No abstract available

[en] Polycyclic aromatic hydrocarbons (PAHs) have been the subject of interdisciplinary research in the fields of chemistry, physics, materials science, and biology. Notably, PAHs have drawn increasing attention since the discovery of graphene, which has been regarded as the “wonder” material in the 21st century. Different from semimetallic graphene, nanoscale graphenes, such as graphene nanoribbons and graphene quantum dots, exhibit finite band gaps owing to the quantum confinement, making them attractive semiconductors for next-generation electronic applications. Researches based on PAHs and graphenes have expanded rapidly over the past decade, thereby posing a challenge in conducting a comprehensive review. This study aims to interconnect the fields of PAHs and graphenes, which have mainly been discussed separately. In particular, by selecting representative examples, we explain how these two domains can stimulate each other. We hope that this integrated approach can offer new opportunities and further promote synergistic developments in these fields.

[en] The experimental Raman spectra of some polycyclic aromatic hydrocarbons (PAHs) belonging to the D_2h symmetry point group, recorded with different exciting laser energies, are presented and compared with simulations obtained by quantum chemical methods in the framework of Albrecht's theory restricted to the A term. It is shown that resonance with the L_a state enhances the activity of the low frequencies in the D-band region, while high frequency components of the D-band are preferentially enhanced by resonance with the B_a state. Moreover, low frequency vibrations, in the region of acoustic phonons, are identified both by computations and experimentally, which are characteristic fingerprints of the size and shape of the D_2h symmetry PAHs

[en] Polyphenylene dendrimers (PPDs) are a unique class of macromolecules because their backbone is made from twisted benzene repeat units that result in a rigid, shape-persistent architecture as reported by Hammer et al. (Chem Soc Rev 44:4072–4090, 2015) and Hammer and Müllen (Chem Rev 116:2103–210, 2016) These dendrimers can be synthetically tailored at their core, scaffold, and surface to introduce a wide range of chemical functionalities that influence their applications. It is the balance between the macromolecular properties of polyphenylene dendrimers with grandiose synthetic ingenuity that presents a template for the next generation of synthetic dendrimers to achieve complex structures other chemistry fields cannot. This perspective will look at how advances in synthetic chemistry have led to an explosion in the properties of polyphenylene dendrimers from their initial stage, as PPDs that were used as precursors for nanographenes, to next-generation dendrimers for organic electronic devices, sensors for volatile organic compounds (VOCs), nanocarriers for small molecules, and even as complexes with therapeutic drugs and viruses, among others. Ideally, this perspective will illustrate how the evolution of synthetic chemistry has influenced the possible structures and properties of PPDs and how these chemical modifications have opened the door to unprecedented applications.

[en] Perylene diimide (PDI) is a promising electron acceptor material for high open circuit voltage bulk heterojunction organic solar cells. However, many PDI molecules have the drawback of strong aggregation leading to intermolecular excited state formation that results in exciton trapping. These traps can effectively limit the diffusion of excitons to the interface where charge separation occurs and thus strongly reduce the charge generation efficiency. In this contribution we study the influence of substitution of PDI molecules with side groups attached to the terminal and to the perylene core positions on the formation of aggregates. In particular transient photoluminescence and absorption spectroscopy are used to probe the impact of aggregation on the dynamics of charge generation and recombination in bulk heterojunction solar cells. Besides, AFM, x-ray and solid state NMR techniques are used to get further insight into the solid state morphology of polymer: PDI blends on different length scales. Finally, we correlate the photophysical properties of the PDI derivatives with the efficiency of bulk heterojunction organic solar cells and present unprecedented efficiencies from polymer: PDI solar cells.

[en] Hexa-peri-hexabenzocoronene (C₄₂H₁₈, HBC) films adsorbed on the Au(111) surface were investigated by means of ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS). The results show that both methods give comparable results for the electronic structure of the occupied states, if the STS is performed at appropriate parameters. Additionally, STS gives an immediate insight into the unoccupied states. The highest occupied state of multilayer films is found 1.3-1.4 eV below the Fermi levels and the lowest unoccupied state 1.8 eV above the Fermi level. The resulting transport gap is compared to optical absorption measurements. Work-function changes of -0.8 eV indicate an interface dipole, i.e., vacuum level alignment does not occur at the HBC-Au interface. Compared to UPS, the voltage range of the STS measurements is limited to prevent sample damage

No abstract available

[en] Full text: Graphene Nanoribbons (GNRs) offer great potential for future electronic and optoelectronic devices due to sizable electronic band gaps that are expected for narrow (<10 nm) GNRs. Recently, we reported a bottom-up fabrication protocol based on on-surface chemical routes to colligate and dehydrogenate specifically designed precursor monomers to form N=7 armchair GNRs (7-AGNRs) with atomic precision, a prerequisite for the control of the band gap magnitude. Here, we report scanning tunneling spectroscopy (STS) and angle-resolved photoelectron spectroscopy (ARPES) results allowing for the determination of band gap and exact band dispersion of 7-AGNRs. Furthermore, ARPES results are compared to Fourier-transformed STS (FT-STS) results, which additionally give direct access to the unoccupied band dispersion. (author)

No abstract available

[en] The hole injection barriers at interfaces between N,N'-diphenyl-N,N'-bis(1-naphthyl)-1-1'biphenyl-4,4''diamine (a-NPD) and chemically modified ITO substrates have been studied by ultraviolet photoelectron spectroscopy (UPS). A decreased hole injection barrier was achieved by an appropriate arrangement of oriented dipoles, formed by chemisorption of strong electron acceptors, i.e., tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) or hexacyano-hexaazatriphenylene[HAT-(CN)]. In both cases thin acceptor layers induce coverage dependent work function shifts of more than 1 eV, thereby modifying the barrier to hole injection into a-NPD by up to 0.4 eV. We observed a linear dependence of the hole injection barrier versus the work function of modified ITO substrates. However, we find constant hole injection barriers for substrate work functions greater than 5.1 eV caused by localized states at the interface