Intersubband decay of 1-D exciton resonances in carbon nanotubes

We have studied intersubband decay of E22 excitons in semiconducting carbon nanotubes experimentally and theoretically. Photoluminescence excitation line widths of semiconducting nanotubes with chiral indicess (n, m) can be mapped onto a connectivity grid with curves of constant (n-m) and (2n+m). Moreover, the global behavior of E22 linewidths is best characterized by a strong increase with energy irrespective of their (n-m) mod(3)= \pm 1 family affiliation. Solution of the Bethe-Salpeter equations shows that the E22 linewidths are dominated by phonon assisted coupling to higher momentum states of the E11 and E12 exciton bands. The calculations also suggest that the branching ratio for decay into exciton bands vs free carrier bands, respectively is about 10:1.Comment: 4 pages, 4 figure

Dependence of exciton transition energy of single-walled carbon nanotubes on surrounding dielectric materials

We theoretically investigate the dependence of exciton transition energies on dielectric constant of surrounding materials. We make a simple model for the relation between dielectric constant of environment and a static dielectric constant describing the effects of electrons in core states, $\sigma$ bonds and surrounding materials. Although the model is very simple, calculated results well reproduce experimental transition energy dependence on dielectric constant of various surrounding materials.Comment: 5pages, 4 figure

Electronic structure and dynamics of optically excited single-wall carbon nanotubes

We have studied the electronic structure and charge-carrier dynamics of individual single-wall carbon nanotubes (SWNTs) and nanotube ropes using optical and electron-spectroscopic techniques. The electronic structure of semiconducting SWNTs in the band-gap region is analyzed using near-infrared absorption spectroscopy. A semi-empirical expression for $E_{11}^{\rm S}$ transition energies, based on tight-binding calculations is found to give striking agreement with experimental data. Time-resolved PL from dispersed SWNT-micelles shows a decay with a time constant of about 15 ps. Using time-resolved photoemission we also find that the electron-phonon ({\it e-ph}) coupling in metallic tubes is characterized by a very small {\it e-ph} mass-enhancement of 0.0004. Ultrafast electron-electron scattering of photo-excited carriers in nanotube ropes is finally found to lead to internal thermalization of the electronic system within about 200 fs.Comment: 10 pages, 10 figures, submitted to Applied Physics

Far-infrared vibrational properties of high-pressure-high-temperature C60 polymers and the C60 dimer

We report high-resolution far-infrared transmission measurements of the 2 + 2 cycloaddition C-60 dimer and two-dimensional rhombohedral and one-dimensional orthorhombic high-pressure high-temperature C60 polymers. In the spectral region investigated(20-650 cm(-1)), we see no low-energy interball modes, but symmetry breaking of the linked C-60 balls is evident in the complex spectrum of intramolecular modes. Experimental features suggest large splittings or frequency shifts of some IhC60-derived modes that are activated by symmetry reduction, implying that the balls are strongly distorted in these structures. We have calculated the vibrations of all three systems by first-principles quantum molecular dynamics and use them to assign the predominant IhC60 symmetries of observed modes. Pur calculations show unprecedentedly large downshifts of T-1u(2)-derived modes and extremely large splittings of other modes, both of which are consistent with the experimental spectra. For the rhombohedral and orthorhombic polymers, the T-1u(2)-derived mode that is polarized along the bonding direction is calculated to downshift below any T-1u(1)-derived modes. We also identify a previously unassigned feature near 610 cm(-1) in all three systems as a widely split or shifted mode derived from various silent IhC60 vibrations, confirming a strong perturbation model for these linked fullerene structures

Vibrational spectra of C60C8H8 and C70C8H8 in the rotor-stator and polymer phases

C60-C8H8 and C70-C8H8 are prototypes of rotor-stator cocrystals. We present infrared and Raman spectra of these materials and show how the rotor-stator nature is reflected in their vibrational properties. We measured the vibrational spectra of the polymer phases poly(C60C8H8) and poly(C70C8H8) resulting from a solid state reaction occurring on heating. Based on the spectra we propose a connection pattern for the fullerene in poly(C60C8H8), where the symmetry of the C60 is D2h. On illuminating the C60-C8H8 cocrystal with green or blue light a photochemical reaction was observed leading to a similar product to that of the thermal polymerization.Comment: 26 pages, 8 figures, to appear in Journal of Physical Chemistry B 2nd version: minor changes in wording, accepted version by journa

Near-Infrared Luminescence in Trinuclear Mixed-Metal Chalcogenolate Complexes of the Types [M2_{2}Ti(EPh)6_{6}(PPh3_{3})2_{2}] (M = Cu, Ag; E = S, Se) and [Na(thf)3_{3}]2_{2}[Ti(SPh)6_{6}]

The optical properties of four new trinuclear chalcogenolato bridged metal complexes [Ag$_{2}$Ti(SPh)$_{6}$(PPh$_{3}$)$_{2}$], [Na(thf)$_{3}$]$_{2}$[Ti(SPh)$_{6}$], [Cu$_{2}$Ti(SePh)$_{6}$(PPh$_{3}$)$_{2}$], and [Ag$_{2}$Ti(SePh)$_{6}$(PPh$_{3}$)$_{2}$] have been investigated by absorption and photoluminescence spectroscopy as well as time-dependent density functional theory (TDDFT) calculations and compared to the results published recently for [Cu$_{2}$Ti(SPh)$_{6}$(PPh$_{3}$)$_{2}$]. All of these compounds are distinguished by efficient near-infrared luminescence at ∼880–1200 nm in the solid state at low temperatures, which remains quite intense for the copper–titanium complexes at ambient temperature with PL quantum yields of 9.5 and 4.8% at λPL = 1090 and 1240 nm for [Cu$_{2}$Ti(EPh)$_{6}$(PPh$_{3}$)$_{2}$], E = S, Se, respectively. According to the calculations, a peculiar feature of the lowest-energy electronic transitions in these complexes is their high localization on the metal and chalcogen atoms, with negligible contributions of the “external” ligand groups. Correspondingly, the type of atoms in the M$_{2}$TiE$_{6}$ (M = Cu, Ag, Na) core structure determines optical properties such as the absorption and emission wavelengths and PL lifetime

Enhancing Platform Economics via Blockchain : Creating a Business Token Model based on the MiCACompliance

Die vorliegende Masterarbeit bietet einen Einblick in den Bereich der Token-Ökonomie und -Gestaltung. Im Rahmen des Design Science Research werden Blockchain-Technologien, Token-Modelle, Plattform-Ökonomie und die MiCA-Verordnung eingehend untersucht, wobei ein besonderer Fokus auf Ethereum und dessen Standards liegt. Aufbauend auf diesem Wissen werden etablierte Token-Modelle mit interessanten Eigenschaften analysiert. Aus den gewonnenen Erkenntnissen wird ein Token-Business-Modell konzipiert, das demonstriert, wie ein MiCA-konformes Token-Modell gestaltet werden kann. Dieses Modell wird anschließend in einer Simulationsumgebung nachgebildet und anhand spezifischer Parameter getestet, um dessen Funktionalität und Nachhaltigkeit zu validieren. Abschließend wird ein erster Entwurf für die technische Umsetzung des Token-Modells vorgestellt. Die Ergebnisse und Erkenntnisse dieser Arbeit werden abschließend diskutiert, und es werden Empfehlungen für die Weiterentwicklung und zukünftige Forschung zum Token-Modell gegeben.The present master's thesis provides a comprehensive insight into the field of token economics and modelling. Within the framework of Design Science Research, blockchain technologies, token models, platform economy and the MiCA regulation are thoroughly examined, with a particular focus on Ethereum and its standards. Building on this knowledge, established token models with notable features are analyzed. Based on the gained insights, a token business model is designed to demonstrate how a MiCA-compliant model can be structured. This model is then recreated in a simulation environment and tested using specific parameters to validate its functionality and sustainability. Finally, an initial draft of the technical implementation of this token model is presented. The results and findings of this research are discussed, and recommendations for further devel-opment and future research on the token model are provided

Heterobimetallic Gold/Ruthenium Complexes Synthesized via Post‐functionalization and Applied in Dual Photoredox Gold Catalysis

The synthesis of heterobimetallic AuI/RuII complexes of the general formula syn- and anti-[{AuCl}(L1∩L2){Ru(bpy)$_{2}$}][PF$_{6}$]$_{2}$ is reported. The ditopic bridging ligand L1∩L2 refers to a P,N hybrid ligand composed of phosphine and bipyridine substructures, which was obtained via a post-functionalization strategy based on Diels-Alder reaction between a phosphole and a maleimide moiety. It was found that the stereochemistry at the phosphorus atom of the resulting 7-phosphanorbornene backbone can be controlled by executing the metal coordination and the cycloaddition reaction in a different order. All precursors, as well as the mono- and multimetallic complexes, were isolated and fully characterized by various spectroscopic methods such as NMR, IR, and UV-vis spectroscopy as well as cyclic voltammetry. Photophysical measurements show efficient phosphorescence for the investigated monometallic complex anti-[(L1∩L2){Ru(bpy)$_{2}$}][PF$_{6}$]$_{2}$ and the bimetallic analogue syn-[{AuCl}(L1∩L2){Ru(bpy)$_{2}$}][PF$_{6}$]$_{2}$, thus indicating a small influence of the {AuCl} fragment on the photoluminescence properties. The heterobimetallic Au$^{I}$/Ru$^{II}$ complexes syn- and anti-[{AuCl}(L1∩L2){Ru(bpy)$_{2}$}][PF$_{6}$]$_{2}$ are both active catalysts in the P-arylation of aryldiazonium salts promoted by visible light with H-phosphonate affording arylphosphonates in yields of up to 91 %. Both dinuclear complexes outperform their monometallic counterparts