Inorganic Chemistry, Vol.53, No.19, 10594-10601, 2014
Shedding Light on the Photochemistry of Coinage-Metal Phosphorescent Materials: A Time-Resolved Laue Diffraction Study of an Ag-I-Cu-I Tetranuclear Complex
The triplet excited state of a new crystalline form of a tetranudear coordination d(10)-d(10)-type complex, Ag2Cu2L4 (L = 2-diphenylphosphino-3-methylindole ligand), containing Ag-I and Cu-I metal centers has been explored using the Laue pump probe technique with approximate to 80 ps time resolution. The relatively short lifetime of 1 mu s is accompanied by significant photoinduced structural changes, as large as the Ag1 center dot center dot center dot Cu2 distance shortening by 0.59(3) angstrom. The results show a pronounced strengthening of the argentophilic interactions and formation of new Ag center dot center dot center dot Cu bonds on excitation. Theoretical calculations indicate that the structural changes are due to a ligand-to-metal charge transfer (LMCT) strengthening the Ag center dot center dot center dot 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 heteronudear coordination complex and provides new information on the nature of photoresponse of coinage metal complexes, which have been the subject of extensive studies.