Martin Presselt

Tuning the Morphology of Solution-Sheared P3HT:PCBM Films

UNLABELLED Organic bulk heterojunction (BHJ) solar cells are a promising alternative for future clean-energy applications. However, to become attractive for consumer applications, such as wearable, flexible, or semitransparent power-generating electronics, they need to be manufactured by high-throughput, low-cost, large-area-capable printing techniques. However, most research reported on BHJ solar cells is conducted using spin coating, a single batch fabrication method, thus limiting the reported results to the research lab. In this work, we investigate the morphology of solution-sheared films for BHJ solar cell applications, using the widely studied model blend P3HT:PCBM. Solution shearing is a coating technique that is upscalable to industrial manufacturing processes and has demonstrated to yield record performance organic field-effect transistors. Using grazing incident small-angle X-ray scattering, grazing incident wide-angle X-ray scattering, and UV-vis spectroscopy, we investigate the influence of solvent, film drying time, and substrate temperature on P3HT aggregation, conjugation length, crystallite orientation, and PCBM domain size. One important finding of this study is that, in contrast to spin-coated films, the P3HT molecular orientation can be controlled by the substrate chemistry, with PEDOT PSS substrates yielding face-on orientation at the substrate-film interface, an orientation highly favorable for organic solar cells.

Molecular Structures and Absorption Spectra Assignment of Corrole NH Tautomers

The individual absorption spectra of the two NH tautomers of 10-(4,6-dichloropyrimidin-5-yl)-5,15-dimesitylcorrole are assigned on the basis of the Gouterman four-orbital model and a quantum chemical TD-DFT study. The assignment indicates that the red-shifted T1 tautomer is the one with protonated pyrrole nitrogen atoms N(21), N(22) and N(23), whereas the blue-shifted T2 tautomer has pyrrole nitrogen atoms N(21), N(22) and N(24) protonated. A wave-like nonplanar distortion of the macrocycle in the ground state is found for both NH tautomers, with the wave axis going through the pyrroles containing N(22) and N(24). The 7C plane determined by the least-squares distances to the carbon atoms C1, C4, C5, C6, C9, C16, and C19 is suggested as a mean corrole macrocycle plane for the analysis of out-of-plane distortions. The magnitude of these distortions is distinctly different for the two NH tautomers, leading to substantial perturbations of their acid-base properties, which are rationalized by the interplay of the degree of out-of-plane distortion of the macrocycle as a whole and the tendency of the pyrrole nitrogen atoms toward pyramidalization, with the former leading to a basicity increase whereas the latter enhances the acidity.

Subbandgap absorption in polymer-fullerene solar cells

We present external quantum efficiency (EQE) studies of poly(3-hexylthiophene-2,5-diyl):[6,6]-phenylC61-butyric acid methyl ester (P3HT:PCBM) based bulk heterojunction polymer solar cells with improved intensity resolution in the subbandgap (SBG) region, i.e., the energy range below the optical bandgaps of the pristine materials. Varying the P3HT:PCBM blending ratio, we find that in addition to a Gaussian profile an exponential tail is needed for a quantitative description of the SBG EQE spectra. While the exponential contribution can be reliably assigned to disorder effects, the SBG EQE Gaussian profile can be due to charge-transfer absorption between P3HT and PCBM or due to absorption of PCBM at the interface or in the polymer-rich phase.

Correlation between near infrared-visible absorption, intrinsic local and global sheet resistance of poly(3,4-ethylenedioxy-thiophene) poly(styrene sulfonate) thin films

The ordinary dielectric function of poly(3,4-ethylenedioxy-thiophene) poly(styrene sulfonate) (PEDOT:PSS) thin films was measured using a combination of spectroscopic ellipsometry and photothermal deflection spectroscopy. This method combination allows for a highly sensitive optical characterization of thin films. Hence, even the detection of weak sub-bandgap and intra-band absorptions is enabled. These intraband transitions of free charge carriers were modeled using a Drude-type oscillator to derive an intrinsic resistances for PEDOT:PSS. These optically derived resistances were compared with those determined by a 4-probe measurement setup for two different types of PEDOT:PSS and for varied annealing temperatures. Good agreement between optical and electrical measurements could be obtained for annealing temperatures smaller than 180∘C. Therefore, we conclude that the proposed combination of our two optical methods is well suited to determine electrical resistances of organic layers.

Stable and Easily Accessible Functional Dyes: Dihydrotetraazaanthracenes as Versatile Precursors for Higher Acenes

A series of new dihydrotetraazaanthracenes and one new dihydrotetraazatetracene as substances for applications in organoelectronic devices and as suitable building blocks for higher azaacenes was synthesised. The condensation of aromatic diamines with dichlorodicyanopyrazine led to these tricyclic/tetracyclic compounds. Syntheses of N-substituted phenylenediamines were developed to enable the introduction of multiple functional groups such as ester, amino, or nitro groups on the chromophoric system. Relationships between the structure and the spectroscopic properties could be derived from UV/Vis absorption and fluorescence spectroscopy, as well as by DFT and TD-DFT calculations of molecular and aggregate structures. The absorption spectra are dominated by π-π* transitions of the single molecules, whereas aggregation needs to be taken into account to obtain reasonable agreement between theory and experiment in certain cases. Single-crystal X-ray analyses were carried out to examine the morphology and solid packing effects. Finally, a dihydrotetraazaanthracene was used as a building-block to create a mesoionic octaazapentacene.

Prediction of Electron Densities, the Respective Laplacians, and Ellipticities in Bond-Critical Points of Phenyl−CH−Bonds via Linear Relations to Parameters of Inherently Localized CD Stretching Vibrations and 1H NMR-Shifts

Electron densities rho, the respective laplacians nabla(2)rho, and ellipticities epsilon in bond-critical points (BCPs) are reactivity-determining characteristics according to the theory of atoms in molecules. These quantities are experimentally detectable only for substances in the crystalline state. To facilitate the determination of rho, nabla(2)rho, and epsilon values of BCPs of dissolved or liquid substances, the relations between DFT-calculated rho, nabla(2)rho, and epsilon and DFT-calculated vibrational and (1)H NMR spectroscopic quantities were studied for a set of 18 monosubstituted benzene derivatives. We found that via linear functions of rho, nabla(2)rho, or epsilon reliable predictions of rho, nabla(2)rho, and epsilon are possible, dependent on at least one of the variables vibrational transition energy, IR intensity, Raman activity of an inherently localized CD-stretching vibration, and the (1)H NMR shift. For the determination of rho, nabla(2)rho, and epsilon values in the ph-CH BCPs, the most important variables are the vibrational transition energy of the CD-stretching vibration and the corresponding (1)H NMR shift. The parameters of the functions best suited to predict rho, nabla(2)rho, and epsilon in the certain CH BCPs of the phenyl ring are presented.

Derivation of Correlation Functions to Predict Bond Properties of Phenyl−CH Bonds Based on Vibrational and 1H NMR Spectroscopic Quantities

The study of electron density properties significantly contributes to the determination of important chemical relations. The experimental determination of the electron density distribution is limited to single crystals. However, equivalent information is often desired for molecules, which do not crystallize in a sufficient manner. Furthermore, it is of high impact to study changes in the electron density distribution (i.e., related reactivities) upon environmental variations. Consequently, here we investigate methods to derive electron density properties from spectroscopic data. In particular correlation functions are introduced, which are able to predict electron density properties in all five CH-bonds of monosubstituted benzene derivatives at once. The prediction performance for electron densities and the corresponding Laplacians is lower as compared to previously introduced local functions [Presselt et al. J. Phys. Chem. A 2009, 113, 3210], but far less spectroscopic input data are needed. However, for ellipticities a higher prediction performance than this obtained for the previously derived local functions could be obtained despite the fact that less spectroscopic data were used. Thus, ellipticities are best predicted using (1)H NMR data for the para position of monosubstituted benzene derivatives.

Ruthenium(II)-bis(4'-(4-ethynylphenyl)-2,2':6', 2''-terpyridine) - A versatile synthon in supramolecular chemistry. Synthesis and characterization

AbstractA homoleptic ethynyl-substituted ruthenium(II)-bisterpyridine complex representing a versatile synthon in supramolecular chemistry was synthesized and analyzed by NMR spectroscopy, mass spectrometry and X-ray diffractometry. Furthermore, its photophysical properties were detailed by UV/Vis absorption, emission and resonance Raman spectroscopy. In order to place the results obtained in the context of the vast family of ruthenium coordination compounds, two structurally related complexes were investigated accordingly. These reference compounds bear either no or an increased chromophore in the 4′-position. The spectroscopic investigations reveal a systematic bathochromic shift of the absorption and emission maximum upon increasing chromophore size. This bathochromic shift of the steady state spectra occurs hand in hand with increasing resonance Raman intensities upon excitation of the metal-to-ligand charge-transfer transition. The latter feature is accompanied by an increased excitation delocalization over the chromophore in the 4′-position of the terpyridine. Thus, the results presented allow for a detailed investigation of the electronic effects of the ethynyl substituent on the metal-to-ligand charge-transfer states in the synthon for click reactions leading to coordination polymers.

Tuning the polarity and surface activity of hydroxythiazoles – extending the applicability of highly fluorescent self-assembling chromophores to supra-molecular photonic structures

A small library of N,N-diethyl- and -diethanolsulfonamides of differently substituted 2-(2-pyridyl)- and 2-pyrazinyl-4-alkoxythiazoles has been synthesized and investigated in terms of their photophysical properties, electronic structure (quantum chemical calculations at the CAM-B3LYP/6-31+G(d,p) level of theory) and thin film morphology (Langmuir–Blodgett- and spin-cast films). By using the Langmuir–Blodgett technique we show how to exert direct control over the degree of aggregation in thin films made from different thiazole type dyes. In combination with spectroscopic investigations, we gained an in-depth understanding of the influence of aggregation on the electro-optical properties of thin films made of the here-investigated substances.

Metal-Mediated Reaction Modeled on Nature: The Activation of Isothiocyanates Initiated by Zinc Thiolate Complexes

On the basis of detailed theoretical studies of the mode of action of carbonic anhydrase (CA) and models resembling only its reactive core, a complete computational pathway analysis of the reaction between several isothiocyanates and methyl mercaptan activated by a thiolate-bearing model complex [Zn(NH(3))(3)SMe](+) was performed at a high level of density functional theory (DFT). Furthermore, model reactions have been studied in the experiment using relatively stable zinc complexes and have been investigated by gas chromatography/mass spectrometry and Raman spectroscopy. The model complexes used in the experiment are based upon the well-known azamacrocyclic ligand family ([12]aneN(4), [14]aneN(4), i-[14]aneN(4), and [15]aneN(4)) and are commonly formulated as ([Zn([X]aneN(4))(SBn)]ClO(4). As predicted by our DFT calculations, all of these complexes are capable of insertion into the heterocumulene system. Raman spectroscopic investigations indicate that aryl-substituted isothiocyanates predominantly add to the C═N bond and that the size of the ring-shaped ligands of the zinc complex also has a very significant influence on the selectivity and on the reactivity as well. Unfortunately, the activated isothiocyanate is not able to add to the thiolate-corresponding mercaptan to invoke a CA analogous catalytic cycle. However, more reactive compounds such as methyl iodide can be incorporated. This work gives new insight into the mode of action and reaction path variants derived from the CA principles. Further, aspects of the reliability of DFT calculations concerning the prediction of the selectivity and reactivity are discussed. In addition, the presented synthetic pathways can offer a completely new access to a variety of dithiocarbamates.