Aromaticity Induced by Electric Field: The Case of Polycalicenes

Abstract

Local and global π-electron delocalization occurring in planar poly-1,7-[N]calicenes is investigated with use of 10 aromaticity measures based on different physical properties. Systematic change of aromatic character is observed along chains of connected calicene units. Multidimensionality of the aromaticity phenomenon is studied with use of principal component analysis (PCA). The structural characteristics are compared with the properties of the isolated calicene molecule exposed to external electric fields of various intensities. Interrelations between the value of electric field applied and physical properties of the calicene molecule are discussed in the context of calicene unit affected by its surroundings in polycalicene chains. The patterns of global π-electron delocalization are described in graph theory terminology, and interconnections between local and global aromaticity in these systems are established.

The response of electronic and energetic properties of conjugated vs aromatic molecules to an external uniform electric field

“…A series of papers was devoted to atomic polarizabilities, that is polarization of the atomic charge distribution in molecules [1][2][3][4][5]. Among other effects, one can mention the tuning of aromaticity of para substituted benzene derivatives [6] and polycalicenes [7] imposed by the field. The most interesting result for us in the first paper was finding the dipole moment direction reversal in paminophenol, p-nitrobenzonitrile, and p-nitrophenol at a sufficiently high field strength and at its proper direction toward the main molecular axes.…”

Tuning Aromaticity ofpara‐Substituted Benzene Derivatives with an External Electric Field

“…It can be observed that the external electric field applied to a para ‐substituted benzene derivative may significantly change the aromaticity of the benzene ring (or, in other words, its aromaticity can be tuned by the presence of the external electric field). Similar aromaticity tuning has been described for a calicene molecule (tuning with an external electric field) and for bicalicene derivatives (tuning with an external electric field or with substituents) . For para ‐substituted benzene derivatives, it is important to point out that the aromaticity tuning is most effective when benzene is substituted with one electron‐donating and one electron‐withdrawing substituent, since in such a case the external electric field, depending on its direction, either reinforces or counteracts the action of both substituents cooperating together in the sense of their substituent effect.…”

Geometrical, electrical, and energetic parameters of hetero-disubstituted cumulenes and polyynes in the presence and absence of the external electric field

“…The molecular wires bridging the junctions are designed to work under the electric field [1,8,9]. Therefore, the role of electric field influencing all above mentioned parameters [10][11][12][13][14][15][16][17][18] also needs to be considered. Action of an electric field on atoms or molecules can be measured and visualized with polarizability, being kind of a measure of the energy increment due to the dislocation of electron density within the molecule under the field.…”