We report on an element-selective study of the fate of charge carriers in photoexcited inorganic CsPbBr3 and CsPb(ClBr)3 perovskite nanocrystals in toluene solutions using time-resolved X-ray absorption spectroscopy with 80 ps time resolution. Probing the Br K-edge, the Pb L3-edge, and the Cs L2-edge, we find that holes in the valence band are localized at Br atoms, forming small polarons, while electrons appear as delocalized in the conduction band. No signature of either electronic or structural changes is observed at the Cs L2-edge. The results at the Br and Pb edges suggest the existence of a weakly localized exciton, while the absence of signatures at the Cs edge indicates that the Cs+ cation plays no role in the charge transport, at least beyond 80 ps. This first, time-resolved element-specific study of perovskites helps understand the rather modest charge carrier mobilities in these materials.

A tuneable repetition rate extreme ultraviolet source (Harmonium) for time resolved photoelectron spectroscopy of liquids is presented. High harmonic generation produces 30–110 eV photons, with fluxes ranging from ∼2 × 1011 photons/s at 36 eV to ∼2 × 108 photons/s at 100 eV. Four different gratings in a time-preserving grating monochromator provide either high energy resolution (0.2 eV) or high temporal resolution (40 fs) between 30 and 110 eV. Laser assisted photoemission was used to measure the temporal response of the system. Vibrational progressions in gas phase water were measured demonstrating the ∼0.2 eV energy resolution.

Coupling matter excitations to electromagnetic modes inside nano-scale optical resonators leads to the formation of hybrid light-matter states, so-called polaritons, allowing the controlled manipulation of material properties. Here, we investigate the photo-induced dynamics of a prototypical strongly-coupled molecular exciton-microcavity system using broadband two-dimensional Fourier transform spectroscopy and unravel the mechanistic details of its ultrafast photo-induced dynamics. We find evidence for a direct energy relaxation pathway from the upper to the lower polariton state that initially bypasses the excitonic manifold of states, which is often assumed to act as an intermediate energy reservoir, under certain experimental conditions. This observation provides new insight into polariton photophysics and could potentially aid the development of applications that rely on controlling the energy relaxation mechanism, such as in solar energy harvesting, manipulating chemical reactivity, the creation of Bose–Einstein condensates and quantum computing.

Intersystem crossing (ISC) rates of transition-metal complexes are determined by the complex interplay of a molecule’s electronic and structural dynamics. To broaden our understanding of these key factors, we investigate the case of the prototypical d8–d8 dimetal complex [Pt­(ppy)­(μ- t Bu2pz)]2 using broad-band transient absorption anisotropy in combination with ultrafast fluorescence up-conversion and ab initio calculations. We find that, upon excitation of the molecule’s metal–metal-to-ligand charge-transfer transition, ISC occurs in hundreds of femtoseconds from the lowest excited singlet state S1 to the triplet state T2, from where the energy relaxes to the lowest energy triplet state T1. ISC to the T2 state, rather than T1, is further rationalized through supporting arguments. Observed vibrational coherences along the Pt–Pt mode are attributed to the formation of nuclear wavepackets on the ground and excited electronic states that dephase prior to ISC because of the structural flexibility of the complex. Beyond demonstrating the relationship between the energy relaxation and structural dynamics of [Pt­(ppy)­(μ- t Bu2pz)]2, our results provide new insights into the photoinduced dynamics of d8–d8 dimetal complexes more generally.