The binuclear complex [Ag(dcpm)](PF) (dcpm = bis(dicyclohexylphosphino)methane) exhibits a structure with a close silver-silver contact mediated by the bridging ligand and thus a weak argentophilic interaction. Upon electronic excitation this cooperative effect is strongly increased and determines the optical and luminescence properties of the compound. We have studied here the ultrafast electronic dynamics in parallel in gas phase by transient photodissociation and in solution by transient absorption. In particular, we report the diverse photofragmentation pathways of isolated [Ag(dcpm)] in an ion trap and its gas phase UV photodissociation spectrum. By pump-probe fragmentation action spectroscopy (λ = 260 nm) in the gas phase, we have obtained fragment-specific transients which exhibit a common ultrafast multiexponential decay. This is fitted to four time constants (0.6/5.8/100/>1000 ps), highlighting complex intrinsic photophysical processes. Remarkably, multiexponential dynamics (0.9/8.5/73/604 ps) are as well found for the relaxation dynamics in acetonitrile solution. Ab initio calculations at the level of approximate coupled-cluster singles-doubles (CC2) theory of ground and electronically excited states of the reduced model system [Ag(dmpm)] (dmpm = bis(dimethylphosphino)methane) indicate a shortening of the Ag-Ag distance upon excitation by 0.3-0.4 Å. In C geometry two close-lying singlet states S (MC(dσ*-pπ), B, 4.13 eV) and S (MC(dσ*-pσ), A, 4.45 eV) are found. The nearly dark S state has not been reported so far. The excitation of the S state carries a large oscillator strength for the calculated vertical transition (266 nm). Two related triplets are calculated at T (3.87 eV) and T (3.90 eV). From these findings we suggest possible relaxation pathways with the two short time constants ascribed to ISC/IVR and propose from the obtained similar values in gas phase that the fast solution dynamics is dominated by intramolecular processes. A further relaxation by IC/IVR in the triplet manifold is likely to account for the observed intermediate time constants. For the acetonitrile relaxation dynamics additional modifications are invoked based on solvent-induced shifts of the energy levels and the possible formation of solvent and counterion exciplexes on a longer timescale.

The hybrid ligand 3-(2,2'-bipyridine-6-ylmethyl)-1-mesityl-1H-imidazolylidene (NHC ) featuring both carbene and N-donor sites, was selectively complexed with various d metal cations in order to examine its coordination behavior with regard to homo and heterometallic structures. Respective silver complexes can be obtained by the silver oxide route and are suitable transmetallation reagents for the synthesis of gold(I) compounds. Starting from the mononuclear complexes [(NHC )AuCl], [(NHC )Au(C F )] and [(NHC ) Au][ClO ], open-chain as well as cyclic heterobimetallic complexes containing Cu , Ag , Zn , Cd , and Hg were synthesized. Furthermore, the homobimetallic species [(NHC ) M ][ClO ] (M=Cu, Ag) were obtained. All bimetallic compounds were fully characterized including single-crystal X-ray analysis. Their photoluminescence (PL) properties were investigated in the solid state at temperatures between 15 and 295 K and compared with those of the mononuclear species. There is a clear difference in PL properties between the open chain and the cyclic heterobimetallic complexes. The latter species show different PL properties, depending on the metals involved. In addition, collision-induced dissociation (CID) experiments were performed on electrosprayed cations of the cyclic heterobimetallic compounds, to compare the metal binding at the carbene and N-donor sites.

Time-resolved pump-probe photoelectron spectroscopy has been used to study the relaxation dynamics of gaseous [Pt2(μ-P2O5H2)4 + 2H](2-) after population of its first singlet excited state by 388 nm femtosecond laser irradiation. In contrast to the fluorescence and phosphorescence observed in condensed phase, a significant fraction of the photoexcited isolated dianions decays by electron loss to form the corresponding monoanions. Our transient photoelectron data reveal an ultrafast decay of the initially excited singlet (1)A2u state and concomitant rise in population of the triplet (3)A2u state, via sub-picosecond intersystem crossing (ISC). We find that both of the electronically excited states are metastably bound behind a repulsive Coulomb barrier and can decay via delayed autodetachment to yield electrons with characteristic kinetic energies. While excited state tunneling detachment (ESETD) from the singlet (1)A2u state takes only a few picoseconds, ESETD from the triplet (3)A2u state is much slower and proceeds on a time scale of hundreds of nanoseconds. The ISC rate in the gas phase is significantly higher than in solution, which can be rationalized in terms of changes to the energy dissipation mechanism in the absence of solvent molecules. [Pt2(μ-P2O5H2)4 + 2H](2-) is the first example of a photoexcited multianion for which ESETD has been observed following ISC.

The recently introduced pump-probe fragmentation action spectroscopy reveals a unique observation of excited state vibrational coherence (430-460 fs) in the isolated metal complex [Ag(Cl)(dcpm))] (dcpm = bis(dicyclohexylphosphino)methane) containing the [AgCl] scaffold. After photoexcitation by an XMCT transition (260 nm) in an ion trap, an unexpected correlation between specific fragment ions (loss of HCl/Cl vs loss of dcpm) and the phase of the wave packet is probed (1150 nm). Based on ab initio calculations, we assign the primary electronically excited state and ascribe the observed coherences (72-78 cm) to contain predominantly Ag-Ag stretch character. We propose specific probe absorption and vibronic coupling at the classical turning points to switch remarkably early on between the different fragmentation pathways. The overall excited state dynamics are fitted to a multiexponential decay with time constants: 0.2-0.4/3-4/19-26/104-161 ps. These findings open new perspectives for further dynamics investigations and possible applications in photocatalysis.

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