In the past decades, I witnessed the emergence of new light sources around world, especially X-ray sources with pulsed structures, first from the third generation synchrotron sources and then the X-ray free electron laser sources, which have brought and will bring tremendous breakthroughs in science. It is fascinating to see recent advances on observing atomic movements on femtosecond time scale and potential future capabilities of observing electron motions using these light sources. In my mind, these results will alter many classical concepts that we have learned in the past.<br/>My research has been involved in dynamic light-matter interactions in my entire career so far from two aspects: 1) using light to trigger chemical, biological and physical changes that are relevant for our understanding of energy dissipation, transport and conversion to provide guidance for materials design; and 2) using advanced methods to detect these changes in various systems, to establish correlations of dynamics, structures and energetics in real time for various systems.<br/>Many photochemical events, such as bond breaking, intersystem crossing and electron/energy transfer, can occur well before excited state vibrational relaxation. Examples will be given in the presentation on our work of tracking excited state pathways for transition metal complexes, such as Cu(I) complexes. Using fs broadband transient spectroscopy and fs X-ray solution scattering, events of light-matter interactions in molecular systems, such as coherent vibrational wavepacket motions can be readily examined. From the time evolution of key vibrational modes, particularly the Pt-Pt stretching mode, we mapped out excited state trajectories on potential energy surfaces of model Pt-dimer complexes for light conversion, including coherent nuclear motions. These studies were carried out in a series of model platinum dimer complexes in solution featuring rich photochemistry and a set of intricate excited state potential energy surfaces on time scale previously unattainable. The combined molecular design, experimental and theoretical approaches enabled quantitative evaluation of the excited state trajectories of a series of Pt-dimer complexes in terms of actual nuclear motions via the Pt-Pt stretch as well as the energetic variations associated with these motions.

Following and controlling excited state structural dynamic trajectories using photons with different energies

ACS Spring Meeting 2021

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