Conference paper Aleksey E. Kuznetsov* Hexabenzocoronene functionalized with antiaromatic S- and Se-core-modified porphyrins (isophlorins): comparison with the dyad with regular porphyrin https://doi.org/10.1515/pac-2021-1105 Abstract: The important and perspective molecular building blocks composed of hexaphenylbenzenes (HPBs) or their oxidized derivatives, hexa-peri-hexabenzocoronenes (HBCs), and metalloporphyrins have recently received significant attention of the researchers. In this study, motivated by recent findings, we have addressed the modifications of structures and properties of HBC-porphyrin compounds by using instead of aromatic porphyrins antiaromatic 20π isophlorin derivatives of thiophene or selenophene. We have reported the first comparative computational investigation of the following systems: (i) HBC with one non-metallated aromatic porphyrin, P(N 4 H 2 ), unit, HBC-P(N 4 H 2 ), (ii) HBC with one S-core-modified antiaromatic porphyrin (S-isophlorin), PS 4 , unit, HBC-PS 4 , and (iii) HBC with one Se-core-modified antiaromatic porphyrin (Se-iso- phlorin), PSe 4 , unit, HBC-PSe 4 . The study has been done employing the B3LYP/6-31G* approach (in the gas phase and in the implicit solvents, benzene and dichloromethane), and comparison with the B3LYP/6-31G** and B3LYP/6-311G* approaches was performed, where relevant. The effects of the core-modified antiaromatic isophlorins on the structures, electronic, and other properties, potentially including reactivity, of the whole building block HBC-isophlorin have been shown to be quite pronounced and to be noticeably stronger than the effects of the original aromatic non-metallated porphyrin. Thus, we have demonstrated theoretically that the complete porphyrin core-modification with other elements, this time with S and Se leading to the formation of the antiaromatic isophlorins, should be considered as a promising way for modifying and tuning structures, electronic properties and reactivity of the hexabenzocoronene-porphyrin(s) building blocks. Keywords: Chemistry and its applications; density functional theory approach; electronic properties; hex- abenzocoronene; molecular electrostatic potential maps; molecular orbitals; NBO analysis; novel molecular building blocks; S- and Se-isophlorins; structural distortions; VCCA-2021. Introduction In last decades, in various subfields of chemistry, such as organic chemistry, nanochemistry, etc., two important molecular building blocks have attracted significant and ever-growing interest of researchers: one block is represented by hexaphenylbenzenes (HPBs) and their oxidized derivatives, hexa-peri-hex- abenzocoronenes (HBCs), and another block is represented by numerous tetrapyrrole compounds. On one hand, hexaphenylbenzenes and hexabenzocoronenes have found applications for approximately 20 years in Article note: A collection of invited papers based on presentations at the Virtual Conference on Chemistry and its Applications (VCCA-2021) held on-line, 9–13 August 2021. *Corresponding author: Aleksey E. Kuznetsov, Department of Chemistry, Universidad Técnica Federico Santa María, Santiago, Chile, e-mail: aleksey.kuznetsov@usm.cl Pure Appl. Chem. 2022; 94(7): 747–765 © 2022 IUPAC & De Gruyter. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. For more information, please visit: http://creativecommons.org/licenses/by-nc-nd/4.0/