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Es wird eine nichtinvasive optische Messtechnik für die Lebensmittelanalytik vorgestellt, die eine zuverlässige Bestimmung des Absolutdrucks in Getränkeflaschen mit karbonisiertem Inhalt ermöglicht. Die Messtechnik nutzt eine durchstimmbare Laserdiode mit einer Emissionswellenlänge um 2004 nm für die Aufzeichnung von drei bis vier Absorptionslinien von CO\(_2\) und wertet die zum Absolutdruck proportionale Druckverbreiterung der Linien aus. Mit der entwickelten Messmethode konnte bei Feldmessungen an versiegelten Softdrinkflaschen aus PET schließlich eine Standardabweichung wiederholter Absolutdruckmessungen bis 5,5 bar von unter 50 mbar erreicht werden. A non-invasive optical measurement technique for food analysis is presented, which allows for a reliable determination of the absolute pressure in beverage bottles with carbonated contents. The method uses a tunable laser diode with an emission wavelength around 2004 nm to record three to four absorption lines of CO\(_2\) and evaluates the pressure broadening of the lines proportional to the absolute pressure. With the developed measuring method, a standard deviation of repeated absolute pressure measurements of up to 5.5 bar of less than 50 mbar could finally be achieved in field measurements on sealed soft drink bottles made of PET.

Terahertz (THz) quantum-cascade lasers (QCLs) are narrow band, high-power, and frequency-agile sources. These properties make them attractive for applications in high-resolution molecular and atomic spectroscopy. In the past few years, various techniques and methods regarding high-resolution spectroscopy with THz QCLs have been developed, namely, direct absorption spectroscopy, detection schemes such as wavelength and frequency modulation, differential spectroscopy, photoacoustic spectroscopy, and heterodyne spectroscopy. We briefly review the most relevant technological and methodological advances in this field, and we discuss perspectives and future directions.

Many natural proteins are, as a whole or in part, intrinsically disordered. Frequently, such intrinsically disordered regions (IDRs) undergo a transition to a defined and often helical conformation upon binding to partner molecules. The intrinsic propensity of an IDR sequence to fold into a helical conformation already in the absence of a binding partner can have a decisive influence on the binding process and affinity. Using a combination of NMR spectroscopy and molecular dynamics (MD) simulations we have investigated the tendency of regions of Axin-1, an intrinsically disordered scaffolding protein of the WNT signaling pathway, to form helices in segments interacting with binding partners. Secondary chemical shifts from NMR measurements show an increased helical population in these regions. Systematic application of MD advanced sampling approaches on peptide segments of Axin-1 reproduces the experimentally observed tendency and allows insights into the distribution of segment conformations and free energies of helix formation. The results, however, were found to dependent on the force field water model. Recent water models specifically designed for IDRs significantly reduce the predicted helical content and do not improve the agreement with experiment.

Wir stellen eine Kopplungsmethode für resonatorgestützte Absorptionsmessungen vor, bei der Licht durch einen im Resonator platzierten akustooptischen Modulator aktiv ein- und ausgekoppelt wird. Dies ermöglicht es, Cavity-Ring-Down-Spektroskopie (CRDS) mit breitbandigen und zeitlich inkohärenten Lichtquellen niedriger spektraler Leistungsdichte durchzuführen. Das Verfahren wird zum ersten Mal mit einer breitbandigen Superkontinuum-Quelle demonstriert. A new coupling scheme for cavity enhanced absorption spectroscopy makes use of an intracavity acousto-optical modulator to actively switch light into (and out of) a resonator. This allows cavity ringdown spectroscopy (CRDS) to be implemented with broadband temporally incoherent light sources with low spectral power densities. The method is demonstrated for the first time using a broadband supercontinuum source.

We review our recent studies of excited state structures and dynamics of chemical and biological systems with pico- and femtosecond X-ray absorption spectroscopy in the liquid phase.

The conjugated polyenes 10, 11, and 17 respectively, with 9-anthryl- and 2-tetraphenylporphyrinyl (TPP) terminal groups and a bicyclooctane unit incorporated into the polyene chain were synthesized by Wittig olefinations. In all cases it was possible to obtain the all-(E) compounds from the (E)/(Z)-isomeric mixtures by chromatographic purification and several recrystallizations. From the UV/Vis spectra the separation of the TPP group and the polyene chain in 10, 11, and 17 can be deduced whereas in 10 and 11 the two conjugated double bonds are amalgamated into the anthryl group. In 17 the anthryl group is electronically separated from the polyene chain, and a selective excitation therefore is possible.

Die vorliegende Arbeit befasst sich mit dem Entwurf, der Herstellung sowie der Charakterisierung von einmodigen DFB-Quantenkaskadenlasern für Anwendungen in der Spurengasanalytik. Die Laser eignen sich zur Detektion der fundamentalen Rotations-Schwingungs-Übergänge von Stickstoffmonoxid im Wellenlängenbereich um 5,35 µm (1870 cm-1) und von Kohlenmonoxid um 4,67 µm (2140 cm-1) mittels hochauflösender Absorptionsspektroskopie. Im Pulsbetrieb ist die Seitenmodenunterdrückung > 27 dB und die maximale Betriebstemperatur > 400 K (127 °C). Typische Linienbreiten liegen bei etwa 100 MHz.

Heck and Sonogashira cross-coupling reactions have been used for the functionalization of the upper rim of a tetraiodinated calix[4] arene. In this way, oligophenylenevinylene (OPV) and oligophenyleneethynylene (OPE) arrays have been constructed on the calix[4] arene core to produce covalent assemblies of four pi-conjugated chromophores. Electrochemical properties have been investigated by cyclic voltammetry in different solvent/electrolyte systems. Both OPV and OPE calixarenes show the simultaneous reduction of three out of four units, followed, at more negative potential, by the reduction of the fourth unit. This behaviour can be rationalized in view of a partial deconjugation in one OPV or OPE unit. On the other hand, these calixarenes show only oxidation processes corresponding to the exchange of one electron, thus demonstrating the lack of electrochemical equivalency of the OPV or OPE units, in contrast to the reduction behaviour. Electronic absorption and emission spectra have been recorded in solvents of different polarity ( toluene, dichloromethane, and benzonitrile). The absorption spectra of the OPV calixarene do not match to the sum of the component units as a consequence of the partial deconjugation of the OPV arms in the calixarene structure. On the contrary, fluorescence spectra, quantum yields and excited state lifetimes of the OPV calixarene are nearly identical to those of the corresponding model compound. The trend of the absorption and emission spectra for the OPE calixarene is reversed relative to that of the OPV counterpart. Absorption spectra are well-matched with those of four trimeric OPE fragments but emission spectra exhibit, besides the typical OPE monomeric fluorescence, a broader and longer-lived emission feature on the low-energy spectral side, attributable to excimer-type interactions. Therefore the arrangement of OPV or OPE units within the same calix-4-arene skeleton brings about different effects on the electronic and luminescence properties of the multicomponent system.

The absolute S1-state absorption cross-section spectrum of eosin Y in methanol has been determined by pico-second second harmonic Nd:glass laser excitation and time-delayed picosecond light continuum probing (probing wavelength region from 400 to 980 nm).

The absolute triplet-triplet absorption cross-section spectrum σT(λ) of eosin Y in methanol at room temperature is determined in the wavelength region from 400 to 1000 nm and at 308 and 1054 nm. The triplet state is populated by XeCl excimer laser excitation to a singlet state and subsequent intersystem crossing. The triplet level population is determined by numerical simulation of the pump pulse absorption dynamics. The triplet-triplet absorption is probed with picosecond spectral light continua which are generated in a D2O sample by a synchronized mode-locked Nd:glass laser. The decay of the triplet level population is studied by delayed picosecond light continua probing. Second order rate constants of k(1)ox = 1.1 × 109 dm3 mol−1 s−1 for oxygen quenching, k(1)TT = 1.3 × 109 dm3 mol−1 s−1 for triplet-triplet annihilation, and k(1)TS = 4 × 108 dm3 mol−1 s−1 for triplet-singlet concentration quenching have been determined.

The photoisomerization dynamics of DODCI (3,3′-diethyloxadicarbocyanine iodide) is analyzed by linear absorption and fluorescence spectroscopic measurements over a wide temperature range. The fluorescence quantum distributions and the fluorescence quantum efficiencies are measured for three excitation wavelengths. The N-isomer and P-isomer contributions to the fluorescence signals are separated. The absorption and stimulated emission cross sections of the N- and P-isomers are determined. The results are discussed by application of an angular configuration coordinate system.

The dyes 4-dicyanovinyl-N,N-diethylaniline (DCVA) and 4-tricyanovinyl-N,N-diethylaniline (TCVA) are investigated spectroscopically in the vapor phase. The absorption and emission spectra are compared with solution spectra. The thermal stability of the dye powder is determined. The saturated vapor density versus temperature is deduced from absorption measurements. The vapor absorption peaks at 382 nm (DCVA) and 437 nm (TCVA). The fluorescence quantum efficiency of both dyes in the vapor phase is approximately 1.5×10 −4 .

Absorption spectra and light-induced absorbance changes of crystals from Rhodopseudomonas viridis reaction centers are recorded. A theoretical analysis of the absorption and circular dichroism spectra is presented, yielding a consistent picture of spectroscopic and structural information.

The nonlinear absorption of single picosecond light pulses (λ = 1.06 μm) in CdS is investigated at very high light intensities. Three-photon absorption and subsequent excited-state absorption of the generated electrons and holes explain the rapid decrease of transmission with increasing intensity. A three-photon absorption cross-section of σ (3) = (2±0.5) × 10 -80 cm 6 s 2 and an average excited state absorption cross-section of σ ex = (7 ± 3) × 10 -18 cm 2 was determined.

The long-wavelength absorption spectrum of DODCI indicates the presence of a thermally populated isomer in the electronic ground state. The energy level of this isomer above the normal form is determined by temperature-dependent absorption measurements. The S 0 -S 1 absorption cross section spectrum of the isomer is determined.

Donor-Acceptor-[2.2]Metacyclophane 1–4 sowie 24 wurden uber die entsprechend substituierten 2,11-Dithia[3.3]metacyclophane 8, 13 und 25 und die davon abgeleiteten Disulfone synthetisiert. Die anti-Verbindung 1 und das syn-Isomere 2 konnten isoliert und charakterisiert werden. Der Versuch der entsprechenden Synthese von 5/6 uber 21 und 22 schlug fehl, da unter Verlust der intraanularen Substituenten und transanularer C C-Verknupfung das Tetrahydropyren-Derivat 23 entstand. Fur spektroskopische Vergleichszwecke wurde 27 uber 28 dargestellt. – Rontgen-Strukturanalysen von 21, 24 und 25 wurden ausgefuhrt. Die Molekulstruktur dieser Verbindungen wird unter den Aspekten der sterischen Spannung und der Donor-Acceptor-Uberlappung diskutiert. Die Strukturanalysen bestatigen die aus 1H-NMR-Daten abgeleiteten Zuordnungen zu den syn- und anti-Reihen. – Die Absorptionsspektren von 1, 2, 3 und 24 werden angegeben, wobei besonders das uberraschende Absorptionsverhalten der Isomeren 1 und 2 mit sehr unterschiedlicher Donor-Acceptor-Uberlappung interessierte. Die Bestimmung der Losungsmittel-Abhangigkeit der Fluoreszenz ergab, das es sich bei den behandelten langwelligen Absorptionen tatsachlich um Charge-Transfer-Absorptionen handelt. Electron Donor-Acceptor Compounds, XXXVIII. Electron Donor-Acceptor [2.2]Metacyclophanes: Synthesis, Structure, and Charge-Transfer Spectra Donor-acceptor [2.2]metacyclophanes 1–4 as well as 24 were synthesized via the correspondingly substituted 2,11-dithia[3.3]metacyclophanes 8, 13, and 25 and their disulfone derivatives. The anti-compound 1 and the syn-isomer 2 were isolated and characterized. The attempt of the analogous synthesis of 5/6 via 21 and 22 failed since with loss of the intraanular substituents and by transanular C C formation the tetrahydropyrene derivative 23 was formed. For spectroscopic comparison 27 was prepared via 28. – X-Ray structure analyses of 21, 24, and 25 were performed. The molecular structures of these compounds are discussed under the aspects of sterical strain and donor-acceptor overlap. The structure analyses confirm the assignment to the syn- and anti-series as derived from 1H NMR. – Absorption spectra of 1, 2, 3, and 24 were measured; especially the surprising absorption behaviour of the isomers 1 and 2 with very different donor-acceptor overlap was of interest. Determination of the solvent dependence of fluorescence made sure that the absorptions dealt with are indeed charge-transfer transitions.