Aromatic Expanded Isophlorins: Stable 30π Annulene Analogues with Diverse Structural Features

Abstract

Synthesis and structural diversity of novel aromatic expanded isophlorins are described. Expanded isophlorins are higher analogues of 20pi isophlorin; 30pi isophlorins are the simplest examples of expanded isophlorins. They are synthesized from easy to make precursors. Owing to the sp(2) carbons along the conjugated network, they represent higher analogues of annulenes which are not realized until date. In contrast to the parent isophlorin 2, expanded isophlorins 7-9 and 11-13 are aromatic (4n + 2)pi systems and also differ in their optical properties and structural features. They exhibit ring inverted structures and the number of ring inversions is dependent on the nature of the heteroatoms present in the core of the macrocycle. This was confirmed by both (1)H NMR spectroscopy and single crystal-ray diffraction analysis. The upfield chemical shifts for the protons of the inverted rings confirmed the diatropic ring current effects as expected for (4n + 2)pi aromatic systems. Solid state analysis revealed a planar conformation for 7 and near planar conformations for other macrocycles. They also show strong intermolecular interactions through C(sp(2))-H...F-C(sp(2)) hydrogen bonds.

An Amphoteric Switch to Aromatic and Antiaromatic States of a Neutral Air‐Stable 25π Radical

“…Macrocycles with seven, nine, and ten thiophene subunits were identified in relatively poor yields. Our analysis of the 20p tetrathiaisophlorin [11] and 30p hexathia hexaphyrin [12] were similar to earlier reports. A green-colored solution obtained by chromatographic separation showed m/z value of 1304.8992 in its high-resolution mass spectrum (see the Supporting Information).…”

An Amphoteric Switch to Aromatic and Antiaromatic States of a Neutral Air‐Stable 25π Radical

“…Macrocycles with seven, nine, and ten thiophene sub‐units were identified in relatively poor yields. Our analysis of the 20π tetrathiaisophlorin11 and 30π hexathia hexaphyrin12 were similar to earlier reports. A green‐colored solution obtained by chromatographic separation showed m / z value of 1304.8992 in its high‐resolution mass spectrum (see the Supporting Information).…”

Computational Studies of Aromatic and Photophysical Properties of Expanded Porphyrins

“…1 Their aromatic character depends on the number and properties of the heteroatoms and what kind of substituents that are conjugated with the main macrocycle. [2][3][4][5][6][7] Many antiaromatic porphyrinoids are stable with interesting properties for technological devices. 2,8,9 The term antiaromatic was used for the first time by Breslow in 1965.…”