Optoelectronic Properties of Polycyclic Aromatic Hydrocarbons of Various Sizes and Shapes: A DFT Study

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Beilstein Arch. 2020, 2020119. https://doi.org/10.3762/bxiv.2020.119.v1

Published 13 Oct 2020

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Polycyclic aromatic hydrocarbons (PAHs) can be considered as graphene nanoflakes in which the edges are hydrogenated. Zigzag and armchair-edged PAHs possessing circular, parallelogram, rectangular and triangular shapes have been studied using M06L/6-31+G(d) level of density functional theory (DFT). Molecular electrostatic potential (MESP) analysis of the PAHs is done to characterize their electron distribution while the time-dependent DFT (TD-DFT) analysis was used for the absorption spectral analysis. MESP analysis clearly showed Clar’s sextet like electronic arrangement in armchair-edged systems whereas zigzag-edged ones showed significant electron localization towards the edges. TD-DFT analysis casts light upon the absorption features of these systems, which followed a linear trends in absorption maximum (lmax) for most of the armchair-edged systems with respect to the number of π-electrons. MESP analysis on the electron rich and electron deficient features of PAH systems led to the design of donor-spacer-acceptor type PAH-π-PAH systems (D-π-A systems) wherein a conjugated diene moiety functions as the π-spacer. Though these systems behaved weakly as D-π-A systems, with the introduction of electron donating functional group NMe2 on one PAH and electron withdrawing group COOH on the other led to the formation of strong D-π-A systems.  The MESP features, frontier molecular orbital (FMO) distribution, and absorption spectral features supported their strong D-π-A character. Among the different shapes studied, the rectangular PAH moiety showed the most efficient tuning of HOMO-LUMO gap. The optical and electronic data of PAH, PAH-π-PAH and functionalized PAH-π-PAH systems shed light upon possible tuning of their optoelectronic properties for practical applications.

Keywords: Polycyclic aromatic hydrocarbon, Molecular electrostatic potential analysis, DFT, TDDFT, M06L, Graphene nanoflakes, Donor-pi-Acceptor systems

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Rakhi, R.; Suresh, C. H. Beilstein Arch. 2020, 2020119. doi:10.3762/bxiv.2020.119.v1

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