condensation reaction of 2‐(2,2,2‐trifluoro‐1‐hydroxyethyl)pyrrole (1) as the first examples bearing meso‐alkyl substituents. Besides these products, porphyrin 2 and two calix[5]phyrins 8 and 9 were also obtained. [28]Hexaphyrin 4 was quantitatively oxidized to [26]hexaphyrin 14 with MnO2. These expanded porphyrins have been characterized by mass spectrometry, 1H and 19F NMR spectroscopy, and UV/Vis spectroscopy. The single‐crystal structures have been determined for 3, 4, 6, 7, and 14. The N‐fused [24]pentaphyrin 3 displays a distorted structure containing a tricyclic fused moiety that is similar to those of meso‐aryl‐substituted counterparts, whereas 8 and 9 are indicated to take roughly planar conformations with an inverted pyrrole opposite to the sp3‐hybridized meso‐carbon atom. Both [28]‐ and [26]hexaphyrins 4 and 14 have figure‐of‐eight structures. Solid‐state structures of the decaphyrin 6 and dodecaphyrin 7 are remarkable, exhibiting a crescent conformation and an intramolecular two‐pitch helical conformation, respectively.

New forms of molecular nanocarbons particularly looped polyarenes adopting various topologies contribute to the fundamental science and practical applications. Here we report on the synthesis of an infinity-shaped polycyclic aromatic hydrocarbon, infinitene 1 (cyclo[c.c.c.c.c.c.e.e.e.e.e.e]dodecakisbenzene) comprising consecutively fused 12-benzene rings forming an enclosed loop with a strain energy of 60.2 kcal·mol-1. Infinitene 1 represents a topoisomer of still-hypothetical [12]circulene, and its scaffold can be formally visualized as the outcome of the “stitching” of two homochiral [6]helicene subunits by their both ends. The synthetic strategy encompasses transformation of a rationally designed dithiacyclophane to cyclophadiene through the Stevens rearrangement and pyrolysis of the corresponding S,S′-bis(oxide) followed by the UV-light mediated twofold photocyclization. The structure of infinitene 1 is a unique hybrid of helicene and circulene with a molecular formula C48H24, which can be regarded as an isomer for kekulene, [6,6]carbon nanobelt ([6,6]CNB), [12]cyclacene, and tetrabenzo[8]circulene as well. Infinitene 1 is a bench-stable yellow solid with green fluorescence, and soluble to common organic solvents. The figure-eight molecular structure of 1 was unambiguously confirmed by X-ray crystallography. The scaffold of 1, reminiscent of a squeezed spring, stem from its enclosed, fully-fused architecture, is significantly compressed as manifested by a remarkably shortened distance (3.152–3.192 Å) between the centroids of two π-π stacked central benzene rings and the closest C···C distance of 2.920 Å. Combined lamellar and herringbone-like crystal packing suggested three-dimensional electronic inter-actions. Fundamental photophysical properties of infinitene 1 were thoroughly elucidated by means of UV-vis absorption and fluorescence spectroscopic studies as well as density functional theory (DFT) calculations. Its configurational stability enabled separation of the corresponding enantiomers (P,P) and (M,M) by a chiral HPLC. Circular dichroism (CD) and circularly polarized luminescence (CPL) measurements revealed that 1 has moderate |gCD| and |gCPL| values.