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Article

Aromaticity Study of Linear and Belt-like Polycyclic Aromatic Hydrocarbons

by
Guilherme A. Salles
1,2,
Paulo R. C. Magalhães
1,2,
Jhonatas R. Carvalho
3,
Matheus Máximo-Canadas
4,
Nathália M. P. Rosa
4,
Julio C. V. Chagas
1,2,5,
Luiz F. A. Ferrão
1,2,
Adelia J. A. Aquino
6,
Itamar Borges Jr.
4,*,
Francisco B. C. Machado
1,2,* and
Hans Lischka
3,*
1
Departamento de Química, Instituto Tecnológico de Aeronáutica, São José dos Campos 12228-900, SP, Brazil
2
Laboratório de Computação Científica Avançada e Modelamento (Lab–CCAM), Instituto Tecnológico da Aeronáutica, São José dos Campos 12228-900, SP, Brazil
3
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
4
Departamento de Química, Instituto Militar de Engenharia (IME), Rio de Janeiro 22290-270, RJ, Brazil
5
Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
6
Department of Mechanical Engineering, Texas Tech University, Lubbock, TX 79409, USA
*
Authors to whom correspondence should be addressed.
Chemistry 2025, 7(6), 178; https://doi.org/10.3390/chemistry7060178 (registering DOI)
Submission received: 16 October 2025 / Revised: 1 November 2025 / Accepted: 4 November 2025 / Published: 7 November 2025
(This article belongs to the Special Issue Aromaticity and Antiaromaticity: Refining Concepts and Expanding Perspectives)
Versions Notes

Abstract

Polycyclic aromatic hydrocarbons (PAHs) play a central role in materials science due to their extended π-conjugated systems, with their stability and reactivity depending critically on their aromatic character. In this work, we systematically investigated the aromaticity and stability of a broad range of linear (acenes, phenacenes, biphenylenes, and cyclobuta-acenes) and belt-like (cyclacenes, cyclophenacenes, and cyclobiphenylenes) PAHs containing five to twelve benzene rings. A diverse set of aromaticity descriptors was employed, including geometric (HOMA), electronic (MCI, FLU) and magnetic (NICS) descriptors, plus the recently developed Q2 indices, based on the components of the distributed multipole analysis (DMA) electric quadrupole tensor. These data were complemented by stability analyses using singlet–triplet energy splitting (ΔES–T) and fractional occupation number-weighted densities (NFOD) values. Our results indicate that acenes and phenacenes follow a comparable aromatic trend, with inner rings possessing lower aromaticity and the edge rings showing a more pronounced aromatic character. A subtle difference is observed in the position of the most aromatic ring, which lies slightly closer to the interior in acenes. Phenacenes, however, exhibit greater overall stability, attributed to their armchair edges. For biphenylenes and cyclobuta-acenes, the antiaromatic cyclobutadiene moiety perturbs the aromaticity only in its direct neighborhood and preserves the aromaticity in the remaining chains. In belt-like systems, cyclacenes exhibit strong radical character and low stability, consistent with longstanding synthetic challenges, whereas cyclophenacenes display enhanced aromaticity and stability with extending size. Cyclobiphenylenes combine localized antiaromatic centers with preserved benzene-like aromaticity in rings distant from the cyclobutadiene unit.
Keywords: polycyclic aromatic hydrocarbons (PAHs); aromaticity descriptors; local aromaticity; DFT; π-electron delocalization polycyclic aromatic hydrocarbons (PAHs); aromaticity descriptors; local aromaticity; DFT; π-electron delocalization

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MDPI and ACS Style

Salles, G.A.; Magalhães, P.R.C.; Carvalho, J.R.; Máximo-Canadas, M.; Rosa, N.M.P.; Chagas, J.C.V.; Ferrão, L.F.A.; Aquino, A.J.A.; Borges Jr., I.; Machado, F.B.C.; et al. Aromaticity Study of Linear and Belt-like Polycyclic Aromatic Hydrocarbons. Chemistry 2025, 7, 178. https://doi.org/10.3390/chemistry7060178

AMA Style

Salles GA, Magalhães PRC, Carvalho JR, Máximo-Canadas M, Rosa NMP, Chagas JCV, Ferrão LFA, Aquino AJA, Borges Jr. I, Machado FBC, et al. Aromaticity Study of Linear and Belt-like Polycyclic Aromatic Hydrocarbons. Chemistry. 2025; 7(6):178. https://doi.org/10.3390/chemistry7060178

Chicago/Turabian Style

Salles, Guilherme A., Paulo R. C. Magalhães, Jhonatas R. Carvalho, Matheus Máximo-Canadas, Nathália M. P. Rosa, Julio C. V. Chagas, Luiz F. A. Ferrão, Adelia J. A. Aquino, Itamar Borges Jr., Francisco B. C. Machado, and et al. 2025. "Aromaticity Study of Linear and Belt-like Polycyclic Aromatic Hydrocarbons" Chemistry 7, no. 6: 178. https://doi.org/10.3390/chemistry7060178

APA Style

Salles, G. A., Magalhães, P. R. C., Carvalho, J. R., Máximo-Canadas, M., Rosa, N. M. P., Chagas, J. C. V., Ferrão, L. F. A., Aquino, A. J. A., Borges Jr., I., Machado, F. B. C., & Lischka, H. (2025). Aromaticity Study of Linear and Belt-like Polycyclic Aromatic Hydrocarbons. Chemistry, 7(6), 178. https://doi.org/10.3390/chemistry7060178

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