Peri-condensed Polycyclic Aromatic Hydrocarbons Research Articles

Crystal-Structure Control of Molecular Semiconductors by Methylthiolation: Toward Ultrahigh Mobility.

ConspectusThe crystal structure of organic semiconductors has been regarded as one of the crucial factors for realizing high-performance electronic devices, such as organic field-effect transistors. However, although the control of crystal structures of organic semiconductors has been examined in the last two decades of intensive efforts of the development of organic semiconductors, active measures to control crystal structures enabling high carrier mobility are still limited. In 2016, our research group noticed that regioselective methylthiolation could provide a selective crystal structure change from an ordinary herringbone structure to a pitched π-stacking structure, similar to the crystal structure of rubrene, in the benzo[1,2-b:4,5-b']dithiophene (BDT) system. Following this serendipitous finding, our group systematically investigated the relationship between the molecular and crystal structures of a range of methylthiolated aromatic and heteroaromatic compounds.This Account provides a comprehensive overview of our research efforts and advancements in the development of methylthiolated small-molecule-based organic semiconductors (molecular semiconductors). We first describe the outline of the past development of molecular semiconductors, focusing on the types of crystal structures of high-performance molecular semiconductors. Then, we describe our findings on the drastic crystal structure change in the BDT system upon methylthiolation, detailing the causes of the change in terms of the intermolecular contacts and intermolecular interaction energies. This is followed by the confirmation of the generality of the crystal-structure change by methylthiolation of a series of acene and heteroacenes, where the herringbone structure in the parent system is unexceptionally transformed into the pitched π-stacking structure, a promising crystal structure for high-mobility molecular semiconductors well exemplified by the prototypical molecular semiconductor, rubrene. In fact, the methylthiolated anthradithiophene afforded comparable high mobility to rubrene in single-crystal field-effect transistors. Then, we demonstrate that the sandwich herringbone structures of peri-condensed polycyclic aromatic hydrocarbons, including pyrene, perylene, and peropyrene, change into brickwork crystal structures upon methylthiolation and that, among these compounds, very promising molecular semiconductors, methylthiolated pyrene and peropyrene, showing ultrahigh mobility of 30 cm2 V s-1, are realized.Through the studies, by gaining insights into the underlying mechanisms driving the crystal structure changes, we lay a strong foundation for tackling challenges related to controlling the crystal structures and developing high-performance molecular semiconductors. This will be a distinct approach from the past activities in the development of molecular semiconductors that mainly focused on molecules themselves, including their synthesis, properties, and characterization. We thus anticipate that our findings and the present Account will open the door to a new era of the development of molecular semiconductors.

Crystal-structure simulation of methylthiolated peri-condensed polycyclic aromatic hydrocarbons for identifying promising molecular semiconductors: discovery of 1,3,8,10-tetrakis(methylthio)peropyrene showing ultrahigh mobility.

The crystal structures of molecular semiconductors critically affect their carrier transport properties. One of the promising crystal structures that afford high carrier mobility is a brickwork structure recently reported for 1,3,6,8-tetrakis(methylthio)pyrene (MT-pyrene) showing ultrahigh mobility. However, such ultrahigh mobility was not realized in other methylchalocogenated pyrenes, owing to subtle differences in the molecular positions in their crystal structures. This means that, for developing superior molecular semiconductors, it is desirable to simulate the crystal structure with sufficient quality before time-consuming and labor-intensive synthetic trials. To realize this, we developed a new computational approach to simulating crystal structures of all methylchalocogenated pyrenes, which was then applied to MT-pyrene-related methylthiolated peri-condensed polycyclic aromatic hydrocarbons including perylene, peropyrene, and terrylene derivatives. Among these, 1,3,8,10-tetrakis(methylthio)peropyrene (MT-peropyrene) was expected to show high mobility based on the simulated crystal structures. We thus chose MT-peropyrene as the synthetic target and developed a new peropyrene synthesis method. Thus synthesized MT-peropyrene has virtually the same crystal structure as the simulated one, and its single-crystal field-effect transistors showed mobility as high as 30 cm2 V-1 s-1 and band-like transport behaviors. These results indicate that the present crystal-structure simulation is a powerful tool for exploring promising molecular semiconductors. This article is protected by copyright. All rights reserved.

Modeling the Adsorption of Polycyclic Aromatic Hydrocarbons on Graphynes: An Improved Lennard-Jones Formulation.

Research on the development of theoretical methodologies for modeling noncovalent interactions governing the adsorption of polycyclic aromatic hydrocarbons (PAHs) on graphene and other two-dimensional materials is being intensely pursued in recent times. Highly accurate empirical potentials have emerged as a viable alternative to first-principles calculations for performing large-scale simulations. Herein, we report exploration of the potential energy surfaces for the adsorption of cata-condensed and peri-condensed PAHs on graphynes (GYs) using the improved Lennard-Jones (ILJ) potential. Initially, the ILJ potential is parametrized against benchmark electronic structure calculations performed on a selected set of PAH-GY complexes using dispersion-corrected density functional theory. The accuracy of the parametrization scheme is then assessed by a comparison of the adsorption features predicted from the ILJ potential with those computed using electronic structure calculations. The potential energy profiles as well as the single point energy calculations and geometry reoptimizations performed on the minimum-energy configurations predicted by the ILJ potential for a broader range of PAH-GY complexes provided a validation of the parametrization scheme. Finally, by an extrapolation of the PAH adsorption energies on various GYs, we estimated the interlayer cohesion energies for the van der Waals bilayer heterostructures of GYs with graphene to be in the range of 25-50 meV/atom.

Ultra-low hydrogen content bowl-shaped polycyclic aromatic hydrocarbons in petroleum

In the ultra-high resolution mass spectrometric analysis of processed petroleums (fossil materials), we observed species with ultra-low hydrogen content (e.g. H/C ratio from 0.1 to 0.4). Some of the observed chemical formula (C20-40H10) can be rationalized by the known corannulene-based peri-condensed Polycyclic Aromatic Hydrocarbons (PAHs). Other formulas (such as C20-40H8, C20-40H6 and C20-40H4) cannot be rationalized with any known structures. We proposed highly curved non-planar PAHs involving multiple connected five member aromatic rings. These structures do not obey the isolated pentagon rule (IPR). The stabilities of the proposed structures were evaluated by density functional theory. Strain energies were calculated based on hypothetical isodesmic conversion of planar structures to the curved non-planar structures. Results showed that the strain energies of the proposed structures are lower than that of fullerenes of the same carbon number, confirming stabilities of the non-IPR structures. The low hydrogen content species are likely formed in the thermal and/or catalytic cracking of the petroleums. They are possible intermediate molecules on the path toward the formation of fullerenes (buckyballs) and other nano-carbon materials

Critical evaluation of HOMA and MBL as local aromaticity indices

AbstractThe harmonic oscillator model of aromaticity (HOMA) index is an excellent structural indicator of aromaticity. We found that HOMA values for internal benzene rings in large pericondensed polycyclic aromatic hydrocarbons are often overestimated because of the local aromaticity of adjacent benzene rings. The occurrence of this phenomenon was confirmed by comparing the HOMA with the corresponding SSE(LA) values; SSE(LA) is a graph‐theoretical index of local aromaticity not disturbed by the aromaticity of the adjacent benzene rings. Mean bond length values were likewise assessed by comparing them with the corresponding HOMA and SSE(LA) values.

Solid-State 1H and 13C Nuclear Magnetic Resonance Spectroscopy of Athabasca Oil Sands Asphaltenes: Evidence for Interlocking π-Stacked Nanoaggregates with Intercalated Alkyl Side Chains

Solid-state 1H and 13C nuclear magnetic resonance (NMR) spectroscopic studies on heptane-extracted Athabasca oil sands asphaltenes show strong support for the “island” or “Yen–Mullins” model. Structural calculations on the deconvolved 13C direct-polarization magic-angle spinning (DP-MAS) NMR spectrum reveal the existence of large, peri-condensed polycyclic aromatic hydrocarbon (PAH) systems. Further support for this model was obtained from the variable contact time and dipolar dephasing experiments. Variable contact time experiments demonstrated decreased mobility of the alkyl groups with increasing proximity to the aromatic core. Furthermore, it was shown that all of the aromatic groups are highly rigid, with no evidence for mobile aromatic moieties pendant from the main aromatic core. The cross-polarization discrimination induced by variable amplitude minipulses (CP-DIVAM) nutation curves enable discrimination between signals from mobile and rigid components and show that the alicyclic groups are conden...

Extended Y-rule method for the characterization of the aromatic sextets in cata-condensed polycyclic aromatic hydrocarbons.

The location, number, and migrating behavior of the sextets in the cata-condensed benzenoid polycyclic aromatic hydrocarbons with available bay regions have been determined by a new proposed topological methodology called the extended Y-rule. The precursor of this rule is the well-known Y-rule method for determining sextets in peri-condensed polycyclic aromatic hydrocarbons. The new methodology has been successfully validated by means of literature information and by theoretical nucleus independent chemical shift (NICS) calculations. Even though the families of polycyclic aromatic hydrocarbons analyzed here comprise the C14H10, C18H12, C22H14, and C26H16 isomers, the procedure can practically be extended to the families C(10+4x)H(8+2x), where x = 1, ..., ∞. It is the first time that a straightforward procedure, easy to apply, has been proposed to obtain the sextets arrangement and behavior in the group of cata-condensed benzenoid polycyclic aromatic hydrocarbons.

Molecular characterization of organic content of soot along the centerline of a coflow diffusion flame.

High-resolution mass spectrometry coupled with nanospray desorption electrospray ionization was used to probe chemical constituents of young soot particles sampled along the centerline of a coflow diffusion flame of a three-component Jet-A1 surrogate. In lower positions where particles are transparent to light extinction (λ = 632.8 nm), peri-condensed polycyclic aromatic hydrocarbons (PAHs) are found to be the major components of the particle material. These particles become enriched with aliphatic components as they grow in mass and size. Before carbonization occurs, the constituent species in young soot particles are aliphatic and aromatic compounds 200-600 amu in mass, some of which are oxygenated. Particles dominated by PAHs or mixtures of PAHs and aliphatics can exhibit liquid-like appearance observed by electron microscopy and be transparent to visible light. The variations in chemical composition observed here indicate that the molecular processes of soot formation in coflow diffusion flames may be more complex than previously thought. For example, the mass growth and enrichment of aliphatic components in an initial mostly aromatic structure region of the flame that is absent of H atoms or other free radicals indicates that there must exist at least another mechanism of soot mass growth in addition to the hydrogen abstraction-carbon addition mechanism currently considered in fundamental models of soot formation.

The Quantum Research on the Nucleophilic Reaction Activity of Polycyclic Aromatic Hydrocarbons

Using the Hartree Fock (RHF) method, we study the most reactive carbon atoms in the polycyclic aromatic hydrocarbons (PAHs). In order to identify the most reactive carbon atoms, the Mulliken charges and the Mayers bond orders were calculated as the criterion. The results demonstrate that the most reactive carbon atoms appear at the locations of the outer C in the inner benzene rings for cata-condensed PAHs, while for peri-condensed PAHs they are the outer C in the outer benzene rings。

Interaction of multiply charged ions with isolated polycyclic aromatic hydrocarbon molecules

The interaction of multiply charged ions (He2+, O3+, and Xe20+, v ≤ 0.6 a.u.) with gas phase pericondensed polycyclic aromatic hydrocarbon (PAH) molecules (pyrene and coronene) was studied. Positively charged ionic products were analyzed with a linear time-of-flight mass spectrometer.

Resonantly Enhanced Multiphoton Ionization and Zero Kinetic Energy Photoelectron Spectroscopy of Chrysene: A Comparison with Tetracene

We report the electronic and vibrational spectroscopy of chrysene using resonantly enhanced multiphoton ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. As an isomer of tetracene, chrysene contains a kink in the middle of the four fused hexagonal rings, which complicates not just the symmetry but, more importantly, the molecular orbitals and hence vibronic transitions. Incidentally, the two nearby electronically excited states of chrysene have the same symmetry, and vibronic coupling introduces no out-of-plane vibrational modes. As a result, the REMPI spectrum of chrysene contains essentially only in-plane ring deformation modes, similar to that of tetracene. However, density functional calculations using gaussian even after the inclusion of vibronic coupling can only duplicate the observed REMPI spectrum in a qualitative sense, and the agreement is considerably worse than our recent work on a few pericondensed polycyclic aromatic hydrocarbons and on tetracene. The ZEKE spectrum of chrysene via the origin band of the intermediate electronic state S(1), however, can be qualitatively reproduced by a straightforward Franck-Condon calculation. The ZEKE spectra from vibrationally excited states of the S(1), on the other hand, demonstrate some degree of mode selectivity: the overall intensity of the ZEKE spectrum can vary by an order of magnitude depending on the vibrational mode of the intermediate state. A scaling factor in the theoretical vibrational frequency for the cation is also needed to compare with the experimental result, unlike tetracene and pentacene.

Zero kinetic energy photoelectron spectroscopy of jet cooled benzo[a]pyrene from resonantly enhanced multiphoton ionization

We report zero kinetic energy (ZEKE) photoelectron spectroscopy of benzo[a]pyrene (BaP) via resonantly enhanced multiphoton ionization (REMPI). Our analysis concentrates on the vibrational modes of the first excited state (S(1)) and those of the ground cationic state (D(0)). Similar to pyrene, another peri-condensed polycyclic aromatic hydrocarbon we have investigated, the first two electronically excited states of BaP exhibit extensive configuration interactions. However, the two electronic states are of the same symmetry, hence vibronic coupling does not introduce any out-of-plane modes in the REMPI spectrum, and Franck-Condon analysis is qualitatively satisfactory. The ZEKE spectra from the in-plane modes observed in the REMPI spectrum demonstrate strong propensity in preserving the vibrational excitation of the intermediate state. Although several additional bands in combination with the vibrational mode of the intermediate state are identifiable, they are much lower in intensity. This observation implies that the molecular structure of BaP has a tremendous capability to accommodate changes in charge density. All observed bands of the cation are IR active, establishing the role of ZEKE spectroscopy in mapping out far infrared bands for astrophysical applications.

Multiple ionization and fragmentation of isolated pyrene and coronene molecules in collision with ions

The interaction of multiply charged ions (He${}^{2+}$, ${\mathrm{O}}^{3+}$, and Xe${}^{20+}$) with gas-phase pericondensed polycyclic aromatic hydrocarbon (PAH) molecules of coronene (C${}_{24}$H${}_{12}$) and pyrene (C${}_{16}$H${}_{10}$) is studied for low-velocity collisions ($v\ensuremath{\leqslant}0.6$ a.u.). The mass spectrometric analysis shows that singly and up to quadruply charged intact molecules are important reaction products. The relative experimental yields are compared with the results of a simple classical over-the-barrier model. For higher molecular charge states, the experimental yields decrease much more strongly than the model predictions due to the instabilities of the multiply charged PAH molecules. Even-odd oscillations with the number of carbon atoms, $n$, in the intensity distributions of the ${\mathrm{C}}_{n}$H${}_{x}^{+}$ fragments indicate a linear chain structure of the fragments similar to those observed for ion-C${}_{60}$ collisions. The latter oscillations are known to be due to dissociation energy differences between even- and odd-$n$ ${\mathrm{C}}_{n}$-chain molecules. For PAH molecules, the average numbers of H atoms attached to the ${\mathrm{C}}_{n}$H${}_{x}$ chains are larger for even-$n$ reflecting acetylenic bond systems.

Water column euxinia and wildfire evidence during deposition of the Upper Famennian Hangenberg event horizon from the Holy Cross Mountains (central Poland)

A palynological study of the uppermost Famennian section from Kowala Quarry (Holy Cross Mountains, central Poland) allowed recognition of two miospore zones: LV (Retispora lepidophyta–Apiculiretusispora verrucosa) and LN (Retispora lepidophyta–Verrucosisporites nitidus). Based on palynology and sedimentology, the black shale within the upper part of the section is identified as equivalent to the Hangenberg Black Shale, which is known globally. This black shale contains compounds characteristic of photic zone euxinia, including isorenieratane and its derivatives. Such compounds are absent in the organic-poor marls and shales occurring below the LN Zone, and are present only as traces in the layers just above the black shale, indicating fluctuations in the oxygen minimum zone during uppermost Famennian sedimentation. Palynofacies show high amounts of amorphous organic matter and prasinophyte concentrations in the black shale, and a subsequent significant decrease of amorphous organic matter concomitant with a rapid increase of terrestrial input (mainly miospores with common tetrads) in the layers above the black shale. This supports the relatively rapid change in the taxonomic composition of phytoplankton caused by fluctuations of the chemocline. The whole succession corresponds to one sea-level rise and fall. The presence of high concentrations of peri-condensed polycyclic aromatic hydrocarbons and large amounts of small charcoal particles at the Hangenberg event horizon indicate the occurrence of wildfires. Such observations suggest that atmospheric O22 levels had exceeded the critical threshold of 13 %, above which wildfires may occur, by latest Famennian time.

Computational study of neutral and cationic pericondensed polycyclic aromatic hydrocarbons

Quantum chemical calculations using density functional theory are presented for small to medium sized pericondensed PAHs including some being reported for the first time. Bond lengths and charge distribution have been computed for these PAHs in both neutral and cationic forms. Upon ionization, significant change in fractional charge on atoms is present particularly for the outer carbon atoms. The charge on the internal carbon atoms tends towards zero in cations. Vibrational frequencies and infrared intensities have been calculated for the optimized structures of PAH neutrals and cations. The drastic intensity alterations occurring upon ionization are discussed and related to specific changes occurring in the charge distribution. The C–H stretch intensity depends on the partial charge on peripheral hydrogen atoms and reduces in cations as hydrogen atoms become more positive. Pericondensed PAHs show better matching with the observed interstellar infrared bands. The co-added model spectra show profiles similar to the observed astrophysical bands.

Time‐dependent Density Functional Theory Calculations of Large Compact Polycyclic Aromatic Hydrocarbon Cations: Implications for the Diffuse Interstellar Bands

We investigate the electronic absorption spectra of several maximally pericondensed polycyclic aromatic hydrocarbon radical cations with time-dependent density functional theory calculations. We find interesting trends in the vertical excitation energies and oscillator strengths for this series containing pyrene through circumcircumcoronene, the largest species containing close to 100 carbon atoms. We discuss the implications of these new results for the size and structure distribution of the diffuse interstellar band carriers.

A Convenient and General Synthesis of Cata- and Peri-Condensed Polycyclic Aromatic Hydrocarbons with a Fjord-Region

Cata- and peri-condensed polycyclic aromatic hydrocarbons (PAHs) 10a-d and 11 have been conveniently synthesized by the application of Suzuki cross-coupling reaction. In three to four steps, these PAHs having fjord-region were obtained in an overall yield of 35-51% from commercially or easily accessible aryl boronic acids and aryl bromides.

Analysis of coal tar pitch: relations between thermal behaviour and composition

This paper discusses the influence of pitch composition on its thermal behaviour. The value of the approach consisting in the characterization of these materials by analysis of their volatile fraction is demonstrated. The pyrolysis of nine coal tar pitches was studied by thermogravimetric analysis (t.g.a.) and derivative thermogravimetry (d.t.g.). The coke yield was closely related to both the rate of weight loss and the temperatures at which the d.t.g. curve reached maxima. To obtain information about the influence of the structures present in pitches on their thermal behaviour, the composition of the volatile fraction (evaluated by gas chromatography) was considered. The degree of condensation and the relative proportions of the different kinds of polycyclic aromatic hydrocarbons in this fraction were related to important thermal parameters deduced through t.g.a. and d.t.g. High coke yields are associated with a highly condensed volatile fraction in which alternant peri-condensed polycyclic aromatic hydrocarbons predominate over non-alternant systems.

Chromatographic evaluation of some selected polycyclic aromatic hydrocarbons of coal tars produced under different coking conditions and pitches derived from them

The volatile fractions of carbon disulfide extracts in tars and pitches have been studied by gas chromatography (GC), using the stationary phase OV-1701. Major polycyclic aromatic hydrocarbons (PAHs) in the fractions were selected as a basis for assessment of differences in the compositions of tars associated with their production. Several coal tars produced by wet charging carbonization in industrial- and semi-industrial-scale ovens with different mean flue heating temperatures were analyzed. The effects of preheating coal at about 200°C prior to the coking process were also studied. From chromatographic data, ratios of different individual compounds or classes of compounds were calculated. They revealed that an increase in the carbonization temperature and coal preheating produced similar effects on tar and pitch composition, leading to a reduction in methyl-substituted PAHs, non-alternant PAH systems and highly reactive compounds such as acenaphthylene. A higher proportion of peri-condensed PAHs and PAHs with a higher degree of condensation were also observed. GC analysis provides an adequate method for estimating the degree of pyrolysis of tars in coke ovens and their thermal stability in pitch production.