Three molecules' worth of reach, then a quarter less inside 400 femtoseconds [5]. Run the arithmetic and the electron-hole pair ends that window spanning about 2.25 molecules, having given up roughly three quarters of a molecule of extent [18] over 0.4 of a picosecond [19]. That is the measurement, and what follows is what it took to get it, and what it does not cover.
The sequence is two pulses. An ultrashort light pulse creates the exciton, and a second, higher-energy pulse ejects electrons out of the bound pair, which is photoemission [7]. The energy and emission direction of those electrons, run through theoretical models, imply the quantum state, and stepping the delay between the two pulses turns single states into frames [8]. Puschnig's group at Graz supplied the inversion: an analytical model that reads the spatial shape and the internal quantum-mechanical phase of the wave function off measured photoelectron images, according to Siegfried Kaidisch, who worked on it for his doctorate [14][13]. Phase is usually modelled rather than observed, so measuring it directly is the part that stands out here.
The specimen matters as much as the laser pulses that probe it. Rod-shaped 6T molecules were deposited in wafer-thin ordered films on a specially prepared copper surface [9], and Monja Stettner, who prepared them, says the precise alignment and the deliberate decoupling from the substrate are what keep the exciton alive long enough for its formation to be visible [10]. Forschungszentrum Julich grew and characterised the films and moved them to Marburg under ultrahigh vacuum [11], where Ulrich Hoefer's group ran the photoemission and analysed the data [12].
The specimen also sets the limits on what can be claimed. The thing this does not tell you is what happens at the step that actually yields current, when the bound pair splits into free charges a device can collect. The measurements described in the phys.org account cover formation and the contraction that follows; no dissociation event, no efficiency figure and no working cell appears in it [20]. An ordered 6T film decoupled from copper is engineered to hold an exciton still enough to photograph, not to generate power. The photovoltaics framing offered around the result [17] is best read as method transfer rather than as a route to better panels.
What is new here is narrower than the light-to-electricity billing and more interesting for it. Photoemission orbital tomography came out of Puschnig's group and has become an established instrument for electronic states in organic materials [15]; the theory added in this paper describes photoemission from excitons specifically [13], which moves an exciton's internal structure from inferred to reconstructed [4]. Excitons have been named and used for decades with that structure largely hidden [3]. This result gives that structure a measured number.
