Control of Intrachain Morphology in the Formation of Polyfluorene Aggregates on the Single-Molecule Level

Controlling the morphology of π-conjugated polymers for organic optoelectronic devices has long been a goal in the field of materials science. Since the morphology of a polymer chain is closely intertwined with its photophysical properties, it is desirable to be able to change the arrangement of the polymers at will. We investigate the π-conjugated polymer poly(9,9-dioctylfluorene) (PFO), which can exist in three distinctly different structural phases: the α-, β-, and γ-phase. Every phase has a different chain structure and a unique photoluminescence (PL) spectrum. Due to its unique properties and the pronounced spectral structure-property relations, PFO can be used as a model system to study the morphology of π-conjugated polymers. To avoid ensemble averaging, we examine the PL spectrum of single PFO chains embedded in a non-fluorescent matrix. With single-molecule spectroscopy the structural phase of every single chain can be determined, and changes can be monitored very easily. To manipulate the morphology, solvent vapor annealing (SVA) was applied, which leads to a diffusion of the polymer chains in the matrix. The β- and γ-phases appear during the self-assembly of single α-phase PFO chains into mesoscopic aggregates. The extent of β- and γ-phase formation is directed by the solvent-swelling protocol used for aggregation. Aggregation unequivocally promotes formation of the more planar β- and γ-phases. Once these lower-energy more ordered structural phases are formed, SVA cannot return the polymer chain to the less ordered phase by aggregate swelling.     

Hydroperoxides and aryl diazonium salts as reagents for the functionalization of non-activated olefins

Hydroperoxides, olefins, and arenediazonium salts selectively combine to give azo compounds via an iron(II)-mediated three-component reaction. Starting with a fragmentation liberating acetic acid, the hydroperoxides act as radical source and the diazonium ions as nitrogen-centered radical scavengers.     

Two-proton radioactivity of 45Fe

In an experiment at the SISSI-LISE3 facility of GANIL, the decay of the proton drip line nucleus 45Fe has been studied. Fragment-implantation events have been correlated with radioactive decay events in a 16x16 pixel silicon-strip detector. The decay-energy spectrum of 45Fe implants shows a distinct peak at (1.14+/-0.04) MeV with a half-life of T(1/2)=(4.7(+3.4)(-1.4)) ms. None of the events in this peak is in coincidence with beta particles. For a longer correlation interval, daughter decays of the two-proton daughter 43Cr can be observed after 45Fe implantation. The decay energy for 45Fe agrees nicely with several theoretical predictions for two-proton radioactivity.     

Neue Bestimmung des kritischen Punktes von leichtem und schwerem Wasser

Zusammenfassung Im Rahmen der internationalen Wasserdampfforschung [1, 2, 3] wurden in den letzten Jahren genaue Messungen verschiedener Zustandsgrößen von leichtem und teilweise auch von schwerem Wasser vorgenommen. In diesem Zusammenhang war auch die Kenntnis genauerer Werte für die kritischen Zustandsgrößen von großem Interesse.In einer zylindrischen, waagerecht liegenden Druckkammer mit durchsichtigen Beobachtungsfenstern wurden beim langsamen Durchlaufen des kritischen Punktes mit sehr geringfügigen Temperaturänderungen von 0,01 bis 0,03 °C/h fortlaufend Temperaturen und Drücke gemessen. Gleichzeitig wurde die Phasentrennfläche zwischen Flüssigkeit und Dampf beobachtet, die beim Durchlaufen des kritischen Zustandes in einem sehr kleinen Temperatur- und Druckbereich verschwindet bzw. wiedererscheint.Es ergaben sich folgende Werte für die kritischen Temperaturen und Drücke von H₂O und D₂O: H₂O t_krit=(373,91±0,03) °C P_krit=(220,45±0,03) bar D₂O t_krit=(370,66±0,03) °C P_krit=(216,59±0,03) bar.Die Temperaturangaben beziehen sich auf die Internationale Praktische Temperaturskala von 1948.

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New determination of the critical point of water and heavy water

The apparatus used for determining the critical data of water and heavy water consists in principle of a horizontal cylindrical pressure chamber of INCONEL X-750. Observation windows of synthetic saphire (Al₂O₃) are located at the ends.During the experiments the critical point was passed with very small rates of temperature change of about 0.01 to 0.03 °C/h. The disappearance and appearance of the meniscus could be observed continuously with a telescope enlarging 10 times, with simultaneous measurement of pressure and temperature.The following results were obtained for the critical temperature and critical pressure of H₂O and D₂O: H₂O t_crit=(373.91±0.03) °C P_crit=(220.45±0.03) bar D₂O t_crit=(370.66±0.03) °C P_crit=(216.59±0.03) bar.These temperatures are related to the International Practical Temperature Scale of 1948.

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Über diese Arbeit wurde auf dem VDI-Thermodynamik-Kolloquium 1967 in Bad Neuenahr berichtet.     

Following the solvent directly during ultrafast excited state proton transfer

Excited state intramolecular proton transfer in 1-chloroacetylaminoanthraquinone is investigated from the perspective of the solvent. Using a new two-dimensional nonlinear optical spectroscopy the solvent response is probed directly as the proton transfer takes place. The measurements indicate that solvent reorganization controls the proton transfer in acetonitrile by dynamically shifting the position of equilibrium in the excited state, even on subpicosecond time scales.     

Solution of the Bethe-Goldstone equation for the reaction matrix in finite nuclei

A method for solving the BG equation for the reaction matrixt in finite nuclei is presented. The application of this method is demonstrated for a one-dimensional case, which is similar to the problem where the internucleon potential acts only in the relatives-state. The single particle potential has a harmonic oscillator form and the phenomenological internucleon potentialv(r) contains a hard core and an attractive part of the Yukawa type. By taking the exclusion principle into account exactly an infinite system of integral equations is obtained. It is proved that the solution of the corresponding finite system converges to the exact solution. An iteration method for solving such a finite system with an arbitrary number of equations is developed. Its main feature consists in the exclusion of the dependence on the hard core part ofv(r) (which is treated as the limit case of a rectangular repulsive potential with a variable heightv ₀). This exclusion transforms the original system to a system of integral equations depending only on the attractive part ofv(r) and to a linear algebraic system. Both these systems can be solved by iteration for all values ofv ₀ as well as for v₀= +. The numerical results confirm the rapid convergence of the proposed iteration method and demonstrate that the solution of the finite system with a sufficiently large number of equations approximates the exact solution very precisely.     

Study of 19Na at SPIRAL

The excitation function for the elastic-scattering reaction p( ¹⁸Ne, p) ¹⁸Ne was measured with the first radioactive beam from the SPIRAL facility at the GANIL laboratory and with a solid cryogenic hydrogen target. Several broad resonances have been observed, corresponding to new excited states in the unbound nucleus ¹⁹Na. In addition, two-proton emission events have been identified and are discussed.     

First observation of 54Zn and its decay by two-proton emission

The nucleus 54Zn has been observed for the first time in an experiment at the SISSI/LISE3 facility of GANIL in the quasifragmentation of a 58Ni beam at 74.5 MeV/nucleon in a (nat)Ni target. The fragments were analyzed by means of the ALPHA-LISE3 separator and implanted in a silicon-strip detector where correlations in space and time between implantation and subsequent decay events allowed us to generate almost background free decay spectra for about 25 different nuclei at the same time. Eight 54Zn implantation events were observed. From the correlated decay events, the half-life of 54Zn is determined to be 3.2(+1.8)(-0.8) ms. Seven of the eight implantations are followed by two-proton emission with a decay energy of 1.48(2) MeV. The decay energy and the partial half-life are compared to model predictions and allow for a test of these two-proton decay models.