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.

Understanding subtle aspects of photophysical behavior is the key to design and synthesize new and improved luminescent materials. We contribute to this with an in-depth photophysical characterization of the binuclear copper complex Cu(i)-NHetPHOS-tris-m-tolylphosphine (1), a member of a recently established emitter class for ultra-efficient, printed organic light-emitting diodes (OLEDs). To this end we studied 1 in solution and in solid form, i.e. neat film and KBr-pellet, by means of femtosecond time-resolved transient absorption/reflectivity, time-correlated single photon counting (TCSPC), and nanosecond time-resolved step-scan FTIR spectroscopy. Using these methods, we explore the photoinduced dynamics from ultrafast Franck-Condon state deactivation until the decay of the luminescent states. Upon photoexcitation, we observed multiexponential dynamics in both solution (e.g. acetonitrile 0.8 ps, 59 ps, 3 ns, 11-13 ns) and in solid state (e.g. neat film 0.3 ps, 35 ps, 670 ps, 0.5-1 μs, 3.5-4.5 μs) with four to five time-constants that significantly depend on the type of sample. Quantum chemical calculations at the DFT level in combination with step-scan vibrational spectroscopy provided structural information about the electronic ground state S and the lowest lying excited state T, and show that the latter is populated within 1 μs after photoexcitation. We found thermally activated delayed fluorescence (TADF) for this complex, which has been suggested to be the cause for its high efficiency in printed OLED devices. The results suggest that non-radiative processes, lowering the luminescence quantum yield in solution, are active on the ns to μs timescale.

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.

Spotlight on a photoexcited heteroleptic Cu(i) complex: elucidation of ultrafast electronic and structural dynamics.

Lanthanide ions (Dy , Eu ) are stabilized by coordination with two Schiff base ligands in compounds [Dy{H L} ](NO )(EtOH)(H O) (1) and [Eu{H L} ](NO )(H O) (3) (H L, 2,2'-{[(2-aminoethyl)imino]bis[2,1-ethanediyl-nitriloethylidyne]}bis-2-hydroxy-benzoic acid). The latter is reported here for the first time. Both luminescence and ultrafast photodynamics after photoexcitation via a ligand absorption band (∼400 nm) have been studied. In solution, only the [Eu{H L} ] ([3] ) complex displays the typical lanthanide emission lines, whereas in gas phase both, [Dy{H L} ] ([1] ) and [3] , show their corresponding transitions depending on excitation energy. The ultrafast excited state dynamics, obtained in gas phase and in solution, are assigned to excited state intramolecular proton transfer processes in the ligands. The antenna ligand moiety of these complexes provides pockets for stabilization of two Mn ions so that we additionally investigated the photophysical behavior of the corresponding tri-nuclear (NHEt ) [Ln{MnL} ](ClO )(H O) (Ln=Dy , Eu ) compounds (2, 4). Interestingly, the related complexes do not show lanthanide emission, neither in solution nor in gas phase. Transient data in solution and gas phase suggests an efficient quenching of the ligand's electronically excited state by strong interaction with the Mn ions. This effect could possibly be developed further into a design principle for luminescence-based sensing devices for metal cations.