Correction: Changes in macrocyclic aromaticity and formation of a charge-separated state by complexation of expanded porphyrin and C60.

Correction for 'Changes in macrocyclic aromaticity and formation of a charge-separated state by complexation of expanded porphyrin and C60' by Won-Young Cha et al., Chem. Commun., 2019, 55, 8301-8304, DOI: .

Noncovalent Intermolecular Interaction in Cofacially Stacked 24π Antiaromatic Hexaphyrin Dimer.

π-π Stacking is omnipresent not only in nature but in a wide variety of practical fields applied to our lives. Because of its importance in a performance of natural and artificial systems, such as light harvesting system and working layer in device, many researchers have put intensive effort into identifying its underlying nature. However, for the case of π-π stacked systems composed of antiaromatic units, the understanding of the fundamental mechanisms is still unclear. Herein, we synthesized a new type of planar ß,ß'-phenylene-bridged hexaphyrin (1.0.1.0.1.0), referred as naphthorosarin which possesses the 24π-electron conjugated pathway. Especially, the corresponding antiaromatic porphyrinoid shows the unique property to form dimeric species adopting the face-to-face geometry which is unprecedented in cases of known annulated naphthorosarins. In order to elucidate the intriguing properties derived from the stacked dimer, the current study focuses on the experimental support to rationalize the observed π-π interactions between the two subunits.

Structurally Isomerized Bis-Biphenyl Moieties Embedded in Hexaphyrin(3.1.1.3.1.1) and Octaphyrin(1.1.1.0.1.1.1.0).

An o-p-biphenyl moiety-incorporated 32π hexaphyrin(3.1.1.3.1.1) is successfully achieved. Replacing ortho with meta connectivity in the biphenyl unit of hexaphyrin leads to the formation of its structural isomer, octaphyrin(1.1.1.0.1.1.1.0). Spectral and structural analyses reveal the lack of planarity in hexaphyrin and the presence of an m-arene unit in octaphyrin, thus affording nonaromatic characteristics.

Bis-4,4'-biphenyl Ring Embedded Octaphyrin with Three Distinct Conformational Structures.

Three distinct conformational structures of carbaoctaphyrins were prepared by incorporating bis-4,4'-biphenyl units in the macrocyclic core. The free-base form adopts a figure-eight conformation, whereas the protonation triggers a conformational change with a pyrrole ring inversion and acquires an open-framework structure. The insertion of bis-RhI metal ion in the macrocyclic core affords a singly twisted conformational structure. Furthermore, the local aromaticity in the bis-4,4'-biphenyl ring dominates the overall macrocyclic aromaticity in all three forms, and thus adopts nonaromatic characteristics. These results are supported by spectral as well as theoretical studies, and they are unambiguously confirmed by X-ray crystal analyses.

Changes in macrocyclic aromaticity and formation of a charge-separated state by complexation of expanded porphyrin and C60.

Significant changes of macrocyclic aromaticity in expanded porphyrins through C60 complexation were studied by 1H NMR spectroscopy and nucleus-independent chemical shift calculations. This work is a detailed research study of how the formation of a complex of dual aromatic expanded porphyrin with fullerene affects the electron densities in the main conjugation pathways and meso-substituents. Furthermore, we found that the formation of the photoinduced charge-separated state and the triplet excited-state populations of the bowl-shaped and rigid expanded porphyrin can be controlled by a simple complexation with C60.

Proton-Coupled Redox Switching in an Annulated π-Extended Core-Modified Octaphyrin.

Proton-coupled electron transfer (PCET) is an important chemical and biological phenomenon. It is attractive as an on-off switching mechanism for redox-active synthetic systems but has not been extensively exploited for this purpose. Here we report a core-modified planar weakly antiaromatic/nonaromatic octaphyrin, namely, a [32]octaphyrin(1.0.1.0.1.0.1.0) (1) derived from rigid naphthobipyrrole and dithienothiophene (DTT) precursors, that undergoes proton-coupled two-electron reduction to produce its aromatic congener in the presence of HCl and other hydrogen halides. Evidence for the production of a [4 n + 1] π-electron intermediate radical state is seen in the presence of trifluoroacetic acid. Electrochemical analyses provide support for the notion that protonation causes a dramatic anodic shift in the reduction potentials of octaphyrin 1, thereby facilitating electron transfer from halide anions (viz. I-, Br-, and, Cl-). Electron-rich molecules, such as tetrathiafulvene (TTF), phenothiazine (PTZ), and catechol, were also found to induce PCET in the case of 1. Both the oxidized and two-electron reduced forms of 1 were characterized by X-ray diffraction analyses in the solid state and in solution via spectroscopic means.

Near-Infrared S2 Fluorescence from Deprotonated Möbius Aromatic [32]Heptaphyrin.

This study revealed S2 fluorescence from deprotonated meso-pentafluorophenyl-substituted Möbius aromatic [32]heptaphyrin(1.1.1.1.1.1.1) that was formed upon treatment of neutral antiaromatic [32]heptephyrin with tetrabutylammonium fluoride. Higher excited-state dynamics and emission were studied by fs-transient absorption spectroscopy and a broad-band fluorescence upconversion technique. This is the first S2 fluorescence from chromophores with twisted Möbius topology, and the observation of S2 fluorescence in the near-infrared region has been unprecedented. The higher excited-state dynamics of neutral and deprotonated [32]heptaphyrins were compared by ultrafast transient absorption spectroscopy to understand the S2 fluorescence origin. In the antiaromatic [32]heptaphyrin, a fast time component of 65 fs was assigned as an internal conversion process from the SB state to the SQ state, which occurs prior to relaxation to the optically dark, lowest electronic state (SD). Therefore, the SQ state of the antiaromatic [32]heptaphyrin acts as a trap state intervening radiative transitions from the SB state to the S0 state. In deprotonated [32]heptaphyrin, the internal conversion from the SB state to the SQ state proceeds with a slower time constant of 150 fs for owing to its rigid structure, helping the observation of its S2 fluorescence.

Hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1): A Dual Site Ligand That Supports Thermal Conformational Changes.

A new expanded porphyrin, hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1), is reported. It was obtained via the condensation of a hexapyrrolic derivative prepared in turn from a bipyrrole dialdehyde and a stable quaterpyrrole precursor. This hexadecaphyrin contains eight direct α-pyrrole-to-α-pyrrole linkages in its structure. It supports the formation of bimetallic complexes of both zinc and cobalt that are characterized by different conformational structures. Furthermore, a mixed zinc/cobalt macrocycle has been prepared. The cobalt bimetallic complex shows two stable conformations with the same oxidation state that are in equilibrium. All compounds have been characterized by common spectroscopic means, and single crystal X-ray diffraction structures were obtained for all macrocyclic compounds. DFT calculations and transient absorption spectra were used to study the electronic features of the complexes and the effect of conformational changes. This system shows promise as an accumulated heat sensor.

An Expanded Porphycene with High NIR Absorptivity That Stabilizes Two Different Kinds of Metal Complexes.

A new expanded porphycene with 26 π-electrons has been prepared by the McMurry coupling of 1,4-bis(3,4-diethyl-2-pyrryl)benzene dialdehyde. Expansion of the porphycene framework provides a ligand capable of stabilizing a bis(rhodium) and a monoruthenium complex. These new porphycene derivatives absorb strongly in the NIR spectral region, with appreciable absorptivity up to 1300 nm. On the basis of their ground- and excited-state spectroscopic features and structural parameters, both the free-base system and the bis(rhodium) complex are considered to be Hückel-type aromatic systems. This conclusion is supported by DFT calculations.

Bicyclic Baird-type aromaticity.

Classic formulations of aromaticity have long been associated with topologically planar conjugated macrocyclic systems. The theoretical possibility of so-called bicycloaromaticity was noted early on. However, it has yet to be demonstrated by experiment in a simple synthetic organic molecule. Conjugated organic systems are attractive for studying the effect of structure on electronic features. This is because, in principle, they can be modified readily through dedicated synthesis. As such, they can provide useful frameworks for testing by experiment with fundamental insights provided by theory. Here we detail the synthesis and characterization of two purely organic non-planar dithienothiophene-bridged [34]octaphyrins that permit access to two different aromatic forms as a function of the oxidation state. In their neutral forms, these congeneric systems contain competing 26 and 34 π-electronic circuits. When subject to two-electron oxidation, electronically mixed [4n+1]/[4n+1] triplet biradical species in the ground state are obtained that display global aromaticity in accord with Baird's rule.