Aromaticity of Heterocirculenes

Abstract

This review summarizes the results on the aromaticity of a series of synthesized and hypothetical neutral heterocirculene molecules and their double charged ions. The aromaticity of heterocirculenes is a direct reflection of their electronic structure responsible for the specific optoelectronic and photophysical properties. We show how the presence of a heteroatom in the outer macrocycle affects the aromaticity of hetero[8]circulenes. In addition, we also describe the change in aromaticity and strain energy for a series of the “lower” (n < 8) and “higher” (n > 8) hetero[n]circulenes. It was demonstrated that the loss of planarity with increased strain leads to an increased antiaromaticity of the lower hetero[n]circulenes, whereas higher hetero[n]circulenes demonstrate a more pronounced aromatic nature because of the small departure from planarity of each heteroarene ring in hetero[n]circulene molecule. Finally, we discuss the aromatic nature of the first examples of π-extended hetero[8]circulenes.

Unraveling the Aromatic Rule of Cyclic Superatomic Molecules in π-Conjugated Compounds

“…The aromaticity of π-conjugated compounds like sulflower, whose origin has puzzled scientists for many years but has not yet been thoroughly understood, remains one of the most interesting and highly debated topics in related chemistry fields. − Various magnetic criteria such as nucleus-independent chemical shift (NICS), − anisotropy of the current-induced density (ACID) plot, and gauge-including magnetically induced current (GIMIC) , are necessary but not sufficient to define a system as aromatic or antiaromatic because only the global character of electron delocalization is concerned . The conventional Hückel’s 4 n + 2 electron rule is applicable to monocyclic conjugated systems but not applicable to common [ n ]­circulenes with a total of 4 n π electrons.…”

Theoretical study on the structures, electronic properties, and aromaticity of thia[4]circulenes

“…The most intriguing aspects are the modulations of their geometries and/or aromaticity depending on the ring size. 23,[52][53][54][55][56][57][58][59][60][61][62] As n increases from 5 to 12 in thia[n]circulenes, density functional theory (DFT) calculations predict that they adopt bowl-(n = 5-7), planar-(n = 8, 9), quasi-planar-(n = 10), and saddleshaped (n Z 11) geometries. 58,60 Additionally, upon increasing the number of n, diatropic current flows along the peripheries are strengthened, and these dominate over paratropic current flows along the central n-membered rings, increasing the global aromaticity.…”

Electronic and optical properties of C16S8and C16S4Se4molecules and crystals

“…Due to their high stability, symmetry, and optical properties [ n ]circulenes can be used in the field of nanoelectronics as promising fluorescent emitters for organic light-emitting diodes and in the construction of solar cells. 1–3…”

“…Due to their high stability, symmetry, and optical properties [n]circulenes can be used in the field of nanoelectronics as promising fluorescent emitters for organic light-emitting diodes and in the construction of solar cells. [1][2][3] [n]circulenes are typically semiconductors with tunable band gaps depending on the stacking features. Moreover, circulenes can be coupled through post-transformation into one-(1D) or twodimensional (2D) materials which demonstrate useful semiconducting or semimetallic properties.…”