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Motivation for Research

Organic Electronics

Electronic devices based on organic chemistry may have several advantages compared to most currently available devices, which are based on silicon, including price, power efficiency, and the possibility to create mechanically flexible devices. On the one hand the idea of cheap solar cells providing clean energy on a large scale sounds intriguing. On the other hand organic light emitting diodes (OLED) are a promising technology for energy efficient light sources and displays. Due to the large number of potential different molecular species and device architectures this technology carries the potential to eliminate problems of current lamps related for example to response times and "colour temperature". Furthermore, OLED technology opens the potential for flexible displays.

Iridium complexes offer very favourable properties for new OLED materials. The heavy transition metal ion opens a pathway for efficient phosphorescence due to relativistic effects, allowing to harvest triplet excitons. Furthermore, a large number of different complexes with highly different spectral properties could be synthesized. However, applications are currently hampered by the instability of these complexes, concerning especially blue emitters. While there is a large experimental effort in the search for new emitting complexes, only rather simple computations were performed for the most part. However, a detailed understanding of the underlying photophysical processes could significantly enhance the design process by providing routes for rational design. It is the purpose of this project to provide such information.

Ir(ppy)3 complex, powered by Claire Plasser

Electronic Defects in DNA

Deoxyribonucleic acid (DNA) has a central role in biology as the carrier of the genetic code. Therefore it is of highest interest to understand the properties of this intriguing molecule in detail. Photostability of DNA, which yields resistance against UV radiation coming from the sun, may have been a decisive factor in early evolution. In particular research has shown that selection pressure for photostability may have had strong influence on the precise molecular structure of the nucleic acid bases that we still have today. Whereas the photophysical properties of isolated DNA bases are fairly well understood, many open questions remain with respect to inter-base interactions, coming either from base pairing or stacking. Experiments have shown that such interactions significantly alter the photophysical properties of DNA but many open questions remain with respect to the precise mechanism. A major part of my research is concerned with these open questions, using the help of computer simulations.

Charge transfer in DNA, i.e. its electric conductivity, is of high interest as well. From a biological viewpoint it is important to understand its relation to oxidative damage and repair mechanisms. DNA has been studied as well because it may be an interesting prototype for nanoelecronics. Experiments on charge transfer in DNA are highly challenging and a wide range of different results has been obtained depending on the precise experimental setup. Simulations are challenging as well because of the size of the system, environmental effects, and coupling between electronic and nuclear motion.