Optical band gap of cross-linked, curved, and radical polyaromatic hydrocarbons

Menon, Angiras; Dreyer, Jochen A.H.; Martin, Jacob W.; Akroyd, Jethro; Robertson, John; Kraft, Markus

doi:10.1039/c9cp02363a

Cited by 51 publications

(40 citation statements)

References 64 publications

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“…Optical band gap theory suggests that we may consider absorption of the refractory particle components to be determined by the size of polycyclic aromatic units (Menon et al 2019). The relationship found between AAE and fringe length (Figure 5a), and AAE and ( Figure 6) support that the light absorption wavelength dependence of soot depends on the size of refractory aromatic units in the soot particle.…”

Section: Optical Band Gap and Refractory Sp-ams Analysismentioning

confidence: 75%

“…The absorption measurements at seven wavelengths allowed us to evaluate AAEs in different wavelength intervals. The high optical band gap energies (Menon et al 2019) and absorption spectra (Huisken et al 2013) associated with non-refractory PAHs observed in the AMS (mainly PAHs with molecular masses of 202-300 Da) suggested that the non-refractory components that were removed in the TD would have only a minor contribution to absorption at wavelengths longer than 660 nm. Therefore, AAEs were evaluated in two wavelength intervals: the full 370-950 nm wavelength interval (AAE 370-950nm ) and for the 660-950 nm wavelength interval (AAE 660-950nm ).…”

Section: Aae In Different Wavelength Intervalsmentioning

confidence: 99%

“…Because the two parameters were correlated, their independent effect on AAE cannot be fully determined. However, calculations of optical bandgaps for differently sized PAHs have shown a relatively small dependence on curvature (Menon et al 2019). It is therefore more likely that the measured change in fringe length is the causal parameter describing the changes in AAE.…”

Section: Aae: Soot Nanostructure and Refractory Organic Soot Componentsmentioning

confidence: 99%

“…Refractory soot components appear as carbon lamellae (i.e., refractory polycyclic aromatic units) in both immature and mature soot (Andreae et al 2006, Miller et al 2013, Huang et al 2016, Malmborg et al 2019. The optical band gap of soot decreases when the size of sp 2 -bonded aromatic clusters increases (i.e., increasing PAH unit size), and a change to larger aromatic clusters is associated with a decreasing wavelength dependence (i.e., Ångström exponent) and increasing absorption cross section (Andreae et al 2006, Laskin et al 2015, Botero et al 2016, Menon et al 2019. A smaller size of carbon lamellae has previously been hypothesized to be the explanation to why some soot have BrC characteristics (Bond 2001, Schnaiter et al 2006.…”

Section: Introductionmentioning

confidence: 99%

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Characteristics of BrC and BC emissions from controlled diffusion flame and diesel engine combustion

Malmborg

Eriksson

Gren

et al. 2021

Aerosol Science and Technology

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Constraining the climate impact of particulate brown carbon (BrC) will require identification of formation mechanisms and isolation of its different components to allow for source apportionment. For fresh combustion aerosols, the light absorption characteristics and the Absorption Ångstrom Exponent (AAE) are principally controlled by the combustion conditions in which the particles formed and evolved. We investigated the influence of combustion temperatures on the BrC or black carbon (BC) emission characteristics for a miniCAST soot generator (propane fuel) and a modern heavyduty diesel engine (petroleum diesel and two renewable diesel fuels). Changes in the AAE, mass spectral signatures, and thermal-optical characteristics were studied. We show that changing operating parameters to gradually reduce the combustion temperatures in these two fundamentally different combustion devices result in a regression from BC dominated to BrC dominated particle emissions. The regression towards BrC was associated with: 1) an increasing mass fraction of particulate non-refractory polycyclic aromatic hydrocarbons (PAHs), 2) an increasing fraction of refractory organic carbon, 3) more curved soot nanostructures and shorter fringe lengths, and 4) increased signal from (refractory) large carbon fragments in IR laser-vaporization aerosol mass spectra. Based on these results we argue that fresh BrC dominated combustion aerosols are attributed to primary emissions from low temperature combustion, highlighting the influence of refractory constituents and soot nanostructure. Higher temperatures favor the growth of conjugated polyaromatic structures in the soot, a progression hypothesized to control the evolution from BrC to BC character of the emitted aerosols.

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Section: Optical Band Gap and Refractory Sp-ams Analysismentioning

confidence: 75%

Section: Aae In Different Wavelength Intervalsmentioning

confidence: 99%

Section: Aae: Soot Nanostructure and Refractory Organic Soot Componentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Characteristics of BrC and BC emissions from controlled diffusion flame and diesel engine combustion

Malmborg

Eriksson

Gren

et al. 2021

Aerosol Science and Technology

View full text Add to dashboard Cite

show abstract

“…64 The UVvisible electronic transitions in sp 2 carbon systems such as PAHs rely on π * -π transitions. 65 Several studies show that there is an inverse power law relationship between optical band gap (OBG) and the number of benzene rings in PAHs 66,67 . An increase in MW of PAHs broadens their absorption bands towards longer wavelengths and red-shifts their emission bands due to the decreasing OBG.…”

Section: Spectral Information From Eem Analysismentioning

confidence: 99%

Excitation-Emission Matrix Spectroscopy for Analysis of Chemical Composition of Combustion Generated Particulate Matter

Mahamuni

Rutherford²,

Davis³

et al. 2019

Preprint

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Analysis of particulate matter (PM) is critical for the assessment of human exposures to potentially harmful agents, notably combustion-generated PM; specifically polycyclic aromatic hydrocarbons (PAHs) found in them and associated with carcinogenic and mutagenic effects. In this study, we quantify the presence and concentrations of PAHs with low molecular weight (LMW) and higher molecular weight (HMW) in combustion-generated PM using excitation-emission matrix (EEM) fluorescence spectroscopy. PM samples were generated in a laminar diffusion inverted gravity flame reactor (IGFR) operated on Ethylene and Ethane. Fuel dilution by Ar in 0% to 90% range controls the flame temperature, the maximum flame temperature decreases with fuel dilution. The colder flames result in lower PM yields; however, the PM PAH content increases significantly. Temperature thresholds for PM transition from low to high organic carbon content were characterized based on the maximum flame temperature (1814K-1864K) and highest soot luminosity region temperature (1600K-1650K). Principal component regression (PCR) analysis of the EEM spectra correlates to GCMS data, R2 values of 0.98 for LMW and 0.99 for HMW PAHs. The agreement demonstrates that EEM analysis can be used to determine relative concentrations of organic carbon and PAH fractions in combustion PM, and can be related to PM health effects and used in the environmental studies.

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Circumpentacene with Open‐Shell Singlet Diradical Character

2023

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Circumacenes (CAs) are a distinctive type of benzenoid polycyclic aromatic hydrocarbons where an acene unit is completely enclosed by a layer of outer fused benzene rings. Despite their unique structures, the synthesis of CAs is challenging, and until recently, the largest CA molecule synthesized was circumanthracene. In this study, we report the successful synthesis of an extended circumpentacene derivative 1, which represents the largest CA molecule synthesized to date. Its structure was confirmed by X‐ray crystallographic analysis and its electronic properties were systematically investigated by both experiments and theoretical calculations. It shows a unique open‐shell diradical character due to the existence of extended zigzag edges, with a moderate diradical character index (y0=39.7 %) and a small singlet‐triplet energy gap (ΔES‐T=−4.47 kcal/mol). It exhibits a dominant local aromatic character with π‐electrons delocalized in the individual aromatic sextet rings. It has a small HOMO–LUMO energy gap and displays amphoteric redox behavior. The electronic structures of its dication and dianion can be considered as doubly charged structures in which two coronene units are fused with a central aromatic benzene ring. This study provides a new route toward stable multizigzag‐edged graphene‐like molecules with open‐shell di/polyradical character.

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Optical band gap of cross-linked, curved, and radical polyaromatic hydrocarbons

Abstract: The impact of cross-linking, curvature, and radical character on the optical band gap of polyaromatic hydrocarbons has been investigated.

Cited by 51 publications

References 64 publications

Characteristics of BrC and BC emissions from controlled diffusion flame and diesel engine combustion

Characteristics of BrC and BC emissions from controlled diffusion flame and diesel engine combustion

Excitation-Emission Matrix Spectroscopy for Analysis of Chemical Composition of Combustion Generated Particulate Matter

Circumpentacene with Open‐Shell Singlet Diradical Character

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