A series of novel carbazole compounds was synthesized and tested for their suitability as host for triplet emitters in an organic-light emitting diode (OLED). In these compounds, a carbazole unit is either connected to other carbazole units to form carbazole dimers and trimers or to fluorene and oxadiazole derivatives to form mixed compounds. The HOMO level of carbazole compounds can be tuned by substitution at the 3, 6, and/or 9 positions. Making oligomers by connecting carbazole molecules via their 3 (3′) positions shifts the HOMO level to higher energy, while replacing alkyl groups at the 9 (9′) positions by aryl groups shifts the HOMO level to lower energy. Furthermore, it has been found that the triplet energy of these compounds is determined by the presence of poly(p-phenyl) chains in the molecular structure. By identifying the longest poly(p-phenyl) chain, one can predict whether a compound will be a suitable host for a high-energy triplet emitter. An overview of HOMO levels, singlet and triplet levels, and exchange energies is given for all carbazole compounds synthesized. Finally, OLEDs employing two selected carbazole compounds as host and fac-tris(2-phenylpyridine)-iridium (Ir(ppy) 3) as guest were constructed and characterized electrically.

Carbazole Compounds as Host Materials for Triplet Emitters in Organic Light-Emitting Diodes: Tuning the HOMO Level without Influencing the Triplet Energy in Small Molecules

Energy will be one of the most important factors to influence human society in the 21st century.1,2 Cost, availability, and sustainability of energy have a significant impact on the quality of our lives, development of global economies, relationships between nations, and the stability of our environment. Scientists are now focusing on the development of renewable energies3 generated from natural resources such as sunlight, wind, rain, tides, and geothermal heat. Among these, the sun has the potential to make the largest energy contribution: only one hour of sunshine (3.8 × 1023 kW) is more than enough to satisfy the highest human demand for energy for an entire year (1.6 × 1010 kW in 2005).4-7 Solar cells, also called photovoltaics,8 are devices based on solar technology which convert sunlight directly into electricity under the photovoltaic effect. Becquerel was the first to recognize this effect in 1839, when he shined light * To whom correspondence should be addressed. E-mail: muellen@ mpip-mainz.mpg.de. † Max Planck Institute for Polymer Research. ‡ BASF SE. Chen Li studied chemistry and completed his Master’s thesis under the supervision of Professor He Tian at the East China University of Science and Technology in 2003. In 2004, he joined the group of Professor Klaus Müllen at the Max Planck Institute for Polymer Research to work on functional rylene dyes for dye-sensitized solar cells. He received his Ph.D. in 2008 from the Johannes Gutenberg University of Mainz. Presently he works in the same group as a project leader, and his research interests are functional dyes and pigments as well as their applications.

Polyphenylene-Based Materials for Organic Photovoltaics

Degradation Mechanisms and Reactions in Organic Light-Emitting Devices.

Highly Efficient Organic Blue Electrophosphorescent Devices Based on 3,6‐Bis(triphenylsilyl)carbazole as the Host Material

Les amines peuvent etre analysees par chromatographie apres reaction avec l'o-phtalaldehyde et des thiols. Divers thiols sont testes afin d'obtenir les derives les plus stables

O-Phtalaldehyde derivatives of amines for high-speed liquid chromatography/electrochemistry

Electrochemical and spectroscopic techniques have been employed in elucidating the anodic oxidation pathways of carbazole and several N‐substituted derivatives. For carbazole and the N‐alkyl or N‐aryl derivatives, ring‐ring coupling is the predominant decay pathway of the carbazole cations; the coupling rates are extremely rapid. N‐N coupling is observed initially for carbazole, but in long‐time electrolysis it is of little consequence. The oxidation products have been synthesized by chemical means and compared with the species formed electrochemically by matching of cyclic polarograms and visible absorption spectra. Molecular orbital calculations give a qualitative picture of active sites with regard to follow‐up coupling reactions in the carbazole series. N‐vinyl, N‐acetyl, N‐benzoyl, and N‐nitroso carbazole were investigated briefly but found to be extremely complicated.

J. F. Ambrose

Papers

Anodic Oxidation Pathways of Carbazoles I . Carbazole and N‐Substituted Derivatives