Seminars Archive

Coherent two-dimensional spectroscopy to investigate molecular function

Abstract
Understanding the photophysics and photochemistry of complex molecular systems requires accessing the interactions between their parts and disentangling different reaction pathways with high spectral and temporal resolution. Coherent two-dimensional (2D) spectroscopy is particularly suited for this purpose, as it combines real-time observation on time scales as short as a few tens of fs with the capability to distinguish contributions arising from different chromophores or states in the frequency domain. In myoglobin, a small protein involved in oxygen storage in muscle tissue, we explored the interaction between the protein active site (haem) and two tryptophan aminoacids located at different positions in the protein scaffold. Not only two-dimensional spectroscopy allowed disentangling the signals of the two tryptophans, but we could also demonstrate that these two aminoacids relax to the haem via different processes.[1] A second example concerns processes of energy relaxation and transfer in polymeric compounds, whose understanding is fundamental for optoelectronics and photovoltaics. Especially the relationship between exciton dynamics and structure is a key parameter that is currently poorly understood. As a paradigmatic example, I will show how coherent two-dimensional spectroscopy can be used to characterize processes of exciton relaxation and energy transfer in the polymer MEH-PPV (poly-[2-methoxy-5-(2‘-ethylhexyloxy)-1,4-phenylenevinylene]), where a disorder-order phase transition can be induced by lowering the temperature below a critical value.[2] [1] C. Consani et al., Science 339, 1586 (2013) [2] C. Consani et al., J. Chem. Phys. 142, 212429 (2015)