Novel materials based on organic–tungsten oxide hybrid systems II: electronic properties of the W–O framework

In this paper we report experimental and theoretical results concerning the band structure of tungsten trioxide and how this system relates to a new class of layered organic–inorganic hybrid materials based on a tungsten oxide framework. UV–visible spectroscopy was performed on various tungsten trioxide samples. Diffuse reflectance on powder samples indicates a single absorption edge centred at 2.8 eV, while transmission and reflectance of thin films show a strong feature at 4.0 eV. This is supported by ab initio calculations, in which a strong peak is seen at 4.0 eV in the density of states. For the hybrid system, 1,n-diaminoalkane tungsten oxide, a change in the calculated band structure is seen compared with the tungsten oxide system; a peak appears just above 3.0 eV in the density of states with a low intensity `tailʹ below this. UV–visible spectra of powder reflectance of hybrid samples indicate a dominant absorption edge centred at 4.0 eV.