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The novel photoswitchable ligand 3,3'‐Azobenz(metPA)2 (1) is used to prepare a [Cu2(1)2](BF4)2 metallocycle (2), whose photoisomerization was characterized using static and time‐resolved spectroscopic methods. Optical studies demonstrate the highly quantitative and reproducible photoinduced cyclic E/Z switching without decay of the complex. Accordingly and best to our knowledge, [Cu2(1)2](BF4)2 constitutes the first reversibly photoswitchable (3d)‐metallocycle based on azobenzene. The photoinduced multiexponential dynamics in the sub‐picosecond to few picosecond time domain of 1 and 2 have been assessed. These ultrafast dynamics as well as the yield of the respective photostationary state (PSSZ = 65 %) resemble the behavior of archetypical azobenzene. Also, the innovative pump‐probe laser technique of gas phase transient photodissociation (τ‐PD) in a mass spectrometric ion trap was used to determine the intrinsic relaxation dynamics for the isolated complex. These results are consistent with the results from femtosecond UV/Vis transient absorption (fs‐TA) in solution, emphasizing the azobenzene‐like dynamics of 2. This unique combination of fs‐TA and τ‐PD enables valuable insights into the prevailing interplay of dynamics and solvation. Both analyses (in solution and gas phase) and quantum chemical calculations reveal a negligible effect of the metal coordination on the switching mechanism and electronic pathway, which suggests a non‐cooperative isomerization process. [ABSTRACT FROM AUTHOR]

Binuclear coinage metal phosphine complexes are examined under ion trap isolation in order to elucidate their noncovalent binding, structural properties and intrinsic electronic spectra. Our survey shows an intriguing order of electronic transitions obtained by in situ synthesis and mass-spectrometrically supported UV photodissociation spectroscopy on a series of six isolated homo- and heterobinuclear complexes of type [MM′(dcpm)2]2+ (M, M′ = CuI, AgI, AuI; dcpm = bis(dicyclohexyl-phosphino)methane). This approach provides the unique opportunity to study all possible coinage metal interactions within a fixed ligand framework. A successive blue-shift (33 700–38 500 cm−1; 297–260 nm) of the lowest-energy bright electronic transition energy in gas phase was observed in the order of Cu2 < CuAu < CuAg < Au2 < AgAu < Ag2. This order was reproduced by quantum chemical calculations using a scalar-relativistic GW-Bethe–Salpeter-equation (GW-BSE) approach. Theory ascribes the electronic bands of all complexes to metal-centered 1MC(dσ*–pσ) transitions revealing a strengthening of metal–metal′ (M–M′) binding upon excitation, in agreement to mass spetrometric results. A test of the correlation of transition energies with M–M′ distance by quantum chemical calculations of single point energies as a function of intermetallic distance indicates qualitative agreement with experimental results. However, the experimentally observed high sensitivity of spectroscopic shifts towards metal composition cannot be accounted for solely by M–M′ distance variation. The differences in electronic transitions are qualitatively rationalized by the varying (n + 1)s (n = 3, 4, 5) orbital contributions (increase from Cu2via CuAu/CuAg to Au2/AgAu/Ag2) within the nd(n + 1)s/p-hybridization for the ground electronic state of the different complexes, whereas the excited state (of (n + 1)p orbital character) shows significantly less variation in energy. In particular, the observed spectroscopic and mass spectrometric sequence for the Ag/Au complexes is traced back to the interplay of Pauli repulsion and variation in metal–ligand bond strength within the orbital hybridization model. [ABSTRACT FROM AUTHOR]

Ultrafast vibrational coherence with metal-metal stretching mode character is observed for phosphine-bridged d10-d10 complexes of different size, containing the binuclear [Ag2Cl]+ chromophore in an ion trap. Fragmentation pathways are governed by the wave packet's phase.

Infrared/femtosecond multiphoton ionization spectroscopy (IR/fsMPI) and fluorescence-detected infrared (FDIR) spectrum are used for examining the structure of isolated 1H-pyrrolo[3,2-h]quinoline (PQ)/[water.sub.n] (n = 1.2) complexes. Findings reveal weaker hydrogen bonding in both 1:1 and 1:2 complexes of PQ with water.

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 ¹A2u state and concomitant rise in population of the triplet ³A2u 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 ¹A2u state takes only a few picoseconds, ESETD from the triplet ³A2u 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. [ABSTRACT FROM AUTHOR]

This article, titled "Cover Feature: A Photoswitchable Metallocycle Based on Azobenzene: Synthesis, Characterization, and Ultrafast Dynamics," highlights the discovery of an azobenzene-based metallocycle that can undergo reversible photoisomerization without disassembly. The cover feature showcases the switching between the (E,E) and (Z,Z) isomers of [Cu2(3,3'‐azobenz(metPA)2](BF4)2. The researchers used femtosecond UV/Vis transient absorption in solution and femtosecond pump-probe photodissociation in the gas phase to study the primary switching dynamics. For more information, readers can refer to the Research Article by C. Riehn, R. Diller, S. Becker, and their colleagues. [Extracted from the article]

We study theoretically strong field effects in rotational femtosecond degenerate four-wave-mixing (DFWM). First, we developed a perturbative approach and calculated the leading correction to the standard (weak field) formula for femtosecond DFWM signal. Second, we constructed a nonperturbative approach for computing femtosecond DFWM signals excited by (short) pulses of arbitrary intensity. Third, we worked out the theory to describe femtosecond DFWM with an extra aligning pulse. We show that the strong-pulse-induced nonadiabatic alignment does explain many experimentally detected features that develop in femtosecond DFWM signals with increasing laser intensity beyond the standard weak field regime. However, we also show that this nonadiabatic alignment cannot solely be responsible for the onset of the heterodyne detection and pronounced constant background in DFWM signals excited by high intensity laser pulses. [ABSTRACT FROM AUTHOR]

A scheme for measuring the IR spectra of photoreactive molecular clusters, which is based on femtosecond multiphoton ionization probing (IR/fsMPI) is presented. The results have demonstrated that size-specific spectra for small complexes could be obtained if the supersonic expansion and excitation conditions are carefully controlled.

The use of femtosecond time-resolved, which degenerates four-wave mixing rotationally resolved spectroscopy to obtain very accurate structural information on the symmetric top cyclohexane is reported. Since, in the chair conformation belongs to the point D3d, it is not possible to employ microwave spectroscopy, which is the most precise structural method in the gas phase for small- and medium-sized molecules.

An investigation of the phenol dimer by high-resolution rotational coherence spectroscopy (RCS) by time-resolved fluorescence depletion (TRFD) determines with high precision, the rotational constants of the ground and electronically excited states. The possible structures of phenol dimer in both, the electronic ground and excited states as obtained by a fitting procedure, using the experimentally determined rotational constants and imposed by the O-H...O hydrogen bond is proposed.

Time resolved rotational spectroscopy is used to determine the precise values for the rotational constants of benzene in both the ground and the electronically excited states. Benzene is served as molecular benchmark for high-resolution rotational coherence spectroscopy (RCS) with the perspective that the influence of vibrations on the equilibrium structure could be studied for medium sized molecules by this method.

Abstract: The hybrid ligand 3‐(2,2′‐bipyridine‐6‐ylmethyl)‐1‐mesityl‐1H‐imidazolylidene (NHCBipy) featuring both carbene and N‐donor sites, was selectively complexed with various d10 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 [(NHCBipy)AuCl], [(NHCBipy)Au(C6F5)] and [(NHCBipy)2Au][ClO4], open‐chain as well as cyclic heterobimetallic complexes containing Cu+, Ag+, Zn2+, Cd2+, and Hg2+ were synthesized. Furthermore, the homobimetallic species [(NHCBipy)2M2][ClO4]2 (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. [ABSTRACT FROM AUTHOR]