PROGRAM:

F. Stienkemeier's abstract:

Nano-structured organic semiconductors are of applied interest for new developments in the field of electronics and opto-electronics. In particular, 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) and its derivatives are studied in connection with organic light emitting devices as well as thin film transistors and solar cells. We use a beam of superfluid helium nanodroplets as a low temperature matrix to study molecules and larger complexes at temperatures of 380 mK. Laser-induced fluorescence is applied to examine electronic properties of PTCDA and MePTCDI. For the first time, vibrational resolved fluorescence spectra are obtained of single molecules as well as selected isomers of molecular dimers. Furthermore, in sandwich-like structures of complexes, clearly exciton transitions can be separated from molecular excitations. Results are discussed in comparison with spectra obtained in films and molecules probed in organic solvents. The second part of the talk will present recent results on femtosecond pump-probe spectroscopy of doped helium droplets. Alkali atoms are used to probe surface excitations of the droplets. Moreover, the formation of alkali-helium exciplexes is followed in real-time. In particular a comparison between superfluid 4He droplets and their normalfluid 3He counterparts is discussed.