In situ photoelectron spectroscopy is used to study the adsorption and photoisomerization of azobenzene multilayers on the layered semiconductor HfS2 at liquid nitrogen temperatures. The measured valence band spectra indicate weak molecule–substrate coupling and provide evidence for reversible switching of azobenzene multilayers by light with different wavelengths. The photoswitching manifests itself in spectral shifts due to changes in the electrical surface conductance and in modifications of the electronic structure consistent with the results of outer valence Green’s function calculations. The photoemission results appear to establish azobenzene as an optoelectrical molecular switch.

In situ ultraviolet photoelectron spectroscopy is used to study the growth of ultrathin films of azobenzene-based functional molecules (azobenzene, Disperse Orange 3 and a triazatriangulenium platform with an attached functional azo-group) on the layered metal TiTe(2) and on the layered semiconductor HfS(2) at liquid nitrogen temperatures. Effects of intermolecular interactions, of the substrate electronic structure, and of the thermal energy of the sublimated molecules on the growth process and on the adsorbate electronic structure are identified and discussed. A weak adsorbate-substrate interaction is particularly observed for the layered semiconducting substrate, holding the promise of efficient molecular photoswitching.

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