Controlled ultrafast ππ*-πσ* dynamics in tryptophan-based peptides with tailored micro-environment

Pump-probe experiments in the gas phase usually target neutral molecules. Here the authors couple an electron spray source with ultrafast pump-probe UV-Vis spectroscopy, to follow the pi pi*-pi sigma* coupling in tryptophan-based ions. Ultrafast charge, energy and structural dynamics in molecules are driven by the topology of the multidimensional potential energy surfaces that determines the coordinated electronic and nuclear motion. These processes are also strongly influenced by the interaction with the molecular environment, making very challenging a general understanding of these dynamics on a microscopic level. Here we use electrospray and mass spectrometry technologies to produce isolated molecular ions with a controlled micro-environment. We measure ultrafast photo-induced pi pi*-pi sigma* dynamics in tryptophan species in the presence of a single, charged adduct. A striking increase of the timescale by more than one order of magnitude is observed when changing the added adduct atom. A model is proposed to rationalize the results, based on the localized and delocalized effects of the adduct on the electronic structure of the molecule. These results offer perspectives to control ultrafast molecular processes by designing the micro-environment on the Angstrom length scale.

Automated summary

Researchers combined an electron spray source with ultrafast pump-probe UV-Vis spectroscopy to study pi pi*-pi sigma* coupling in tryptophan-based ions and used mass spectrometry to produce isolated molecular ions with a controlled micro-environment. They measured ultrafast photo-induced pi pi*-pi sigma* dynamics in tryptophan species in the presence of a single, charged adduct, observing a significant increase in timescale when changing the added adduct atom. A model was proposed to rationalize the results based on the effects of the adduct on the electronic structure of the molecule, offering perspectives on controlling ultrafast molecular processes by designing the micro-environment on the Angstrom length scale.