In the past few years conjugated polymers have attracted considerable interest owing to their high potential for applications in optoelectronic devices, such as organic light-emitting diodes, solar cells, and ink-jet printed electronic circuits ("plastic electronics"). Despite the progress in the field of device fabrication, a full understanding of the dynamics of electronic excitations and the intrinsic electronic and optical properties of these functional materials is far from being complete. To gain further insight into these issues a model conjugated polymer (methyl-substituted ladder-type poly(para-phenylene), MeLPPP) was investigated by two-photon and time-resolved spectroscopy on thin films as well as single-molecule fluorescence spectroscopy. Employing continuous-wave two-photon fluorescence-excitation spectroscopy on MeLPPP the symmetry properties of the vibronic wave functions of the lowest electronically excited states were studied. It was found that the symmetry selection rules for optical transitions are rather strictly fulfilled, demonstrating the high intra-chain order in MeLPPP. The time-resolved experiments utilising a Streak-camera technique revealed the full relaxation dynamics of electronic excitations within the density of electronically excited states prior to the emission process. Finally, low-temperature single-molecule spectroscopy on MeLPPP in combination with pattern recognition techniques for data analysis allowed to retrieve the electron-phonon coupling strength in a conjugated polymer for the first time. For MeLPPP a weak electron-phonon coupling was found, which is consistent with the efficient excitation energy transfer processes observed by time-resolved spectroscopy.


Seminar, 3^rd of December, 12:00h. Conference Room

Hosted by Prof. Niek van Hulst