Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) allows recording of molecular diffusion paths (notably, the probability distribution of molecular displacements over typically micrometers, covered during an observation time of typically milliseconds) and has thus proven to serve as a most versatile means for the in-depth study of mass transfer in complex materials. This is particularly true with nanoporous host materials, where PFG NMR enabled the first direct measurement of intracrystalline diffusivities of guest molecules. Spatial resolution, i.e., the minimum diffusion path length experimentally observable, is limited by the time interval over which the pulsed field gradients may be applied. In “conventional” PFG NMR measurements, this time interval is determined by a characteristic quantity of the host-guest system under study, the so-called transverse nuclear magnetic relaxation time. This leads, notably when considering systems with low molecular mobilities, to severe restrictions in the applicability of PFG NMR. These restrictions may partially be released by performing PFG NMR measurements in combination with “magic-angle spinning” (MAS) of the NMR sample tube. The present review introduces the fundamentals of this technique and illustrates, via a number of recent cases, the gain in information thus attainable. Examples include diffusion measurements with nanoporous host-guest systems of low intrinsic mobility and selective diffusion measurement in multicomponent systems.

Ein vielversprechendes Design für organische lichtemittierende Dioden (OLEDs) verwendet eine Wirt-Gast-Strategie durch Dispergieren einer kleinen Menge eines hocheffizienten Emitters (der Gast) in eine passende Transportmatrix (der Wirt). Die Aufgabe des Wirts ist den Exzitonentranport zum Emitter sicherzustellen und den Zerfall von Triplet-Exzitonen zu verhindern, und damit eine hohe Bauteilperformance zu erreichen. Die vorliegende Arbeit konzentriert sich auf die Beziehung zwischen Molekülstruktur und optoelektrischer Eigenschaften von Carbazol/Dibenzothiophen-Derivaten. Die Untersuchung umfasst sieben dieser Derivate für den Wirt, bei denen die Carbazoleinheit als Donator und die Dibenzothiopheneinheit als Akzeptor fungiert, wobei beide durch einen oder mehrere Phenylabstandshalter verbunden sind. Diese Wahl der Wirtsmaterialien erlaubt es den Einfluss der erweiterten Phenylabstandshalter und der unterschiedlichen molaren Verhältnisse von Akzeptor zu Donator zu untersuchen. Es ergab sich, dass eine kürzere Phenylabstandshalterlänge die Bauteilperformance durch eine größere Löcher- und Elektronendichte in der Emitterschicht verbessert; und ein 1:1 Carbazol-zu-Dibenzothiophen-Verhältnis der Bauteilperformance zuträglich ist, da es zu einem Ladungsträgergleichgewicht in der Emitterschicht führt. Diese Arbeit zeigt, unter Verwendung dieser Wirtsmaterialien, blaue FIrpic-basierte phosphoreszierende OLEDs (PhOLEDs) und grüne 4CzIPN-basierte thermisch aktivierte verzögerte Phosphoreszenz (TADF) OLEDs. Die blauen PhOLEDs und grünen TADF OLEDs mit mDCP zeigten Effizienzen von 43 cd/A (18.6%) beziehungsweise 66 cd/A (21%). / A particularly interesting organic light-emitting diodes (OLEDs) design adopts a host-guest strategy by dispersing a small amount of highly efficient emitter (the guest) into an appropriate transport matrix (the host). The host is utilized to transfer excitons to the emitter and to prevent triplet exciton quenching, thus high device performance can be achieved. The present thesis focuses on the relationship between the molecular structure and opto-electrical properties of carbazole/dibenzothiophene derivatives. The investigation encompasses seven of these derivatives for the host, in which the carbazole unit acts as a donor and the dibenzothiophene as an acceptor while they are linked through phenyl spacer(s). This choice of host materials enables to assess the impact of extended phenyl spacers and different acceptor to donor molar ratios. It was found that decreasing the phenyl spacer length enhances the device performance due to the larger both hole and electron densities in the emitting layer; and a 1:1 carbazole to dibenzothiophene ratio is favorable for device performance, since it balances the charge carriers in the emitting layer. Using these host materials, the work presented in this thesis demonstrates high-performance blue FIrpic-based phosphorescent OLEDs (PhOLEDs) and green 4CzIPN-based thermally activated delayed fluorescence (TADF) OLEDs. The blue PhOLEDs and green TADF OLEDs with mDCP showed efficiencies of 43 cd/A (18.6%) and 66 cd/A (21%), respectively.