Electron transfer from molecular chromophores to semiconductors probed with two-photon-photoemission

Heterogeneous electron transfer from the excited state of a molecular chromophore to empty electronic states of a solid is an important process in a variety of fields ranging from photochemistry to molecular electronics. Light-induced heterogeneous electron transfer is investigated mainly with transient absorption in polycrystalline or nano-crystalline samples with anchored chromophores. Transient two-photon photoemission (TR-2PPE) is capable of detecting the signals of submonolayer chromophore coverage on single crystal surfaces and gives information about the electron transfer dynamics, the position of the electronic levels at the surface, and the adsorption geometry of the molecules on the surface. Comparing the different 2PPE transients and the corresponding transient absorption measurements for identical systems reveals the origin of unexpected short time constants in the transient absorption measurements.