Florian Latteyer

B3N3 Borazine Substitution in Hexa-peri-Hexabenzocoronene: Computational Analysis and Scholl Reaction of Hexaphenylborazine

The doping of graphene molecules by borazine (B(3)N(3)) units may modify the electronic properties favorably. Therefore, the influence of the substitution of the central benzene ring of hexa-peri-hexabenzocoronene (HBC, C(42)H(18)) by an isoelectronic B(3)N(3) ring resulting in C(36)B(3)N(3)H(18) (B3N3HBC) is investigated by computational methods. For comparison, the isoelectronic and isosteric all-B/N molecule B(21)N(21)H(18) (termed BN) and its carbon derivative C(6)B(18)N(18)H(18) (C6BN), obtained by substitution of a central B(3)N(3) by a C(6) ring, are also studied. The substitution of C(6) in the HBC molecule by a B(3)N(3) unit results in a significant change of the computed IR vibrational spectrum between 1400 and 1600 cm(-1) due to the polarity of the borazine core. The properties of the BN molecule resemble those of hexagonal boron nitride, and substitution of the central B(3)N(3) ring by C(6) changes the computed IR vibrational spectrum only slightly. The allowed transitions to excited states associated with large oscillator strengths shift to higher energy upon going from HBC to B3N3HBC, but to lower energy upon going from BN to C6BN. The possibility of synthesis of B3N3HBC from hexaphenylborazine (HPB) using the Scholl reaction (CuCl(2)/AlCl(3) in CS(2)) is investigated. Rather than the desired B3N3HBC an insoluble and X-ray amorphous polymer P is obtained. Its analysis by IR and (11)B magic angle spinning NMR spectroscopy reveals the presence of borazine units. The changes in the (11)B quadrupolar coupling constant C(Q), asymmetry parameter η, and isotropic chemical shift δ(iso)((11)B) with respect to HPB are in agreement with a structural model that includes B3N3HBC-derived monomeric units in polymer P. This indicates that both intra- and intermolecular cyclodehydrogenation reactions take place during the Scholl reaction of HPB.

Thin‐Film Properties of DNA and RNA Bases: A Combined Experimental and Theoretical Study

The structures of the DNA and RNA bases cytosine, uracil, and thymine in thin films with a nominal film thickness of about 20 nm are studied by using X-ray photoemission spectroscopy (XPS) and Fourier-transform infrared spectroscopy. The molecules are evaporated in situ from powder on a gold foil. The experimental results indicate that cytosine is composed of two energetically close tautomeric forms, whereas uracil and thymine exist in only one tautomeric form. Additionally, quantum chemical calculations are performed to complement the experimental results. The relative energies of the tautomeric forms of cytosine, uracil, and thymine are calculated using Hartree-Fock (HF), density functional theory (DFT), and post-HF methods. Furthermore, the assignment of the XPS spectra is supported by using simple model considerations employing Koopmans ionization energies and Mulliken net atomic charges.

Electronic Structure and Interface Properties of a Model Molecule for Organic Solar Cells

We study the electronic structure of 4,7-bis(5-methylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (MTBT) and its interface properties with gold using X-ray photoemission spectroscopy (XPS), valence-band ultraviolet photoemission spectroscopy (UPS), X-ray absorption spectroscopy (XAS), as well as resonant photoemission (ResPES). MTBT can be regarded as a model molecule for PCPDTBT, a promising candidate for efficient bulk heterojunction solar cells. Almost no contribution of sulfur and only a weak contribution of nitrogen to the HOMO level is found. At the interface with gold, a strong chemical interaction between the sulfur of the benzothiadiazole and gold occurs, which may have consequences for interface properties in devices.

Chloroaluminum phthalocyanine thin films: chemical reaction and molecular orientation

AbstractThe chemical transformation of the polar chloroaluminum phthalocyanine, AlClPc, to μ-(oxo)bis(phthalocyaninato)aluminum(III), (PcAl)2O, in thin films on indium tin oxide is studied and its influence on the molecular orientation is discussed. The studies were conducted using complementary spectroscopic techniques: Raman spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In addition, density functional theory calculations were performed in order to identify specific vibrations and to monitor the product formation. The thin films of AlClPc were annealed in controlled environmental conditions to obtain (PcAl)2O. It is shown that the chemical transformation in the thin films can proceed only in the presence of water. The influence of the reaction and the annealing on the molecular orientation was studied with Raman spectroscopy and NEXAFS spectroscopy in total electron yield and partial electron yield modes. The comparison of the results obtained from these techniques allows the determination of the molecular orientation of the film as a function of the probing depth. Illustration of the dimerization reaction of MClPc to (PcM)2O.

Vibrational and electronic characterisation of Staphylococcus aureus wall teichoic acids and relevant components in thin films

This work reports an investigation of S. aureus wall teichoic acid (WTA) and compares this biopolymer with its major occurring components, d-alanine and glycerol phosphate. Detailed insight into molecular structures and electronic properties is obtained by vibrational and photoemission spectroscopy. Calculations are performed to support the analysis of our experimental vibrational spectra. It is shown that there are contributions of positive and negative charges in WTAs, but the number of negative charges is expected to be higher. The presence of both positive and negative charges on WTA may offer a route for modification of surfaces with the objective of avoiding the formation of biofilms.