Vanadium oxide nanocrystalline films were prepared by spin-coating from vanadium (V) oxoisopropoxide sol and thermally treated at 150 degrees C, in order to deposit them on PET-ITO substrates. The sols were made from either isopropanol or its mixture with n-butanol, both exhibiting similar rheological behaviour and a viscosity of the order of magnitude of 10(-3) Pa s. A cross-hatch test revealed the excellent adhesion of these films on the ITO surface and delamination occurred preferentially at the ITO-plastic interface when the films were subjected to deliberate bending. The electrochemical and optical properties of the vanadium oxide films were analysed using in-situ UV-vis absorbance spectroelectrochemistry. The response was correspondingly lower than with films deposited on FTO-glass. Ex-situ IR reflection-absorption spectroscopy showed that vanadyl V-O-A and superimposed bridging V-O-B-V and 3V-O-C bands appear at lower frequencies compared to crystalline V2O5, due to the hydrated nanocrystalline structure. An intercalation induced red-shift of the vanadyl mode and the disappearance of the superimposed V-OB-V and 3V-O-C bands, but the spectrum was restored to the initial situation after deintercalation. The modulation of polaron absorption that extends from the near to mid-IR spectral region up to 2000 cm(-1) was not visible due to transfer of the films from electrochemical cell to the IR spectrometer. The electrochromic properties of the vanadium oxide films deposited on PET-ITO substrate were tested in a liquid electrolyte-based cell with an electrochromically active PEDOT film and 1 M LiClO4/propylene carbonate electrolyte. (C) 2011 Elsevier B.V. All rights reserved.