Shedding
Light on the Photochemistry of Coinage-Metal
Phosphorescent Materials: A Time-Resolved Laue Diffraction Study of
an Ag<sup>I</sup>–Cu<sup>I</sup> Tetranuclear Complex
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Abstract
The
triplet excited state of a new crystalline form of a tetranuclear
coordination d<sup>10</sup>–d<sup>10</sup>-type complex, Ag<sub>2</sub>Cu<sub>2</sub>L<sub>4</sub> (L = 2-diphenylphosphino-3-methylindole
ligand), containing Ag<sup>I</sup> and Cu<sup>I</sup> metal centers
has been explored using the Laue pump–probe technique with
≈80 ps time resolution. The relatively short lifetime of 1
μs is accompanied by significant photoinduced structural changes,
as large as the Ag1···Cu2 distance shortening by 0.59(3)
Å. The results show a pronounced strengthening of the argentophilic
interactions and formation of new Ag···Cu bonds on
excitation. Theoretical calculations indicate that the structural
changes are due to a ligand-to-metal charge transfer (LMCT) strengthening
the
Ag···Ag interaction, mainly occurring from the methylindole
ligands to the silver metal centers. QM/MM optimizations of the ground
and excited states of the complex support the experimental results.
Comparison with isolated molecule optimizations demonstrates the restricting
effect of the crystalline matrix on photoinduced distortions. The
work represents the first time-resolved Laue diffraction study of
a heteronuclear coordination complex and provides new information
on the nature of photoresponse of coinage metal complexes, which have
been the subject of extensive studies