Capturing a photoexcited molecular structure through time-domain x-ray absorption fine structure

Area of Science:

• * Physical Chemistry
• * Materials Science
• * Spectroscopy

Background:

• * Understanding transient molecular structures in solution is crucial for reaction dynamics.
• * Photoexcitation of metalloporphyrins can lead to complex structural changes.

Purpose of the Study:

• * To determine the transient molecular structure of a photoexcited nickel-tetraphenylporphyrin (NiTPP) intermediate.
• * To investigate the structural dynamics following photoexcitation in solution.

Main Methods:

• * Utilized X-ray absorption fine structure (XAFS) spectroscopy.
• * Employed a third-generation synchrotron source for high temporal resolution (14-nanosecond scale).
• * Studied photoexcitation of NiTPP-L2 (NiTPP, nickeltetraphenylporphyrin; L, piperidine) in solution.

Main Results:

• * Photoexcitation rapidly removes both axial ligands from NiTPP-L2.
• * A transient square-planar NiTPP intermediate is formed with a lifetime of 28 nanoseconds.
• * The transient structure closely resembles the ground-state NiTPP structure.

Conclusions:

• * The photodissociated intermediate adopts a square-planar geometry, similar to the ground state.
• * This transient structure exists in noncoordinating solvents before ligand recombination.
• * The findings provide insights into the ultrafast structural dynamics of metalloporphyrins.