Morphologische Untersuchungen ultradünner Pentacen-Filme

In dieser Arbeit wurde die nachträglich thermisch angeregte Entnetzung ultradünner Pentacenfilme auf Siliziumdioxid untersucht

Coupling between diffusion and orientation of pentacene molecules on an organic surface.

The realization of efficient organic electronic devices requires the controlled preparation of molecular thin films and heterostructures. As top-down structuring methods such as lithography cannot be applied to van der Waals bound materials, surface diffusion becomes a structure-determining factor that requires microscopic understanding. Scanning probe techniques provide atomic resolution, but are limited to observations of slow movements, and therefore constrained to low temperatures. In contrast, the helium-3 spin-echo (HeSE) technique achieves spatial and time resolution on the nm and ps scale, respectively, thus enabling measurements at elevated temperatures. Here we use HeSE to unveil the intricate motion of pentacene admolecules diffusing on a chemisorbed monolayer of pentacene on Cu(110) that serves as a stable, well-ordered organic model surface. We find that pentacene moves along rails parallel and perpendicular to the surface molecules. The experimental data are explained by admolecule rotation that enables a switching between diffusion directions, which extends our molecular level understanding of diffusion in complex organic systems.The authors acknowledge financial support from the EPSRC (EP/E0049621, B.A.J.L., D.J.W., D.M.C., A.P.J., J.E., W.A.), the Austrian Academy of Sciences (B.A.J.L.), the Royal Society (A.P.J.), the E.U. ERASMUS programme (A.M.) and the Deutsche Forschungsgemeinschaft (GRK 1782, P.R.). Underlying data are available at the University of Cambridge Research data repository (https://www.repository.cam.ac.uk).This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nmat457

Kinetic Modeling of Transient Photoluminescence from Thermally Activated Delayed Fluorescence

A simplified state model and associated rate equations are used to extract the reverse intersystem crossing and other key rate constants from transient photoluminescence measurements of two high performance thermally activated delayed fluorescence materials. The values of the reverse intersystem crossing rate constant are in close agreement with established methods, but do not require a priori assumption of exponential decay kinetics, nor any additional steady state measurements. The model is also applied to measurements at different temperatures and found to reproduce previously reported thermal activation energies for the thermally activated delayed fluorescence process. Transient absorption measurements provide independent confirmation that triplet decay channels (neglected here) have no adverse effect on the fitting

Research data supporting "Coupling of diffusion and orientation of pentacene on an organic surface"

The package contains a series of experimental Helium Spin-Echo measurements (HeSE) describing the dynamics of pentacene molecules on a pentacene monolayer grown on a Cu(110) surface.This record supports "Coupling of diffusion and orientation of pentacene on an organic surface" which has now been published in Nature Materials.This work was supported by the EPSRC [grant number EP/E0049621], Royal Society, Austrian Academy of Sciences, E.U. ERASMUS programme and Deutsche Forschungsgemeinschaft [grant number GRK 1782]

Persistent Dimer Emission in Thermally Activated Delayed Fluorescence Materials

We expose significant changes in emission color of carbazole-based thermally activated delayed fluorescence (TADF) emitters that arise through the presence of persistent dimer states in thin films and organic light-emitting diodes(OLEDs). Direct photoexcitation of this dimer state in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) reveals the significant influence of dimer species on the color purity of its photoluminescence and electroluminescence. The dimer species is sensitive to the sample preparation method and its enduring presence contributes to the widely reported concentration-mediated redshift in the photoluminescence and electroluminescence of evaporated thin films. This discovery has significant implications on the usability of these, and similar, molecules for OLEDs and explains disparate electroluminescence spectra presented in the literature for these compounds. The significant dimerization-controlled changes observed in the TADF process and photoluminescence efficiency mean that careful consideration of dimer states is imperative in the design of future TADF emitters and the interpretation of previously reported studies of carbazole-based TADF materials