Optoelectronic Properties of Polycyclic Benzenoid Hydrocarbons of Various Sizes and Shapes for Donor‐π‐Acceptor Systems: A DFT Study

Abstract

The zigzag and armchair‐edged benzenoid polycyclic aromatic hydrocarbons (PAHs) possessing circular, parallelogram, rectangular and triangular shapes have been studied for a systematic evaluation of their optoelectronic properties for the design of donor‐π‐acceptor (D‐π‐A) systems 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 showed Clar's sextet like electronic arrangement in armchair‐edged systems whereas zigzag‐edged ones showed significant electron localization towards the edges. The absorption spectra revealed a linear trend in absorption maximum (λmax) for most of the armchair‐edged systems with respect to the number of π‐electrons. MESP based assessment of the electron rich/deficient features of PAH systems led to the design of PAH‐π‐PAH type D‐π‐A systems wherein a conjugated diene moiety functions as the π‐spacer. The D‐π‐A behaviour of these systems significantly enhanced with the introduction of electron donating functional group NMe2 on donor PAH and electron withdrawing group COOH on the acceptor PAH. The MESP features, frontier molecular orbital (FMO) distribution, and absorption spectral features supported the strong D‐π‐A character of functionalized PAH‐π‐PAH. Among the different shapes studied, the rectangular PAH moiety showed the most efficient tuning of HOMO‐LUMO gap. The optical and electronic properties of PAH, PAH‐π‐PAH and functionalized PAH‐π‐PAH systems suggest the high tunable character of these properties with respect to the size and shape of the PAH.

BenzAI: A Program to Design Benzenoids with Defined Properties Using Constraint Programming

“…Benzenoids are polycyclic aromatic hydrocarbons (PAHs) made of fused six-membered rings only. They are well-studied in various domains because of their electronic and optical properties . They are also studied in detail in interstellar chemistry because they are suspected to be present in interstellar clouds and are believed to act as catalysts for chemical reactions taking place in space .…”

“…They are well-studied in various domains because of their electronic and optical properties. 1 They are also studied in detail in interstellar chemistry because they are suspected to be present in interstellar clouds and are believed to act as catalysts for chemical reactions taking place in space. 2 The aromatic character of benzenoids can be studied using the Clar sextet rule for ground states.…”

Electrostatic Potential for Exploring Electron Delocalization in Infinitenes, Circulenes, and Nanobelts

“…56 The Clar's sextet-like electronic arrangement in armchair-edged systems reported by Rakhi and Suresh is well discernible here. 57 This feature is also evident from their bond lengths (1.35 to 1.36 Å) and other bond lengths, which lie in the range of 1.42 to 1.48 Å (Figure 1a). The X-ray crystal structure data show a range of 1.33 to 1.36 Å for the shorter C−C bonds and 1.40 to 1.48 Å for the longer ones.…”

Molecular electrostatic potential analysis: A powerful tool to interpret and predict chemical reactivity

“…Rakhi and Suresh performed MESP analysis for zigzag and armchair‐edged benzenoid PAHs having circular, parallelogram, triangular, and rectangular shapes to assess their optoelectronic properties (Figure 11f). 222 The armchair‐edged PAH system showed better Clar's aromatic sextet features whereas the zigzag‐edged systems showed more localization effect of electron density. Attempts were also made to enhance the aromaticity of LPAs by dihydropyrazine annulation 223 .…”