Structural information on electronically excited neutral molecules can be indirectly retrieved, largely through pump-probe and rotational spectroscopy measurements with the aid of calculations. Here, we demonstrate the direct structural retrieval of neutral carbonyl disulfide (CS2) in the " excited electronic state using laser-induced electron diffraction (LIED). We unambiguously identify the ultrafast symmetric stretching and bending of the field-dressed neutral CS2 molecule with combined picometre and attosecond resolution using intra-pulse pump-probe excitation and measurement. We invoke the Renner-Teller effect to populate the " excited state in neutral CS2, leading to bending and stretching of the molecule. Our results demonstrate the sensitivity of LIED in retrieving the geometric structure of CS2, which is known to appear as a two-centre scatterer. SignificanceLaser-induced electron diffraction is a molecular-scale electron microscope that captures clean snapshots of a molecule's geometry with sub-atomic picometre and attosecond spatio-temporal resolution. We induce and unambiguously identify the stretching and bending of a linear triatomic molecule following the excitation of the molecule to an excited electronic state with a bent and stretched geometry. We show that we can directly retrieve the structure of electronically excited molecules that is otherwise possible through indirect retrieval methods such as pump-probe and rotational spectroscopy measurements.2 Many important phenomena in biology, chemistry and physics can only be described beyond the Born-Oppenheimer (BO) approximation, giving rise to nonadiabatic dynamics and the coupling of nuclear (vibrational and rotational) and electronic motion in molecules (1-7). One prominent example where the BO approximation breaks down is the Renner-Teller effect (8,9): in any highly symmetric linear molecule with symmetry-induced degeneracy of electronic states, non-adiabatic coupling of (vibrational) nuclear and electronic degrees of freedom can lead to the distortion of the nuclear framework on a timescale comparable with electronic motion. The system's symmetry is then reduced by the bending of the molecule to split the degenerate electronic state into two distinct potential energy surfaces (PESs), leading to a more stable, bent conformer.Here, we demonstrate the direct imaging of Renner-Teller non-adiabatic vibronic dynamics in neutral CS2 with combined picometre and attosecond resolution through intra-pulse pump-probe excitation and measurement with laser-induced electron diffraction (LIED) (10-16). Our results shed light on the vibronic excitation of a neutral linear molecule in the rising edge of our laser field that causes bending and stretching of the molecule. High momentum transfers experienced by the electron wave packet (EWP; Up = 85 eV) with large scattering angles enable the electron to penetrate deep into the atomic cores, allowing us to resolve a strongly symmetrically stretched and bent CS2 molecule most likely in the B " & B ' excited elec...

Predicting the energetics of chemical transformations requires localizing stationary points on a potential energy surface. While educts and products of a chemical reaction may be known, transition state optimization is challenging as good guesses may be unavailable. Extending stationary point searches to the excited state leads to additional difficulties as several states may be close in energy, requiring efficient state tracking. Here, we report the implementation of pysisyphus, an external optimizer, that allows localization of stationary points not only in the ground state but also for excited state by providing several state-tracking algorithms. pysisyphus offers all necessary tools for calculating reaction paths, starting from the optimization of the reactants, running chain-of-states methods such as the nudged elastic band or the growing string method with subsequent transition state optimization, and a concluding intrinsic reaction coordinate calculation.

Community efforts in the computational molecular sciences (CMS) are evolving toward modular, open, and interoperable interfaces that work with existing community codes to provide more functionality and composability than could be achieved with a single program. The Quantum Chemistry Common Driver and Databases (QCDB) project provides such capability through an application programming interface (API) that facilitates interoperability across multiple quantum chemistry software packages. In tandem with the Molecular Sciences Software Institute and their Quantum Chemistry Archive ecosystem, the unique functionalities of several CMS programs are integrated, including CFOUR, GAMESS, NWChem, OpenMM, Psi4, Qcore, TeraChem, and Turbomole, to provide common computational functions, i.e., energy, gradient, and Hessian computations as well as molecular properties such as atomic charges and vibrational frequency analysis. Both standard users and power users benefit from adopting these APIs as they lower the language barrier of input styles and enable a standard layout of variables and data. These designs allow end-to-end interoperable programming of complex computations and provide best practices options by default.

The photophysical properties of a series of rhenium­(I) tricarbonyl and platinum­(II) bis­(acetylide) complexes containing a triphenylamine (TPA)-substituted 1,10-phenanthroline ligand have been examined. The complexes possess both metal-to-ligand charge-transfer (MLCT) and intraligand charge-transfer (ILCT) transitions that absorb in the visible region. The relative energies and ordering of the absorbing CT states have been successfully controlled by changing the metal center and modulating the donating ability of the TPA group through the addition of electron-donating methoxy and electron-withdrawing cyano groups. The ground-state properties behave in a predictable manner as a function of the TPA substituent and are characterized with a suite of techniques including electronic absorption spectroscopy, resonance Raman spectroscopy, electrochemistry, and time-dependent density functional theory calculations. However, systematic control over the ground-state properties of the complexes does not extend to their excited-state behavior. Unexpectedly, despite variation of both the MLCT and ILCT state energies, all of the luminescent complexes displayed near-isoenergetic emission at 298 K, yet the emissive lifetimes of the complexes vary from 290 ns to 3.9 μs. Excited-state techniques including transient absorption and transient resonance Raman, combined with a suite of quantum-chemical calculations, including scalar relativistic effects to elucidate competitive excited-state relaxation pathways, have been utilized to aid in assignment of the long-lived state in the complexes, which was shown to possess differing 3MLCT and 3ILCT contributions across the series.

Observing changes in molecular structure requires atomic-scale Ångstrom and femtosecond spatio-temporal resolution. We use the Fourier transform (FT) variant of laser-induced electron diffraction (LIED), FT-LIED, to directly retrieve the molecular structure of H2O + with picometre and femtosecond resolution without a priori knowledge of the molecular structure nor the use of retrieval algorithms or ab initio calculations. We identify a symmetrically stretched H2O + field-dressed structure that is most likely in the ground electronic state. We subsequently study the nuclear response of an isolated water molecule to an external laser field at four different field strengths. We show that upon increasing the laser field strength from 2.5 to 3.8 V/Å, the O-H bond is further stretched and the molecule slightly bends. The observed ultrafast structural changes lead to an increase in the dipole moment of water and, in turn, a stronger dipole interaction between the nuclear framework of the molecule and the intense laser field. Our results provide important insights into the coupling of the nuclear framework to a laser field as the molecular geometry of H2O + is altered in the presence of an external field.

The optical properties of two Re­(CO)3(bpy)Cl complexes in which the bpy is substituted with two donor (triphenylamine, TPA, ReTPA2) as well as both donor (TPA) and acceptor (benzothiadiazole, BTD, ReTPA-BTD) groups are presented. For ReTPA2 the absorption spectra show intense intraligand charge-transfer (ILCT) bands at 460 nm with small solvatochromic behavior; for ReTPA-BTD the ILCT transitions are weaker. These transitions are assigned as TPA → bpy transitions as supported by resonance Raman data and TDDFT calculations. The excited-state spectroscopy shows the presence of two emissive states for both complexes. The intensity of these emission signals is modulated by solvent. Time-resolved infrared spectroscopy definitively assigns the excited states present in CH2Cl2 to be MLCT in nature, and in MeCN the excited states are ILCT in nature. DFT calculations indicated this switching with solvent is governed by access to states controlled by spin–orbit coupling, which is sufficiently different in the two solvents, allowing to select out each of the charge-transfer states.

The metal‐free, highly selective synthesis of biaryls poses a major challenge in organic synthesis. The scope and mechanism of a promising new approach to (hetero)biaryls by the photochemical fusion of aryl substituents tethered to a traceless sulfonamide linker (photosplicing) are reported. Interrogating photosplicing with varying reaction conditions and comparison of diverse synthetic probes (40 examples, including a suite of heterocycles) showed that the reaction has a surprisingly broad scope and involves neither metals nor radicals. Quantum chemical calculations revealed that the C−C bond is formed by an intramolecular photochemical process that involves an excited singlet state and traversal of a five‐membered transition state, and thus consistent ipso–ipso coupling results. These results demonstrate that photosplicing is a unique aryl cross‐coupling method in the excited state that can be applied to synthesize a broad range of biaryls.

A light-responsive paper strip as CO-releasing material (CORMA) for convenient and efficient CO-release with colorimetric response.