The functionality of interfaces in hybrid inorganic/organic (opto)electronic devices is determined by the alignment of the respective frontier energy levels at both sides of the heterojunctions. Controlling the interface electronic landscape is a key element for achieving favourable level alignment for energy and charge transfer processes. Here, it is shown that the electronic properties of polar ZnO surfaces can be reversibly modified using organic photochromic switches. By employing a range of surface characterization techniques combined with density functional theory calculations, it is demonstrated that self-assembled monolayers (SAMs) of photochromic phosphonic acid diarylethenes (PA-DAEs) can be employed to reversibly change the electronic properties of polar ZnO/ SAM structures by light stimuli. The highest occupied molecular orbital level of PA-DAE is raised by 0.7 eV and the lowest unoccupied one lowered by 0.9 eV, respectively, upon illumination by ultraviolet light and the levels shift back to their original position upon illumination by green light. The results thus provide a pathway to tailor hybrid interface electronic properties in a dynamic manner upon simple light illumination, which can be exploited to reversibly tune the electrical properties of photoswitchable (opto)electronic devices.

Light-switching-induced changes in the electronic properties of photochromic diarylethene, i.e., 1,2-bis(2-methyl-5-p-tolylthiophen-3-yl)cyclopent-1-ene (DAE1), thin films at interfaces to a gold electrode and two polymer semiconductors are investigated by direct and inverse photoelectron spectroscopy. The photoisomerization is achieved by in situ irradiation of ultraviolet and visible light. Efficient and reversible switching between the open and closed isomers of DAE1 is evidenced at all interfaces, with profound impact on the energy-level alignment. The frontier occupied level of DAE1 changes by 0.8 eV with respect to the Au Fermi level upon switching. Corresponding sizable changes in the electron and transport level offsets between the two polymers and DAE1 in its open and closed form are determined. This gives rise to fundamentally different functionality of these interfaces in terms of charge transport. Our study proves the viability of light-controlled energy-level manipulation at various interfaces in photoswitchable opto-electronic devices.

No abstract

Light-switching induced changes in the electronic properties of photochromic diarylethene, i.e., 1,2-bis(2-methyl-5-p-tolylthiophen-3-yl)cyclopent-1-ene (DAE1), thin films at interfaces to a gold electrode and two polymer semiconductors were investigated by direct and inverse photoelectron spectroscopy.

The Front Cover picture shows that the photochromic diarylethene derivative (DAE1) on the Au surface undergoes a photoisomerization process upon the irradiation of external light. Ring‐open and ring‐closure reactions are reversibly switched under the green and UV light irradiation. The HOMO‐LUMO difference of the switch exhibits different values with respect to different isomer states. More information can be found in the Full Paper by N. Koch and co‐workers on page 722 in Issue 7, 2017 (DOI: 10.1002/cphc.201601442).