Modelling the absorption properties of polycyclic aromatic hydrocarbons and derivatives over three European cities by TD-DFT calculations

Brown carbon is a type of carbonaceous aerosol with strong light absorption in the ultraviolet and visible wavelengths that leads to radiative forcing. However, it is difficult to correlate the chemical composition of brown carbon with its atmospheric light absorption properties, which translates into significant uncertainty. Thus, a time-dependent density functional theory (TD-DFT) approach was used to model the real-world absorption properties of 14 polycyclic aromatic hydrocarbons (PAHs) over three regions of the Basque Country (Spain): Bilbao, Urretxu, and Azpeitia. The data were corrected for atmospheric concentration. The results show that the absorption spectra over each region are qualitatively identical, with the absorption intensities being significantly higher over Bilbao than over Azpeitia and Urretxu. Furthermore, it was found that the light absorption by PAHs should be more relevant for radiative forcing when it occurs at UVA and (sub)visible wavelengths. Finally, among the 14 studied PAHs, benzo[b]fluoranthene, pyrene, fluoranthene, benzo[a]pyrene, and benzo[k]fluoranthene and benzoperylene were identified as the molecules with larger contributions to radiative forcing.

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

10.3762/bxiv.2020.119.v1 ◽

2020 ◽

Author(s):

Ramachandran Rakhi ◽

Cherumuttathu H Suresh

Keyword(s):

Polycyclic Aromatic Hydrocarbons ◽

Aromatic Hydrocarbons ◽

Density Functional ◽

Optoelectronic Properties ◽

Frontier Molecular Orbital ◽

Functional Theory ◽

Practical Applications ◽

Td Dft ◽

Polycyclic Aromatic ◽

Electron Withdrawing Group

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.

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Photoprocessing of large PAH cations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007063 ◽

2019 ◽

Vol 15 (S350) ◽

pp. 388-389

Author(s):

Gabi Wenzel ◽

Sarah Rodriguez Castillo ◽

Giacomo Mulas ◽

Ming-Chao Ji ◽

Anthony Bonnamy ◽

...

Keyword(s):

Polycyclic Aromatic Hydrocarbons ◽

Cross Sections ◽

Aromatic Hydrocarbons ◽

Vacuum Ultraviolet ◽

Young Stars ◽

Radiative Cooling ◽

Td Dft ◽

Polycyclic Aromatic ◽

Synchrotron Light

AbstractIn cosmic environments, polycyclic aromatic hydrocarbons (PAHs) strongly interact with vacuum ultraviolet (VUV) photons emitted by young stars. Trapped PAH cations ranging in size from 30 to 48 carbon atoms were irradiated by tunable synchrotron light (DESIRS beamline at SOLEIL). Their ionization and dissociation cross sections were determined and compared with TD-DFT computed photoabsorption cross sections. Evidence for radiative cooling is reported.

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Enhanced N-directed Electrophilic C-H Borylation Generates BN-[5]- and [6]-helicenes with Improved Photophysical Properties

10.26434/chemrxiv-2021-xnr5j ◽

2021 ◽

Author(s):

Kang Yuan ◽

Daniel Volland ◽

Sven Kirschner ◽

Marina Uzelac ◽

Gary Nichol ◽

...

Keyword(s):

Polycyclic Aromatic Hydrocarbons ◽

Dft Calculations ◽

Supramolecular Chemistry ◽

Asymmetric Catalysis ◽

Aromatic Hydrocarbons ◽

Materials Science ◽

Photophysical Properties ◽

Frontier Orbitals ◽

Significant Interest ◽

Polycyclic Aromatic

Helicenes are chiral polycyclic aromatic hydrocarbons (PAHs) of significant interest e.g. in supramolecular chemistry, materials science and asymmetric catalysis. Herein an enhanced N-directed electrophilic C-H borylation methodology has been developed that provides access to azaborine containing helicenes (BN-helicenes). This borylation process proceeds via protonation of an aminoborane with bistriflimidic acid. DFT calculations reveal the borenium cation formed by protonation to be more electrophilic than the product derived from aminoborane activation with BBr3. The synthesised helicenes include BN-analogues of archetypal all carbon [5]- and [6]helicenes. The replacement of a CC with a BN unit (that has a longer bond) on the outer helix increases the strain in the BN congeners and the racemization half-life for a BN-[5]helicene relative to the all carbon [5]helicene. BN incorporation also increases the fluorescence efficency of the helicenes, a direct effect of BN incorporation altering the distribution of the key frontier orbitals across the helical backbone relative to carbo-helicenes.

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