The growth and electronic structure of azobenzene-based functional molecules on layered crystals

Abstract

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.

Electronic structure, adsorption geometry, and photoswitchability of azobenzene layers adsorbed on layered crystals

“…41 Strong chemisorption, however, can be ruled out in our case, as it usually results in a significant broadening of the p* resonances which is not observed here. The XPS results and the observed low desorption temperature 20 also indicate weak substrate-adsorbate coupling. We therefore assume that the contribution of the second effect can be neglected.…”

“…26 Clean crystal surfaces were prepared by cleaving in vacuo and azobenzene molecules (Sigma-Aldrich) were deposited in situ using a home-built sublimation setup. 20 ARPES spectra were recorded using a He gas-discharge source (hn = 21.22 eV) and a hemispherical SPECS Phoibos 150 photoelectron analyzer in a normal emission geometry. For these measurements, the energy resolution was E40 meV.…”

“…18,19 Here, we further explore the idea to reduce the moleculesubstrate interactions of flat-lying azobenzene molecules via the use of layered transition-metal dichalcogenides (TMDC) as substrates. 20,21 These compounds consist of strongly bound chalcogen-metal-chalcogen triple layers which are held together by weak van der Waals-like forces (Fig. 1a), so that by cleaving these crystals an atomically flat and chemically saturated surface is easily obtained.…”

“…The valence electronic structure of azobenzene on such substrates has previously been investigated. 20,21 Here, we will first clarify how the electronic and structural properties of the azobenzene-substrate interface depend on the substrate electronic structure and the adsorbate layer thickness. We will then determine to which degree the adsorbed azobenzene molecules can be photoswitched upon irradiation with 365 nm light.…”

Interplay between TiO2 Surfaces and Organic Photochromes: A DFT Study of Adsorbed Azobenzenes and Diarylethenes

“…19,20 Other studies have investigated how the nature of the substrate and the strength of the electronic coupling affect the switching of adsorbed AZB derivatives. 21,22 Another commonly investigated photochrome, diarylethenes, and their popular thiophene-containing subset, dithienylethenes (DTEs, Scheme 1), are notable for their thermo-and photostabilities and their fatigue resistance. DTEs feature a high-yield interconversion between the poorly conjugated and more stable open isomer and the strongly conjugated but less stable closed isomer.…”