The photochromic properties of a hybrid compound comprised of the surfactant cation cetyltrimethylammonium [(C16H33)N(CH3)3]+ and the isopolytungstate anion [H2W12O40]6− is investigated.

We investigate the spontaneous reduction of a photochromic surfactant/ polyoxotungstate hybrid during repeated X-ray photoelectron spectroscopy (XPS) scans and show how this effect may confound attempts to use soft X-rays to characterise materials of this nature. The W4f core-level spectra revealed a progressive increase of W 5+ and W 4+ species at the expense of W 6+ as irradiation time increased. The samples developed a blue colour attributed to the presence of W 4+ and/or W 5+ . The progressive photoreduction is also associated with a shift of the W 6+ peak within the W4f spectrum to lower binding energies. This work highlights the need to consider inadvertent changes in oxidation state during X-ray photoelectron spectroscopy characterisation of samples containing photoreducible transition metals.