We used the Langmuir-Blodgett (LB) technique to construct a well-defined and structure-control I able photochromic material-a highly ordered multilayer film composed of dioctadecylamine and 12-molybdophosphoric acid (PMo12). We identified well-ordered lamellar structures using Xray diffraction, polarized IR, and Raman spectra, and we determined a packing model of the two components in the LB film. We found the Keggin structure and fundamental features of the PMo12 ion to be maintained in the hybrid film. This hybrid LB film displayed photochromic properties upon UV light irradiation and we observed the following process from first-order kinetics. The photochromism exhibited the ability to switch between colorless and blue. A fading process occurred when the film was exposed to ambient air or 02 in the dark. During the color change, the packing structure of the film was well maintained. We also examined the electrochemical behavior of the hybrid LB film by cyclic voltammetry in detail and we propose different kinetic mechanisms for the film before and after irradiation. (C) 2007 Elsevier Inc. All rights reserved.