FIG. 3. Calculated equilibrium density profiles of a deformable 4 He cylinder rotating around its symmetry axis at fixed L SF =N He ¼ 7.83ℏ for different numbers of vortices. Streamlines are shown in black. The positions of the vortex cores are marked by red dots for visualization. The color bar shows the density in units of Å −3 .

The success of many emerging molecular electronics concepts hinges on an atomistic understanding of the underlying electronic dynamics. We employ picosecond time-resolved Xray Photoemission Spectroscopy (tr-XPS) to elucidate the roles of singlet and triplet excitons for photoinduced charge generation at a copper-phthalocyanine-C 60 heterojunction. Contrary to common belief, fast intersystem crossing to triplet excitons after photoexcitation is not a loss channel but contributes to a significantly larger extent to the time-integrated interfacial charge generation than the initially excited singlet excitons. The tr-XPS data provide direct access to the diffusivity of the triplet excitons D CuPc = (1.8 ± 1.2) x 10-5 cm 2 /s and their diffusion length L diff = (8 ± 3) nm. Main Text Metal-organic heterojunctions, such as metal-phthalocyanine (MePc) donor-C 60 acceptor systems [1-5], provide an important platform to advance understanding the electronic dynamics underlying many emerging molecular electronics concepts for photochemical and photovoltaic applications [6-16]. The prevailing picture for efficient charge generation is through singlet exciton dissociation at the donor-acceptor interface within less than 1 ps after photoexcitation in order to avoid photon energy loss to non-dissociating triplet excitons by fast intersystem crossing [17,18]. We employ picosecond time-resolved X-ray Photoemission Spectroscopy (tr-XPS), a technique of choice for measuring electronic structure with elemental and chemical site-specificity [19,20], to directly determine the triplet exciton diffusivity and the ratio of singlet and triplet exciton dissociation efficiencies in a copper-phthalocyanine (CuPc)-C 60 planar heterojunction (PHJ). Contrary to common belief, ultrafast intersystem crossing from

The ultrafast dynamics of photon-to-charge conversion in an organic light-harvesting system is studied by femtosecond time-resolved X-ray photoemission spectroscopy (TR-XPS) at the free-electron laser FLASH. This novel experimental technique provides site-specific information about charge separation and enables the monitoring of free charge carrier generation dynamics on their natural timescale, here applied to the model donor-acceptor system CuPc:C60. A previously unobserved channel for exciton dissociation into mobile charge carriers is identified, providing the first direct, real-time characterization of the timescale and efficiency of charge generation from low-energy charge-transfer states in an organic heterojunction. The findings give strong support to the emerging realization that charge separation even from energetically disfavored excitonic states is contributing significantly, indicating new options for light harvesting in organic heterojunctions.

Progress in the development of plasmon-enabled light-harvesting technologies requires a better understanding of their fundamental operating principles and current limitations. Here, we employ picosecond time-resolved X-ray photoemission spectroscopy to investigate photoinduced electron transfer in a plasmonic model system composed of 20 nm sized gold nanoparticles (NPs) attached to a nanoporous film of TiO2. The measurement provides direct, quantitative access to transient local charge distributions from the perspectives of the electron donor (AuNP) and the electron acceptor (TiO2). On average, approximately two electrons are injected per NP, corresponding to an electron injection yield per absorbed photon of 0.1%. Back electron transfer from the perspective of the electron donor is dominated by a fast recombination channel proceeding on a timescale of 60±10 ps and a minor contribution that is completed after ≈1 ns. The findings provide a detailed picture of photoinduced charge carrier generation in this NPsemiconductor junction, with important implications for understanding achievable overall photon-to-charge conversion efficiencies.