Photoelectron Spectroscopy Study of Photoresponsive Change in Electronic Structure of Amorphous Photochromic Diarylethene Film

Abstract

The photoresponsive change in the electronic structure of photochromic diarylethene, 1,2-bis(5-(2,4-diphenylphenyl)-2,4-dimethyl-3-thienyl) perfluorocyclopentene (DAE) is observed by photoelectron spectroscopy. UV and visible light irradiation introduce clear differences in the spectral shape of photoelectron spectra of the DAE thin film. In the photoelectron spectrum after UV light irradiation, the highest occupied molecular orbital (HOMO) of the DAE film appears at around 1.5 eV below the Fermi level. In contrast, under visible light irradiation, the HOMO of the DAE film has higher binding energy. The variation of the HOMO peak can be reproduced repeatedly by UV and visible light irradiation. These differences correspond to the difference in the electronic structure between the closed-ring and the open-ring isomer of DAE. The molecular orbitals of the DAE isomers are calculated with the density functional theory, and the results are in good agreement with the photoelectron results. Cyclic voltammetry measurement of the closed-ring isomer shows the first oxidation waves at 0.6 V (vs Ag/Ag+) whereas the open-ring isomer shows the first oxidation wave at 1.1 V. The consistency between the photoelectron results and other methods suggests that photoelectron spectroscopy has a powerful potential to reveal the electronic structure of photochromic molecules.