Ultrafast photoexcitation dynamics in tri-nuclear metal-metal bonded M-PtPOP (M=AG, Tl) transition-metal complexes

Speaker:  Philipp Lenzen, Technical University of Denmark (DTU)

Program Description:
While optical laser have been available on sub-picosecond timescales for some time, using them  to study molecular structural dynamics requires a model of the coupling between energy levels  and structure, which is not a given for every molecule. To circumvent this limitation, x-ray  scattering techniques have been proposed to resolve atomic movements. 

With the construction and improvement of free electron x-ray lasers in recent decades, x-ray  sources with unprecedented brilliance and pulse lengths in the sub 100 femtosecond range have  become available and thereby allowing such experiments. 

Transition-metal complexes have been objects of interest for their photochemical and photophysical properties, making many compounds interesting for applications in catalysis or  solar energy conversion. Following excitation they can undergo structural changes accompanied by changes to the chemical properties, which can be resolved with time resolved wide-angle x-ray scattering (TR-WAXS)(fig. 1).[1] The measurements occur in solution to reflect real chemical conditions, allowing the identification and characterization of heat dissipation, solvation cage and laser induced anisotropy.[2] 

The [AgPt2(H2P2O5)4]3- (AgPt2POP4) and [TlPt2(H2P2O5)4]3- (TlPt2POP4) complexes investigated  in this study is a close relative of the intensively studied Pt2POP4[1,3], and allow for deeper insight in structural dynamics and the nature of metal-metal bonding. 

Fig. 1. TR-WAXS setup for liquid jets with AgPt2POP4 at the Linac Coherent Light Source (LCLS) [4] 

Acknowledgments 

We thank the Danmarks Frie Forskningsfond (DFF) for funding the project and DANSCATT for supporting the beamtime efforts. 

References 

[1] Harry B. Gray et al., Electronic structures and photophysics of d8-d8 complexes,  Coordination Chemistry 

Reviews,  345, (2017).  

[2] Elisa Biasin et al.,  Anisotropy enhanced X-ray scattering from solvated transition metal complexes, Journal of 

Synchrotron Radiation, 25, (2018) 

[3] Kristoffer Haldrup et al., Analysis of time-resolved X-ray scattering data from solution-state systems, Acta Cyst., 

66, (2010) 

[4] Tim Brandt van Driel et al., Disentangling detector data in XFEL studies of temporally                                                                       

resolved solution state chemistry, Faraday Discuss., 177, 443 (2015)