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

The rare observation of transient Rh···Rh\nexcimer\nformation in a single crystal is reported. The estimated excited-state\nlifetime at 100 K is 2 ns, which makes it the shortest-lived small-molecule\nspecies caught experimentally using the laser-pump/X-ray-probe time-resolved\nLaue method. Upon excitation with 390 nm laser light, the intermolecular\nRh···Rh distance decreases from 3.379(4) to 3.19(1)\nÅ, and the metal–metal contact gains more bonding character.\nOn the basis of the experimental results and theoretical modeling,\nthe structural changes determined with 100 ps time resolution reflect\nprincipally the S<sub>0</sub> → S<sub>1</sub> electronic transition.