Non-equilibrium dynamics of di-platinum complexes and molecular dyes in solution: Insights from transient absorption and two-dimensional Fourier transform spectroscopy

Unraveling the interplay between electronic- and vibrational degrees of freedom on the earliest time scales of physical, chemical and biological processes is crucial to gaining insight into the mechanisms that govern the world around us, since it is during these primary steps that the fate of the excitation energy - be it solar, chemical or physical - is decided. A tiny structural change during the first 10s of femtoseconds can for example predetermine the dynamics of a system over microseconds, and newly developed techniques in time-domain spectroscopy have proved to successfully capture exactly these pivotal mechanisms.

In this thesis I use ultrafast spectroscopy to investigate the non-equilibrium dynamics of a prototypical di-platinum complex. Transient absorption spectroscopy is complemented with transient absorption anisotropy and fluorescence up-conversion to identify the spectral features of the intermediate excited states. The results show that the intersystem crossing from the singlet- to the triplet manifold of states happens on a 0.6 to 0.9 picosecond time scale, slower than previously assumed. As a consequence, the observable coherence is associated with a singlet excited state, rather than a triplet, and dephases prior to the intersystem crossing. The study further illustrates the importance of having a good understanding of the transient spectral signatures and yields insight into the structural dynamics of di-platinum complexes.

In addition, I have built and commissioned a two-dimensional photon echo experiment that is capable of acquiring broadband excitation- and detection frequency resolved transient spectra in the visible with a temporal resolution of approx. 10 femtoseconds. All relevant steps of the development are outlined in this thesis and 2D spectra of four different dye solutions highlight the capabilities of the experiment. The temporal evolution of the 2D spectra of nile blue is analyzed as an example and shows the information content that is contained within the data.