Nanosecond-Lived Excimer Observation in a Crystal of a Rhodium(I) Complex via Time-Resolved X‑ray Laue Diffraction

The rare observation of transient Rh···Rh
excimer
formation in a single crystal is reported. The estimated excited-state
lifetime at 100 K is 2 ns, which makes it the shortest-lived small-molecule
species caught experimentally using the laser-pump/X-ray-probe time-resolved
Laue method. Upon excitation with 390 nm laser light, the intermolecular
Rh···Rh distance decreases from 3.379(4) to 3.19(1)
Å, and the metal–metal contact gains more bonding character.
On the basis of the experimental results and theoretical modeling,
the structural changes determined with 100 ps time resolution reflect
principally the S0 → S1 electronic transition.